Patent Application
20230292749
Some pathogens continue to develop resistance to some prior art antibiotics. Sojib Bin Zaman et al. in their review described that antibiotic resistance occurs when a drug loses its ability to inhibit bacterial growth effectively. Bacteria become ‘resistant’ and continue to multiply in the presence of therapeutic levels of the antibiotics. Bacteria, which replicate even in the presence of the antibiotics, are called resistant bacteria [1].
According to Banin et al., one of the modes by which bacteria exert antimicrobial resistance is through their ability to form biofilms. Biofilms are surface-attached bacteria encased in a self-produced extracellular polymeric matrix. The biofilm increases the pathogen resistance to a wide range of stressors including antimicrobials, disinfectants and antibiotics. The mechanisms underlying this resistance are complex [2].
Hall and Mah provide insights into these resistance mechanisms, which include the interaction of antibiotics with matrix components, reduced growth rates and a range of genetic determinants that specifically mediate resistance in the biofilm mode of growth. Notably, it is usually not one single mechanism that provides antimicrobial resistance, but rather a combination of several of these resistance mechanisms that manifests the extremely high resistance observed within biofilm cells [3].
Yang and Walsh in their review discuss the variety of different toxin-antitoxin (TA) systems that are currently known, and their role as drivers in the maintenance of antimicrobial resistance in pathogen populations. They also discuss how TA systems are often associated with antimicrobial genes present on the same plasmid as the toxin-antitoxin itself, and how that coincidence can act to maintain the antimicrobial resistance genes even in the absence of the drug. In addition, they highlight how the mutagenic SOS system, which is induced by many commonly used antimicrobial drugs, activates some TA systems, placing a continuing selective pressure on certain TA systems to be mobilized throughout bacterial populations [4].
Mazel et al. teach a few common scenarios of microbes multi-drug resistance development:
Hyde et al. characterized the antibiotic resistant bacterial populations from colony-reared Aedes aegypti larvae and adults and two field caught mosquito species Coquillettidia perturbans and Ochlerotatus canadensis. The cultured bacterial populations were dominated by isolates belonging to the class Gammaproteobacteria. Among the antibiotic resistant populations, they found bacteria resistant to carbenicillin, kanamycin, and tetracycline, including bacteria resistant to a cocktail of all three antibiotics in combination. Isolates were characterized by 16S rRNA gene sequencing, and clustering into Operational Taxonomic Units (OTUs; 99% sequence identity). 27 antibiotic resistant OTUs were identified, although members of an OTU did not always share the same resistance profile. This suggests the clustering was either not sensitive enough to distinguish different bacteria taxa or different antibiotic resistant sub-populations exist within an OTU. Finally, the antibiotic selection opened up a niche to culture mosquito-associated fungi, and 10 fungal OTUs (28S rRNA gene sequencing) were identified. Two fungal OTUs both classified to the class Microbotryomycetes were commonly identified in the field-caught mosquitoes [6].
Menendez-Arias reported that viral resistance is caused by mutations in the HIV genome coding for structural changes in the target proteins that can affect the binding or activity of the antiretroviral drugs. Their review provided an overview of the molecular mechanisms involved in the acquisition of resistance to currently used and promising investigational drugs, emphasizing the structural role of drug resistance mutations [7].
Jiang et al. reported about the resistance mechanisms of herpes simplex virus (HSV) to Acyclovir (ACV): (a) decreased production of viral TK, (b) complete deficiency in viral TK activity, and (c) viral TK protein and DNA polymerase with altered substrate specify. The viral mutations conferring resistance to ACV are located in activating/phosphorylating genes (TK, UL23 kinase) and the viral DNA pol enzyme (UL30), consistently with the above mechanisms of action. The viral mutations in the TK gene generally result in incomplete or deficient enzymes because of the addition or deletion of nucleotides in long homopolymeric runs of Gs and Cs. Approximately 95% of ACV-resistant HSV clinical isolates have a TK-deficient phenotype. The target of anti-HSV drugs is primarily the DNA pol gene of HSV. A single mutation in DNA pol enzyme may confer resistance to many anti-HSV agents [8].
Gaudieri et al. have shown that the efficacy of specifically targeted anti-viral therapy for hepatitis C virus (HCV) (STAT-C), including HCV protease and polymerase inhibitors, is limited by the presence of drug-specific viral resistance mutations within the targeted proteins. Genetic diversity within these viral proteins also evolves under selective pressures provided by host human leukocyte antigen (HLA)-restricted immune responses, which may therefore influence STAT-C treatment response. The frequency of the variations varied according to individual STAT-C drug and HCV genotype/subtype. Of individuals infected with subtype 1a, 21.5% exhibited genetic variation at a known drug resistance site. Furthermore, they identified areas in HCV protease and polymerase that are under both potential HLA-driven pressure and therapy selection and identified six HLA-associated polymorphisms (P≤0.05) at known drug resistance sites [9].
Niimi et al. have shown that the resistance of oral fungi to azoles has two components: one is the resistance of individual cells, and the other is resistance conferred by growth as a biofilm. The mechanisms of azole resistance occurring in monoculture in vitro are well understood, and high-level resistance is often caused by the expression of efflux pumps. The nature of antifungal resistance seen clinically in vivo is more complex: it is multifactorial and in part the result of growth as a biofilm. Although efflux pumps may play a role in azole resistance early in biofilm development, interactions with other microorganisms, the biofilm extracellular matrix, and the response of the fungi to stress all contribute to the drug resistance of biofilms [10].
Berman et al. reported about antifungal heteroresistance of Cryptococcus neoformans and Cryptococcus gattii, and is an intrinsic property of these species. Extra copies of an individual chromosome are associated with cryptococcal heteroresistant isolates; the degree to which heteroresistance is due to a particular aneuploidy seems to be strain-specific. In Cryptococcus, one molecular mechanism of heteroresistance seems to involve extra copies of the chromosome carrying both ERG11, the target of azoles, and AFR1, a major efflux pump. However, some Cryptococcus heteroresistant isolates do not have obvious aneuploidies. C. glabrata isolates exhibit a range of heteroresistance levels and highly heteroresistant isolates exhibit increased levels of efflux activity; however, the molecular mechanisms that yield heteroresistance in C. glabrata and in non-aneuploid Cryptococcus isolates are not known. Very few studies have analyzed the role of heteroresistance in in vivo persistence of a fungal pathogen in animal tissues after antifungal treatment [12].
In some prior art, the biocidal coatings are not permanent, and become exhausted within weeks of initial use. Silver nanoparticles, copper nanoparticles, and others which are not bound to the coating, can shed from the coating. In some prior art the biocidal coating becomes less active with time due to chemical degradation. And in some prior art, the biocidal becomes completely inert with time.
In other prior art, the biocidal is most effective when the biocidal is conductive. However, the conductivity of some prior art biocidals can become reduced over time. In prior art biocidals containing MoS2 flakes, the flakes are active biocidals when the flakes are electrically conductive, with the conductive 1T chemical structure, but their effectiveness is reduced as the MoS2 flake inevitably converts from the 1T structure to the 2H structure, that is, converts from being conductive to becoming semiconductive.
Kim et al. have shown the antibacterial activities of 1T-phase MoS2, WS2, and MoSe2 flakes. The flakes were investigated by a microbial viability test using E. coli DH5a as model bacteria. Their study shows the loss of E. coli viability after 3 h incubation with TMD nanosheets where the loss of viability is calculated from the equation: loss of viability (%)=(counts of control−counts of samples incubated with TMD nanosheets)/counts of control×100%. E. coli cells incubated under identical conditions in the absence of TMD nanosheets were used as a control sample. The obtained results revealed that 1T-phase WS2 nanosheets inactivated the bacterial viability the most where the loss of E. coli viability incubated with 1T-phase WS2 (0.05 mg ml-1) is approximately 72.4%, with that of MoS2 being higher than that of MoSe2 [13].
Basu et al. introduce that defects on varied MoS2 surfaces by suitable doping of nitrogen atoms in a sulfur-rich reaction environment, resulting in stable and scalable phase conversion from 2H to 1T. The experimental characterizations along with the theoretical calculations within the framework of density functional theory establish the impact of nitrogen doping on stabilization of defects and reconstruction of the 2H to 1T phase. The as-synthesized MoS2 samples exhibit excellent dye removal capacity in the dark, facilitated by a synergistic effect of reactive oxygen species (ROS) generation and adsorption. Positron annihilation spectroscopy and electron paramagnetic resonance studies substantiate the role of defects and associated sulfur vacancies toward ROS generation in the dark. Further, on the basis of its ample ROS generation in the dark and in the light, the commendable antimicrobial activity of the prepared MoS2 samples against fungal pathogen Alternaria alternata has been demonstrated [14].
Yu summarizes the generation of Reactive Oxygen Species (R.O.S): “When a semiconductor photocatalyst is bombarded with photons, which have more energy than its and-gap energy, the electrons on the photocatalyst surface are excited and jump from the valence band (VB) to the conduction band (CB). At the same time, positively charged holes are created in the VB.20, 21 The redox potentials of these photogenerated electrons and holes are determined by the band-edge positions of the semiconductor photocatalyst. In general, the smaller (or larger) the potential of the CB (or VB), the stronger the reductive (or oxidative) capacity of the photogenerated electrons (or holes). Those photogenerated electrons with enough reductive power can react with oxygen molecules to form O2·— radicals, which serve as precursors to the generation of ·OH and singlet oxygen (IO2), whereas the photogenerated holes with enough oxidative power can react with water or hydroxide ions to form ·OH·22 MoS2 is a semiconducting material, and electron transfer can be induced under external stimuli, such as visible-light illumination, causing the electron-hole (e−-h+) pairs. 1T ACTION When the thickness of MoS2 is reduced to one or a few layers, the physicochemical properties of MoS2 become very different from those of bulk MoS2 due to the confinement of charge carriers in MoS2's basal plane directions. Bulk MoS2 exhibits an indirect band gap of 1.3 eV, whereas the monolayer MoS2 shows a direct band gap of 1.9 eV with a significant enhancement of light absorption efficiency.23-25 This leads MoS2 to be widely explored in photocatalysis.26 In terms of the ROS formation potential, the band positions of monolayer MoS2, few-layer vertically aligned (FLU) MoS2, bulk MoS2, and two common photocatalysts (TiO2 and g-C3N4) are compared in
Wang et al. have reported about facile synthesis of a defect-rich adhesive molybdenum disulfide (MoS2)/rGO vertical heterostructure (VHS) through a one-step microwave-assisted hydrothermal method is reported. This method for rapid material synthesis enables extremely uniform and well-dispersed MoS2/rGO VHS with abundant S and Mo vacancies and rough surfaces. They demonstrated experimentally and theoretically that the as-prepared MoS2/rGO VHS possesses defect and irradiation dual-enhanced triple enzyme-like activities (oxidase, peroxidase, and catalase) for promoting free-radical generation, owing to much more active edge sites exposure. Meanwhile, the VHS-achieved rough surface exhibits excellent capacity for bacterial capture, with elevated reactive oxygen species (ROS) destruction through local topological interactions. As a result, optimized efficacy against drug-resistant Gram-negative and Gram-positive bacteria can be explored by such defect-rich adhesive nanozymes [15].
Ali Mohammadi et al. have investigated the antimicrobial mode-of-action of 2D nanomaterials. The viability measurements of the bacteria species (i.e., B. subtilis as a Gram+ and E. coli as a Gram− classes) treated with the vertically aligned and randomly oriented MnO2 and MoS2 flakes confirm that the sharp edges of the flakes play a significant role in damaging the bacterial cell wall and reducing membrane integrity. Although MnO2 and MoS2 flakes show different antibacterial activities against the bacteria species, in both cases, Gram+ bacteria show higher loss in membrane integrity. Ali proposed that the PM in bacteria cell wall is likely the primary target of the 2D flakes, which is supported by the experimental observation that shows that 2D flakes show a higher antibacterial activity toward Gram+ species. Finally, although Ali proposes PM as an important target of the 2D flakes, more studies are needed to understand the molecular-level nature of the interaction. Ali's study shows that vertically aligned 2D flakes motif show a higher antibacterial activity against both bacteria classes than 2D flakes that have been previously investigated [16].
Ashraful Islam et al. have shown that 2D MoS2 films with vertically-aligned layers exhibit numerous 2D edge sites which are predicted to offer superior chemical reactivity owing to their enriched dangling bonds. This enhanced chemical reactivity coupled with their tunable band gap energy can render the vertical 2D MoS2 unique opportunities for environmental applications that go beyond the conventional applications of horizontal 2D MoS2. Islam reports that MoS2 films with vertically-aligned 2D layers exhibit excellent visible light responsive photocatalytic activities for efficiently degrading organic compounds in contaminated water such as harmful algal blooms [17].
Kiani et al. have shown the effect of graphene oxide (GO) flakes on the antibacterial activity of CuO nanowire arrays under visible light irradiation is shown. A combined thermal oxidation/electrophoretic deposition technique was employed to prepare three-dimensional networks of graphene oxide flakes hybridized with vertically aligned CuO nanowires. With the help of standard antibacterial assays and X-ray photoelectron spectroscopy, it is shown that the light-activated antibacterial response of the hybrid material against gram-negative Escherichia coli is significantly improved as the oxide functional groups of the GO flakes are reduced. In order to explore the physicochemical mechanism behind this behavior, ab-initio simulations based on density function theory were performed and the effect of surface functional groups and hybridization were elucidated. Supported by the experiments, a three-step photoantibacterial based mechanism is suggested: (i) injection of an electron from CuO into rGO, (ii) localization of the excess electron on rGO functional groups, and (iii) release of reactive oxygen species lethal to bacteria [18].
Pandit et al. have recently demonstrated that vertically aligned coatings of graphene-based nanomaterials provide strong antibacterial effects on various surfaces. Here we investigated whether BN, a nanomaterial with extensive similarities to graphene, might exhibit similar antibacterial properties. To test this, we developed a novel composite material using BN and low density polyethylene (LDPE) polymer. The composite was extruded under controlled melt flow conditions leading to highly structured morphology, with BN oriented in the extrusion flow direction. Nanocomposite extruded surfaces perpendicular to the flow direction were etched, thus exposing BN nanoparticles embedded in the matrix. The antimicrobial activity of extruded samples was evaluated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus by the colony forming units (CFUs) counting method. Furthermore, the bactericidal effect of oriented BN against E. coli and S. aureus was evaluated by scanning electron microscopy (SEM) and live/dead viability assay. Our results suggest that BN flakes on the extruded BN/LDPE composite physically interact with the bacterial cellular envelope, leading to irreparable physical damage. Therefore, we propose that BN-polymer composites might be useful to develop polymer based biomedical devices protected against bacterial adhesion, and thus minimize device associated infections [19].
Pandit et al. reported that graphene, a 2D carbon-based material, can be effectively used to prevent bacterial attachment. The key parameter for this effect is the orientation of graphene with respect to the coated surface. Chemical vapor deposition (CVD) graphene, deposited horizontally on the surface, exhibits no antibacterial effect. By contrast, an array of graphene flakes grown perpendicularly to the surface by a plasma-enhanced CVD (PECVD) process prevent biofilm formation. Electron microscopy reveals that the exposed edges of vertically aligned graphene flakes penetrate the bacterial membrane and drain the cytosolic content. Bacteria are not able to develop resistance to this killing mechanism during multiple exposures [20].
Wei et al. reported that graphene-based nanomaterials (GBNs) are known to exhibit biocidal activities, however, the combined effect of GBNs based on physical disruption and oxidative stress on different types of bacteria remain unclear. Here, we use both Gram-negative (Escherichia coli and Salmonella typhimurium) and Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) bacteria to investigate the antimicrobial properties of vertically and horizontally aligned graphenes grown on semiconductor silicon (Si) and insulator silicon dioxide (SiO2). It is found that the bacteria show different sensitivity to isomeric-structured GNBs. Gram-negative bacteria are more vulnerable to graphene-coated Si substrates than to SiO2, because the less negatively charged membrane enhances the electron transfer effect that extracts the electrons from the microbial membranes, and Gram-positive bacteria seem to show more susceptibility to physical puncturing of vertically aligned graphene than to horizontally aligned graphene due to the nature of the compound and the shape of the membrane structure [21].
Susarrey-Arce et al. have fabricated and characterized multiscale-functional nanotopographies with three levels of functionalization: (1) nanostructure topography in the form of silicon nanowires, (2) covalent chemical modification with (3-aminopropyl)triethoxysilane, and (3) incorporation of chlorhexidine digluconate. Cell viability assays were carried out on two model microorganisms E. coli and S. aureus over these nanotopographic surfaces. Using SEM we have identified two growth modes producing distinctive multicellular structures, i.e. in plane growth for E. coli and out of plane growth for S. aureu [22].
Yu et al. reported about synthesis of different from most studies of 2D materials with their atomic layers parallel to substrate, having developed layer vertically aligned 2D material nanofilms. Built on these developments, they demonstrated the synthesis of vertical heterostructure of n-type MoS2 and p-type WSe2 with vertically aligned atomic layers. Thin film of MoS2/WSe2 vertical structure was successfully synthesized without significant alloy formation. [24].
Yi's work is representative of many researchers art. Many researchers will develop layers of films with their atomic layers parallel to the substrate, and these researchers will describe their devices as vertically aligned, or vertically stacked, whereas in truth, the layers of atoms are horizontal in their orientation. In this application, the atomic layers are normal to the substrate or member, and the major axis of the flake is approximately normal to the substrate or member.
So from the prior art examples described above, the prior art sometimes teaches a vertically aligned dichalcogenide flake. However, it is difficult to perform these orientation techniques at scale to afford economies for mass production.
The following patents do not teach a flake shape coupled with vertical flake orientation:
Regarding the generating of holes and electrons, there are structural means whereby the output of radicals is increased. For example, the IT structure of MoS2 generates holes and electrons. In addition, strain due to compression causes MoS2 shift to the 1T structure, generating holes and electrons. Impurities, also known as dopants, cause flakes to generate holes and electrons. If permeants like air or water could contact the flakes buried in the coating of other particles, the additional permeants would increase the quantity of radicals generated. If heterojunctions were formed in the composite particles, the lifetime of electrons could be lengthened, allowing more electrons to be emitted to air and water to generate radicals. Prior art also teaches using silver nanoparticles and copper nanoparticles, which ultimately become chemically degraded, and no longer function.
It would be an advance in the art if the 1T structure of MoS2 was permanent. It would be an advance in the art if strain caused by compression caused MoS2 to permanently shift to the 1T structure. It would be an advance n the art if impurities improved the generation of holes and electrons. It would be an advance in the art if permeants could contact portions of the flakes buried in the coating of other particles. It would be an advance in the art if the composite particles and other particles would form heterojunctions to allow more time for the electrons and holes to emit to the ambient air or liquid solution. And it would also be an advance in the art if the composite particle had virtually unending effectiveness.
Prior art teaches small volume laboratory methods to vertically orient the flakes. Some of the prior art teaches that a vertically oriented flake has more vacancies and available molybdenum atoms to catalyze. Still other prior art teaches laboratory scale methods to vertically orient the flake so that light and oxygen and moisture is proximal to the catalytic sites of the flake. And still other prior art teaches laboratory vacuum deposition to grow vertically oriented flakes, wherein the pathogen becomes lacerated when contacting the edges of the flake. But none of the prior art methods are suitable to scale to economical mass production.
Pandit et al. teach “ . . . as long as a predominantly vertical alignment of the flakes can be achieved on the surface, sufficient antibacterial effects can probably be attained with a simpler coating method.” Based on Pandit's teaching, it would be an advance in the art if the composite particles could be deposited with a preferential orientation, at low cost, using mass production methods.[19]
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In some embodiments, the composite biocidal particle is comprised of a flake shape particle and a binder, or a flake shape particle and other particles. The flake shape particle is oriented such that a portion of the flake protrudes into the ambient atmosphere and water vapor, or protrudes into a liquid containing water, and, in some embodiments, the binder binds the composite biocidal particle to a member surface.
In other embodiments, the composite biocidal particle is comprised of a flake shape semiconductive particle and a binder, or a flake shape semiconductive particle and other particles. In some embodiments containing MoS2 semiconductive flakes, since a portion of the flake shape particle is proximal to atmosphere, air and oxygen and water vapor and water, all can be catalyzed by the available molybdenum atoms at the edges of the MoS2 flake and within the voids lacking sulfur atoms, absent from the basal planes of the MoS2 flake. And unlike a horizontally oriented flake which is influenced by nearby solid materials, the vertically oriented flakes and their molybdenum atoms are available to air and oxygen and water vapor and water, without dangling bonds to interfere.
The composite particle is not a vertical stack, with atomic layers parallel to the member surface. Rather the vertically aligned flakes protrude away from the other particles comprising the composite particle, protruding into the ambient surroundings. Some scientists teach a “vertical stack”. A vertical stack is a composite comprised of a first flake shaped layer, with its major axis largely parallel to the substrate it adheres to. The other flake shaped layers are stacked upon the first layer, again with its major axis parallel to the substrate. This arrangement of 2D flakes does not function as well as that of a 2D flake protruding from the other components of the particle, protruding from the top surface of the coating, and protruding into the environment.
Here is a non-limiting list of 2D flakes and other materials which are suitable as flakes for the composite particle: MoS2, graphene, reduced graphene, graphene oxide, black phosphorous, BCN-graphene, fluorographene, hexagonal boron nitride, white phosphorous, WS2, MoSe2, WSe2, MoTe2, WTe2, NbSe, NbS2, TaS2, TiS2, NiSe, SnS2, ZrS2, MnS, MnTe, ZnS, GeS2, ZrSe2, GeS, GeS2, GaSe, GaTe, InSe, Bi2Se3, Mica, BSCCO, MoO3 WO3, TiO2, MnO2, V2O5, TaO3, RuO2, LaNb2O7, (Ca, Sr)2Nb3O10, Bi4Ti3O12, Ca2Ta2TiO10, Ni(OH)2, Eu(OH)2, ZnO2, Nickel Oxide, and Cu2O, and mixtures of these.
These flakes are generally called 2D flakes, or plates, or sheets, or blades, and these thin flakes have unique properties different from their bulk form. But 2D flakes have unique properties in various thicknesses, not just monolayer atom thicknesses. Scientists have determined that flakes which are 3 layers of atoms thick, and 4 layers of atoms thick, and other thickness dimensions upwards of 100 nanometers thick have valuable characteristics, different from their bulk form and advantageous from their bulk form. MoS2 in particular is a flake which is a triad of atoms, one layer of sulfurs, a middle layer of molybdenum atoms, and another layer of sulfur atoms. And a MoS2 particle is commonly comprised of a few triads to several triads to tens of tens of triads thick.
In some embodiments the composite biocidal particle also includes radiation curing pre-polymers, thermoplastic polymers, electrons, holes, anti-infective agents, biocidals, dopants, metal particles, or mixtures thereof.
In still other embodiments the other particles include particles which cause the bulk of the coating to shrink. And in other embodiments, voids are present in the plurality of other particles which allows atmospheric air, oxygen, water vapor and water to directly contact the composite particle, including the flake shape particle. In these embodiments, this coating containing voids would be described as an open cell foam layer. In these embodiments, the molybdenum atoms are available to catalyze reactions with atmospheric air, oxygen, water vapor, and water. In still other embodiments, the other particles include materials which are highly permeable to water, oxygen and water vapor. Materials like cellulose, or silicone, or polymeric alcohols allow water, oxygen, and water vapor to permeate to contact the flakes within the plurality of other particles.
Zhao et al. have demonstrated that molybdenum disulfide (MoS2) flakes can be an excellent solar disinfection agent for multi-drug resistant (MDR) bacteria with disinfection efficiencies 499.9999% in only 30 min. Distinct from other reactive oxygen species (ROS)-dependent photocatalysts, both ROS generation and size decrease contributed to the high antibacterial efficiencies of MoS2 [25].
Yang et al. report that the ce-MoS2 sheets could produce reactive oxygen species (ROS), different from previous report on graphene-based materials. Particularly, the oxidation capacity of the ce-MoS2 sheets toward glutathione oxidation showed a time and concentration dependent trend, which is fully consistent with the antibacterial behavior of the ce-MoS2 sheets. The results suggest that antimicrobial behaviors were attributable to both membrane exchange distortion and oxidation stress. The antibacterial pathways include MoS2-bacteria contact induced membrane stress, superoxide anion (O2·—) induced ROS production by the ce-MoS2, and the ensuing superoxide anion-independent oxidation. Yang's study thus indicates that the tailoring of dimension of nanomaterials and their electronic properties would manipulate antibacterial activity [26].
Liu et al. have shown the therapeutic effect of reactive oxygen species (ROS)-involved cancer therapies is significantly limited by shortage of oxy-substrates, such as hypoxia in photodynamic therapy (PDT) and insufficient hydrogen peroxide (H2O2) in chemodynamic therapy (CDT). Liu reports a H2O2/O2 self-supplying nanoagent, (MSNs@CaO2-ICG)@LA, which consists of manganese silicate (MSN)-supported calcium peroxide (CaO2) and indocyanine green (ICG) with further surface modification of phase-change material lauric acid (LA). Under laser irradiation, ICG simultaneously generates singlet oxygen and emits heat to melt the LA. The exposed CaO2 reacts with water to produce 02 and H2O2 for hypoxia-relieved ICG-mediated PDT and H2O2-supplying MSN-based CDT, acting as an open source strategy for ROS production. Additionally, the MSNs-induced glutathione depletion protects ROS from scavenging, termed reduce expenditure [27].
Tan et al. discussed the mechanisms of hydrogen peroxide (H2O2) decomposition and reactive oxygen species (R.O.S.) formation on the catalyst surface is always a critical issue for the environmental application of Fenton/Fenton-like reaction. Tan teaches activating H2O2 in a co-catalytic Fenton system with oxygen incorporated MoS2, namely MoS2-xOx flakes. The MoS2-xOx flake assisted co-catalytic Fenton system exhibited superior degradation activity of emerging antibiotic contaminants (e.g., sulfamethoxazole). Combining density functional theory (DFT) calculation and experimental investigation, Tan demonstrated that oxygen incorporation could improve the intrinsic conductivity of MoS2-xOx flakes and accelerate surface/interfacial charge transfer, which further leads to the efficacious activation of H2O2. Moreover, by tuning the oxygen proportion in MoS2-xOx flakes, Tan modulated the generation of ROS and further directed the oriented conversion of H2O2 to surface-bounded superoxide radical (·O2-surface) [28].
Sarniak et al. reported that the main cellular source of reactive oxygen species (ROS) is mitochondrial respiratory chain and active NADPH responsible for the “respiratory burst” of phagocytes. In addition R.O.S. are produced in endoplasmic reticulum, peroxisomes, with the participation of xanthine and endothelial oxidase and during autoxidation process of small molecules. The mitochondrial respiratory chain is the main cellular source of ROS. It is considered that in aerobic organisms R.O.S. are mainly formed during normal oxygen metabolism, as byproducts of oxidative phosphorylation, during the synthesis of ATP. The intermembranous phagocyte enzyme-activated NADPH oxidase, responsible for the “respiratory burst” of phagocytes, which is another source of ROS, plays an important role in defense of organism against infections [29].
Liu et al. show that the physiologically relevant reactive oxygen species (ROS) generation supported by the complex II substrate succinate occurs at the flavin mononucleotide group (FMN) of complex I through reversed electron transfer, not at the ubiquinone of complex III as commonly believed. Indirect evidence indicates that the unknown ROS-generating site within complex I is also likely to be the FMN group. It is therefore suggested that the major physiologically and pathologically relevant ROS-generating site in mitochondria is limited to the FMN group of complex I [30].
Fu et al. have shown that the overproduction of ROS can induce oxidative stress, resulting in cells failing to maintain normal physiological redox-regulated functions (31). The damage in cell function and development includes oxidative modification of proteins to generate protein radicals, initiation of lipid peroxidation, DNA-strand breaks, modification to nucleic acids, modulation of gene expression through activation of redox-sensitive transcription factors, and modulation of inflammatory responses through signal transduction, leading to cell death and genotoxic effects.
In some of these embodiments which generate hydroxyls, radicals, oxidizers and the like, the pathogen does not need to physically contact the biocidal, as the hydroxyls, radicals, and oxidizers transit throughout the ambient environment or liquid to stress and deactivate the pathogens.
The radicals can stress and deactivate the cell membranes and lipids, the nucleic acids, proteins, and antioxidant systems.
An interesting feature of metal nanoparticle (NP) is their strong plasmon field created by surface plasmon resonance. The field intensity decreases with the distance from the metal surface. When a fluorophore or PS is placed at the vicinity of the metal NP (about 10 nm from the metal surface) the electrons of the PS that are involved in the excitation/emission process, interact with the plasmon field of the metal NP. The interaction results in quenching or enhancement of the fluorescence level of PS and consequently of radical species and/or 102 [31].
Scharff et al. reported about the ability of photo excited supramolecular composites containing fullerenes C60 immobilized at nanosilica particles to generate reactive oxygen species (ROS) in cells of two types (rat thymocytes, and transformed cells of ascite Erlich carcinoma, EAC, and leucosis L1210). Scharff identified the damaging effect of photo excited C60-composites, which appeared to be selective and manifested in transformed cells, but not in thymocyte. Scharff showed during the irradiation of f aqueous solutions or cell suspensions in the presence of fullerene C60, the generation of reactive oxygen species is observed [32].
Yang et al. found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the bulk MoS2 powders used for the synthesis of ce-MoS2 sheets possibly due to the 2D planar structure (high specific surface area) and higher conductivity of the ceMoS2. Yang investigated the antibacterial mechanisms of the ce-MoS2 sheets and proposed their antibacterial pathways. Yang found that the ce-MoS2 sheets could produce reactive oxygen species (ROS), different from previous report on graphene-based materials. Particularly, the oxidation capacity of the ce-MoS2 sheets toward glutathione oxidation showed a time and concentration dependent trend, which is fully consistent with the antibacterial behavior of the ce-MoS2 sheets. The results suggest that antimicrobial behaviors were attributable to both membrane and oxidation stress. The antibacterial pathways include MoS2-bacteria contact induced membrane stress, superoxide anion (O2·—) induced ROS production by the ce-MoS2, and the ensuing superoxide anion-independent oxidation. The Yang study thus indicates that the tailoring of dimension of nanomaterials and their electronic properties would manipulate antibacterial activity [34].
Zhao et al. have demonstrated that molybdenum disulfide (MoS2) flakes can be an excellent solar disinfection agents for multi-drug resistant (MDR) bacteria with disinfection efficiencies 499.9999% in only 30 min. Distinct from other reactive oxygen species (ROS)-dependent photocatalysts, both ROS generation and size decrease contributed to the high antibacterial efficiencies of MoS2 [35].
Lakshmi Prasanna et al. have prepared a systematic and complete antibacterial study on well-designed and well-characterized microparticle (micro), nanoparticle (nano), and capped nano ZnO has been carried out in both dark and light conditions with the objective of arriving at the mechanism of the antibacterial activity of ZnO, particularly in the dark. The present systematic study has conclusively proven that reactive oxygen species (ROS) such as ·OH, ·O2—, and H2O2 are significantly produced from aqueous suspension of ZnO even in the dark and are mainly responsible for the activity in the dark up to 17%, rather than Zn2+ ion leaching as proposed earlier. Prasanna's work further confirms that surface defects play a major role in the production of ROS both in the presence and absence of light. In the dark, superoxide (·O2—) radical mediated ROS generation through singly ionized oxygen vacancy is proposed for the first time, and it is confirmed by EPR and scavenger studies [36].
Sarkar et al. have shown that electrospray-deposited silver ions react with the MoS2 NSs at the liquid-air interface, resulting in Ag2S nanoparticles which enter the solution, leaving the NSs with holes of 3-5 nm diameter. Specific reaction with the S atoms of MoS2 NSs leads to Mo-rich edges. Such Mo-rich defects are highly efficient for the generation of active oxygen species such as H2O2 under visible light which causes efficient disinfection of water. 105 times higher efficiency in disinfection for the holey MoS2 NSs in comparison to normal MoS2 NSs is shown. Experiments are performed with multiple bacterial strains and a virus strain, demonstrating the utility of the method for practical applications [37].
Morones et al. reported that when bacterial cells were treated with silver, changes took place in its membrane morphology that produced a significant increase in its permeability affecting proper transport through the plasma membrane, leaving the bacterial cells incapable of properly regulating transport through the plasma membrane, and resulting in cell death. It is observed that silver nanoparticles penetrate inside the bacteria and cause damage by interacting with phosphorus and sulfur containing compounds such as DNA and regulating enzymes [38].
Black phosphorus flakes can cause physical damage to the cell wall by triggering intracellular periplasmic and cytoplasmic leakage. Similar observations of physical damage to cell membrane by macro-knife like behavior of 2D flakes penetrating the cell membrane were noted by Alimohammadi et al [39].
The thickness of some embodiments of 2D flakes varies from 0.3 nanometers to more than 100 nanometers. The height and width of these flakes varies from twice the thickness of its width to hundreds of times its thickness. Some scientists describe the flake edges as atomically sharp. These dimensions form edges that creates pores, or holes, or tears in the pathogen membrane. The longest axis length of a typical pathogen is approximately one micron, whereas the size of a typical human or mammalian cell is 50 microns.
And due to the randomness of the edge features of the myriad of flake profiles, some flakes have edges not unlike the serrations of a knife blade. Graphene has strength comparable to steel, whereas MoS2 has half the strength of a comparable dimension steel flake. The pathogens become lacerated upon the blade like flake edges of the composite particle.
The primary reason why these blade shaped flakes do not harm human cells or mammalian cells, is that these cells are very specialized and also much larger than microorganism cells. For example, a typical pathogen cell is only about 1-2 microns in its longest dimension. But human cells are much larger, around 25 microns in size. So the effect of the flake edge is limited relative to the size of a mammalian cell, whereas the flake edge causes substantial damage to the pathogen cell membrane. In addition, holes in the pathogen membrane allow radicals from the ambient to also stress the pathogen.
The pathogen is lacerated as the result of a number of events. As the pathogen increases in volume, it contacts the flake edge. And as it continues to increase in volume, the expansion of the membrane forces the flake edge deeper into the membrane of the pathogen.
During mitosis, new cells arise in an area which was formerly occupied by 1 cell, causing the newly formed cell membranes to sometimes contact and sometimes apply pressure to the flake edge, causing the flake edge to bury into the cell.
Vibration, air currents, cell expansion and contraction, changes in temperature and humidity—all can cause the pathogen to vibrate and move, repeatedly putting the pathogen into contact with the flake edge.
In some embodiments the semiconductive flake inundates the pathogen with radicals, when exposed to light or without light activation, in the dark, 24/7, 365 days a year. The semiconductive flake generates a multitude of electrons and holes. The ambient air or water provides a nearly unlimited source of reactants such as oxygen atoms, water molecules, and others which are converted into radicals. Whereas the single cell pathogen is not able to produce a comparable multitude of antioxidants. The pathogen is swamped by the multitude of radicals, and the constituents of the pathogen are stressed and ultimately deactivated by the multitudes of radicals.
Moreover, due to the inherent mechanical strength of the flakes, and their relatively high melting temperature (basMoS2 has a melting point exceeding 2,000 degrees Fahrenheit), and their broad chemical resistance, the flakes permanently stress and deactivate pathogens—for years.
The antibacterial activities of graphene oxide and reduced GO were reported by Hu et al. in 2010. They observed that GO and rGO suspensions can efficiently inhibit the viability of Escherichia coli (E. coli) bacteria by damaging the cell integrity. They also found that GO has stronger antibacterial activities and lower cytotoxicity than rGO because of the distinct charges and functional groups on the surfaces [40].
Xiao et al. found that a small amount of graphene oxide (GO) flakes have a strong effect on sensitizing lipid membranes to the peptide melittin and dramatically decrease the threshold concentration of melittin for the killing of bacteria. Molecular leakage tests from model vesicles showed that pretreatment of membrane with GO, even at a low concentration of 0.1 μg mL-1, decreased the threshold working concentration of melittin to less than half of the initial value, while in the living bacteria tests, such sensitizing effect of GO reduced the MIC value of melittin by almost 10 times. By combining experiments and simulations, Xiao found that the sensitizing effect of GO was derived from its similar mechanical disturbance to cell membranes as that of melittin at high concentrations in membrane structures including lipid diffusion, packing state, and pressure distribution. Xiao's results provide a cost-effective strategy to enhance the antibacterial efficiency of AMPs for clinical use [41].
The metallic phase of 1T-MoS2 nanoflowers (NFs) and the semiconducting phase of 2H—MoS2 NFs were prepared by a facile solvothermal and combustion method. The antibacterial activities, reactive oxygen species (ROS) generation, and light-driven antibacterial mechanism of metallic 1T-MoS2 NFs and semiconducting 2H—MoS2 NFs were demonstrated with the bacterium Escherichia coli (E. coli) under light irradiation. Results of the bacterial growth curve and ROS generation analyses revealed higher light-driven antibacterial activity of metallic 1T-MoS2 NFs compared to semiconducting 2H—MoS2 NFs. Electron paramagnetic resonance (EPR) spectroscopy demonstrated that the ROS of the superoxide anion radical ·O2— was generated due to the incubation of 1T-MoS2 NFs and E. coli with light irradiation. Furthermore, E. coli incubated with metallic 1T-MoS2 NFs exhibited significant damage to the bacterial cell walls, complete bacterial destruction, and abnormal elongation after light irradiation. The light-driven antibacterial mechanism of metallic 1T-MoS2 NFs was examined, and it was found that, under light irradiation, photoinduced electrons were generated by metallic 1T-MoS2 NFs, and then the photoinduced electrons reacted with oxygen to generate superoxide anion radical which induced bacterial death [42].
Basu et al. Introduced defects on varied MoS2 surfaces by suitable doping of nitrogen atoms in a sulfur-rich reaction environment, resulting in stable and scalable phase conversion. The experimental characterizations along with the theoretical calculations within the framework of density functional theory establish the impact of nitrogen doping on stabilization of defects and reconstruction of the 2H to 1T phase. The as-synthesized MoS2 samples exhibit excellent dye removal capacity in the dark, facilitated by a synergistic effect of reactive oxygen species (ROS) generation and adsorption. Positron annihilation spectroscopy and electron paramagnetic resonance studies substantiate the role of defects and associated sulfur vacancies toward ROS generation in the dark. Further, on the basis of its ample ROS generation in the dark and in the light, the commendable antimicrobial activity of the prepared MoS2 samples against fungal pathogen Alternaria alternata was demonstrated [43].
Han et al. report a Cu, Pd co-doped MoS2 particle as an efficient and stable Hydrogen Evolution Reaction (HER) electrocatalyst, which partially resolves the problem of hole and electron recombination and leads to high overall performance. Specifically, Han improves the electric conductivity of the MoS2 by Cu dopant and realizes the phase transition of MoS2 from pristine 2H phase to stable 1T phase by Pd dopant [44].
Achieving a heterojunction using molybdenum disulfide or graphene or composites thereof extends the lifetimes of holes and electrons and keeps some of them from recombining and becoming inactive. The holes or electrons escape from recombination, and are available to reduce or oxidize nearby oxygen or water moisture and form oxides, radical, and hydroxyls.
Ji et al designed a facile one-pot solvothermal method to synthesize porous 1T-MoS2 that is integrated with atomic doping of Cu atoms [45].
Wei et al proposed simple high-temperature calcination method was used to produce metallic molybdenum disulfide (1 T-LixMoS2). The proposed method converts the 2H phase to the 1 T phase by doping commercial MoS2 with lithium ions [46].
Gan et al reported about developed a simple yet effective method, cyclic voltammetry, to successfully tune the 2H/1T phase transition of multilayer MoS2 nanosheets without using intercalation species. The phase transition is triggered by the electrochemical incorporation of S vacancies (obtained by electrochemical etching), which on the one hand injects electrons into the framework of S—Mo—S and on the other hand facilitates the sliding of S planes [47].
Altay Unal et al. have shown inhibition of the viral infection was tested in vitro with four viral clades, Ti3C2Tx in particular, was able to significantly reduce infection only in SARS-CoV-2/clade GR infected Vero E6 cells. This difference in the antiviral activity, among the four viral particles tested, highlights the importance of considering the viral genotypes and mutations while testing antiviral activity of potential drugs and nanomaterials. Among the other MXenes tested, Mo2Ti2C3Tx also showed antiviral properties [48].
Galante et al. in their work demonstrates a coal-derived functionalized Graphene oxide coating applied to fabrics that exhibits antiviral properties even after mechanical abrasion or bleach washing. Graphene oxide is chemically exfoliated from low cost coal and functionalized with octadecylamine to render repellency properties. The functionalized graphene oxide is applied to polyethylene terephthalate (PET) fabric after wet etching which roughens the microfiber surface for better coating adhesion and liquid repellency. An additional polydimethylsiloxane (PDMS) layer on top of the functionalized graphene oxide further improves the repellency and durability. The functionalized nano-graphene oxide/PDMS coating robustly repels droplets of water and human saliva. Additionally, Galante demonstrates the antiviral properties with human adenovirus type 5 (HAdV5), herpes simplex virus type 1 (HSV-1), and betacoronavirus (CoV) even after mechanical abrasion and bleach washing [49].
Khamati et al. in their review show that the development of efficient antimicrobial agents against pathogenic bacteria is needed, especially for antibiotic-resistant bacteria and bacterial biofilms that are typically hard to be treated with conventional antibiotics. MXenes demonstrated attractive properties such as highly active sites, significant chemical stability, hydrophilicity, large interlayer spacing, huge specific surface area, and superior sorption-reduction capacity. These two-dimensional materials demonstrated efficient antibacterial properties against pathogenic bacteria. Additionally, antiviral effects of MXenes, as well as their immune compatibility and anti-inflammatory effects of them on human immune cells were illustrated [50].
Rozmyslowska-Wojciechowska et al. have shown the ability to stabilize the surface properties of MXenes has been demonstrated here through surface charge engineering. It was thus determined how changing the surface charges of two-dimensional (2D) Ti3C2 MXene phase flakes using cationic polymeric poly-L-lysine (PLL) molecules affects the colloidal and biological properties of the resulting hybrid 2D nanomaterial. Electrostatic adsorption of PLL on the surface of delaminated 2D Ti3C2 flakes occurs efficiently, leads to changing an MXene's negative surface charge toward a positive value, which can also be effectively managed through pH changes. Analysis of bioactive properties revealed additional antibacterial functionality of the developed 2D Ti3C2/PLL MXene flakes concerning Escherichia. coli Gram-negative bacteria cells [51].
Shamsabadi et al. demonstrated antibacterial properties of two-dimensional (2D) nanomaterials are of great interest in fields such as environmental engineering, biomedical engineering, and medicine. Ti3C2Tx MXene, a novel 2D nanomaterial, has been reported to have excellent antibacterial activity against both Gram-negative and Gram-positive bacteria. This paper presents the first study aimed at determining the primary antibacterial mode-of-action of the MXene. Shamsabadi studied the antibacterial properties of MXene nanosheets with lateral sizes of 0.09, 0.35, 0.57, and 4.40 μm against Escherichia coli and Bacillus subtilis bacteria for 3 and 8 h in the dark. Quantitative analyses of bacteria species performed with complementary techniques, fluorescence imaging, and flow cytometry confirmed that the antibacterial activity of the MXene nanosheets is both size- and exposure-time-dependent. Smaller nanosheets showed higher antibacterial activities against both bacteria [52].
Malina et al. demonstrated its toxicological effects of graphene oxide (GO) on aquatic organisms have not been properly investigated. Malina compared the toxicity of differently oxidized graphene oxide systems towards the green alga Raphidocelis subcapitata and the cyanobacterium Synechococcus elongatus. The cyanobacterium exhibited higher GO sensitivity and more rapid growth inhibition than the alga, in keeping with the established antibacterial properties of GO. The toxic effects of GO included shading/aggregation of GOs and nutrient depletion; however a detailed mechanistic study revealed that GO acted against R. subcapitata via an additional, new mechanism. Remarkably, lightly oxidized GO samples induced significantly greater membrane integrity damage than more heavily oxidized GO samples. Flow cytometry and microscopy experiments revealed that lightly oxidized GO can act as a blade that causes mechanical damage to algal cells, probably because of the comparatively low coverage of oxygen-bearing functionalities at the edges of such GO sheets [53].
MoS2 flakes (with or without iron) were vertically coated on titanium substrate via a one-step hydrothermal process, and their in vitro antibacterial mechanism was studied systematically under dark conditions. The results solidly evidenced that the antimicrobial efficacy of such MoS2 nanosheets is a combined effect of ROS generation and ion release, which is independent on light illumination. Doping of iron in terms of FeMoO4 strengthens the bactericidal capability of the MoS2 coatings through releasing ferrous ion and boosting ROS generation via Fenton-like reactions. These results provide new insights into the antibacterial mechanism of MoS2 and may promote applications of the materials in biomedical devices [54].
Begun et al. reported the design of a novel composite platform using melittin antimicrobial peptide-attached MoS2. Begun reported data showing that 100% of superbugs are killed using an antimicrobial peptide-attached PEG-MoS2-AMP platform via a synergistic killing mechanism. Reported experimental data indicates that only 45% of MDRB killing is possible via MoS2 flake-based PTT and PDT processes together, and it is mainly due to the lower heat generation during PTT and a small amount of ROS formation during PDT in the presence of 670 nm light. Begun reported data also show that about 20% of superbugs can be killed by the melittin antimicrobial peptide alone, whereas 100% of superbugs can be killed using melittin antimicrobial peptide-attached MoS2 flakes with NIR light. This is due to the fact that, in the presence of the melittin antimicrobial peptide attached PEG-MoS2-AMP composite platform, initially the melittin antimicrobial peptide makes pores on the surface of MDRB, and the pores help to diffuse heat and ROS easily during PDT and PTT. Due to the possible synergistic multimodal killing mechanism, 100% of MDRB were killed [55].
Chitosan exfoliated MoS2 flakes were successfully synthesized by a simple, one-step green process. Electron microscopy of the synthesized flakes showed high degree of exfoliation of bulk MoS2 into monolayered and few-layered flakes of uniform size. The flakes were also found to be highly stable and well dispersed in aqueous solution. Evaluation of antibacterial activity of the CS—MoS2 flakes revealed the excellent potential of these flakes to cause growth inhibition of both Gram-negative and Gram-positive bacteria in a concentration and time-dependent manner. Detailed investigations into elucidating the mechanism of antibacterial action showed that the CS—MoS2 flakes induced bacterial cell death through a combined action of membrane damage, metabolic inactivation, and oxidative stress. The synthesized flakes were also found to possess antibiofilm activity and showed high biocompatibility toward mammalian cells. It is of great significance to highlight the fact that the antibacterial and antibiofilm action of the chitosan exfoliated MoS2 flakes were observed without the need for any additional surface functionalization of the flakes with complex ligands, biocidal nanoparticles, antimicrobial peptides, photosensitizers, or antibiotics and even in the absence of NIR assisted photothermal action [56].
Pandit et al. report a proof-of-principle study to evaluate the potential of functionalized two-dimensional chemically exfoliated MoS2 (ce-MoS2) toward inhibitory and bactericidal property against two representative ESKAPE pathogenic strain∂a Gram-positive Staphylococcus aureus (MRSA) and a Gram-negative Pseudomonas aeruginosa. More significantly, the mechanistic study establishes a different extent of oxidative stress together with rapid membrane depolarization in contact with ce-MoS2 having ligands of varied charge and hydrophobicity. The implication of these results is discussed in the light of the lack of survivability of planktonic bacteria and biofilm destruction in vitro. A comparison with widely used small molecules and other therapeutics conclusively establishes a better efficacy of 2D ce-MoS2 as a new class of antibiotics [57].
Perkas et al. reported about silver nanoparticles (NPs) were synthesized sonochemically by the reduction of silver ions with ethylene glycol and simultaneously deposited on different forms of TiO2 powders (commercial Degussa P-25, synthetic anatase and mesoporous titania). The antimicrobial properties of Ag—TiO2 were tested against a number of Gram-positive and Gram-negative bacteria. A high bactericidal effect was found in the absence of UV light. The reduction in bacterial viability was between 3 and 4.2 logs. Based on the experimental data it was concluded that enhanced antimicrobial activity of the Ag—TiO2 originated from both the oxidative stress generated by silver nanoparticles and the presence of silver ions on the surface of the silver-titania composite [58].
Fonseca et al. reported on poly(lactic acid) (PLA) composites with titanium oxide (TiO2)˜ 10-nm nanoparticles were produced by the melting process and their main properties were evaluated. The particles are homogeneously dispersed in the matrix with a low degree of agglomeration, as seen by transmission electron microscopy (TEM). The crystallinity temperature increased ˜12% when 5 wt. % of TiO2 was added, showing that the particles acted as nucleating agents this trend was confirmed by optical images. Regarding biocidal properties, after 2 h of contact the PLA/TiO2 composites with 8 wt. % TiO2 showed a reduction of Escherichia coli colonies of ˜82% under no UVA irradiation compared to pure PLA [59].
Wojciechowski et al. describe multilayered Ti3C2 MXene-based materials such as Ti3C2/Al3+, Ti3C2/In and Ti3C2/Ga, obtained by modifying the MXene surface with aluminum-, indium- and gallium alkoxides. In the synthesis of these materials, organometallic compounds of group 13 metals (Et3Al, Me3In, and Et3Ga) were chosen as precursors for the alkoxides to modify the surface. To attach organometallic compounds to the MXene surface, their high reactivity towards the terminal OH, ═O and F groups present on the MXene surface was used. In the next step, exposure of the surface-attached aluminum-, indium and gallium alkyls to air allowed their transformation into metal alkoxides due to the high reactivity of the metal-carbon bonds to oxygen and water. In this method of MXene modification, the alkoxide precursors can be extended to other organometallic compounds, such as groups 1, 2 and 12 alkyls. Microbiological studies of the developed 2D Ti3C2/Al3+, Ti3C2/In and Ti3C2/Ga alkoxides showed no acute ecotoxicity to the tested microorganisms. The obtained materials did not influence bioluminescent/biosensor-type microorganisms nor reduce the viability of other types of microorganisms, such as Staphylococcus aureus, Escherichia coli or Candida albicans [60].
Camilli et al. have shown that chemical vapour deposition on catalytic metals has become a well developed approach for the growth of graphene and hexagonal boron nitride (BN), very few alternative approaches for synthesis on non-reactive supports have been explored so far. Camilli reports the growth of BN on gold, using magnetron sputtering of B in N2/Ar atmosphere, a scalable method using only non-toxic reagents. Scanning tunnelling microscopy at low coverage shows primarily triangular monolayer BN islands exhibiting two ‘magic’ orientations on the Au(111) surface [61].
Non-limiting examples of linkers or binders or ligands for MoS2 are chitosan, ctab, dbsa, 3-mercaptoproprionic acid, 3-mercaptopropyl trimethoxysilane, and COOH+HEMA.
Galoppini collected in his review the synthesis and properties of sensitizers consisting of chromophore-linkers arrays where the linkers are based on alkyl chains, rigid-rods, or tripod-shaped molecules [62].
Xu et al. demonstrate a simple strategy to achieve high magnesium storage capability for Ti3C2 MXene by preintercalating a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Density functional theory simulations verify that intercalated CTA+ cations reduce the diffusion barrier of Mg2+ on the MXene surface, resulting in the significant improvement of the reversible insertion/deinsertion of Mg2+ ions between MXene layers [63].
Hao et al. have shown a routine for mesoporous silica nanomaterials of different shapes (film, platelet, sphere, rod) were synthesized simply by tuning the mole ratio of dual cationic surfactant templates, cetyltrimethylammonium bromide (CTAB) and tetrabutylammonium iodine (TBAI). The film showed the most potent antibacterial activity against mycobacteria [64].
Mody et al have prepared review article that provides a glimpse to some simpler nanoparticles which are being currently modified for their potential applications in biomedical imaging using MRI, CT, ultrasound, PET, SERS, and optical imaging [65].
Rai et al have shown that nanotechnology provides a novel platform for the development of potential and effective agents by modifying the materials at nanolevel with remarkable physicochemical properties, high surface area to volume ratio and increased reactivity. Among metal nanoparticles, silver nanoparticles have strong antibacterial, antifungal and antiviral potential to boost the host immunity against pathogen attack. Nevertheless, the interaction of silver nanoparticles with viruses is a largely unexplored field. The present review discusses antiviral activity of the metal nanoparticles, especially the mechanism of action of silver nanoparticles, against different viruses such HSV, HIV, HBV, MPV, RSV . . . [66].
Hoseinnejad et al have described many inorganic and metal nanoparticles have been implemented to synthesize active food packaging materials and to extend the shelf-life of foods. Packaging with nanocomposites containing these nanoparticles offers advantages, such as reduction in the usage of preservatives and higher rate of reactions to inhibit the microbial growth. Nevertheless, the safety issues of employing the metal and inorganic nanoparticles in food packaging are still a major concern and more studies along with clinical trials need to be carried out prior to the mass production of these promising food containers. In this review, we have evaluated recent studies plus the applications of inorganic and metal nanoparticles mostly in food packaging applications along with their antimicrobial properties and reaction mechanisms [67].
Non-limiting examples of nanoparticles are gold nanoparticles, silver nanoparticles, FeO, Fe3O4, Fe2O3, Cui, TiO2, ZnO, CuO, MgO, SiO2, Alumina, and CuO.
Ashraful Islam et al. teach that two-dimensional molybdenum disulfide (2D MoS2) presents extraordinary optical, electrical, and chemical properties which are highly tunable by engineering the orientation of constituent 2D layers. 2D MoS2 films with vertically-aligned layers exhibit numerous 2D edge sites which are predicted to offer superior chemical reactivity owing to their enriched dangling bonds. This enhanced chemical reactivity coupled with their tunable band gap energy can render the vertical 2D MoS2 unique opportunities for environmental applications. Herein, we report that MoS2 films with vertically-aligned 2D layers exhibit excellent visible light responsive photocatalytic activities for efficiently degrading organic compounds in contaminated water such as harmful algal blooms [68].
Yang et al described that two-dimensional (2D) materials, graphene and hexagonal-boron nitride (h-BN) are famous for protective coatings, because of their excellent chemical resistance, barrier property, impermeability along with thermal stability, and a large number of these properties are particularly suitable for protective coatings. However, the applications of graphene for metal protection have been limited by galvanic corrosion issues. Also, h-BN nanosheets are also explored as potential materials for corrosion protecting, especially, electrical insulation of h-BN is influential in solving electrochemical reaction and uniquely suitable to be used as an anticorrosion material [69].
Mazinani et al have shown that recently, 2-dimensional (2D) materials such as graphene oxide (GO), MXene, and hexagonal boron nitride (hBN) have received considerable attention for surface modifications showing their antibacterial properties. In this paper, a comparative study on the effect of partial deposition of these three materials over PEO titania substrates on the antibacterial efficiency and bioactivity is presented. Their partial deposition through drop-casting instead of continuous film coating is proposed to simultaneously address both antibacterial and osseointegration abilities. Our results demonstrate the dose-dependent nature of the deposited antibacterial agent on the PEO substrate. GO-PEO and MXene-PEO samples showed the highest antibacterial activity with 70 (±2) % and 97 (±0.5) % inactivation of S. aureus colonies in the low concentration group, respectively. Furthermore, only samples in the higher concentration group were effective against E. coli bacteria with 18 (±2) % and 17 (±4) % decrease in numbers of colonies for hBN-PEO and GO-PEO samples, respectively [70].
Lui et al have shown that graphene oxide (GO) was thought to be a promising antibacterial material. In his work, graphene oxide coatings on polymer substrate were prepared and the antibacterial activity against E. coli and S. aureus was investigated. It was demonstrated that the coatings exhibited stronger antibacterial activity against E. coli with thin membrane than S. aureus with thick membrane. Take into consideration the fact that the coatings presented smooth, sharp edges-free morphology and bonded parallelly to substrate, which was in mark contrast with their precursor GO nanosheets, oxidative stress mechanism was considered the main factor of antibacterial activity [71].
All of these printing processes are compatible with field generating equipment, including electrical field generating equipment. These printing processes charge composite particles in a liquid dispersion or powder with a potential as the composite particles are emitted from the printing device orifices or roller. In addition, all of these printing processes can be designed to keep separate the composite particles from contaminants until the moment of printing deposition, so that the composite particles remain sterile. If equipped with a computer controlled cutter, the actual working area of the plotting knife is relatively small, and the sterile medical device cleanliness could be maintained with a small area hepa filtered hood or similar accessory. And in some embodiments, the newly printed coating and substrate can be subject to rapid heating and ultraviolet exposure to maintain the sterile field as the newly printed and custom cut sterile medical device exits the printer. In some embodiments, a single medical device could be custom printed, exclusive to the patient's need, just in time, for application by the health professional.
There are many dozens of chemicals with flake-shaped particle morphology which fulfill this application. Without limiting the practice of this application, I will emphasize MoS2 in fulfilling this application.
MoS2 has been exfoliated worldwide for decades, with no significant toxicity. For decades MoS2 has been used as a lubricant in automotive oil. The piston and cylinder walls of an automobile rotating at 7,000 r.p.m. are similar to a laboratory homogenizer rotating at 7,000 r.p.m. Government agencies world wide, including the Environmental Protection Agency have been analyzing automobile exhaust for decades without noting significant toxicity from MoS2. Molybdenum is a trace element for humans as is sulfur. MoS2 is currently allowed as a lubricant for food processing machines, and has been rigorously tested by the Food and Drug Administration.
Exfoliated MoS2 is water clear.
Bulk MoS2 is a diamagnetic, indirect bandgap semiconductor, with a bandgap of 1.23 eV. All forms of MoS2 have a layered structure, in which a plane of molybdenum atoms is sandwiched between planes of sulfide ions. These three strata form a monolayer triad of MoS2. Bulk MoS2 consists of stacked triads, triads which are held together by weak Van der Waals interactions.
Crystalline MoS2 naturally occurs in two phases, 2H—MoS2 and 3R—MoS2, where the “H” and the “R” indicate hexagonal and rhomboidal geometry, respectively. In these structures each molybdenum atom exists at the center of a trigonal prismatic coordination sphere and is covalently bound to six sulfide ions. Each sulfur atom has pyramidal coordination and is bound to three molybdenum atoms. Both the 2H- and 3R-phases are semiconducting phases of MoS2.
The 1T form of MoS2 is trigonal in its geometry. In this phase, MoS2 exhibits metallic properties. The metallic phase has ≈105 Siemens (or higher) electrical conductivity compared to the semiconducting phase. The 1T phase has superior electron transfer capability.
The MoS2 flake has few or no dangling bonds. Along the thin edge of the flake, some of the Molybdenum atoms have valence domains which are available to form associations. Voids in the sulfur layers make it possible for more associations to form with the Molybdenum atoms available.
The Van der Waals forces between the interlayers or triads of MoS2 are very weak. Therefore, individual layers can be isolated using traditional mechanical cleavage techniques, such as chemical exfoliation, ball milling, and intercalation, among many other exfoliation techniques.
MoS2 is relatively nonreactive and has a low coefficient of friction. Weak interlayer Van der Walls interaction present between the triads facilitates the exfoliation of bulk crystal into few layer or monolayer crystals or flakes, which exhibit layer dependent properties. In addition, monolayer MoS2 has high electron mobility.
Another important property of MoS2 monolayers is their high exciton binding energy (˜0.5-1 eV) arising from substantially reduced dielectric screening relative to the bulk. This promotes strong and long-lived excitons.
The monolayer MoS2 is a crystalline structure, whereby the upper and lower layers are planes composed of sulfur atoms, and the middle is a layer of metal molybdenum atoms. Each molybdenum atom in the layer covalently bonds with six sulfur atoms to form the Mitsubishi columnar coordination structure. Meanwhile, each sulfur atom combines with three molybdenum atoms through covalent bonding.
The structure of the layered metal dichalcogenides includes one hexagonal packed sheet of metal atoms sandwiched between two hexagonal sheets of chalcogen atoms. The coordination of the metal atoms by the chalcogen atoms is either hexagonal (e.g. titanium disulfide and Vanadium disulfide) or trigonal prismatic (e.g. molybdenum disulfide and niobium disulfide). The MX layers are kept together by Van der Waals forces and several stacking polytypes exist. There is weak bonding between triads, where a layer consists of a monolayer of metal atoms clad together by covalently bonded chalcogens.
The coordination and the oxidation state of the metal atom determine the electronic properties of the material. For example, the group V metal atoms (niobium and tantalum) are in a trigonal prismatic coordination and the corresponding dichalcogenide materials are metals, while group VI atoms (molybdenum and tungsten) are also in a trigonal prismatic coordination but have a full dz band and hence are semiconductors. Molybdenum disulfide has both a hexagonal and a trigonal prismatic coordination and can thus be either metallic or semiconducting respectively.
The major axis of the dichalcogenide flake shape refers to the longest portion of the dichalcogenide flake shape when being observed from the thickness direction thereof.
In some embodiments the metallic component of the chalcogenide is titanium, Zirconium, hafnium, Vanadium, tantalum, niobium, molybdenum, tungsten, or tin. Or gallium, or indium, or thallium. Or two-dimensional semiconductor includes at least one of a transition metal dichalcogenide, a CdTe single-layer, Gas, GaSe, GaS1-Sez, CdI2, PbI2, K2Al4 (Si Al2O23) (OH, F) 4, PbI2, K2Al4 (Si Al2O23) (OH, F) 4, Molybdenum disulfide (MoS2), molybdenum diselenide (MoSe), molybdenum ditelluride (MoTex), tungsten disulfide (WS), tungsten diselenide (WSez), tungsten ditelluride (WTe), niobium disulfide (NbS), niobium diselenide (NbSez), niobium ditelluride (NbTex), tantalum disulfide (TaS), tantalum diselenide (TaSe), tantalum ditelluride (TaTe), hafnium disulfide (HfS), hafnium diselenide (HfSez), hafnium ditelluride (HfTez), titanium disulfide (TiS), titanium diselenide (TiSex), and titanium ditelluride.
The layered metal chalcogenides include any compounds comprising metal atoms and chalcogen atoms in a layer-type structure. Examples include layered metal dichalcogenides and layered metal monochalcogenides. The layered metal dichalcogenides have the chemical formula MX wherein M represents a metal and X represents a chalcogen (i.e. sulfur, selenium or tellurium). The structure of the layered metal dichalcogenides preferably includes one sheet of metal atoms sandwiched between two sheets of chalcogen atoms. In the layered metal dichalcogenides, the metallic component M is preferably selected from transition metals Such as titanium, zirconium, hafnium, vanadium, tantalum, niobium, molybdenum and tungsten and non-transition metals such as tin. More preferred are niobium, molybdenum, tantalum, tin and tungsten, and most preferred are niobium, molybdenum and tantalum. More preferred chalcogens are sulfur, selenium and tellurium, and most preferred are sulfur and selenium. Metals that form monochalcogenides which may be suitable include gallium, indium and thallium.
Implanting impurities into dichalcogenides using laser beam energy is similar to the doping of silicon using impurities (dopants) and laser energy.
The laser serves two major functions: (i) creation of sulfur vacancies in the dichalcogenide flakes and coincidentally (ii) breaking the bonds of the dopant impurities, and then the released ions and fragments then diffuse and implant into the empty sulfur vacancy sites within the crystal lattice structure of the dichalcogenide.
In our workshop in one embodiment we doped MoS2 by irradiating it using a 450 nanometer laser, in another embodiment a 523 nanometer laser, and in another embodiment a 780 nanometer laser.
The dopants are deposed proximal to the dichalcogenides. The dopant can be in a liquid solution and deposed onto the dichalcogenide or proximal to the dichalcogenide, or the dopant can be deposited as a powder on to the dichalcogenide, and in some embodiments the dopant can be in a gaseous state.
Laser doping of dichalcogenides differs from the doping of silicon as the laser doping of monolayer and few layer dichalcogenides is very fast, and because the dopants are implanted throughout the flake layers. In some embodiments, the masking of the dichalcogenide flakes is quite simple, as the top surface of the dielectric layer forms an impenetrable barrier to the impurities, and also attenuates the laser energy.
Silicon wafers require considerably more time to reach sufficient doping compared to dichalcogenides, due to the thickness of the silicon wafer, to achieve a sufficient level of doping within the first few hundred nanometers of the thickness profile of the wafer. With dichalcogenides, however, after exfoliation, the dichalcogenides are sometimes monolayer, few layer, and many layer. Since the dichalcogenides are thin flake shaped, the dopant impurities can quickly penetrate within the few nanometer thick profile of the dichalcogenide within short time durations (e.g. immediately).
Since the dichalcogenides dope so quickly, in some embodiments the flakes can be laser irradiated and doped continuously using a printing press.
A laser beam is a device that emits light through a process of optical amplification based on the simulated emission of electromagnetic radiation.
Electron-beam curing is a method of curing paints and inks without the need for traditional solvent. Electron-beam curing produces a finish similar to that of traditional solvent-evaporation processes, but achieves that finish through a polymerization process, typically without using photoinitiators.
Ion beams can also cure acrylates similar to laser beams or electron beams.
Dissociation in chemistry is a general process in which molecules (or ionic compounds such as salts and complexes) separate or split into smaller particles such as atoms, ions, or radicals.
During crosslinking of some ultraviolet curing resins, the volume dimensions of the ultraviolet coating shrinks and compresses. This is called by some as NC, or normal compression. Moeck et al. (3) of Rahn teach “The volume shrinkage of acrylates and methacrylates occurs during polymerization and is due to the replacement of long-distance connections via weak Van der Waals force by strong short covalent bonds between the carbon atoms of different monomer units. This volume shrinkage causes serious problems including a large build-up of internal stress, which results in defects formation, and dimensional changes . . . .”
Voiry et al. teach: “ . . . different phases in single layer TMDs can also be realized. A single layer of TMDs can have a trigonal prismatic” (crystal lattice structure) “phase or an octahedral” (crystal lattice structure) “phase. The trigonal prismatic phase, is also referred to as the 2H phase (or 1H in the case of a single-layer) and can be described by a hexagonal symmetry (D3h group) and corresponds to a trigonal prismatic coordination for the metal atoms. This geometry means that in single-layers, the sulfur atoms are vertically aligned along the z-axis and the stacking sequence is then AbA where A and b denote chalcogen and metal atoms, respectively The octahedral phase has a tetragonal symmetry (D3d) and corresponds to an octahedral coordination of the metal atoms. In the octahedral phase, conventionally referred to as the 1T phase, one of the sulfur layer is shifted compared to the others resulting in an AbC stacking sequence. The filling of the d orbitals of the metal directly influences the atomic structure of the TMD layers. For the 1H phase, the d orbital splits into 3 degenerate states dz2, dx2-y2, xy and dxy, yz with an energy gap of ˜1 eV between the dz2 and dx2-y2-xy orbitals. For the tetragonal symmetry of the 1T phase, the d orbitals of the metal degenerate into dxy, yz, zx (t2g) and dx2-y2, z2 (eg) orbitals. Up to 6 electrons can fill the egg orbital. Since the p orbitals of chalcogens are located at much lower energy than the Fermi level, only the filling of the d orbitals determines the nature of phases in MX2 compounds. Completely filled orbitals give rise to semiconducting behavior while partial filling induces metallic behavior.”
Bhattacharyya et al. teach the strain engineering of dichalcogenides: “The applied NC” (normal compressive) “strain leads to S-M” (semiconducting to metallic) “transition for all the multilayers and bulk MoS2. The band gap reduces smoothly and becomes zero at a threshold strain.” “The change in the electronic structure under the application of strain was analyzed for each multilayer . . . .” “With the increase in normal compression, the degenerate bands begin to split . . . . The splitting is observed to be more prevalent in the valence band (VB) as compared to the conduction band (CB). The VB as well as the CB start to move towards the Fermi level with strain, reducing the band gap smoothly . . . . An S-M transition occurs when the VB crosses the Fermi level . . . .”
Scientists teach that 1T MoS2 is unstable and metastable, and reverses spontaneously to non 1T phases.
In our workshop we demonstrated that the buried portion of the flake which was immersed in polymerizing pre-polymer that was shrinking, was converted to metallic conductivity, while the protruding portion of the flake remained semiconductive conductivity, thus forming a strain engineered heterojunction. The laser doping made the protruding portion of the flake more n-type. We also demonstrated that our construction permanently locks the differing phases of the flake, so the heterojunction was stable.
UV resins exert compressive stain on materials contained within them due to a reduction in volume when exposed to UV light. The UV light radically cleaves the photo initiator molecules present in the resin mixture which initiates polymerization and increases crosslinking density. This causes an increase in polymer density through the forming of complex matrices within the coating. When a material is contained within the resin during the curing process a compressive strain causes the material to shrink and be compressed. In some embodiments, there is an attractive force that binds the resin to the material being compressed. This attractive force could be bonds, electrostatic attractions or as simple as Van der Waals forces. This compression can alter material characteristics through molecular geometry shifts, leading to smaller band gaps, differing conductive properties as well as other novel effects. The resin molecules themselves do not shrink, however the polymerization and cross linking draw these molecules closer together and create an increased crosslink density.
During our development of these novel embodiments, we observed that during ultraviolet curing, that the conductivity of the buried flakes changed from semiconductive to metallic. Also, during our development of these novel embodiments, we observed that the metallic conductivity of the buried flakes maintained for months after the ultraviolet curing, with virtually no change in the conductivity of the buried flakes. We concluded that the ultraviolet curing monomers mutually compressed the buried MoS2 flakes, as the monomers polymerized, and changed from long-distance connections to short covalent bonds. Bond lengths between the sulfur atom and the molybdenum atom are elongated as a result of compressive force from the resins shrinking during polymerization. The elongation of the crystal lattice allows the valence band and the conduction band to become much closer in energy, thus allowing for much easier charge transfer when compared to the valence-conduction band energy gap in a semiconductor. The band gap must be sufficiently small enough that electrons can freely jump in energy level and create effective conductive charge transfer.
The compression of the flakes shifts the crystal lattice of the MoS2 from rhomboidal 2H geometry exhibiting semiconductive nature, to the lattice geometry of 1T octahedral. Said geometry change aligning the valence and conduction band so that the flake exhibits metallic characteristics. This creates a smaller band gap, thus giving the electrons higher mobility between the two bands resulting in higher conductivity.
In MoS2, the 1T arrangement is catalytically active on its basal sides as well as its edges.
Other non-limiting methods apply compressive strain to buried dichalcogenide flakes, such as the capillary forces developed during the evaporation of water from a mixture, solvent induced shrinkage, curing under pressure of an epoxy like SU7, and heat shrinkage (e.g. “shrinky dink” polystyrene.)
Some acrylate resins are known to shrink during polymerization, to reduce the actual coating volume of the acrylate resins. In some embodiments, the resin is comprised of acrylate resins and other materials that densely crosslink, with bonds that shorten during polymerization. In some embodiments, the acrylate resins and polymerization initiators polymerize with exposure to ultraviolet radiation, or near visible lightradiation, or visible light radiation. Some non-limiting xamples of acrylate resins which shrink during curing are TMPTA (Trimethylolpropane triacrylate), HDDA (1,6-hexanediol diacrylate), and 2-PEOA (2-Phenoxyethyl Acrylate). In some embodiments the resins are cured using electron beam radiation or ultrasonic radiation or high frequency radiation.
In some embodiments, a portion of the dichalcogenide flake is buried in the coating comprised of other particles, and the remainder of the dichalcogenide flake protrudes from the coating. The plurality of other particles surrounds the dichalcogenide flake, and contacts the many corners, facets, planes and edges of the random dichalcogenide flake shape. Some of the other particles may have chemical bonds to the dichalcogenide flakes. As the bonds of the coating partly comprised of other particles shorten and the yaer of other particles shrinks and reduces in volume, the layer of other particles coincidentally applies compressive strain to the many corners, facets, planes, and edges of the buried portions of the dichalcogenide flakes, causing strain upon the dichalcogenide flakes.
In some embodiments, the layer of other particles includes adhesion promoters which promote the bonding between the layer of other particles and the dichalcogenide flakes. In some embodiments, these adhesion promoters occupy available sulfur vacancies, and likewise bond to the ingredients of the layer of other particles
This compressive strain upon the buried portion of the dichalcogenide flake converts the buried portion of the flake from semiconducting to metallic conductivity.
MoS2 is strongly responsive to electromagnetic fields. And the MoS2 flake has its strongest electromagnetic response along the major axis of the flake, which is synonymous with the longest axis of the flake.
Electromagnetic field deposition of dichalcogenides occurs as a result of industrial deposition processes such as inkjet printing, continuous inkjet printing (CIJ), xerography, electrophotography, photocopying, laser printing, electrophoretic aka electrophoresis, pressure less printing, corona poling, electrostatic spraying, flocking, powder coating among other processes.
During electromagnetic deposition processes, an electrical charge is applied proximal to the MoS2 flakes. The charge potential can be positive or negative. After an electrical charge is applied to the MoS2 flakes, the flakes are brought into proximity to a substrate or electrode of the opposite electrical charge, causing the flakes to be attracted to the oppositely charged substrate or electrode.
Since the greatest charge polarity is along the major axis of the flakes, each flake is planted with its major axis approximately normal to the electrode or substrate. The wording particles oriented in a direction “approximately normal” to said substrate, as referred to in these embodiments, includes, as a matter of course, the case where any angle formed by the major axis of each particle and the top surface is 90 degrees. The wording also includes the case where a deviation from 90 degrees to an extent such that the foregoing angle can be considered to be substantially normal is present (for example, the case where the foregoing angle deviates from normal by 10 degrees or less, or the foregoing angle deviates from normal by 5 degrees or less, and preferably the foregoing angle deviates from normal by 2 degrees or less.)
In these embodiments, the major axis of each composite particle and a top surface of said substrate are oriented approximately normal to each other. When these elements are approximately normal to each other, the angle formed by each other is within the range that the effects of these embodiments are achieved.
In some embodiments, as the mixture of dichalcogenide flakes and solvent transit, the solvent evaporates as the motion of the flake continues. It is attracted to the oppositely charged substrate or electrode, and buries a portion itself into the layer of other particles, with its major axis having an orientation approximately normal to the substrate or electrode. If the flake has a major axis longer than the thickness of the layer of other particles, then the opposite end of the flake remains protruding from the surface of the layer of other particles. In some embodiments the protruding portion of the flake is modified with dopants or impurities which change the characteristics of the flake, generally changing the work function of the protruding portion. In some embodiments the layer of other particles functions as a mask or barrier preventing the impurities from penetrating into the layer of other particles and contaminating the portion of the flake buried in the layer of other particles. In some embodiments the protruding portion of the flake is doped with atoms like Oxygen, Nitrogen, Rhenium, Niobium, Zinc, Tungsten, Molybdenum, Iron, Chromium, Manganese, Vanadium, Selenium, Sulfur, Tellurium, Phosphorus, Potassium, Hydrogen, and Chlorine. In these embodiments the flake is described as bi-phasic. In these embodiments the portion of the flake which is buried in the layer of other particles retains the original characteristics of the flake, while the portion of the flake protruding from layer of other particles is changed by the impurities. After doping, the flake has two phases, that is, it is a heterojunction. But since the dichalcogenide is a single continuous flake, it is a heterojunction with little or no contact resistance between the n type portion of the flake and the p type portion of the flake.
In some embodiments, the coating changes phase relative to temperature. Examples of phase change coatings are hot melt glues and thermoplastic toner ingredients used in copiers and laser copiers. Exemplary hot melt glues are polyethylene and polyvinyl acetate. Exemplary toner ingredients are waxes.
In some embodiments, the viscosity of the coating layer can change as the result of phase change or polymerization or ultraviolet curing or other processes. In some embodiments, the characteristics of the coating change dramatically from a relatively low viscosity fluid, and change to a gel, or a stiff gel, or a solid, changing from a liquid phase to a solid phase. Examples of viscosity changing materials are gelatins, gels, gums, hot melt glues, thermoplastic toner ingredients, fast polymerizing materials, ultraviolet curing resins, and other materials. Once the coating has assumed a semi-solid or solid phase, the orientation of the major axis of the dichalcogenide flake is fixed.
In some embodiments the coating layer includes thickeners chosen from the group comprising thixotropics, resins, foams, sol-gels, gels, gelatins, cellulosics, acrylamides, acrylates, polymers, rheology agents, inorganic thickeners, ultraviolet curing resins, and additives.
In some embodiments the coating changes from a liquid to a stiff gel or semi solid as a solvent or water evaporates from the coating. Examples of these coatings are gelatin, agar, gums, and various celluloses. While the coating is in a low viscosity phase, a charge is applied to the coating, or a second electrode in contact with the coating. Then a device gives a second electrode an electrical charge opposite that of the second electrode. The dichalcogenide flakes are then are attracted to the second electrode. As the flakes transit to the second electrode coating, the flake is oriented with its major axis coincident with the electromagnetic field lines, which is generally normal to the coating on the second electrode. Once a portion of the flake is buried in the coating, the orientation of the flake is maintained by the interaction of the charge on the dichalcogenide flake, and the opposite charge of the coating electric field, again coincident with the electromagnetic field lines. As the solvent or water evaporates from the gate layer, the coating changes state to a stiffer gel, a semi-solid, or a solid phase. Once the coating has changed state to a semi solid or solid or stiff gel, the flake is permanently fixed in its orientation, and the electrical fields can be discontinued.
The flake shape of the dichalcogenide allows easy penetration through the dielectric coating and embedding the edge of the flake into the charge transfer layer and electrode layer.
In some embodiments, the coating changes phase relative to temperature. Examples of phase change coatings are hot melt glues and thermoplastic toner ingredients used in copiers and laser copiers. Exemplary hot melt glues are polyethylene and polyvinyl acetate. Exemplary toner ingredients are waxes.
In some embodiments the major axis of each flake is oriented nonparallel with respect to the device. In some of these embodiments the plurality of flakes are disposed at the same angle. But in other embodiments, the major axis of the flakes varies from flake to flake, with orientation angles which differ from flake to flake, disordered.
In some embodiments the gate layer is a mixture of ultraviolet curing resins. During exposure to ultraviolet light, the mixture of ultraviolet curing resins, change state, from a low viscosity fluid, to a gel, to a semi-rigid gel, or to a solid resin mixture. In some embodiments the coating is a mixture of ultraviolet curing resins and ionic liquid, sometimes called an ionic liquid gel. Exemplary components of ultraviolet curing resins are; photo initiators, additives, crosslinkers like TMPTA, and acrylates like TEGDA. In some embodiments, the dichalcogenide flakes are deposited using electrostatic processes and similar electromagnetic processes. During electrostatic deposition or electromagnetic deposition, the dichalcogenide flakes penetrate the mixture of ultraviolet curing resins and the flakes contact the conductive substrate underneath the resin. But after ultraviolet curing the ultraviolet curing resin mixture changes from a low viscosity fluid into a stiff gel or a solid. The solid state of the ultraviolet curing resin fixes the orientation of the major axis of the flake relative to the underlying first electrode or substrate. After curing, the flake is locked into intimate contact with the first electrode. In some embodiments, the barrier properties of the gate layer prevent oxidants, water, and contaminants from affecting the flake. In some embodiments, the gate layer resin functions as a mask, and inhibits the impurities or dopants from implanting to the dichalcogenide flakes and prevents the dopants from changing the character of the buried portion of the flakes.
There are a number of methods to emit and deposit the plurality of biocidal composite particles with their longest axis aligned approximately normal to the electrical potential applied to the substrate or member. Here are some of the methods to emit and deposit the biocidal composite particles: inkjet printing, continuous inkjet printing, xerography, electrophotography, photocopying, laser printing, electrophoresis, pressure less printing, corona poling, electrostatic spraying, electroless spraying, flocking, and powder coating. Here are a few non limiting examples:
Heat is applied to a thermoplastic film sheet.
At approximately the glass transition temperature of the film, a potential is applied to the film, and a potential of the opposite sign is applied to the flakes.
The coercive electrical field causes the flakes to transit to the thermoplastic film sheet, and the flakes partly embed into the film surface, with some of the flake protruding from the film sheet surface.
As the thermoplastic film cools below its glass transition temperature, the flake becomes fixed and oriented approximately normal to the substrate.
An ultraviolet curing or visible light curing resin is applied as a coating to a film sheet. Then a potential is applied to the film, and an opposite potential is applied to the flakes.
Under the coercive effect of the electrical field, the flakes transit to the ultraviolet curing coating.
The flakes bury one portion of the flake into the uv curing resin, while the remainder of the flake remains protruding from the composite flake into the ambient air.
Ultraviolet light or visible light cures the resin, and the flake becomes fixed and oriented approximately normal to the substrate.
In some embodiments, additional materials are deposited to contact the 2D flake.
A potential is applied to a substrate. In some embodiments, there is a coating on this substrate.
The opposite potential is applied to a liquid dispersion including molybdenum disulfide flakes. In some embodiments the dispersion includes binder particles or binder resin.
Drops of the composite particles are emitted, and they transit to the substrate or substrate and coating. During the transit of the composite particles, the volatile solvent carrier or water which is proximal to the molybdenum disulfide flake evaporates away. The newly solvent free flake embeds itself into the substrate or coating under the influence of the electrical field.
A potential is applied to a substrate. A potential is applied to a toner like mixture. The toner like mixture is comprised of water or solvent, 2d flakes, and thermoplastic particles. As the toner like mixture becomes proximal to the charged substrate, the 2D flakes and thermoplastic particles are deposited on to the substrate. The substrate continues to have potential. The toner like mixture also maintains its potential. As the toner like mixture approaches the substrate, the flakes AND the toner transit to the substrate. Heat is applied to the substrate, and heat causes the thermoplastic particles in the toner to melt and flow and adhere to the substrate. Since the potential is continuously applied to the substrate, the composite particles maintain their normal orientation to the substrate. As the heat temperature is reduced, the thermoplastic resins change state and change from being a glassy resin and become a rigid resin, fixing the aligned 2d flakes into their normal orientation.
A potential is applied to a substrate. A coating is applied to this same substrate. The opposite potential is applied to a dispersion of 2D flakes in a solvent. The dispersion is emitted by a spray nozzle, and the major axis of the flake is oriented normal to the top surface of the coating as the flakes are embedded into the coating on the substrate. The durometer and the viscosity of the coating applied to the substrate is sufficient to allow the flakes to embed into the coating, and the flakes' normal position is maintained in the coating under the influence of the field, without the coating being excessively disturbed. The coating is subjected to a curing means, and the coating becomes rigid, trapping the 2d flake aligned normal to the top surface of the coating
A potential is applied to a substrate.
The opposite potential is applied to a mixture of powder coating compatible resin and flakes.
The mixture of powder coating resin and flakes transit to the substrate.
Heat is applied to the substrate, causing the powder coating resin to melt and conform to the substrate and the vertically aligned flakes.
The powder coating fixes the flakes normal to the substrate.
Non-limiting examples of animal devices: bandages, teat protectors, cages, collars, feeding troughs, pen surfaces, barn surfaces, egg roll out nests, nursery beds, bandages, teat protectors, cages, collars, feeding troughs, pen surfaces, barn surfaces, egg roll out nests, nursery, and identification plate.
Non-limiting examples of human devices: contact lenses; cannulae; Catheters, in particular urological catheters such as bladder catheters or urethral catheters; tubing, fluid bags, septa, stopcocks, clamps, filters, catheters, needles, cannulae; central venous catheters; Venous catheters or inlet or outlet catheters; Dilatation balloons; Catheters for angioplasty and biopsy; Catheters used for the insertion of a stent, a graft or a kavafilter; Balloon catheters or other expandable medical devices; endoscopes; Larnygoskopen; Tracheal devices such as endotracheal tubes; A-tem devices and tracheal suction devices; bronchoalveolar irrigation catheters; Catheters used in coronary angioplasty; Pacemaker parts; Cochlear implants; Dental implant tubes for feeding; Dranageschlauchen; Guidewires; Gloves; Stents and other implants; extracorporeal blood tubes; Membranes, as for dialysis; Blood filters; Apparatus for circulatory support; Dressing materials for wound care; Harnbeuteln; ostomy bags; Implants containing a medically effective agent, such as medically acting stents or for balloon surfaces or for contraceptives; Endoscopes, laryngoscopes and feeding tubes.
In other embodiments, the composite flakes can coat the interior of pipes, valves, heat exchangers, condensers power plants, oil and gas pipelines, public water supply systems, sewers], marine engineering infrastructure, water cooled heat exchangers, radioactive disposal facilities, water treatment membranes to inhibit biofouling.
In some embodiments, the composite particles can be added to liquids such as water, without the composite particles binding to a member or surface. Pathogens contained within the water and contact the flakes are lacerated. Holes generated by the composite particles ultimately reduce water to form hydroxyls, which deactivates the pathogens within the liquid.
In more embodiments the composite biocidal particle can be applied to flora including organic crops for animal consumption and organic crops for human consumption. MoS2 is a natural nutrient found in nature and does not need much post extraction chemistry. MoS2 is biodegradable and molybdenum and sulfur are soil nutrients.
In further embodiments, the biocidal coating can be applied topically to cows, chickens, sheep, fish, pork and more. MoS2 can adhere to feathers, skin, hides, hair, beaks, horns, and hooves, as the Zeta Potential of MoS2 can be exploited to bind to keratin.
The words used in this document can be used interchangeably and have similar meanings: flake, plate, sheet, blade, bidimensional, 2D, and fewlayer or few layer. Sometimes the words have a prefix like micro as in microflake, or microplate.
An added advantage of 2D antimicrobials is taught by many scientists, that these novel 2D antimicrobials do not encourage antibiotic resistance.
Papi teaches: “These mechanisms are less likely to induce bacterial resistance and have a long-term effect, being based on mechanical action and independent to any drug reservoir” [74].
