Patent Application
20090258355
Self-assembled nanosystems consisting of inorganic “building blocks” are typically driven by a symmetric functionalization which limits control over assembly morphology and binding properties. Thus, the ability to easily fabricate discrete blocks with anisotropic interactions may aid in the creation of diverse classes of nanoparticulate monomers, clusters, or groupings, which is a current goal of soft nanotechnology.
The use of DNA to bind nanomaterials into organized 1D groupings, 2D scaffolds, or in 3D assembled crystals, has revealed the strength of using biomolecular tunability, flexibility, and mechanical rigidity in the organization of monomeric building-blocks. However, the design and fabrication of well-defined clusters, containing 2-10 nanoparticles apiece, for example, with controlled anisotropy, high yields, and under high concentrations, has remained elusive. The investigation of controlled nanoparticle clustering with DNA was pioneered by Alivisatos and co-workers, who have elegantly utilized nanoparticles with a precise number (˜1) of DNA attached. This approach has led to well-defined clusters, whose morphologies mimic the DNA scaffold motif used. In addition, such quantized groupings allow for advanced structure-function studies related to surface enhanced Raman spectroscopy (SERS), surface plasmon phenomenology, and metal enhanced fluorescence (MEF). Despite the strength of this scaffolding approach, the necessity for preparation and purification of mono-functionalized DNA-particles, as well as assembled product purification, has many shortcomings with respect to fabrication yields, simplicity, and modularity.
Scheme 1 in
Diagram 1 in
Despite the initial advances in this type of assembly with mono-functionalized particles, present forms have a number of limitations that deleteriously affect their full scale adoption and commercial viability. A few of these limitations involve present approaches to controlling nanoparticle assembly into quantized groupings, requiring extensive purification steps of both monomeric building blocks and intermediate and final products. This results in low final yields (number of groupings), as well as introducing impurities in the system as a result of separation via gel electrophoresis and liquid chromatography which, while separating singletons from groupings of multiple particles, introduce impurities from the techniques themselves into the batch of singletons.
The present invention overcomes many of the limitations of the prior art. The invention is a first of its kind solid-state assembly/disassembly route. Using encoded solid supports, particles are assembled/disassembled and functionalized in an easily controllable and high yield approach which utilizes biomolecules (e.g., DNA, RNA, peptides) to encode interactions and anisotropy.
The present invention has several advantages over the prior art including: designing a general approach towards controlled anisotropy in nano-scale systems, where, for example, particular binding interactions (such as with DNA) are confined to particular areas of the particles; designing a general approach which illustrates the ability to self-assemble “Janus”-like morphologies, where each hemisphere of a nanoparticle contains different interactions or functionalization; designing and implementing a high throughput approach, which can be easily scaled, and which contains a “plug and play” modularity which may lead to the introduction of multiple classes of materials and interactions.
In particular, the nanoclusters and the methods of making the nanocluster (i.e., “Nano-Assembly platform using Encoded Solid Supports (NAESS)”) assembles nanomaterials at a colloidal substrate in a layer-by-layer fashion in which interactions between layers have been encoded using biomolecules, allowing for controlled interactions, purification of side products, modularity, and construction of complex architectures. In addition, the approach allows fabrication of nanoparticles with anisotropic interactions, Janus particles.
The invention improves the ability to impart anisotropy in nanoscale assembly systems using a solid-state assembly approach. It results in: 1) DNA-addressed specificity between particles or DNA layers with solid support; 2) a solid support easily derivatized for particle assembly and disassembly; and 3) interactions driven by biomolecular interactions, and assembly and dis-assembly requiring no change to environmental conditions, including, pH change, temperature change, buffer change, and radiation exposure.
In the present invention, planar or colloidal surfaces are grafted with biomolecules, which allows for a specific immobilization of corresponding bio-encoded nano-objects. A cluster can thus be built via the sequential attachment of recognition encoded components from the solution. Such components include bio-functionalized nano-objects or biomolecular linkers, which allows for the ability to control interparticle distances and cluster geometry.
In one embodiment, the present invention provides a method of making a nanocluster. The method comprises providing a surface comprising at least one anchoring biomolecule, wherein the surface is in a solution; adding an initial recognition-nano-component to the solution wherein the initial recognition-nano-component comprises i) a nanoparticle and one specifically-bindable-biomolecule, or ii) a nanoparticle and two different types of specifically-bindable-biomolecules, wherein a biomolecule of the initial recognition-nano-component specifically binds to the anchoring biomolecule; and adding a releasing biomolecule to the solution, wherein the releasing biomolecule binds to the anchoring biomolecule with a greater binding strength than the anchoring biomolecule binds to the initial recognition-nano-component, or wherein the releasing biomolecule binds to the initial recognition-nano-component with a greater binding strength than anchoring biomolecule binds to the initial recognition-nano-component, thereby making a nanocluster.
In some embodiments, the method further comprises (a) providing a plurality of recognition-nano-components, wherein a recognition-nano-component comprises i) a specifically-bindable-nanoparticle, ii) a nanoparticle and one specifically-bindable-biomolecule, or iii) a nanoparticle and two different types of specifically-bindable-biomolecules; (b) adding a recognition-nano-component to the solution, wherein the recognition nano-component specifically binds to a biomolecule of the initial recognition-nano-component; (c) subsequently adding a recognition-nano-component to the solution, wherein the recognition nano-component specifically binds to a biomolecule of most recently added recognition-nano-component of the nanocluster. Step (c) is repeated until a desired number of recognition-nano-components are sequentially specifically bonded to the nanocluster.
In some embodiments, the method further comprises adding a series of capping-moieties to the solution wherein the capping-moieties specifically bind to the unreacted biomolecules of the nanocluster except for the biomolecule of the most recently added recognition-nano-component of the nanocluster.
In some embodiments, the method further comprises adding an isolating surface to the solution wherein the isolating surface specifically binds to the unreacted biomolecules of the most recently added recognition-nano-component of the nanocluster, and washing away unreacted biomolecules.
In some embodiments, the method further comprises purifying the solution before a recognition-nano-component is added.
The nanocluster can comprise about two to about one hundred recognition-nano-components. A typical nanocluster comprises two recognition-nano-components.
The nanocluster can comprise a metal nanoparticle, a semiconductor nanoparticle, an organic nanoparticle, silica, or combinations thereof. Preferably, the metal nanoparticle is a gold nanoparticle, a silver nanoparticle, a copper nanoparticle, a platinum nanoparticle or a palladium nanoparticle.
In some embodiments, the method further comprises adding a linker to the solution before adding a recognition nano-component, wherein the linker specifically binds to a biomolecule on each of two sequentially added recognition-nano-components, thereby attaching a linker between the two sequentially added recognition-nano-components. The linker can be added so that the approximate ratio of a linker to a recognition-nano-component is about 1:1 to about 10:1. In a preferred embodiment, the linker is added so that the approximate ratio of a linker to a recognition-nano-component is about 5:1.
The specifically-bindable biomolecules of the nanocluster can comprise single-stranded nucleic acid molecules; antigens; moieties that bind antigens; or combinations thereof. Typically, the single-stranded nucleic acid molecules comprises about six to about 200 bases, or about ten to about thirty bases.
In one embodiment of the present invention, a method of detecting the presence of a particular target biomolecule with a dimer in a sample is provided. The method comprises (a) providing a detection dimer, wherein the detection dimer comprises a first recognition nano-component attached to a second recognition nano-component, wherein the first recognition nano-component comprises a first nanoparticle and a first specifically-bindable biomolecule, wherein the second recognition nano-component comprises a second nanoparticle and a second specifically-bindable biomolecule. In one embodiment, the first recognition nano-component is attached to the second recognition nano-component by binding of the first biomolecule to the second biomolecule, wherein the first biomolecule binds to the second biomolecule with an initial binding strength. In another embodiment, the first recognition nano-component is attached to the second recognition nano-component by a linker which binds the first biomolecule to the second biomolecule, wherein the linker binds the first biomolecule to the second biomolecule with an initial binding strength. A sample is contacted with the detection dimer. If the target biomolecule is present in the sample, then (i) the target biomolecule binds to either the first biomolecule or the second biomolecule with a detection binding strength, wherein the detection binding strength is greater than the initial binding strength; or (ii) the target biomolecule binds to the linker with a detection binding strength, wherein the detection binding strength is greater than the initial binding strength. It is determined whether the first recognition nano-component became detached from the second recognition nano-component to form monomers, wherein if monomers were formed to a sufficient level, then the target biomolecule is present.
In another embodiment of the present invention, a method of detecting the presence of a particular target biomolecule with a trimer in a sample is provided. The method comprises (a) providing a detection trimer. The detection trimer comprises a first recognition nano-component attached to a second recognition nano-component and a third recognition nano-component, wherein the first recognition nano-component comprises a first nanoparticle and a first single strand nucleic acid molecule, wherein the second recognition nano-component comprises a second nanoparticle and a second single strand nucleic acid molecule, and wherein the third recognition nano-component comprises a third nanoparticle and a third single strand nucleic acid molecule, wherein the first recognition nano-component is attached to the second recognition nano-component by a single stranded nucleic acid linker which binds i) the portion of the first nucleic acid molecule which is more proximate to the first nanoparticle to ii) the second nucleic acid molecule, wherein the linker binds the first nucleic acid molecule and the second nucleic molecule with an initial binding strength; wherein the first recognition nano-component is attached to the third recognition nano-component by the binding of i) the portion of the first nucleic acid molecule which is more distal to the first nanoparticle to ii) the third nucleic acid molecule, wherein the first nucleic acid molecule and the third nucleic molecule bind with an initial prime binding strength. The sample is contacted with the detection trimer. If the first target biomolecule is present in the sample, the first target biomolecule binds either the portion of the first nucleic acid molecule which is more proximal to the first nanoparticle or the second nucleic acid molecule or the linker with a detection binding strength, wherein the detection binding strength is greater than the initial binding strength; and (ii) wherein if the second target biomolecule is present in the sample the second target biomolecule binds either the portion of the first nucleic acid molecule which is more distal to the first nanoparticle or the third nucleic acid molecule with a detection prime binding strength, wherein the detection prime binding strength is greater than the initial prime binding strength. It is then determined whether the first recognition nano-component became detached from the second recognition nano-component and/or third recognition nano-component to form dimers and/or monomers, wherein if dimers and/or monomers were formed to a sufficient level, then the first target biomolecule and/or second target biomolecule is present.
The present method provides for the rational design and fabrication of nanoclusters using bio-encoded nanoscale building blocks in a stepwise assembly and release at a solid substrate. Using programmable recognition biomolecules as a nanoparticle encoding motif, the nanoparticles have been imparted with anisotropy for both the assembly and disassembly at a colloidal substrate, which allowed for the fabrication of well defined multi-particle clusters and Janus nanoparticles, with remarkably high fidelity and yields. In addition, the described method is highly modular, which allowed for ease of incorporation of different nano-components for the assembly of systems with regulated optical properties, thus, demonstrating its versatility for fabrication of designed nanomaterials.
In one aspect, the invention provides a highly controllable method of making nanoclusters. A nanocluster is made by sequentially adding nanocluster “building blocks” by which the nanocluster is self-assembled layer by layer. This method takes place in solution with a growing nanocluster immobilized on a solid support. The “building blocks” of a nanocluster are termed “recognition-nano-components.”
A “recognition-nano-component” is a nanoparticle with the ability to specifically bind one or two types of biomolecules. The nanoparticle has the ability to specifically bind biomolecules due to i) having one or two specifically bindable-biomolecules attached to its surface, or ii) its intrinsic ability to bind affinity tags. By means of this specific binding, recognition-nano-components of different types (i.e., different species) can precisely be attached to one another.
In particular, a recognition-nano-component of the present invention comprises (or consists essentially of): i.) a nanoparticle and one attached specifically-bindable-biomolecule, ii.) a nanoparticle and two different types of attached specifically-bindable-biomolecules, wherein the two different types of attached specifically-bindable-biomolecules have low affinity for one another, or iii.) a specifically-bindable-nanoparticle.
A description of the specific components of recognition-nano-components follows.
In this specification, a “nanoparticle” refers to a metal particle, semiconductor particle, organic particle or silica particle with a diameter in the nanometer (nm) range. Preferably, the nanoparticle has a minimum diameter of about 1 nm and a maximum diameter of about 100 nm, more typically from about 2 nm to about 50 nm.
The metal nanoparticle can be any metal, metal oxide, or mixtures thereof. Some examples of metals useful in the present invention include gold, silver, platinum, and copper. Examples of metal oxides include iron oxide, titanium oxide, chromium oxide, cobalt oxide, zinc oxide, copper oxide, manganese oxide, and nickel oxide.
The metal or metal oxide can be magnetic. Examples of magnetic metals include, but are not limited to, iron, cobalt, nickel, manganese, and mixtures thereof. An example of a magnetic mixture of metals is a mixture of iron and platinum. Examples of magnetic metal oxides include, for example, iron oxide (e.g., magnetite, hematite) and ferrites (e.g., manganese ferrite, nickel ferrite, or manganese-zinc ferrite).
The semiconductor nanoparticle is capable of emitting electromagnetic radiation upon excitation. Some examples of semiconductors include Group II-VI, Group III-V, and Group IV semiconductors. The Group II-VI semiconductors include, for example, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, and mixtures thereof. Group III-V semiconductors include, for example, GaAs, GaN, GaP, GaSb, InGaAs, InP, InN, InSb, InAs, AlAs, AlP, AlSb, AlS, and mixtures therefore. Group IV semiconductors include, for example, germanium, lead, and silicon.
The semiconductor can also include mixtures of semiconductors from more than one group, including any of the groups mentioned above.
The semiconductor nanoparticles used in the invention preferably have the capability of absorbing radiation over a broad wavelength band. The wavelength band includes gamma radiation to microwave radiation.
The semiconductor nanoparticles preferably have the capability of emitting radiation within a narrow wavelength band of about 40 nm or less, preferably about 20 nm or less. A narrow emission band permits the simultaneous use of a plurality of differently colored semiconductor nanoparticle complexes with different semiconductor nanoparticles without overlap (or with a small amount of overlap) in wavelengths of emitted light when exposed to the same energy source.
The frequency or wavelength of the narrow wavelength band of light emitted from the semiconductor nanoparticle may be further selected according to the physical properties, such as size, of the semiconductor nanoparticles.
In a preferred embodiment, the semiconductor nanoparticle is fluorescent. The fluorescence of the semiconductor nanoparticle is preferably preserved (e.g., is not quenched).
Organic nanoparticles comprise mainly organic materials such as polymers (e.g., polystyrene) or complexes of smaller organic molecules. Examples of organic nanoparticles include liposomes, dendrimers, carbon nanomaterials and polymeric micelles. Liposomes are phospholipid vesicles (50-100 nm) that have a bilayer membrane structure similar to that of biological membranes and an internal aqueous phase. Dendrimers are highly branched synthetic polymers (<15 nm) with layered architectures constituted of a central core, an internal region and numerous terminal groups that determine dendrimer characteristics. Carbon nanomaterials include fullerenes in the form of a hollow sphere, ellipsoid, tube, or plane. Carbon nanotubes are formed of coaxial graphite sheets (<100 nm) rolled up into cylinders. Examples of polymeric micelles include polystyrene beads.
Additionally, polymers can be incorporated into silica to form silica semiconducting polymer nanocomposites.
Specifically-Bindable Biomolecules
Various types and classes of specifically-bindable biomolecules are attached to nanoparticles to form the recognition nano-components of the present invention. Examples include, for instance, base-pairing nucleic acids, and other moieties.
The following discussion describes base-pairing nucleic acids used in recognition-nano-components of the present invention.
A nucleic acid is a macromolecule composed of chains of monomeric nucleotides. Nucleotides consist of three joined structures: a nitrogenous base, a sugar, and a phosphate group.
The nitrogenous bases can be any naturally-occurring purines and pyrimidines or modified purines and pyrimidines. Typically, the bases of the present invention are adenine, guanine, cytosine, thymidine and uracil.
The bases can be modified, for example, by the addition of substituents at one or more positions on the pyrimidines and purines. The addition of substituents may or may not saturate any of the double bonds of the pyrimidines and purines. Examples of substituents include alkyl groups, nitro groups, halogens and hydrogens. The alkyl groups can be of any length, preferably from one to six carbons. The alkyl groups can be saturated or unsaturated; and can be straight-chained, branched or cyclic. The halogens can be any of the halogens including, bromine, iodine, fluorine or chlorine.
Further modifications of the bases can be the interchanging and/or substitution of the atoms in the bases. For example, the positions of a nitrogen atom and a carbon atom in the bases can be interchanged. Alternatively, a nitrogen atom can be substituted for a carbon atom; an oxygen atom can be substituted for a sulfur atom; or a nitrogen atom can be substituted for an oxygen atom.
Another modification of the bases can be the fusing of an additional ring to the bases, such as an additional five or six-membered ring. The fused ring can carry various further groups.
Specific examples of modified bases include 2,6-diaminopurine, 2-aminopurine, pseudoisocytosine, E-base, thiouracil, ribothymidine, dihydrouridine, pseudouridine, 4-thiouridine, 3-methlycytidine, 5-methylcytidine, inosine, N6 methyladenosine, N6 isopentenyladenosine, 7-methylguanosine, queuosine, wyosine, etheno-adenine, etheno-cytosine, 5-methylcytosine, bromothymine, azaadenine, azaguanine, 2′-fluoro-uridine and 2′-fluoro-cytidine.
The bases are attached to a molecular backbone. The backbone comprises sugar or non-sugar units. The units are joined in any manner known in the art.
In one embodiment, the units are joined by linking groups. Some examples of linking groups include phosphate, thiophosphate, dithiophosphate, methylphosphate, amidate, phosphorothioate, methylphosphonate, phosphorodithioate and phosphorodiamidate groups.
Alternatively, the units can be directly joined together. An example of a direct bond is the amide bond of a peptide.
The sugar backbone can comprise any naturally-occurring sugar. Examples of naturally-occurring sugars include ribose and deoxyribose, for example 2-deoxyribose.
The sugars of the backbone can be modified in any manner. Examples of modified sugars include 2′-O-alkyl ribose, such as 2′-O-methyl ribose and 2′-O-allyl ribose. Preferably, the sugar units are joined by phosphate linkers. The sugar units may be linked to each other by 3′-5′, 3′-3′ or 5′-5′ linkages. Additionally, 2′-5′ linkages are also possible if the 2′ OH is not otherwise modified.
The non-sugar backbone can comprise any non-sugar molecule to which bases can be attached. Non-sugar backbones are known in the art.
In one embodiment, the non-sugar backbone comprises morpholine rings (tetrahydro-1,4-oxazine). The resulting base-pairing segment is known as a morpholino oligo. The morpholine rings are preferably joined by non-ionic phosphorodiamidate groups. Modified morpholines known in the art can also be used in the present invention.
In another embodiment, the non-sugar backbone comprises modified amino acid units linked by, for example, amide bonds. The amino acids can be any amino acid, including natural or non-natural amino acids. The amino acids can be identical or different from one another. The amino acids are preferably amino alkyl-amino acids, such as (2-aminoethyl)-amino acid.
Bases are attached to this backbone by molecular linkages. Examples of linkages are methylene carbonyl, ethylene carbonyl and ethyl linkages. The resulting pseudopeptide is known as a peptide nucleic acid (PNA). (Nielsen et al., Peptide Nucleic Acids-Protocols and Applications, Horizon Scientific Press, pages 1-19; Nielsen et al., Science 254: 1497-1500.)
A preferred example of a PNA is N-(2-aminoethyl)-glycine. Further examples of PNAs include cyclohexyl PNA, retro-inverso, phosphone, propionyl and aminoproline PNA.
Other examples of artificial nucleic acids include locked nucleic acid (LNA), glycol nucleic acid (GNA) and threose nucleic acid (TNA). Each of these is distinguished from naturally-occurring DNA or RNA by changes to the backbone of the molecule.
The single-stranded nucleic acid molecules used as the biomolecules of the recognition-nano-components comprise about six to about 200 bases, about ten to about thirty bases, or about fifteen to twenty bases.
Various types of biomolecules, other than nucleic acids, can be attached to nanoparticles to form the recognition nano-components of the present invention. Examples of specifically binding moieties, other than nucleic acids, include receptors and their ligands, antibodies and their antigens (both protein and non-protein antigens), and protein affinity tags and moieties recognized by the tags.
Antibodies include whole antibodies, functional equivalents thereof, monoclonal antibodies, and functional equivalents derived from monoclonal antibodies.
Suitable equivalents of antibodies include any fragment that comprises a sufficient portion of the hypervariable region to bind specifically to an antigen. Such fragments may, for example, contain one or both Fab fragments, or the F(ab′)2 fragment. Preferably, the antibody fragments contain all six complementarity determining regions of the whole antibody, although functional fragments containing fewer than all of such regions, such as three, four or five CDRs, may also be suitable. The preferred fragments are single chain antibodies, or Fv fragments.
Examples of antibodies are members of any class of immunoglobulins, such as: IgG, IgM, IgA, IgD, or IgE, and the subclasses thereof. The preferred antibodies are members of the IgG1 subclass.
A preferred example of biomolecule is coxsackievirus-adenovirus receptor (CAR) D1 domain which serves as a receptor for group B human coxsackievirus and many adenovirus serotypes. Examples of ligands which are suitable as biomolecules include ligands of the aforementioned immunoglobulins. A preferred example of a ligand is the knob protein domain of an adenovirus. Examples of serotypes of adenovirus include serotype 2, serotype 5 and serotype 12.
A receptor-ligand pair is another example of a biomolecule pair suitable for the invention. Ligands can be natural or synthetic molecules, such as hormones (e.g., gastrointestinal peptidic hormones) or neurotransmitters, which specifically bind to a receptor. Some examples of receptor-specific ligands include bombesin and transferrin.
Other examples include cytokine receptors, e.g., interleukin-1 receptor type I, interleukin-1 receptor type II precursor (IL-1R-2, IL-1R-beta, CD121b antigen), platelet-derived growth factor receptor (PDGFR), interleukin-6 receptor alpha chain precursor (IL-6R-alpha,CD126 antigen), macrophage colony-stimulating factor 1 receptor precursor (CSF-1-R, CD115 antigen), mast/stem cell growth factor receptor precursor (SCFR, c-kit, CD117 antigen), basic fibroblast growth factor receptor 1 precursor (FGFR-1, Tyrosine kinase receptor CEK1), vascular endothelial growth factor (VEGF) receptor, and epidermal growth factor (EGF) receptors, e.g., HER-1, HER-2, HER-3, and HER-4. Another example of a biomolecule pair suitable for the invention is biotin-avidin.
A specifically-bindable-nanoparticle is a nanoparticle which can specifically bind to a biomolecule, for example, can specifically bind to an affinity tag. Affinity tags can be generated against the surfaces of metallic particles. For instance, a poly-histidine tag can be used to bind to a nickel-nitrilotriacetic acid (Ni-NTA) modified particle. Generation of such specifically-bindable-nanoparticle is known in the art. See Table I acquired from Sarikaya et al., “Molecular Biomimetics: Nanotechnology through Biology,” Nature Materials 2:577-585 (2003).
aIsoelectric points and bMolecular masses of peptides are calculated using Compute pl/Mw tool (http://us.expasy.org/tools/pl_tool.html).
cCalculated by subtracting the number of basic residues (R and K) from the number acidic residues (D and E).
dUnpublished by the authors.
eMost frequently observed sequences.
In the method, a surface (i.e., a solid support) having at least one anchoring biomolecule, typically a plurality of anchoring biomolecules, is provided. An anchoring biomolecule is a specifically-binding biomolecule as described above. Preferably the anchoring biomolecule is a nucleic acid.
The surface is any type of solid support such as, for example, planar surfaces and colloidal surfaces. Examples of planar surfaces include silicon wafers and polystyrene microtiter plates. Examples of colloidal surfaces include magnetic beads. The surface is in a solution, such as an aqueous buffer solution, made by methods known in the art.
A first recognition nano-component, termed “initial recognition nano-component, is then added to the solution.” The initial recognition-nano-component comprises a nanoparticle and two different types of specifically-bindable-biomolecules wherein one biomolecule specifically binds to the anchoring biomolecule.
Different recognition-nano-components are then sequentially added to the solution in a series of steps. In each step, one species (i.e., type) of recognition-nano-component is added. In the first step, a recognition nano-component is added that specifically binds to a biomolecule of the initial recognition-nano-component. Subsequently, different species of recognition-nano-components are sequentially added to the solution, wherein at each step, a particular recognition nano-component specifically binds to the biomolecule of the most recently added recognition-nano-component of the nanocluster. The nanocluster can be thought of as a structure with different “layers” of recognition nano-components. The most recently added recognition-nano-component of the nanocluster can be thought of as the “top layer” of the nanocluster.
Due to geometric constraints and steric hindrance between the biomolecules within one species of biomolecules, the linking of additional recognition-nano-components occurs only on the top hemisphere of the nanoparticles, which results in anisotropically functionalized clusters. This feature enables the ability of the nanoclusters to self-assemble.
Some of the biomolecules within a nanocluster may remain unreacted. Accordingly, in some embodiments, the method further comprises adding a series of capping moieties to the solution. The series of capping moieties specifically bind to each species of unreacted biomolecules within each layer but are otherwise essentially inert. Alternatively, in some embodiments, capping moieties are added for each species of unreacted biomolecule except for the biomolecules of the top layer.
Recognition nano-components are added sequentially until a desired number of layers make up the nanocluster. Once a desired number of layers is obtained, a releasing biomolecule (i.e., fuel biomolecule) is added to the solution to release the nanocluster from the surface. The releasing biomolecule binds to the anchoring biomolecule with a greater binding strength than the anchoring biomolecule binds to the initial recognition-nano-component, or the releasing biomolecule binds to the initial recognition-nano-component with a greater binding strength than anchoring biomolecule binds to the initial recognition-nano-component, thereby releasing the one-component nanocluster.
The number of layers of recognition nano-components in a nanocluster is not critical. Typically, the nanocluster comprises about two to about one hundred layers or about five to about fifty layers. A nanocluster comprising two layers of recognition-nano-components is termed a “dimer.” If a one component nanocluster is desired, then the nanocluster is released from its surface after the binding of the initial recognition-nano-component.
Nanoclusters which have an unreacted layer have anisotropy, and thus are Janus nanoclusters. One manner by which to obtain a Janus nanocluster is by adding the capping moieties for each species of unreacted biomolecule except for the biomolecules of the top layer, and having the releasing biomolecule bind to the initial recognition-nano-component. Another manner by which to obtain a Janus nanocluster is by adding the capping moieties for each species of unreacted biomolecule, and having the releasing biomolecule bind to the anchoring biomolecule.
The resulting nanocluster product can be isolated from the solution by several methods. The methods are based on contacting the solution with a surface or surfaces (i.e., “isolating surface(s)”) that specifically bind unreacted recognition-nano-components in the solution.
In one embodiment, unreacted recognition-nano-components (i.e., recognition-nano-components which did not bind to the nanocluster) are removed from the solution to isolate the resulting nanocluster. The unreacted recognition-nano-components can be removed before each step of adding a new species of recognition-nano-component to the solution, or the unreacted recognition nano-components can be removed after the nanocluster product has been assembled. In this embodiment, more than one isolating surface is necessary. In particular, since each surface would bind a different recognition-nano-component, as many isolating surfaces are needed as species of unreacted recognition-nano-components.
In a preferred embodiment, the top layer of recognition-nano-components of the nanocluster is left unreacted, and an isolating surface which specifically binds to the unreacted biomolecules is contacted with the solution and the isolating surface is then removed from the solution. In this embodiment, only one isolating surface is necessary.
Depending on the specific isolating surface used, isolation involves either surface removal (e.g. via centrifugation and removal of the aqueous solution) or separation of magnetic beads by magnetic field followed by rinsing and re-dispersion in a new solution. In cases where the synthesis is performed on a planar surface (e.g., microtiter plate), the solution can be removed directly, after which the wells are washed to remove any unreacted molecules.
The resulting nanocluster can comprises more than one type of nanoparticle. For example, the nanocluster can comprise one or more metal nanoparticles and one or more semiconductor nanoparticles. The metal and semiconductor nanoclusters can be of different types.
In some embodiments, the nanoclusters have linkers in between some or all of the species of recognition-nano-components. In these embodiments, the method of the invention further comprises adding a linker to the solution before adding a recognition nano-component. The linker specifically binds two sequentially added recognition-nano-component species.
The linkers used between two recognition-nano-component species depend upon what two species are being linked.
If the biomolecules of two recognition-nano-components are single stranded nucleic acids, then the linker that links the two recognition nano-components are single stranded nucleic acids. The linkers can include from about two to about 100 bases, more typically about five to about twenty bases, and most typically about eight to about fifteen bases.
If the two recognition-nano-components to be linked contain: i) two biomolecules other than single stranded nucleic acids; ii) one biomolecule other than single stranded nucleic acid and one specifically-bindable-nanoparticle; or iii) two specifically-bindable-nanoparticles, then the linker used is a “linker peptide.”
A linker peptide is a peptide comprising (or consisting essentially of) two recognition regions and separated by a spacer. Each recognition region specifically binds to one of the recognition nano-components to be linked.
The recognition region can be peptide that is specifically bindable to the biomolecules described above. Examples include peptide receptors (e.g., CAR, VEGF-receptors, EGF receptors, cytokine receptors), protein ligands (e.g., Knob protein), and antibodies (typically, the binding domain of an antibody).
If the recognition-nano-component to be linked is a specifically-bindable-nanoparticle, then the recognition region of the linker peptide is an affinity tag. The affinity tag directly binds to the nanoparticle, i.e., the affinity tag binds to the nanoparticle without the nanoparticle having an attached biomolecule. Affinity tags are described above.
The spacer of the linker peptide can be any sequence of amino acids of about two to about twenty-five amino acids; more typically, about four to about twenty amino acids; and most typically about six to about fifteen amino acids. Preferably, the amino acids are rich in serine and glycine since they provide a flexible structure. An example of a spacer sequence is Gly-Gly-Ser-Gly-Gly-Ser-Gly-Gly.
An example of a linker peptide follows: A linker peptide consisting essentially of a first affinity tag which directly binds to the surface of nanoparticle 1 (e.g. a gold particle), a spacer sequence of six to fifteen amino acids rich in serine and glycine, and a second affinity tag which directly binds to the surface of nanoparticle 2 (e.g., a silver nanoparticle).
Another example of a linker peptide follows: A linker peptide consisting essentially of a first affinity tag which directly binds to the surface of a quantum dot, a flexible spacer sequence, followed by the CAR protein. In some embodiments, the linker peptide can be a recombinant CAR protein that has the affinity tag region plus the spacer sequence fused to either its C-terminal or N-terminal end. Such a peptide can be made with standard molecular biological techniques expressed under control of the T7 promoter.
In some embodiments, the two biomolecules of a recognition-nano-component are an antigen and a nucleic acid. In such case, on one hemisphere, the recognition-nano-component could be specifically bond to a DNA linker; and on the other hemisphere, the recognition-nano-component could be specifically bond to an antibody.
“Building blocks” (i.e., recognition-nano-components) of nanoclusters and various examples of nanoclusters follow,
Examples of Nanoclusters:
1. (Surface-ss)-(ss-NP)-(RR-spacer-RR)-(NP).
2. (Surface-BM)-(BM-NP)-(RR-spacer-RR)-(BM-NP).
3. (Surface-ss)-(ss-NP)-(RR-spacer-RR)-(BM-NP-ss)-(ss-NP).
4. (Surface-ss)-(ss-NP-ss)-(ss-spacer-ss)-(ss-NP-BM)-(BM-NP).
The amount of a linker added to the solution with respect to the amount of a recognition-nano-component can affect the structure of the resulting nanocluster. For example, to synthesize a dimer, the approximate ratio of a linker to a recognition-nano-component is typically about 1:1.
In some embodiments of the present invention, a plurality of “small” nanoparticles is placed on a “main nanoparticle.” These nanoclusters are termed “strawberry-like nanoclusters” or “strawberry structures.” In these embodiments, a linker is added so that the approximate ratio of a linker to a recognition-nano-component having the main nanoparticle is from about 2:1 to about 10:1. Then the small nanoparticle is added. If the small nanoparticle is much smaller than the main nanoparticle, then the relative amount of linker added determines the number of small nanoparticles that become attached to the main nanoparticle. However, the size of a small nanoparticle can also influence the number of small nanoparticles that can fit on a main nanoparticle.
In some embodiments, the main nanoparticle is about 2 nm to about 100 nm, and the small nanoparticles are about 4 nm to about 20 nm. Some illustrative examples of how the relative amount of linkers added and the relative size of the small nanoparticles influence the amount of small nanoparticles on the main nanoparticle follows.
Example: Main nanoparticle is about 50 nm. Linkers are added at ratio of 5× the main nanoparticles. Then 10 nm small nanoparticles are added. Result: about five small nanoparticle are attached to the main nanoparticles.
Example: Large nanoparticle is about 100 nm. Linkers are added at ratio of 5× the large nanoparticles. Then 20 nm small nanoparticles are added. Result: about five small nanoparticles are attached to the main nanoparticle.
Example: Large nanoparticle is about 100 nm. Linkers are added at ratio of 5× the large nanoparticles. Then 10 nm small particles are added. Result: about ten small nanoparticles are attached to the main nanoparticle.
Example: Large nanoparticle is about 100 nm. Linkers are added at ratio of 10× the large nanoparticles. Then 10 nm small particles are added. Result: about 10 small nanoparticles are attached to the main nanoparticle.
Example: Large nanoparticle is about 100 nm. Linkers are added at ratio of 10× the large nanoparticles. Then 2 nm small particles are added. Result: about 10 small nanoparticles are attached to the main nanoparticle.
Example: Large particle is about 100 nm. Linkers are added at ratio of 10× the large particles. Then 25 nm small particles are added. Result: about 5 small nanoparticles are attached to the main nanoparticle.
A typical nanoparticle of 10 nm has ˜50-60 DNA grafted to the surface. The amount depends on the diameter of a nanoparticle in quadratic way, as area. The amount of linkers attached to those DNA strands can be regulated, from 1 to ˜10-20
There are many diverse applications of the nanoclusters of the present invention, including for example, biosensors and catalyst dispensers.
In one embodiment, the nanoclusters are dimers which can be used as biosensors. The dimer can be used for a method of detecting the presence of a particular target biomolecule in a sample.
A detection dimer comprises a first recognition nano-component attached to a second recognition nano-component. The first recognition nano-component comprises a first nanoparticle and a first specifically-bindable biomolecule. The second recognition nano-component comprises a second nanoparticle and a second specifically-bindable biomolecule. The first recognition nano-component can be attached to the second recognition nano-component directly or by means of a linker. In particular, the first recognition nano-component is attached to the second recognition nano-component by binding of the first biomolecule to the second biomolecule with an initial binding strength. Alternatively, the first recognition nano-component is attached to the second recognition nano-component by a linker which binds the first biomolecule to the second biomolecule. The linker binds the first biomolecule to the second biomolecule with an initial binding strength.
A sample is contacted with the detection dimer. If a target biomolecule is present in the sample, then (i) the target biomolecule binds to either the first biomolecule or the second biomolecule with a detection binding strength; or (ii) the target biomolecule binds to the linker with a detection binding strength. The detection binding strength is greater than the initial binding strength.
In some embodiments, the detection dimer comprises a specifically bindable nanoparticle 1 directly bond to an affinity tag recognition region of linker peptide. The second recognition region of the linker peptide recognizes and specifically binds a biomolecule attached to nanoparticle 2 of the dimer with an initial binding strength. Thus, the second recognition region has low strength affinity to a molecule conjugated to the surface of nanoparticle 2, and a higher affinity to a target biomolecule. The presence of the target biomolecule results in its binding to the affinity tag and the concomitant dissociation of the dimer.
A sample is contacted with the detection dimer. If a target biomolecule is present in the sample, then the second recognition region of the linker peptide binds to the target biomolecule with a detection binding strength. The detection binding strength is greater than the initial binding strength.
An example of a biosensor dimer follows: A linker peptide consisting essentially of affinity tag 1 which directly binds to the surface of a quantum dot, a flexible spacer sequence, followed by the CAR protein. For instance, affinity tag 1 can have the following sequence: NNPMHQN, and bind directly to a ZnS-capped cadmium selenide (CdSe) quantum dot, while the CAR protein moiety would recognize a gold nanoparticle that was functionalized with a modified Knob protein (Knob-M). The modification of the Knob protein creates a weaker affinity between CAR and Knob-M than between CAR and the wild type Knob protein (Knob-wt). Thus the dimer is a quantum dot bound via a protein linker to a gold nanoparticle. The presence of the gold particle would result in quenching of fluorescence of the quantum dot. If the Knob-wt protein is present in a sample, then the CAR protein would dissociate from Knob-M and bind to Knob-wt. This would result in dissociation of the particle dimer, which can be detected due to increased fluorescence of the sample.
It is then determined whether the first recognition nano-component became detached from the second recognition nano-component to form monomers. If monomers were formed to a sufficient level, then the target biomolecule is deemed to be present in the sample.
The nanoclusters of the present invention can also be in the form of trimers which can be used a biosensors. The trimer can be used for a method of detecting the presence of a first target biomolecule and/or a second target biomolecule in a sample.
In one embodiment, the detection trimer comprises nucleic acid molecules and is Y-shaped. In this embodiment, the detection trimer comprises a first recognition nano-component attached to a second recognition nano-component and a third recognition nano-component. The first recognition nano-component comprises a first nanoparticle and a first single strand nucleic acid molecule. The second recognition nano-component comprises a second nanoparticle and a second single strand nucleic acid molecule. The third recognition nano-component comprises a third nanoparticle and a third single strand nucleic acid molecule. See
The first recognition nano-component is attached to the second recognition nano-component by a single stranded nucleic acid linker which binds two areas. In particular, the linker binds i) the portion of the first nucleic acid molecule which is more proximal to the first nanoparticle to ii) the second nucleic acid molecule. The linker binds the first nucleic acid molecule and the second nucleic molecule with an initial binding strength. The first recognition nano-component is attached to the third recognition nano-component by the binding of i) the portion of the first nucleic acid molecule which is more distal to the first nanoparticle to ii) the third nucleic acid molecule. The first nucleic acid molecule and the third nucleic molecule bind with an initial prime binding strength. The linker preferably contains a spacer sequence which would not specifically bind to the first, second or third single strand nucleic acid molecule.
A sample is contacted with the detection trimer. If the first target biomolecule is present in the sample, the first target biomolecule binds either the portion of the first nucleic acid molecule which is more proximal to the first nanoparticle or binds the second nucleic acid molecule or binds the linker with a detection binding strength. If the second target biomolecule is present in the sample, the second target biomolecule binds either the portion of the first nucleic acid molecule which is more distal to the first nanoparticle or the third nucleic acid molecule with a detection prime binding strength. The detection prime binding strength is greater than the initial prime binding strength.
It is then determined whether the first recognition nano-component became detached from the second recognition nano-component and/or third recognition nano-component to form dimers and/or monomers. If dimers and/or monomers were formed to a sufficient level, then the first target biomolecule and/or second target biomolecule is present.
Trimers can also be formed with biomolecules other than nucleic acids. Typically, these trimers have a fairly linear structure. An example of such a biosensor trimer follows: an affinity tag with low strength binding to a molecule conjugated to the surface of particle 1, a spacer sequence rich in Ser and Gly, a region with one or several cysteines or histidines that allow binding to the surface of the second particle, a linker sequence rich in Ser and Gly, and an affinity tag with low strength binding to a molecule conjugated to the surface of particle 3; preferably, particles 1 and 3 are quantum dots with different fluorescent properties, and particle 2 is a gold particle. Depending on the surface modification of the gold particle, thiol chemistry can be used to bind the cysteines, or Ni-NTA modification will allow binding of histidines.
There are numerous methods by which to determine whether the dimers and trimers of the present invention disassemble to form monomers and/or dimers.
In one embodiment, dimer/trimer disassembly is determined by Dynamic Light Scattering. In particular, the hydrodynamic diameter of a molecule in solution is determined from a measurement of the mobility (in terms of the translational diffusion coefficient in dilute solution) of the molecule by dynamic light scattering experiments.
In another embodiment, dimer/trimer disassembly is determined by fluorescence. In particular, in this embodiment, a recognition nano-component has fluorescent properties (e.g., a quantum dot) that are quenched by the close proximity and/or attachment of another recognition nano-component (e.g. a gold particle).
In order for a metal nanoparticle to quench the fluorescence of a quantum dot, there must be a maximal distance between the quantum dot and the metal nanoparticle, as known in the art. The length of the spacer sequences in a dimer or trimer can be adjusted to create the optimal length with maximum quenching.
Dimer disassembly will result in fluorescence. Depending on the equipment utilized, fluorescence can be detected at many different levels, including minute levels; For example, the fluorescence of a single quantum dot can be measured, thus detecting the presence of a single target biomolecule.
Other methods by which to detect dimer/trimer disassembly include plasmon shift (spectroscopy) and gel electrophoresis.
The biosensors can be constructed to detect any type of target biomolecules by methods known in the art. Clinical applications or applications related to Homeland Security may require detection of any organism of interest. For example, not only human viruses (such as, for example, human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B virus (HVB), small pox, Ebola, human papilloma virus (HPV), and flu viruses) but also viruses of agricultural importance, (such as, for example, viruses causing hoof and mouth disease), bacteria (including, for example, Anthrax, Staphylococcus, Streptococcus, and Borrelia), and infection-causing protozoa.
Also, the method can be used for the real time detection of toxicity markers, including the detection of specific stress proteins, and stress induced changes in expression and modification of DNA and RNA. In particular, the methods could be used to detect changes in gene expression, changes in gene regulation detectable via the induction of specific siRNAs, SNP, target DNAs secreted by specific tumor lines, etc.
The binding strength between two single-stranded nucleic acids is based on the strength of hybridization between the nucleic acids.
The strength of hybridization between two single-stranded nucleic acids can be adjusted by routine experimentation to achieve proper functioning. For example, the strength is a function of the length of hybridized nucleotides, the G-C content, and number of destabilizing mismatches.
In particular, the greater the length of hybridized nucleotides between two nucleic acid molecules, the greater the binding strength is between the two nucleic acids. In one embodiment, the first biomolecule and the second biomolecule of a detection dimer has about 10% to about 30% less hybridized nucleic acids between them as compared with the hybridized nucleic acids between a target biomolecule and the first biomolecule or the second biomolecule. For example, the first biomolecule and the second biomolecule of a detection dimer can have about 8 hybridized nucleic acids whereas the target biomolecule and the first biomolecule can have about 10 hybridized nucleic acids.
In another embodiment, if the releasing biomolecule, the anchoring biomolecule and the biomolecule on the initial recognition-nano-component (hereinafter “initial biomolecule”) are nucleic acids, then the length of the hybridized nucleotides in the releasing molecule and the anchoring biomolecule is greater than the length of the hybridized nucleotides in the anchoring molecule and the initial biomolecule. In addition to length, the strength of the hybridization can be reduced between the initial biomolecule and the anchoring biomolecule vis-a-vis the releasing biomolecule and the anchoring biomolecule by decreasing the G-C content and/or by inserting destabilizing mismatches in the nucleotides.
For the detection of biomolecules other than nucleic acids, the principle is based on the initial binding strength between two biomolecules with low affinity (but strong enough to keep the dimer pair stable). Examples of such biomolecules include proteins, peptides, cytokines, and specific metabolites. Subsequent binding of a biomolecule showing superior affinity to one of the binding partners, or the linker, results in dimer dissociation.
An example follows. A His-tagged CAR (coxsackie and adenovirus receptor) protein functionalizes particle 1, and has low affinity binding to particle 2 (e.g., a quantum dot) functionalized with a modified Knob protein. The modification of the Knob protein is a change in an amino acid in the epitope region. Such modification provides the low affinity binding. Once the wild-type Knob protein is available, e.g. because the adenovirus is present in a sample, the CAR protein and wild-type Knob protein will bind with high affinity, resulting in dimer dissociation. Alternatively, an affinity tag can be used (instead of the CAR protein) which recognizes the Knob protein. The affinity tag shows a strong binding to the wild-type protein, and a modified Knob protein (modified in the epitope region recognized by the affinity tag) is used to functionalize the second particle in the binding pair.
This method can revolutionize the field of real time detection, including that of toxicity markers. For instance, the method can be used to detect a specific antigen (to which the antibody used in the dimer formation has a superior affinity), but also for antibody detection when binding of a low affinity antibody is replaced by that of a high affinity antibody.
“Strawberry structures” were discussed above. A strawberry nanocluster detector comprises a metal nanoparticle and a plurality of attached fluorescent quantum dots. The metal nanoparticle is the “main” nanoparticle and the quantum dots are the “small” particles. For example, about five quantum dots can be attached to the metal nanoparticle. The quantum dots are attached to the metal nanoparticle by specifically bindable biomolecules. The quantum dots fluoresce at different colors. The quantum dots are quenched when attached to the metal nanoparticle. The specifically bindable biomolecules which attach the quantum dots to the main nanoparticle are different from one another and correspond to a particular color quantum dot. Thus, the strawberry nanocluster can detect as many target biomolecules as it has quantum dots.
Upon exposure of the strawberry nanocluster detector to a sample, a particular quantum dots will be released if a specific target molecule binds to the bindable biomolecule with higher affinity than the quantum dot binds to the main nanoparticle. When the quantum dot detaches from the main nanoparticle, it fluoresces at a particular color thereby indicating the presence of a particular target biomolecule in a sample.
In another embodiment, the “small” nanoparticles of a “strawberry-structure” each contain different catalyst thereby forming a multifunctional catalyst system.
A demonstration is given of how 10-nm nanoparticles can be functionalized with anisotropic binding interactions using a solid-state assembly approach. This approach utilizes DNA-derived interactions at nanoscale interfaces in a step-by-step approach. The approach is highly modular, and produces high quality and high yields of building blocks in a first of its kind high throughput fashion.
A simplistic view of the novel process is depicted in
Scheme 2 in
In a particular example of the application of the inventive technology, DNA-encapsulated nanoparticles and magnetic-colloid supports were utilized (Scheme 3). Each assembly step is encoded for specificity via a particular 15- to 20-base-pair double-stranded DNA interaction. After each step the system is purified via a magnetic field, and clean solution and products are then added, which aids fabrication fidelity. This magnetic purification process takes place in minutes in a benign environment and typically yields ≧98% desired product.
Scheme 3 in
Thus, a novel nano-assembly platform using encoded solid supports (NAESS) for the fabrication of nanoparticle monomers with controlled anisotropy is demonstrated. Accordingly, well defined doublet groupings, or Janus-type constructions, can be made. Anisotropy is driven by DNA interactions in a layer-by-layer fabrication. Scheme 1 shows an illustration of the NAESS approach. Gold nanoparticles (Au, 11.1±1.2 nm), were first functionalized with either a one- or two-component single-stranded DNA (ssDNA) shell structure following both established protocols and other recent work, and then assembled in a step-wise manner onto large (1-4 μm) DNA-capped colloidal magnetic particles. (NOTE: In the description that follows, elements are mapped to the figures by way of reference numerals which are found before the name of the element.) In step 1, a DNA-capped gold nanoparticle of mixed ssDNA composition (1-ssDNA, 2-ssDNA: [1]=[2]), may be used to facilitate moderate binding of the 2-ssDNA via 15 bp hybridization to a 1-ssDNA capped magnetic colloid (1-Mag), while preserving the 3-ssDNA as a second addressable binding site. After assembly of the 2, 3-Au to the 1-Mag, 1-3 hrs, and subsequent solution color change from ruby-red to clear, the system was purified via magnetic field, and washed via multiple rinsing with PBS buffer (10 mM phosphate buffer, 0.2 M NaCl, pH=7.4). In step 2, a 33-base cross-linker (4-ssDNA) is added at a ˜3× ratio ([4-ssDNA]/[2, 3-Au]=3), and allowed to anneal for 5-12 h under stirring before the supernatant solution is removed, and purified. In step 3, a 5-capped Au, which is complementary to the free linker end of the 4-ssDNA cross-linker, is added at a strict 1:1 ratio with the first particle layer (i.e., [2, 3-Au]/[4-Au]=1) and allowed to react for 3 h. Upon magnetic separation, the solution is optically clear, signaling the absorption of the second Au to layer 1 at the 1-Mag solid-support. Control experiments with non-complementary nanoparticles revealed less than 1% non-specific adsorption over 5 days. After each step, assembly yields were calculated based on UV-visible measurements (UV-vis), and typically yielded >98% of particle assembly to the solid support.
Once purified, an excess (1000×) of a 6-ssDNA fuel strand is added to the solution ([6-ssDNA]/[1-ssDNA]=1000) and is mixed gently for 4-12 h. The fuel 6-ssDNA selectively binds via 18 bp to the 1-ssDNA at the 1-Mag interface, which replaces the 15-bp binding of the 2-ssDNA of the 2, 3-Au interface, thus liberating the assembled doublet without the need to increase temperature (T=25° C.), or perform DNA ligation. The product solution was shown to gradually become red, illustrating the release of gold nanoparticle dimers into solution. Once disassembled, a 15-base, 7-ssDNA ([7-ssDNA]/[4-ssDNA]=1), is added to the solution, which effectively passivates any free cross-linkers in the system (e.g., 4-ssDNA), thus limiting any further assembly after release solution. The products could then be cleansed free of any 1-Mag via magnetic field, and additionally purified via a 0.2 μm sephadex filter. The assembled Au dimers were then stored at 4° C. in PBS buffer.
a shows a typical TEM micrograph of the released NAESS products. Clearly, the particles assembled into the pre-designed, doublet morphologies, as was demonstrated with multiple grid locations, samples, and trials. Statistical analysis of multiple TEM micrographs demonstrate a remarkable assembly yield of 70˜85% doublet morphologies (
The observed dimer construction and release from a solid support via entirely DNA-based interactions is remarkable given no change in assembly conditions (i.e., temperature, ionic strength, etc.) is required. However high dimer yields were not attained for all assembly conditions used. First, 2,3-Au loading was used on the 1-Mag of only ˜50% of the accessible DNA at the 1-Mag, thereby limiting the ability of the second layer of Au (i.e., 5-Au) to bridge Au of the first layer, a result which was observed in early experiments at maximum adsorption. Secondly, a ssDNA cross-linker ratio of ˜3× ([2, 3-Au]/[4-ssDNA]=3) dramatically increased the assembly kinetics and yield of the doublets, compared to an obvious choice of a 1× ratio. This may be due to standard errors in DNA or Au concentrations, or to the possibility of single Au particles receiving multiple cross-links at a ˜1× ratio (i.e., stochastic distribution). The use of the 7-ssDNA quenching strand was observed to greatly enhance the stability of the released doublets, limiting additional cross-linking of any free 4-ssDNA cross-linkers. Ease in purification of the system after each assembly step via magnetic separation greatly enhanced assembly yields, removing excess nanoparticles and DNA cross-links, thus limiting any re-assembly in the solution.
In addition to this step-by-step assembly of highly discrete nanoparticle clusters, the NAESS approach can be utilized to fabricate nanoparticles with a high degree of anisotropic binding character. Such anisotropy is extremely limited in particle nanosystems due to the complexities of using purely surface chemistry based particle modification. However, examples of anisotropic bindings, including colloidal particle systems, have been observed. In addition, initial results using nanoparticles of different sizes have been reported by Mirkin and co-workers.
Great numbers of researchers focus on the optical, scattering, and hydrodynamic properties of these types of assembled materials, including clusters and particularly dimers. To gain insights into the characteristics of the described systems, we employed UV-visible spectrophotometry (UV-vis), dynamic light scattering (DLS), and in situ small angle x-ray scattering (SAXS) measurements (
An additional strength of the NAESS fabrication method is its modular design, which allows for the use of different cross-linking ssDNA, e.g., for length control, as well as multiple sized or multi-component nanoparticles, such as hetero-dimers.
A schematic of the developed approach, and the required nano-components (particles, DNA, etc) are shown in
These assembled and released nano clusters were collected and visualized using Transmission Electron Microscopy (TEM) without any additional purification procedures.
Similar results were visualized at multiple TEM grid locations, and reproducible trials with dimer yields consistently between 70-83% (
The assembled dimer structures were further probed after assembly and release using dynamic light scattering (DLS).
In addition to the ease in fabrication of nanoparticle dimers, this encoded solid-support based assembly route can also routinely fabricate nanoparticle monomers with strong anisotropic binding character, i.e. Janus particles. The ability to impart nano-objects with controlled anisotropy is currently under a great deal of focus for the fabrication of one-dimensional plasmonic structures and potential for material design. To produce such Janus-monomers, nanoparticles are released from the support after step-2, which allows the linker (A′B′-ssDNA) to impart anisotropy. For instance, large A′/B-capped Au (˜50 nm) were assembled onto the A-Mag via step-1 (
The optical properties of nanoscale clusters, such as dimers, has attracted much interest recently for studies focused on harnessing particle-particle surface plasmon coupling by designing hot spots for surface enhanced raman spectroscopy (SERS), and single molecule detection, and plasmon quenching of fluorescence. The present invention exploits the modularity of its encoded solid-support assembly strategy to produce dimers containing various particle sizes and compositions. Their respective surface plasmon band (SP-band) coupling characteristics via ultraviolet-visible spectrophotometry (UV-vis) were measured.
Δλ/λ0≈C1exp(−(d/D)/τ)+y0, where C1 is a constant, and τ is the decay constant. The observed τ for our dimer systems, 0.14±0.03, is slightly lower than in-plane polarized measurements of gold nanodisks on silicon, fabricated by e-beam lithography.
The encoded solid-support method can also be utilized to produce hetero-clusters of different nanoparticles.
Nanoparticle Synthesis & DNA-functionalization: Gold nanoparticles of 11 nm,(S1) 55 nm, and 75 nm, (S2) were synthesized following literature procedures and quantified using measured extinction coefficients (ε11 nm(λ=518 nm)=1.1×108 cm−1 M−1, ε55 nm=(λ=538 nm) 2.4 1010 cm−1 M−1, ε75 nm=(λ=545 nm)=4.7×1010 cm−1 M−1). Thiol-modified single stranded oligonucleotides were purchased from Integrated DNA Technologies Inc. as disulfides, Table S1. Before nanoparticle functionalization, the oligonucleotides were first reduced by dissolving the lyophilized samples (100˜300 nmoles) for 30 minutes with 0.3 ml of a 100 mM dithiothreitol (DTT) solution in purified water or buffer. The reduced DNA was loaded onto a freshly purified sephadex column (G-25, Amersham Bioscience) and eluted with 2.5 ml 10 mM phosphate buffer (pH=7.4). The DNA was quantified using UV-Vis analysis with the specific DNA extinction coefficient. Streptavidin-functionalized magnetic colloids (1-4 μm) were purchased from Pierce Biotechnology Inc., and modified using biotinylated ssDNA following manufacturers directions.
The synthesized Au were functionalized with a ssDNA following methods for high DNA coverage reported by Mirkin and co-workers.(S3) In a typical experiment, an aliquot (1-50 μl) of a purified DNA 50-300 μM solution was added to a 1 ml solution of Au ([Au]=10-30 nM). The ssDNA+Au solutions were incubated at room temperature in a non buffered solution for at least 3 hr before adding phosphate buffer to bring its concentration to 10 mM (pH=7.4). The solution was left to anneal at 25° C. for 4 hr before the addition of NaCl (0.025M). The salt concentration was then increased gradually from 0.025 to 0.3 M NaCl over 24 hr, and left to anneal for an additional 24 hr at 0.3M. The excess DNA next was removed from the solutions by centrifugation for 30 minutes at 4,500 g.
Dimer Fabrication: In a typical experiment, a 0.1M PBS solution (300-1000 μl, 10 mM phosphate buffer, pH=7.4, 0.1M NaCl) consisting of ˜10 nM A′/B—Au is quantified using UV-vis. Next, ˜75 μl of A-Mag ([Mag]˜0.2 mg/ml) is added, and the mixture is allowed to incubate for 3-6 h with stirring. During this process, the gradual decrease in ruby-red color (Au SP-band) to optically transparent, was monitored using UV-vis, demonstrating absorption of A′/B—Au to the solid support. Upon separation via a magnetic field, the supernatant is removed, any un-assembled Au is quantified, and the sample is redispersed with fresh buffer. This separation process is repeated at least 3 times. Next, the B′C′-linker is added at a 3× molar ratio to the assembled A′/B—Au ([B′C′-linker]/[A′/B—Au]=3), and allowed to incubate during mixing for 6-12 h, upon which the system is purified as described above. Next, the C′—Au is added in a strict 1:1 ratio with the assembled concentration of A′/B—Au (i.e., first layer), and allowed to assemble for 6-12 h. The assembly process was again followed with UV-vis. Upon successful second layer assembly, accompanied by a second color change from ruby-red to transparent, beads were separated from a reaction solution. The final assembled product was redispersed in fresh 0.1M PBS, and a 1000× excess of A″-ssDNA fuel strand was added under mixing, and incubated for 3-12 h at room temperature. This process was followed by UV-vis which monitored the release of Au dimers via rise in absorption at 525 nm. Finally, a C″-ssDNA quenching strand was added in a 1:1 ratio of B′C′-ssDNA linker, which passivated any free linkers in the system. The released solution containing dimers were separated from A-Mag via magnetic field, and stored at 4° C. at desired concentrations.
We note that a number of conditions were investigated to optimize this assembly system, and dimer yields. First, we used a low A′/B—Au loading (<10%) on the A-Mag compared to the accessible A-DNA at the A-Mag ([A]˜0.3 nmoles). This increases separation of dimers at the surface, thereby limiting the ability of the second layer of Au (i.e., C—Au) to bridge Au of the first layer, a result which was observed in early experiments at maximum loading. Secondly, a B′C′-ssDNA cross-linker ratio of ˜3× was found to dramatically increased the assembly kinetics and yield of the dimers, compared to a 1× ratio. Third, the use of the C″-ssDNA quenching strand was observed to greatly enhance the stability of the released doublets, limiting additional cross-linking of any free B′C′-ssDNA cross-linkers. Finally, the ease in purification of the system after each assembly step via magnetic separation, greatly enhanced assembly yields, removing excess nanoparticles, DNA cross-links, or impurities from the final dimer solution. In addition, these dimers where also extremely robust, as confirmed by DLS and TEM results for aged samples, which showed little Dh change, or decreased morphology yields, respectively.
Janus Particle Fabrication: The assembly and release of Janus-particle monomers was achieved using identical conditions to dimer fabrication. The exception being the particles were disassembled via A″-ssDNA after step-2. The released Janus-particles were quantified using UV-vis, and a desired ratio of C—Au was added, and allowed to assemble free in solution for at least 12 h before sampling for TEM, DLS, and UV-vis.
UV-Visible Spectrophotometry (UV-vis): UV-vis spectra were collected on a Perkin-Elmer Lambda 35 spectrometer (200-1100 nm). Melting analysis was performed in conjunction with a Perkin-Elmer PTP-1 Peltier Temperature Programmer and was performed between 20-75° C. with a temperature ramp of 1° C./min while stirring, in a 10 mM phosphate buffer, 0.21 M NaCl, pH=7.1, buffer solution.
Transmission Electron Microscopy (TEM): TEM micrographs were collected on a JEOL-1200 microscope operated at 120 kV. The samples were prepared by dropcasting an aqueous nanoparticle or dimer solution onto a carbon coated copper grid, followed by the slow removal of excess solution with filter paper after 5 minutes.
Dynamic Light Scattering (DLS): The DLS measurements were obtained with a Malvern Zetasizer ZS instrument. The instrument is equipped with a 633 nm laser source, and a backscattering detector at 173°. ([Au, Dimers]=˜2 nM, 10 mM phosphate buffer, 0.1M NaCl, pH=7.4, T=25° C.).
Dimer Modeling: Diffusion of two connected nanoparticles is approximated as a diffusion of ellipsoidal object with the major axis length (a) of ellipsoid equal to the longest dimension of particles doublet and the minor axis length (b) of ellipsoid equal to size of individual particle. The diffusion coefficient for the ellipsoid D0 can be described as an average of diffusion coefficients D∥ and D⊥ in three orthogonal directions D0=1/3(D∥+2D⊥) (S4). Direction for D∥ is parallel to the major axis of the ellipsoid and directions for D⊥ are perpendicular to the axis.
D∥=kT/f∥ and D⊥=kT/f⊥, where f∥ and f⊥ are friction coefficients for ellipsoid movements in corresponding directions. The friction coefficients can be related to ellipsoidal dimensions a and b as follows
f
∥=16πηa/((a/b)2(2β+a∥)) and f⊥=16πηa/(2(a/b)2β+a⊥)
where η is the liquid viscosity, β=cos h−1(a/b)/((a/b)((a/b)2−1)0.5),
a
∥=2((a/b)2β−1)/((a/b)2−1), and a⊥=(a/b)2(1−β)/((a/b)2−1)
b was taken as the hydrodynamic size of the single particle (26 nm) and a=2b+l, where l is and estimated separation between monomers in a doublet (˜11 nm). The diffusion coefficient was calculated with the above parameters and the size of equivalent sphere de=kT/(3πηD0)=37.4 nm was compared with the dimmer size obtained with DLS d=37 nm.
Small Angle X-ray Scattering (SAXS): SAXS experiments were performed in-situ at the National Synchrotron Light Source's (NSLS) X-21A beamline. The scattering data were collected with a MAR CCD area detector and converted to 1D scattering intensity vs. wavevector transfer, q=(4π/λ)sin(θ/2), where λ=1.5498 Å, and θ, are the wavelength of incident X-ray and the scattering angle respectively. The data are presented as the structure factor S(q) vs q. The values of q were calibrated with silver behenate (q=0.1076 A−1) standards. S(q) was calculated as Ia(q)/Ip(q), where Ia(q) and Ip(q) are background corrected 1D scattering intensities extracted by angular averaging of CCD images for a system under consideration and un-aggregated Au, respectively. The peak positions in S(q) are determined by fitting a Lorenzian form.
Thus, it has been demonstrated that the use of bio-recognition between nano-objects at an encoded solid substrate allows for the high-throughput fabrication of both symmetric and asymmetric nanoparticle dimers with regulated interparticle distances, as well as Janus-type nanoparticles. The programmability of DNA motifs, the growing ability to functionalize nanomaterials with DNA, and the modularity of this approach may allow for incorporation of different bio- and nano-topological elements, leading to the development of a technological platform for assembly of rationally designed hetero-architectures.
In summary, a nano-assembly platform using encoded solid supports (NAESS) for the fabrication of high quality assembled nanoparticle doublets, and anisotropic Janus-clusters, using the versatility and tailorability of DNA-binding has been demonstrated. This high throughput approach utilizes a step-by-step assembly at colloidal substrates, which allows for anisotropic growth of doublets or Janus cluster morphologies with high yields under high concentration conditions. The modular nature of this fabrication route make these dimer materials ideal substrates for use in empirically exploring novel surface plasmon resonance phenomenology, changes in biological conformations, dynamically reconfigurable nano systems, as well as in studies related to energy transfer.
This assembly system is simple, allows for high throughput fabrication, and is modular. The method provides a cheap and low maintenance approach to controlling nanoparticle assembly. This system utilizes commercially available ssDNA strands, and is performed in aqueous solution without strenuous environmental controls.
This invention can be used for complex interparticle DNA-scaffolding. In one embodiment, additional classes of nanoparticles, especially semiconductive and magnetic particles, are be employed. In addition, this approach can be utilized for non-DNA systems, including the use of monolayer capped particles, peptides, and hybrid systems.
While the foregoing description has been made with reference to individual embodiments of the invention, it should be understood that those skilled in the art, making use of the teaching herein, may propose various changes and modifications without departing from the invention in its broader aspects.
This invention was made with Government support under contract number DE-AC02-98CH10886, awarded by the U.S. Department of Energy. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61044224 | Apr 2008 | US |
