Patent Application
20100311103
The present invention concerns a transparent solid support coated with at least one layer of metal and with at least one layer of transparent conductive oxide (TCO), in particular tin-doped indium oxide (ITO), to form a solid support that can be used at the same time or independently for detection by SPR and by an electrochemical method. The invention comprises a process for producing such supports, especially by depositing thin films by cathode sputtering using a device comprising a radiofrequency (RF) generator, this device also being included in the invention. The invention also concerns a kit and a method for detection or identification of organic or mineral compounds by surface plasmon resonance (SPR) and/or electrochemical plasmon resonance comprising or using such supports.
Surface plasmon resonance (SPR) is a sensitive spectroscopic technique that has now proven its usefulness as an analytical tool for monitoring interfacial processes or for characterizing thin films (1-3). The SPR technique allows detection without marking. The selectivity of the method comes from the stimulation of the electromagnetic fields at the metal-dielectric interface owing to the surface plasmons created. These surface plasmons are excited on metal surfaces (gold, for example) when a polarized light p illuminates the metal/dielectric interface via a prism whereof the total reflection is adjusted, coupling, from certain angles, the incident light with the surface plasmon modes. The formation of the plasmon is shown by the marked attenuation of the intensity of the reflected light (measured by a photodiode) at a certain incidence angle value Θ, noted resonance angle ΘSPR. The position of this peak ΘSPR, its minimum reflection factor Rmin as well as its width at mid-height (noted FWHM for “Full Width at Half Maximum”) are extremely sensitive to any variations in the refraction index (n) of the adjacent medium and its optical depth.
The choice of metal film in contact with the dielectric medium is a critical parameter. As the metal film is an absorbent medium at the working wavelength, the refraction index of the metal layer considerably influences the characteristics of the absorption peak of the plasmon curve (4-7). Appropriate metals include in particular silver, gold, copper and aluminum (4, 8, 9). Silver provides a much narrower or pointed SPR signal than that of gold (the full width at half maximum is 10.67° for gold and 0.71° for silver in the air (10)). The origin of this result is the low value of the real part n′ and the high value of the imaginary part n″ of the refraction index n (n=n′+in″) of the metal. Silver is also described as having increased sensitivity to the variations of the refraction index and optical depth relative to gold (7, 9-11). Moreover, while the penetration length of the evanescent wave produced by a gold film 50 nm thick is 164 nm with a light source adjusted to λ=630 nm, that of a silver film with the same depth is 219 nm (12). Although the silver appears to be the ideal candidate as metal film in a SPR chip, gold is more used because it has stable chemical and optical properties compared to those of silver. Indeed, the surface of silver is chemically unstable in reactive mediums. Exposed to air, silver oxidizes quickly, this oxidation being accelerated in aqueous solution. This is why the use of the silver interface/adjacent medium cannot be considered for optical measurements, also long-lasting, essential during monitoring of reactions and biological interactions (13). The use of a silver film therefore implies that its surface is covered with a uniform protective layer in order to preserve its advantageous optical properties. Different approaches have been considered for this protection; for example: the additional deposition of organic monofilm making it possible to obtain both an interface sensitive to the ion-H+ interaction and allowing near field coupling, as with polyionene (14) or aluminum tris-(8-hydroxyquinoline) (15).
Today, the SPR measurement technique is widely used for real-time detection of molecular and biomolecular events such as the study of protein-DNA interaction, DNA-DNA interaction, cell adhesion, DNA hybridization reactions.
The chemistry used for fixing biological components to the surface of the gold film of the chip (or SPR support) is primarily based on the use of thiolated compounds (16-21), conductive polymers (22-24) or a monolayer of functionalized dextran (Biacore system) (25). One can also cite the coupling chemistry of silane used with oxides allowing the fixing of the biomolecules. The process then consists of covering the noble metal, such as gold, with a fine layer of silicon oxide SiOx. One can cite in particular the processes for manufacturing a solid support coated with a layer of gold on which a layer of SiOx of uniform and stable depth has been deposited using the plasma-enhanced chemical vapor deposition (PECVD) technique (26-27). Although these films of SiOx are interesting for electrochemical measurements, nevertheless remain very resistive.
Thus, in light of the preceding, it would be desirable to be able to have a process making it possible to modify a solid support adapted to SPR measurement, with the aim of obtaining a solid support that can also be used for electrochemical measurements while broadening the electroactive window usually used. Preferably, it would be advantageous for this modification made to the SPR support also to be able to significantly improve the stability of its interface if this support was, for example, provided with a silver or copper metal film, while also keeping its advantageous optical properties compared to those of gold (for example: analysis depth doubled in the reactive medium; measurement window Δn of the refractive index of the adjacent medium increased). Also preferably, it would be advantageous for this modification made to the SPR support to also be able to facilitate covalent coupling of organic compound(s) at its surface.
This is the object of the present invention.
The inventors have shown that depositing a thin film of a transparent conductive oxide (TCO), such as tin-doped indium oxide (ITO), on a support adapted to SPR detection having a metal layer of gold, silver or copper on its surface, made it possible to obtain such a support that could be used at the same time or independently for detection by SPR and by an electrochemical method.
The ITO deposited in a thin layer is known to be widely used as electrode both conductive for the electrical current and transparent in the visible and the near infrared regions. These thin layers are used in devices such as liquid crystal displays (LCD), organic light-emitting devices (OLED), solar cells, detectors, window, mirror or lens heating devices, heat absorption reflective layers, electrochrome devices, etc.
The ITO is an n-type degenerate semiconductor. Its broad forbidden band (>3.5 eV) explains its transparency in the visible region. The electrical conductivity of the ITO results from the contribution of load carriers (electrons) on levels close to the bottom of the conduction band, on one hand by creating oxygen holes, and on the other hand by substitution, in the crystalline structure, of indium ions by tin ions.
Thus, under a first aspect, the present invention concerns a solid support characterized in that it comprises a transparent solid support coated in part or in whole with:
at least one layer of at least one metal to form a solid support that can be used for detection by SPR;
at least one layer of transparent conductive oxide (TCO);
and, if applicable, an attachment layer.
Preferably for the solid support according to the invention, said TCO layer makes it possible to form a solid support that can be used for detection by SPR and/or for electrochemical detection, also preferably to form a solid support that can be used for detection by SPR and for electrochemical detection.
Thus, for said TCO layer to have this conductive nature, it will preferably be chosen among the group of compounds made up of In2O3-x with 0<x<3; ZnO1-x with 0<x<1; SnO2-x with 0<x<2; CdO1-x with 0<x<1; Ga2O3-x with 0<x<3; Tl2O3-x with 0<x<3; PbO2-x with 0<x<2; Sb2O5-x with 0<x<5; MgO1-x with 0<x<1 and TiO2-x with 0<x<2, the values of x of the intervals being those making it possible to obtain a good, or even better conductance, in addition to the transparent nature of this oxide layer.
A transparent material is a material whereof the ratio between the light intensity passing through the material and the incident light intensity on the material is not zero in at least one range of wavelengths.
In one preferred embodiment, the solid support according to the invention is characterized in that said transparent conductive oxide (TCO) layer has a defined and stable depth.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer comprises at least one transparent conductive oxide preferably chosen from the group of In2O3; ZnO, SnO2; CdO; Ga2O3; Tl2O3; PbO2; Sb2O5; MgO; TiO2.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer comprises at least one transparent conductive oxide made up of a combination of at least two binary oxides.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer also comprises a component capable of doping the TCO.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer is a layer comprising indium oxide In2O3.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer is a layer comprising tin-doped indium oxide (ITO), preferably synthesized from a target material made up of a mixture 90% In2O3 and 10% SnO2 by mass.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer is a layer comprising tin-doped indium oxide (ITO) deposited at ambient temperature and with a mainly amorphous structure.
In one preferred embodiment, the solid support according to the invention is characterized in that said TCO layer has a depth between 3 nm and 200 nm, preferably the depth is between 2 nm and 20 nm, between 4 nm and 10 nm being the most preferred values. For example: 4 nm is the most preferred value for SPR supports made up of at least one gold film and used for detection by SPR and/or by an electrochemical method; 4 nm is the most preferred value for SPR supports made up of at least one silver film and used for detection by SPR; 10 nm is the most preferred value for SPR supports made up of at least one silver film and used for detection by SPR and/or by an electrochemical method.
In one preferred embodiment, the solid support according to the invention is characterized in that said layer made up of at least one metal is a layer whereof the metal is chosen in the group made up of gold, silver, copper and aluminum or by any combination of these metals or of their respective alloys.
In one particular embodiment, said layer of at least one metal is made up of or comprises metal nanoparticles, preferably whereof the diameter is between 2.5 nm and 100 nm.
In one preferred embodiment, the solid support according to the invention is characterized in that said layer made up of at least one metal has a depth between 10 nm and 200 nm, preferably between 30 and 50 nm.
In one preferred embodiment, the solid support according to the invention is characterized in that said solid support is coated with an attachment layer before said layer made up of at least one metal, preferably with a depth between 1 nm to 10 nm, 5 nm±1 nm being the preferred depth.
In one preferred embodiment, the solid support according to the invention is characterized in that said attachment layer is a metal layer whereof the metal is chosen from the group made up of titanium, chrome, nickel, tantalum, molybdenum, thorium, copper, aluminum or tin or by any combination of these metals or of their respective alloys, oxides and/or hydroxides.
In one preferred embodiment, the solid support according to the invention is characterized in that said attachment layer is a metal oxide MOx layer, with oxygen gradient, with M designating at least one metal chosen from the group of gold, silver, copper and aluminum, or by any combination of these metals or of their respective alloys.
In one particularly preferred embodiment, the solid support according to the invention is characterized in that said attachment layer is preferably a layer of titanium.
In one preferred embodiment, the solid support according to the invention is characterized in that said solid support is made up of at least one organic or inorganic transparent material or a combination of transparent materials such as glass or transparent solid polymers such as polymethylpentene (TPX), polyethylene, polyethylene terephthalate (PET), polycarbonate.
Said solid support is preferably chosen in glass.
In one particular embodiment, the solid support according to the invention is characterized in that said layer of at least one metal to form a solid support that can be used for detection by SPR is a layer made up of metal nanoparticles, preferably chosen among the supports shown in
In one particular embodiment, the metal film comprising said metal nanoparticles, preferably gold or silver, is obtained by evaporation.
In another preferred embodiment, the solid support according to the invention is characterized in that said transparent conductive oxide (TCO) layer is coated with a layer made up of metal nanoparticles, preferably as shown in
In still another particular embodiment, the solid support according to the invention is characterized in that said transparent conductive oxide (TCO) layer is coated with a layer made up of metal nanoparticles, the latter layer of metal nanoparticles itself being coated with a TCO layer, preferably as shown in
Obtaining, on a solid support, a metal film made up of or comprising metal nanoparticles, preferably gold or silver, is well known by those skilled in the art and will not be developed here. Non-limitingly, one can cite, for example, the direct deposition of commercially available metal nanoparticles, with a diameter preferably between 2.5 nm and 100 nm, on the glass or metal oxide surface (the glass surface being able to be silanized beforehand to ultimately present groups of positive charges for better fixing of those particles (in general presented in monodispersed form and with negative charges). One can also cite the obtaining of such a layer thermally (evaporation/curing of a metal film with small depth), or by electrochemical deposition on an ITO-type conductive film.
In one preferred embodiment, the solid support according to the invention is characterized in that at least one TCO layer has hydroxyl groups.
Preferably, the hydroxyl groups are chemically activated so as to be able to bind through covalent bonding to reactive groups such as silanes, if applicable, these silane groups themselves being functionalized by groups chosen from the thiol, amine, acid, cyanide, aldehyde groups, electrochemically active, photoactivable, etc. groups, but also with other molecules carrying active functionalities for the hydroxyl groups (acid, amine, etc.).
The TCO surfaces, in particular ITO, having activated hydroxyl groups can be used for the anchoring, by covalent coupling, of silane compounds functionalized with thiol groups. These thiol groups can then easily form a disulfide bridge with a bifunctional reagent having a thiol function and a terminal amine function (for example by reaction with the 2-(2-pyridinyldithio)ethanamine hydrochloride compound). This amine group is then used to fix a curing agent (crosslinker) there, the latter being chosen to be capable of fixing the chosen probe, for example DNA or a protein, for a given detection method. The advantage of the presence of a disulfide bridge is to be able to reuse or recycle the support after eliminating the probe through a reduction reaction (28).
For the surface chemistry making it possible to graft biomolecules such as proteins or nucleic acids, on the ITO layer having activated hydroxyl groups, one can also cite the method by which one performs the deposition of the (N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTS) compound on a glass support coated with at least one ITO layer using the chemistry of the N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide and the N-hydroxysuccinimide (EDC/NSH)) (29). For grafting of nucleic acids (RNA or DNA), one can graft amino groups beforehand to one of the ends of these nucleic acids and come back to use this same type of reagent (EDC/NHS).
In one preferred embodiment, the solid support according to the invention is characterized in that said hydroxyl groups and/or the functional groups having reacted with said hydroxyl groups can be desorbed from said TCO layer by exposure to ultraviolet radiation or by chemical reduction.
Under a second aspect, the present invention concerns a method for manufacturing a solid support for detection by surface plasmon resonance (SPR) and by electrochemical methods, characterized in that it comprises the following steps:
the deposition on at least a same surface of the solid support and superimposed,
of at least one layer made up of at least one metal to form a solid support that can be used for detection by SPR; and
of at least one transparent conductive oxide (TCO) layer, preferably said TCO layer is made up of at least one transparent conductive oxide (TCO) layer to form a solid support that can be used for detection by SPR and/or for electrochemical detection, preferably able to be used for detection by SPR and for electrochemical detection.
The transparent conductive oxide (TCO) layer is deposited here to (i) facilitate the covalent grafting of organic compound(s); (ii) form a solid support that can also be used for electrochemical measurements; (iii) protect, if necessary, the metal layer from any outside attack(s).
In one preferred embodiment, the process according to the invention is characterized in that the deposition of the TCO layer is done in a vacuum chamber, preferably provided with a residual pressure between 10−5 and 10−7 mbar or less.
In one preferred embodiment, the process according to the invention is characterized in that the deposition of the TCO layer is done in partial vacuum in the presence of at least one rare gas, preferably argon, or in the presence of a mixture of a rare gas (preferably argon) and a gas containing the oxygen element (preferably dioxygen), preferably at a pressure of about 0.009 torr of rare gas/dioxygen mixture, preferably with a pO2/pAr ratio equal to about 5.1.10−4.
In one preferred embodiment, the process according to the invention is characterized in that the TCO layer is deposited on the solid support by cathode sputtering in that the cathode sputtering housing comprises at least one generator, preferably a radiofrequency (RF) generator, and in that the radiofrequency power used for the deposition is calculated as a function of the area of the target surface (source material of the TCO layer), the distance separating the target from the solid support (substrate), preferably between 0.1 W/cm2 and 4 W/cm2 for a distance between 10 mm and 150 mm, preferably 0.86 W/cm2 for a target-substrate distance of 78 mm.
In one preferred embodiment, the process according to the invention is characterized in that the depth of said TCO layer is controlled by the duration of the deposition, preferably at a speed of 0.6 nm/min at 0.86 W/cm2 for a target/substrate distance of 78 mm.
It has been shown that the deposition by cathode sputtering (
On the contrary, we have recently shown the possibility of depositing, at ambient temperature, such transparent conductive layers on temperature-fragile substrates, such as plastic films having small radiofrequency or hyperfrequency losses, for example on transparent plastic polymers such as Zeonex® (copolyolefin manufactured by NIPPON ZEON), polymethylpentene (TPX), Transphan® (cyclic olefin polymer having a high vitreous transition temperature available from Lofo High Tech Film, GMBH, Germany) or Arton G® or Artong® (manufactured by the company Japan Synthetic Rubber Co., Tokyo, Japan).
In one preferred embodiment, the process according to the invention is characterized in that said TCO layer comprises at least one transparent conductive oxide chosen from the group made up of In2O3-x with 0<x<3; ZnO1-x with 0<x<1; SnO2-x with 0<x<2; CdO1-x with 0<x<1; Ga2O3-x with 0<x<3; Tl2O3-x with 0<x<3; PbO2-x with 0<x<2; Sb2O5-x with 0<x<5; MgO1-x with 0<x<1 and TiO2-x with 0<x<2, preferably chosen among In2O3; ZnO, SnO2; CdO; Ga2O3; Tl2O3; PbO2; Sb2O5; MgO; TiO2.
In one preferred embodiment, the process according to the invention is characterized in that said TCO layer comprises at least one oxide made up of a combination of at least two binary oxides.
In one preferred embodiment, the process according to the invention is characterized in that said TCO layer comprises any combination of the TCOs with a component capable of doping those TCO such as Sn for In2O3.
In one particularly preferred embodiment, the process according to the invention is characterized in that said TCO layer is a layer comprising indium oxide In2O3.
In one even more particularly preferred embodiment, the process according to the invention is characterized in that said TCO layer is a layer comprising tin-doped indium oxide (ITO), preferably synthesized from a target material made up of a mixture of 90% In2O3 and 10% SnO2 by mass.
In still another preferred embodiment, the process according to the invention is characterized in that said TCO layer is a layer comprising tin-doped indium oxide (ITO) deposited at ambient temperature and with a mainly amorphous structure.
In one preferred embodiment, the process according to the invention is characterized in that said TCO layer has a depth between 3 nm and 200 nm, preferably the depth is between 3 nm and 20 nm, between 4 nm and 10 nm being the most preferred values. For example: 4 nm is the most preferred value for SPR supports made up of at least one gold film and used for detection by SPR and/or by an electrochemical method; 4 nm is the most preferred value for SPR supports made up of at least one silver film and used for detection by SPR; 10 nm is the most preferred value for SPR supports made up of at least one silver film and used for detection by SPR and/or by an electrochemical method.
By cathode sputtering and without heating the substrate, we synthesized mainly amorphous ITO layers, but having electrical conduction and transparency characteristics comparable to those of polycrystalline ITO layers (30, 31). The choice of a set of sputtering conditions comprising a high pressure, a continuous current power (DC) or modest radiofrequency (RF), and a great target-substrate distance, favors the thermalization of the atoms arriving on the substrate, and therefore favors the obtaining of an amorphous layer (31-33).
Moreover, it has been shown that tin does not contribute to the creation of carriers in amorphous ITO, such that what is said about amorphous ITO can also be applied to pure and amorphous In2O3 (34-36).
To obtain optimal properties of the In2O3 or the amorphous ITO, the partial oxygen pressure in the working atmosphere is critical (
The layers obtained do not require any treatment after coming out of the enclosure, and they are stable at ambient up to a temperature of about 125-180° C., after which temperature they begin to crystallize with notable speed, in our experience and according to various authors (35, 37, 38). This threshold temperature is compatible with many applications, in particular when the substrate is organic, and therefore itself temperature-fragile. Moreover, it is probable that the absence of curing limits surface reconstruction phenomena of the oxide (39) and that it preserves better reactivity, useful, in particular, for applications of the molecular grafting type. Moreover, ITO being a sub-stoichiometric oxide, the molecular grafting is all the more simple relative to (i) a surface made up of precious metals (Au) or semi-precious metals (Ag, . . . ) and (ii) opens a new path for chemisorption (chemical surface structuring using electroactive organic layers, for example).
The good conductance of the deposited oxide is also crucial for the electrical contacts on the multilayer when an electrochemical measurement or detection is contemplated (in parallel to the surface plasmon detection).
In one preferred embodiment, the process according to the invention is characterized in that said layer made up of at least one metal is a layer whereof the metal is chosen in the group made up of gold, silver, copper and aluminum or by any combination of these metals or of their respective alloys, gold, silver and copper being the most preferred.
In one preferred embodiment, the process according to the invention is characterized in that said layer made up of at least one metal has a depth between 10 nm and 200 nm, preferably between 30 and 50 nm.
In one preferred embodiment, the process according to the invention is characterized in that said solid support is first coated with an attachment layer.
In one preferred embodiment, the process according to the invention is characterized in that said attachment layer has a depth between 1 and 10 nm, before the deposition of said layer made up of at least one metal, preferably with a depth of 5 nm±1 nm.
In one preferred embodiment, the process according to the invention is characterized in that said attachment layer is a metal layer whereof the metal is chosen from the group made up of titanium, chrome, nickel, tantalum, molybdenum, thorium, copper, aluminum, tin, or by any combination of these metals or of their respective alloys, oxides and/or hydroxides.
In one preferred embodiment, the process according to the invention is characterized in that said attachment layer is a layer of metal oxide MOx, with oxygen gradient, with M designating at least one metal chosen in the group made up of gold, silver, copper and aluminum, or by any combination of these metals or of their respective alloys.
In one particularly preferred embodiment, the process according to the invention is characterized in that said attachment layer is a layer of titanium.
In one preferred embodiment, the process according to the invention is characterized in that said solid support is first coated with an attachment layer and said layer made up of at least one metal, before the deposition of said TCO layer.
In one preferred embodiment, the process according to the invention is characterized in that if necessary, said attachment layer and said layer made up of at least one metal is (are) also deposited by cathode sputtering.
The interest of the invention also lies in the absence of any temperature transition of the ITO/metal/ . . . layer, the problems of diffusion and/or delamination between layers are avoided whereas they are encountered by others with multilayers based on polycrystalline ITO (40-42).
In one preferred embodiment, the process according to the invention is characterized in that, if necessary, said attachment layer, said layer made up of at least one metal and said TCO layer are successively deposited on said solid support by cathode sputtering within a same device comprising an enclosure provided with a system of at least two targets, one of which is made up of the metal or alloy used to develop said layer made up of at least one metal, and the other of which is made up of the material used to develop said TCO layer, and, if applicable, of a target made of metal or alloy used to develop said attachment layer, and, if necessary, any useful target, said device being provided with at least one vacuum pump to create a partial vacuum in the enclosure and at least one controlled inlet for rare gas, preferably argon, and, if necessary, additional controlled inlets for reactive gas(es), preferably a carrier gas of the oxygen element, preferably dioxygen, and/or of at least one controlled inlet for a pre-established mixture of rare gas and reactive gas(es), preferably a carrier gas of the oxygen element, preferably dioxygen.
In one preferred embodiment, the process according to the invention is characterized in that said solid support is made up of at least one organic or inorganic transparent material or a combination of transparent materials.
Preferably, said transparent material is chosen among glass or transparent solid polymers such as polymethylpentene (TPX), polyethylene, polyethylene terephthalate (PET), polycarbonate, in particular when the manufacturing method uses the cathode sputtering technique at ambient temperature, glass being the most preferred solid support.
Under a third aspect, the present invention concerns a process for determining at least one organic or mineral compound in a sample or for monitoring at least one reaction in a complex mixture by SPR and/or electrochemical detection, characterized in that it uses a solid support according to the invention or capable of being obtained by a process according to the invention.
The invention also concerns the use of a support according to the invention or capable of being obtained by a process according to the invention for the detection in a sample of chemical or mineral compound(s), comprising in particular polymers or heavy metals, organic or biological compounds or structures comprising in particular nucleic acids, polypeptides or proteins, carbon hydrates, organic particles such as liposomes or vesicles, inorganic particles (such as micro- or nanospheres, cellular organelles or cells).
Under a fourth aspect, the present invention concerns a kit or supplies to determine the presence and/or quantity of at least one compound or to monitor at least one reaction in a sample by SPR and/or by electrochemistry, characterized in that it comprises a support according to the invention or capable of being obtained by a process according to the invention.
Under a last aspect, the invention concerns a diagnostic or analysis device comprising a support according to the invention or capable of being obtained using a process according to the invention.
Said device preferably comprises an enclosure provided with a system of at least two targets, one of which is made up of the metal or alloy used to develop said layer of at least one metal, and the other of which is made up of the material used to synthesize said TCO layer, and, if necessary, of a target made up of the metal or alloy used to develop said attachment layer, and if necessary, of any useful target as defined in one of the claims according to the invention, said device being provided with at least one vacuum pump to create a partial vacuum in the enclosure and at least one controlled intake for rare gas, preferably argon, and, if necessary, additional controlled intakes for reactive gas(es), preferably a carrier gas of the oxygen element, preferably dioxygen, and/or at least one controlled intake of a pre-established mixture of rare gas and reactive gas(es), preferably of a carrier gas of the oxygen element, preferably dioxygen.
Other features and advantages of the invention will appear in the continuation of the description with the examples and figures, the legends of which are shown hereinafter.
It will be understood by all practitioners experienced in the development of thin layers that the conditions cited in the examples below can vary (in particular depending on the equipment) without being detrimental to the interest of the invention.
Although we have only shown one ITO target, the housing advantageously has multiple targets to avoid breaking the vacuum between successive depositions of films of different natures.
The bottom diagram, obtained before curing, shows at 2Θ≈25°, a diffusion peak due to the amorphous state of the glass substrate, on which at 2Θ≈31° another diffusion peak is superimposed that is characteristic of the indium oxide in amorphous state. One notes the presence of several peaks of very low intensity at 2Θ≈30.3°; 35.2°; 50.5° and 60.2° that are due to the diffraction of the cleavage planes of the indium oxide in the polycrystalline state (in extremely small quantity).
The upper diagram, obtained after curing of this same sample, was offset upwardly for better readability. The diffusion peak of the substrate still exists, the diffusion peak of the In2O3 around 31° has completely disappeared, and the diffraction peaks of the cleavage planes are exalted.
These diagrams demonstrate that the curing has completely converted the raw ITO layer of essentially amorphous deposition into a polycrystalline layer without preferential orientation.
Note the very smooth appearance of the surface morphology, also related to the amorphous state of the ITO.
Potassium chloride (KCl), potassium hexacyanoferricyanide (Fe(CN)6−4), pyrrole, methanol, ethanol, hexane, 1-butanol, 2-propanol, 1-hexanol, 1,3-propanediol are obtained from Aldrich and used without additional purification.
The thin film of ITO is deposited at ambient temperature by RF cathode sputtering from an ITO ceramic target (purity=99.999% and composition≈90% In2O3-10% SnO2 by mass) of 75 mm in diameter, and in a newly cleaned and degassed enclosure, according to the rules of the art. The pumping is done by a turbomolecular pump, and the threshold pressure Po in the enclosure is better than 5.10−7 mbar. The process gasses, Ar and O2, are introduced during the deposition by two gas lines equipped with mass flowmeters, from pure gas bottles (
The bilayer, after reception, is positioned directly on the substrate holder. It does not undergo any prior treatment. It is then introduced, via a load lock, into the deposition enclosure (
After pumping to P≦10−6 mbar, the ITO target undergoes a pre-sputtering for 30 minutes (parameters grouped together in table 1) in order to free itself of any memory effect of the surface of the target related to the preceding deposition. The deposition of the ITO material on the bilayer is then done (parameters grouped together in table 2). The depth of the ITO film is controlled by the deposition time, after determining the deposition speed.
The technique for developing ITO films at ambient temperature makes it possible to perform the deposition on a presynthesized bilayer using another technique (evaporation in this case) without particular surface preparation. The mechanical resistance of the ITO on gold has been validated. No delaminating or interdiffusion effect between the 3 materials was revealed. The plasmon response of these samples was also validated.
In this example, the ITO layer is synthesized to:
Very narrow SPR peaks are obtained by using a metal provided with a low value n′ associated with a strong value n″ of its refraction index n (n=n′+in″). A “silver” SPR chip will therefore have a better theoretical sensitivity than a “gold” chip (table 3A), as previously manufactured. However, since silver oxidizes and/or sulfonates spontaneously whether in open air or by immersion in the solution to be analyzed, this type of chip (Ag/Ti) therefore cannot be used and consequently marketed, unless a protective layer is deposited on the surface of the layer of silver.
For this we use the same deposition housing used in example 2, which is in fact a multitarget enclosure allowing the deposition of 3 distinct materials (
The synthesis of the ITO/Ag/Ti trilayer is done using the process comprising the following steps:
The depth of the attachment sub-layer will preferably be around 5 nm, depth from which there is percolation of the first Ti islands, which makes it possible to ensure the effective adhesion of the upper layer of silver.
In this example, the ITO layer is synthesized to:
A “copper” SPR chip will therefore have a theoretical sensitivity greater than that of a “gold” SPR chip, as a result of the higher numerical value of the imaginary part n″ of the refraction index n of the copper (table 3A). However, in this case as well, since copper oxidizes spontaneously whether in open air or by immersion in the solution to be analyzed, this type of chip therefore cannot be marketed without a layer of TCO being deposited on its surface (ITO in this example).
For this, we use the same deposition housing used in example 3, replacing the silver target with the copper target (
The advantages of the ITO deposition on the surface of the copper are equivalent to those developed in example 3.
A) Substitution of the material used for the attachment layer
a) For the attachment sub-layer of Ti, another material can be substituted such as: Cr, Ni—Cr, Al, Ta or Th.
b) For the attachment sub-layer of Ti, the oxide of the metal used for the plamson response can be substituted, i.e.: AuOx, AgOx, AlOx and/or CuOx.
Indeed, by creating an oxygen concentration gradient in the metal layer with:
This layer can be made from any material belonging to the TCO (Transparent Conductive Oxide) family (45-50).
This technique for developing SPR chips at ambient temperature also makes it possible to make these chips on fragile or temperature-sensitive organic substrates, such as Zeonex® transparent polymers (copolyolefin manufactured by NIPPON ZEON), polymethylpentene (TPX), Transphan® (cyclic olefin polymer having a high vitreous transition temperature available from Lofo High Tech Film, GMBH, Germany) or Arton G® or Artone (manufactured by the company Japan Synthetic Rubber Co., Tokyo, Japan) (51).
The electrochemical measurements were done using the Autolab 30 potentiostat (Eco Chemie, Utrecht, The Netherlands). The electrode cell used is not the conventional 3 electrode one, but that with two channels of the Autolab SPRINGLE apparatus (Eco Chemie, Utrecht, The Netherlands) allowing simultaneous electrochemical measurement and SPR detection. The configuration of this equipment is described in references 52 and 53. In summary, a polarized laser beam (A=670 nm) illuminates the rear surface of the sensor via a hemispherical lens placed on a prism (BK7 type with a refraction index n=1.52). The reflected light is detected by a photodiode. The incidence angle measured is modified by the use of a mirror oscillating at a frequency of 44 Hz. The SPR curves are recorded with a movement of the mirror from front to back. The reflectance minimum is measured, then averaged.
The measuring apparatus is equipped with an open tank, with a capacity between 20 and 150 μl where the Ag/AgCl reference electrode, the platinum auxiliary electrode and the SPR support with electrical contact on the surface of the sample are submerged. The active surface of the electrode is 0.07 cm2.
The quality of the SPR signal depends critically on several parameters, but essentially on the refraction index of the metal layer and its depth. The refraction index n (characterized by the values of its real part n′ and its imaginary part n″ such that n=n′+in″) of the metal layer has an influence almost as important as its depth (4) on: (i) the angular value of the minimum of the resonance peak (ΘSPR); (ii) the full width at half maximum of this resonance peak (FWHM); (iii) the slopes SL and ST of the resonance peak around ΘSPR, signal head slope and signal tail slope, respectively; (iiii) the reflectance minimum at the resonance angle ΘSPR (Rmin).
During the SPR detection, the movement of the angle ΘSPR (ΔΘSPR) on the angular scale is measured. For a light beam of given wavelength and a fixed prism, there is an optimal depth of the film for which the intensity of the resonance peak Rmin will be minimal and the full width at half maximum FWHM the narrowest, which will allow a very fine detection of the angular position ΘSPR. These values depend on the refraction indexes (i) of the prism; (ii) of the metal film; (iii) of any layer(s) placed on the surface of the metal film and of course on the respective depth of each of these layers. However, the low adhesion of the film of precious or semiprecious metal to the surface of an oxide (for example, glass) requires the use of an attachment layer (for example, a film of titanium) positioned between the surface of the glass and the metal layer. This attachment layer must be as fine as possible in order to cause minimal disruption of the plasmon signal while also ensuring optical adhesion of the metal layer.
At our working wavelength (λ=670 nm) and with a BK7 prism of index n=1.52, the optimal depths dmin of the metal films used for SPR detection are Au (40 nm); Ag (38 nm); Cu (44 nm); Ti (5 nm). Their respective complex refraction indexes are provided in table 3A. If a metal layer depth d greater than dmin is used, then there will be attenuation of the intensity of the evanescent field due to the reflection of the incident light beam. Rmin will tend toward 1 as d increases. In parallel, the full width at half maximum FWHM and the slopes SL and ST will also be altered.
It is consequently necessary to protect the silver film from any degradation, in this case chemical here. The deposition of a fine layer of ITO is one solution (see example 3).
This ITO deposition can also be done on an Au chip, which does not require particular protection. In this case, a widening of the SPR signal is observed (ΔFWHM=2.8°) as well as an offset (ΘSPR=2.3°) (table 6) in comparison with the Au/Ti bilayer. The chemical stability of the new ITO/Au/Ti heterostructure is comparable to that with silver.
A number of surface plasmon measurement apparatuses are based on the detection and determination of the value of the angular position ΘSPR. In this case, the precision of the measurement depends directly on the narrowness of the SPR peak. Thus, the ITO/Ag/Ti heterostructure combining (i) extreme fineness of the SPR peak, (ii) steep SL and ST slopes, (iii) great chemical stability, will be the ideal chip.
However, other apparatuses integrate, regarding their sensitivity, other parameters such as the amplitude of the movement of the angle ΘSPR as a function of the variation of the refraction index of the reactive medium. It is therefore a combination between the fineness of the SPR peak and its movement amplitude that will define the sensitivity of the signal.
Another aspect of the sensitivity of these biochips is their capacity to detect refraction index variations as low as 10−5 (for example, for biological applications on the nanometric scale).
The electrochemical measurements were done using the Autolab 30 potentiostat (Ag/AgCl reference electrode) at the scanning speed of 50 mV/s and with a solution of KCl with a concentration of 0.1 mol·L−1.
The electroactive window of the Au—Ti support is between −1.5V<E<+1.2V (
The deposition of 4 nm of ITO on an Au/Ti chip makes it possible to widen the electroactive window of the new biochip manufactured: −1.5V<E<+1.9V:
by increasing the polarization at the anodic potentials: the ITO layer prevents the passage into solution of Au+, as shown by the voltammogram of
by increasing the polarization at the cathodic potentials: the ITO layer allowing the grafting of silane functions, measurements at cathodic potentials less than 0.5V are therefore possible (55).
Biochip: ITO/Ag/Ti
The voltammogram obtained with the ITO(4 nm)/Ag(38 nm)/Ti(5 nm) support, as working electrode, is deformed compared to that obtained with the Au(50 nm)/Ti(4 nm) support (
The deposition of a TCO film on the surface of the Au/Ti, Ag/Ti or Cu/Ti supports allows the electrochemical deposition of a fine layer of conductive polymer at their surface. Thus, a film of 5 nm of polypyrrole was deposited on the 3 heterostructures: ITO/Ag/Ti, Au/Ti and ITO/Au/Ti, using the process described in reference 56.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0759748 | Dec 2007 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/067356 | 12/11/2008 | WO | 00 | 6/11/2010 |
