Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/28—Electrolytic cell components
  • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
  • G01N27/307—Disposable laminated or multilayered electrodes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
  • B01L3/00—Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
  • B01L3/50—Containers for the purpose of retaining a material to be analysed, e.g. test tubes
  • B01L3/502—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures
  • B01L3/5027—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip

Definitions

• the present invention relates to an electrode for a microfluidic system.
• Microfluidic systems are known structures used in chemistry, physico-chemistry & biology, particularly in the following areas:
• microreaction which aims to produce all kinds of compounds (molecules, particles, emulsions, etc.) from starting reagents introduced into a microfluidic system which acts as a synthesis reactor,
• microfluidic systems performs the function of detector.
• the role of microfluidic systems is not however limited to the aforementioned functions; in particular, microfluidic systems may be designed to function as heat exchangers, filters, mixers, extractors, separators (for example operating by electrophoresis), devices for generating droplets of given size or solid particles, or as devices allowing to carry out particular operations (cell lysis, amplification of DNA, ).
• miniaturization of chemical or biological analysis systems is a marked trend in chemistry and analytical biochemistry. This makes it possible, on the one hand, to reduce the analysis times and, on the other hand, to reduce the quantity of reagents required. Miniaturization also makes it possible to integrate in the same system several steps of a detection protocol, which increases automation and therefore reduces handling costs. Miniaturization implies ever weaker detection volumes, hence the development of detection techniques and the development of increasingly sensitive detection components. Under these components, detection electrodes, in particular electrochemical electrodes, which are generally based on gold or platinum, are known to guarantee electrochemical stability and biological and chemical compatibility.
• these noble materials are deposited on rigid substrates or substrates based on inorganic material (silico-soda-lime glass) or organic material, in particular thermoplastics (polycarbonate, polymethylmethacrylate, polyimide, etc.).
• inorganic material silicon-soda-lime glass
• thermoplastics polycarbonate, polymethylmethacrylate, polyimide, etc.
• the present invention proposes to overcome the drawbacks of the electrochemical detection electrodes of the prior art by proposing a biologically compatible and electrochemically stable metallic layer electrode configuration (stability in operation and stability during eventual storage).
• the detection electrode for a microfluidic system is characterized in that it comprises a substrate of which at least one surface portion is coated by a stack of thin layers comprising a metal layer with intrinsic properties of electrical conductivity, said metal layer being associated with a so-called electrochemical barrier layer, said electrochemical barrier layer being associated with a terminal layer ensuring the biological compatibility and the electrochemical functionality (exchange of electric charges with molecules of the sample). This last layer also ensures the chemical and biological inertness of the electrode.
• this particular stacking structure it is possible to obtain, at lower cost, a detection electrode having an electrochemical resistance and a chemical and biological compatibility which makes its use possible within microfluidic analysis systems.
• the end layer further allows an exchange of electrical charges with molecules of the biological sample. This last layer also ensures the chemical and biological inertness of the electrode.
• the single figure shows the oxidation of the electrode as a function of the applied voltage.
• the metal layer is based on a pure material chosen from silver, or copper, zinc, or aluminum
• the electrochemical barrier layer is based on a metal or on the basis of a nitride of this metal, this metal possibly being, for example, titanium, or an electron-conduction oxide of the aluminum doped zinc oxide type (ZnO: A1); , mixed indium tin oxide (ITO), mixed indium zinc oxide (IZO) -
• the chemical and biological compatibility layer is based on a noble metal material selected for example from gold or platinum or any other metal compatible with the products to be tested.
• the thickness of the metal layer is between 50 to 1000 nm preferably between 150 to 500 nm, and even more preferably substantially close to 200 nm.
• the thickness of the electrochemical barrier layer is between 10 and 100 nm, preferably between 15 and 50 nm, and even more preferably substantially close to 20 nm.
• the thickness of the chemical and biological compatibility layer is between 10 to 100 nm, preferably between 15 to 50 nm, and even more preferably substantially close to 20 nm.
• the thickness of the layer of hooking between 2 and 10 nm it comprises a stack of layers of the Cu / TiNi / Au or TiN / Ag / Ti / Au type.
• the detection electrode for a microfluidic system has an electrical resistivity of between 0.1 and 10 ohm. square, which makes its use as a perfectly satisfactory electrode.
• it has a total thickness of between 200 and 500 nm.
• the electrode according to the invention is deposited, for example, by vacuum deposition techniques (for example by magnetic field assisted sputtering) or by electroplating on a substrate, which will thus constitute with the electrode a microfluidic system.
• the substrate of the microfluidic system can be made of materials of different kinds.
• polymer silicon or metal.
• these materials are unsatisfactory in many ways: the polymers are most often sensitive to certain organic solvents, are difficult to withstand prolonged treatments at temperatures above 200-300 ° C., deform under the effect of pressure, and are not entirely chemically inert (they can adsorb compounds present in the fluids, possibly salting them out later).
• the surface condition of the polymers is difficult to control, in particular because it can change over time.
• some polymers are not adapted to detection techniques operating by spectroscopy, in particular Raman, because of the disturbances they may cause.
• metals are likely to corrode, are not transparent or compatible with certain biological fluids, and are not compatible with the use of electrical function.
• support substrate for the electrode according to the invention glass, glass-ceramic or ceramic.
• a metal layer with intrinsic properties of electrical conductivity which is based on a pure material chosen from silver, or copper, zinc, aluminum and whose thickness is between 50 and 1000 nm, preferably between between 150 to 500 nm, and even more preferably substantially close to 200 nm.
• an electrochemical barrier layer which is based on a metal or on the basis of a nitride of this metal, this metal possibly being, for example, titanium or an electronically conductive oxide of the ZnO: Al, ITO, IZO type;
• a chemical and biological compatibility layer which is based on a noble metallic material chosen from gold and platinum.
• a hooked layer of a few nanometers, for example 1 and 10 nm, is deposited between the substrate and the metal layer. This layer of hooked can be based on titanium, chromium, nickel
• CVD Chemical Vapor Deposition
• electroplating electroplating
• spraying etc.
• an exemplary embodiment of an electrode for a microfluidic system according to the invention is given below.
• the glass is 0.7 mm sodocalcic and coated with a stack of Cu / TiNi / Au type magnetron deposited thin films.
• This electrode has a resistivity of 1 Ohm. square and a biological compatibility allowing the electrochemical interaction of the electrode with proteins in solution, without degrading them.
• the electrochemical detection electrode then undergoes surface treatments which, after removal of material forming the stack, form a plurality of detection cells.
• the array of detection cells can be obtained by physical etching, in particular by sand blasting or by irradiation using a CO 2 laser (JP-A-2000-298109), or by chemical etching of stacking.
• the detection cell array in several steps (depositAg / etchAg - depositTi / etchTi depositAu / etchAu), which makes it possible to modulate the lateral dimensions of each of the deposits, in particular to overcome any contamination by the edges.
• a deposition method based on electrodeposition is also well suited.
• the glass-function substrate advantageously has large dimensions so that several patterns can be made simultaneously, and therefore a large number of detection cells can be obtained in a single operation.
• substrates having a surface area of up to several square meters which makes it possible to make several thousand detection cells on a single substrate that can be subsequently cut into complete unit elements.
• the detection cells obtained in accordance with the invention have microstructures having a substantially square or rectangular cross section, which may be slightly rounded at the level of the substrate, having a depth that may range from several tens of microns to a few ⁇ m, or even less than micron.
• Systems entirely made of glass are interesting in that the substrate or substrates which constitute them have a small thickness and are transparent, which allows their use in complementary techniques of optical detection.
• the pure Ag electrode is oxidized as early as 0.4 V with an oxidation peak centered around 0.5-0.6 (dashed curve).
• An overlay of 20 nm Au slightly limits the oxidation of Ag (square dot curve).
• the most effective protection is obtained with the Ti electrochemical barrier layer (12 nm) where the Ag starts to be oxidized only from 1.5 V (DC line curve).
• the electrode undergoes an oxidation cycle using a so-called 'three-electrode' assembly with a working electrode (studied electrode), a reference electrode (saturated calomel electrode). ) and a counter-electrode (glass + 500 nm ITO) immersed in a liquid electrolyte H3PO4 (orthophosphoric acid).
• a working electrode studied electrode
• a reference electrode saturated calomel electrode
• a counter-electrode glass + 500 nm ITO immersed in a liquid electrolyte H3PO4 (orthophosphoric acid).

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• General Physics & Mathematics (AREA)
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• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
• Apparatus Associated With Microorganisms And Enzymes (AREA)

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• 2007
  • 2007-09-18 FR FR0757646A patent/FR2921157A1/fr not_active Withdrawn
• 2008
  • 2008-09-08 EP EP08835770A patent/EP2193363A1/de not_active Withdrawn
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