WO1995021934A1 - Hexacyanoferrate modified electrodes - Google Patents
Hexacyanoferrate modified electrodes Download PDFInfo
- Publication number
- WO1995021934A1 WO1995021934A1 PCT/GB1995/000265 GB9500265W WO9521934A1 WO 1995021934 A1 WO1995021934 A1 WO 1995021934A1 GB 9500265 W GB9500265 W GB 9500265W WO 9521934 A1 WO9521934 A1 WO 9521934A1
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- Prior art keywords
- enzyme
- electrode
- analyte
- modified
- electrodes
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- UETZVSHORCDDTH-UHFFFAOYSA-N iron(2+);hexacyanide Chemical compound [Fe+2].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] UETZVSHORCDDTH-UHFFFAOYSA-N 0.000 title claims description 11
- 108090000790 Enzymes Proteins 0.000 claims abstract description 50
- 102000004190 Enzymes Human genes 0.000 claims abstract description 50
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 34
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims abstract description 30
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims abstract description 23
- 239000008103 glucose Substances 0.000 claims abstract description 23
- DCYOBGZUOMKFPA-UHFFFAOYSA-N iron(2+);iron(3+);octadecacyanide Chemical compound [Fe+2].[Fe+2].[Fe+2].[Fe+3].[Fe+3].[Fe+3].[Fe+3].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] DCYOBGZUOMKFPA-UHFFFAOYSA-N 0.000 claims abstract description 18
- 239000011248 coating agent Substances 0.000 claims abstract description 17
- 238000000576 coating method Methods 0.000 claims abstract description 17
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 claims abstract description 16
- 239000011668 ascorbic acid Substances 0.000 claims abstract description 16
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 15
- 235000010323 ascorbic acid Nutrition 0.000 claims abstract description 15
- 239000013225 prussian blue Substances 0.000 claims abstract description 15
- 229960003351 prussian blue Drugs 0.000 claims abstract description 15
- 229940072107 ascorbate Drugs 0.000 claims abstract description 7
- 239000008280 blood Substances 0.000 claims abstract description 5
- 210000004369 blood Anatomy 0.000 claims abstract description 5
- 229960005489 paracetamol Drugs 0.000 claims abstract description 5
- 229910021397 glassy carbon Inorganic materials 0.000 claims abstract description 4
- 239000010439 graphite Substances 0.000 claims abstract description 4
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 4
- 229940088598 enzyme Drugs 0.000 claims description 49
- 239000012491 analyte Substances 0.000 claims description 20
- 239000000758 substrate Substances 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 10
- 238000000034 method Methods 0.000 claims description 10
- 229910052799 carbon Inorganic materials 0.000 claims description 8
- LEHOTFFKMJEONL-UHFFFAOYSA-N Uric Acid Chemical compound N1C(=O)NC(=O)C2=C1NC(=O)N2 LEHOTFFKMJEONL-UHFFFAOYSA-N 0.000 claims description 7
- TVWHNULVHGKJHS-UHFFFAOYSA-N Uric acid Natural products N1C(=O)NC(=O)C2NC(=O)NC21 TVWHNULVHGKJHS-UHFFFAOYSA-N 0.000 claims description 7
- 238000012544 monitoring process Methods 0.000 claims description 7
- 239000000126 substance Substances 0.000 claims description 7
- 229940116269 uric acid Drugs 0.000 claims description 7
- 230000002452 interceptive effect Effects 0.000 claims description 6
- 108010015776 Glucose oxidase Proteins 0.000 claims description 5
- 239000004366 Glucose oxidase Substances 0.000 claims description 5
- 239000012530 fluid Substances 0.000 claims description 5
- 229940116332 glucose oxidase Drugs 0.000 claims description 5
- 235000019420 glucose oxidase Nutrition 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 4
- 230000000717 retained effect Effects 0.000 claims description 4
- 108090000854 Oxidoreductases Proteins 0.000 claims description 2
- 102000004316 Oxidoreductases Human genes 0.000 claims description 2
- 239000003112 inhibitor Substances 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 210000002381 plasma Anatomy 0.000 claims description 2
- 210000002966 serum Anatomy 0.000 claims description 2
- 238000011144 upstream manufacturing Methods 0.000 claims description 2
- 238000001514 detection method Methods 0.000 abstract description 3
- 238000004070 electrodeposition Methods 0.000 abstract description 3
- 229910052739 hydrogen Inorganic materials 0.000 abstract 1
- 239000001257 hydrogen Substances 0.000 abstract 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 abstract 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 14
- 239000000243 solution Substances 0.000 description 13
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 12
- 230000004044 response Effects 0.000 description 10
- 229960005070 ascorbic acid Drugs 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- AWDBHOZBRXWRKS-UHFFFAOYSA-N tetrapotassium;iron(6+);hexacyanide Chemical compound [K+].[K+].[K+].[K+].[Fe+6].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] AWDBHOZBRXWRKS-UHFFFAOYSA-N 0.000 description 8
- 241000899717 Itaya Species 0.000 description 6
- 230000003647 oxidation Effects 0.000 description 6
- 238000007254 oxidation reaction Methods 0.000 description 6
- 229910052697 platinum Inorganic materials 0.000 description 6
- 239000001103 potassium chloride Substances 0.000 description 6
- 235000011164 potassium chloride Nutrition 0.000 description 6
- 238000007792 addition Methods 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 230000008859 change Effects 0.000 description 5
- 238000002484 cyclic voltammetry Methods 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 150000001721 carbon Chemical class 0.000 description 4
- 239000004020 conductor Substances 0.000 description 4
- 230000005518 electrochemistry Effects 0.000 description 4
- 239000003822 epoxy resin Substances 0.000 description 4
- 239000012528 membrane Substances 0.000 description 4
- 229920000647 polyepoxide Polymers 0.000 description 4
- 239000008367 deionised water Substances 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 230000000144 pharmacologic effect Effects 0.000 description 3
- 239000008057 potassium phosphate buffer Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 2
- -1 aliphatic alcohols Chemical class 0.000 description 2
- 238000004082 amperometric method Methods 0.000 description 2
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 2
- 239000003814 drug Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- YAGKRVSRTSUGEY-UHFFFAOYSA-N ferricyanide Chemical compound [Fe+3].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] YAGKRVSRTSUGEY-UHFFFAOYSA-N 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000004814 polyurethane Substances 0.000 description 2
- 229920002635 polyurethane Polymers 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 229910052709 silver Inorganic materials 0.000 description 2
- 239000004332 silver Substances 0.000 description 2
- RPGGYYVWJTWVMS-ZPSVQYCPSA-N (8r,9s,10r,13s,14s,17r)-17-ethynyl-10,13-dimethyl-1,2,3,6,7,8,9,11,12,14,15,16-dodecahydrocyclopenta[a]phenanthren-17-ol;(8r,9s,13s,14s,17r)-17-ethynyl-13-methyl-7,8,9,11,12,14,15,16-octahydro-6h-cyclopenta[a]phenanthrene-3,17-diol Chemical compound OC1=CC=C2[C@H]3CC[C@](C)([C@](CC4)(O)C#C)[C@@H]4[C@@H]3CCC2=C1.C1CC[C@]2(C)[C@H]3CC[C@](C)([C@](CC4)(O)C#C)[C@@H]4[C@@H]3CCC2=C1 RPGGYYVWJTWVMS-ZPSVQYCPSA-N 0.000 description 1
- 229920003319 Araldite® Polymers 0.000 description 1
- 102100026189 Beta-galactosidase Human genes 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 108010059881 Lactase Proteins 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N SnO2 Inorganic materials O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 description 1
- 108010005774 beta-Galactosidase Proteins 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 150000001718 carbodiimides Chemical class 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 206010012601 diabetes mellitus Diseases 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- ZPWVASYFFYYZEW-UHFFFAOYSA-L dipotassium hydrogen phosphate Chemical compound [K+].[K+].OP([O-])([O-])=O ZPWVASYFFYYZEW-UHFFFAOYSA-L 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000002255 enzymatic effect Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000001727 in vivo Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- BQZFDPZOAJMUIU-UHFFFAOYSA-N iron(3+);hexacyanide Chemical compound [Fe+3].[Fe+3].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] BQZFDPZOAJMUIU-UHFFFAOYSA-N 0.000 description 1
- 229940116108 lactase Drugs 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000001404 mediated effect Effects 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical class C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- VPKDCDLSJZCGKE-UHFFFAOYSA-N methanediimine Chemical compound N=C=N VPKDCDLSJZCGKE-UHFFFAOYSA-N 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000011527 polyurethane coating Substances 0.000 description 1
- GNSKLFRGEWLPPA-UHFFFAOYSA-M potassium dihydrogen phosphate Chemical compound [K+].OP(O)([O-])=O GNSKLFRGEWLPPA-UHFFFAOYSA-M 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000007974 sodium acetate buffer Substances 0.000 description 1
- 239000012064 sodium phosphate buffer Substances 0.000 description 1
- 239000011550 stock solution Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000011287 therapeutic dose Methods 0.000 description 1
- 238000006276 transfer reaction Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
- C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
- C12Q1/001—Enzyme electrodes
- C12Q1/005—Enzyme electrodes involving specific analytes or enzymes
-
- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
- C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
- C12Q1/001—Enzyme electrodes
- C12Q1/004—Enzyme electrodes mediator-assisted
-
- 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
- G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
- G01N27/3271—Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood
Definitions
- This invention relates to hexacyanoferrate (or Prussian blue) modified electrodes which may be coupled with enzymes, particularly oxidoreductase enzymes e.g. glucose oxidase for the amperometric determination of analytes such as glucose.
- enzymes particularly oxidoreductase enzymes e.g. glucose oxidase for the amperometric determination of analytes such as glucose.
- Amperometric enzyme electrodes have proved to be an important approach for sensing in medicine, in the food industry and for environmental monitoring. (See, for example, Newman, J.D. and Turner, A.P.F., Essays in Biochemistry, 27, 147-159, 1992.)
- Amperometric biosensors generally work by monitoring oxygen consumed or hydrogen peroxide produced during enzymatic oxidation of the analyte.
- An artificial electron acceptor may be used instead of the natural electron acceptor oxygen (see e.g. Cass et al . , Anal.Chem. 56, 667-671 1984; Matthews et al., Diabetic Medicine. 5_, 248-252, 1987).
- This enables the sensor to be operated at a low potential thus reducing the effect of interfering compounds commonly observed at the high operating potential employed for hydrogen peroxide detection.
- the majority of experimental prototype implantable biosensors based on hydrogen peroxide detection utilise platinum as the base electrode as opposed to the cheaper alternative carbon, the reason being that hydrogen peroxide can be detected at a lower potential at platinum than at carbon.
- modified electrodes of the same general type as those prepared by Itaya et al have particular advantages for certain analytical applications, particularly in biosensors.
- an enzyme electrode comprising:
- an enzyme retained on or adjacent said coating said enzyme being selected such that a substrate or product thereof is capable of being electrochemically oxidised or reduced at said modified electrode.
- an amperometric biosensor comprising a cell for receiving an analyte, and electrodes for contacting analyte in the cell, said electrodes comprising a sensing electrode, a standard electrode and, optionally, a counter electrode, and wherein said sensing electrode comprises a modified electrode comprising:
- biosensor including an enzyme selected such that a substrate or product thereof is capable of being electrochemically oxidised or reduced at said modified electrode; said enzyme being disposed in relation to the modified electrode so that, in the operation of the biosensor, the enzyme affects the amount of said substrate or product and thereby affects a signal current of said cell.
- the enzyme may be retained on or adjacent said coating of the modified electrode which thus constitutes an enzyme electrode.
- the biosensor may include means defining a fluid flow path through said cell, and wherein said enzyme is disposed in the flow path upstream of the cell so as to affect the composition of the fluid flow reaching the cell.
- a preferred type of embodiment is adapted for determining glucose in whole blood, serum or plasma.
- the invention provides a method of determining the amount of an analyte in a sample comprising contacting a solution comprising said analyte with an enzyme electrode according to the first aspect and with a standard electrode, applying a potential between said electrodes, and monitoring the electrical current.
- the analyte may be a substrate for the enzyme, or an inhibitor or an activator thereof.
- the invention provides a method of determining hydrogen peroxide in an analyte solution in the presence of one or more potentially interfering substances selected from ascorbate, uric acid and 4- acetamidophenol ("paracetamol” or “acetaminophen”), comprising contacting said analyte solution with a modified electrode comprising:
- the invention provides a method of determining an analyte by means of an affinity reaction using an enzyme label, wherein the amount of enzyme label is detected amperometrically by determining a substrate or product thereof by means of a modified electrode comprising: (a) a conductive element having a surface and
- An electrode as used in preferred embodiments of the invention can be much cheaper than a platinum electrode (e.g. using carbon as the underlying conductor) and can offer excellent resistance to interfering substances.
- a modified electrode for use in the present invention may be a conductor with a PB coating applied as disclosed by Itaya in the papers referred to above.
- the conductor preferably of carbon, may be placed in a solution of hexacyanoferrate ( "HCF" ) II and/or III and connected into an electrolytic circuit with another electrode and a source of potential.
- HCF hexacyanoferrate
- the potential of the conductor is cycled between a low or zero value and a positive value.
- Electrochemical deposition can provide suitable reaction kinetics to allow the formation of the complex.
- Prussian blue analogues display characteristic cyclic voltammagrams, hence cyclic voltammetry can be used to determine if film deposition has been successful.
- a simple test to see if the deposited layer is suitable for biosensor application would be to poise the electrode at a relevant operating potential ( amperometry ) and immerse it in a solution containing the biological element. Once the background current has stabilised, aliquots of the substrate for the biological element can be introduced into the cell and the change in current as a result of this addition can be recorded. If current change is proportional to the substrate concentration then the modified electrode is suitable.
- FIG. la and b are schematic sectional views of two embodiments of enzyme electrodes of the invention.
- Fig. 2 is a schematic sectional view on a smaller scale of an analytical cell including the electrode of Fig. la.
- Fig. 3 is a cyclic voltammogram of a HCF-modified graphite electrode.
- Fig. 4 is a calibration graph of glucose concentration versus current for the cell of Fig. 2.
- Figs. 5-7 are bar charts showing the response of bare and HCF-modified electrodes to various circumstances.
- Figs. 8 and 9 are graphs showing the effects on glucose determination, using modified and unmodified electrodes, of ascorbate and 4-acetamidophenol in concentrations typically found in the blood of persons taking therapeutic doses.
- Fig. 10 is a bar chart showing the effects of high concentrations of ascorbic acid and 4-acetamidophenol on glucose determination using modified and unmodified electrodes.
- Fig. 11 is a cyclic voltammogram for demonstrating electrode stability.
- Glucox PS (E.C.I.1.3.4., 35000 International Units/g from As erqrillus Nlcrer ) was obtained from Rhone Poulenc Chemicals (Stockport, Cheshire, UK).
- Glucose, dipotassium hydrogen phosphate, potassium dihydrogen orthophosphate, potassium chloride, potassium hexacyanoferrate III and 1-ascorbic acid were all of analytical grade and purchased from BDH (Poole, Dorset, UK).
- l-Cyclohexyl-2-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate for enzyme immobilisation was purchased from Sigma (Dorset, Poole, UK).
- Electrodes 10 as shown in Fig. la were prepared as follows.
- Graphite rods 12 (1cm in length) were washed in a large stirred volume of boiling deionised water for 15 minutes. The rods were then rinsed in acetone and left to air dry in a drying cabinet at 80 degrees Celsius for approximately two hours. The rods were sealed in plastic capillary pipettes 14 and wire 16 was threaded through one end and bonded with silver loaded epoxy resin 18 to form a contact. Araldite 05 TM' epoxy resin 20 was used to insulate the sides of the electrodes. All electrodes were polished prior to use.
- the working electrode was cycled fifteen times between 0-2.5V vs SCE at a scan rate of 0.2V/s in potassium hexacyanoferrate (III) dissolved in deionised water (0.1M, 5ml) to deposit a layer 22.
- the ferricyanide solution was continually stirred during cycling.
- the modified electrodes were washed in a large, stirred, volume of water until the initial pale blue colour was no longer observed. (These electrodes were used for experiments not requiring enzyme activity. )
- Glucose oxidase was immobilised onto the surface of the modified carbon electrodes using carbodimide immobilisation.
- a modified electrode was placed in a beaker containing stirred l-cyclohexyl-3-(2- morpholinoethyl) carbodiimide (0.15M, 5ml) in sodium acetate buffer (O.IM, pH5.5) for ninety minutes. The electrodes were washed thoroughly with deionised water.
- Glucose oxidase (lO ⁇ l 200mg/ml) in sodium phosphate buffer (0.02M, pH7) containing potassium chloride (O.IM) was deposited onto the electrode surface and left to dry for four hours, to produce an immobilised enzyme layer 24.
- a semipermeable membrane 24' coating the enzyme layer 24 was produced as follows. Using micropipettes, two layers of Nafion solution and two layers of polyurethane solution were applied. The Nafion solution was 5% in aliphatic alcohols plus water, as supplied by Aldrich. The electrode was dried for 5 minutes after the first layer, and for 1 hour after the second layer. The polyurethane solution was 10% in 9:1 w/v THF/DMF. The coated electrode was stored at 4°C overnight to dry. The dried electrodes were stored in potassium phosphate buffer at 4 degrees Celsius until use. Type 2 'minature' electrodes as shown in Fig lb were prepared by a similar process, starting from "pencil lead" carbon rods.
- Each rod 112 was first modified with HCF (III), producing a film 122 over an end region.
- HCF HCF
- layers of enzyme 124 and (preferably) semipermeable membrane were also applied, over the HCF layer.
- Supports for the rods were produced by cutting about 5cm of the narrow end off a "CIO Pipetteman" tip.
- a rod 112 was fed (modified end first) into the truncated tip 114, from the wide end.
- Wire 116 was fed part way, just into the well defined in the tip.
- a small plug of epoxy resin 120 was placed near the bottom of the well, for sealing.
- a larger plug 118 of silver-loaded epoxy resin closed off the top of the device and connected the wire 116 to the rod 112.
- the enzyme electrode response to glucose was determined by immersing the electrode in 10ml of stirred potassium phosphate buffer 25 (0.02M, pH7) containing potassium chloride (0.1M) in a water- jacketed (26) cell, thermostated at 25 degrees Celsius.
- the cell contained a saturated calomel electrode (SCE) 28 and a platinum wire counter-electrode 30.
- SCE saturated calomel electrode
- a potential of +450mV vs SCE was applied to the electrode.
- successive 2 ⁇ l injections of glucose (IM) in potassium phosphate buffer (0.02M, pH7) containing potassium chloride (O.IM) were introduced into the cell giving a concentration range of up to 2.8mM.
- the steady state response after each addition was recorded.
- a calibration plot for the glucose sensor is shown in figure 4.
- glucose oxidase was immobilised on to the surface of these modified electrodes and the resulting enzyme electrode was used to monitor glucose.
- a typical sensor of this type exhibited a linear range up to 1.5mM glucose and sensitivity of 4.97 ⁇ A mmolar ⁇ cm" 1*
- the use of outer membranes such as the polyurethane coating used herein, was found to extend the linearity. The membranes act to restrain diffusion.
- Figure 8 shows that physiological levels of ascorbic acid produced no significant interference in sensor output when added to 5mM glucose at miniature modified carbon base electrodes. However, an approximately 10-fold increase in current was observed at miniature unmodified carbon base electrodes operated under similar conditions.
- Fig. 9 shows that a 1-2-fold increase in sensor output was observed when normal levels of 4-acetamidophenol were added to 5 millimolar glucose at miniature modified carbon-base electrodes The same effect was observed at pharmacological levels (800 ⁇ M) of ascorbic acid and paracetamol (Fig. 10). Itaya et al .
- Hydrogen peroxide molecules may by virtue of their small size be able to penetrate the modified lattice and undergo subsequent oxidation whereas larger molecules such as ascorbic acid may be hindered from penetrating the lattice. Additionally in the case of anions such as ascorbic acid, charge repulsion may also contribute to the failure of such ions to reach the iron centres.
- the modified electrodes were surprisingly stable and offer the commercially important advantages of operation at low potential and selectivity.
- the apparent absence of leaching will have important implications for In vivo monitoring of analytes such as glucose, where stable, continuous output of the sensor is essential.
- This invention may also find general applications in biosensors and chemical sensors.
- HCF(III) modified graphite disc electrodes were repeatedly cycled at 200 mV/s in O.IM potassium chloride. Traces are shown for scan nos 2, 15 and 30. It can be seen that there is remarkably little change. Different embodiments may use different enzymes. Thus a wide range of analytes could be measured e.g. glucose, lactase, alcohol and many more.
- Carbon is inexpensive and particularly amenable to mass production technology e.g. screen printing, thus improving the electrochemistry of H 2 0 2 at carbon so that it is as good as at platinum is useful.
- Electrodes may also exhibit good electrochemistry at this surface, so that the utility of such electrodes is not restricted to systems generating H 2 0 2
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Abstract
Amperometric biosensors, e.g. for determining blood glucose, employ electrodes, preferably of graphite or glassy carbon, which have been modified by electrochemical deposition of a Prussian blue - type coating. Such electrodes are capable of amperometric detection of hydrogen peroxide, largely unaffected by potential interferents including ascorbate and paracetamol. A hydrogen peroxide-generating enzyme may be immobilised on the electrode or otherwise coupled to it so that the system becomes a biosensor.
Description
Hexacvanoferrate Modified Electrodes
Technical Field
This invention relates to hexacyanoferrate (or Prussian blue) modified electrodes which may be coupled with enzymes, particularly oxidoreductase enzymes e.g. glucose oxidase for the amperometric determination of analytes such as glucose. Background Art
Amperometric enzyme electrodes have proved to be an important approach for sensing in medicine, in the food industry and for environmental monitoring. (See, for example, Newman, J.D. and Turner, A.P.F., Essays in Biochemistry, 27, 147-159, 1992.)
Amperometric biosensors generally work by monitoring oxygen consumed or hydrogen peroxide produced during enzymatic oxidation of the analyte. An artificial electron acceptor (mediator) may be used instead of the natural electron acceptor oxygen (see e.g. Cass et al . , Anal.Chem. 56, 667-671 1984; Matthews et al., Diabetic Medicine. 5_, 248-252, 1987). This enables the sensor to be operated at a low potential thus reducing the effect of interfering compounds commonly observed at the high operating potential employed for hydrogen peroxide detection. The majority of experimental prototype implantable biosensors based on hydrogen peroxide detection utilise platinum as the base electrode as opposed to the cheaper alternative carbon, the reason being that
hydrogen peroxide can be detected at a lower potential at platinum than at carbon.
There has been some academic work on the electrochemistry of electrodes modified with Prussian blue, by Itaya and co-workers. Thus Itaya et al . . Electrochem. Sci. and Technol., 129(7) , 1498-1500, (1982) disclose the preparation of Prussian blue ( "PB" ) modified electrodes by electrochemical deposition from ferric-ferricyanide solutions onto platinum, glassy carbon or Sn02. Itaya et al . , J.A.C.S. , 106, 3423-3429 (1984) describe investigations on PB-modified electrodes including catalysed hydrogen peroxide oxidation at rotating PB-modified glassy carbon disc electrodes. Disclosure of Invention
The present invention results from the discovery that modified electrodes of the same general type as those prepared by Itaya et al . have particular advantages for certain analytical applications, particularly in biosensors.
In one aspect the invention provides an enzyme electrode comprising:
(i) a modified electrode comprising:
(a) a conductive element having a surface; and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface; and
(ii) an enzyme retained on or adjacent said
coating, said enzyme being selected such that a substrate or product thereof is capable of being electrochemically oxidised or reduced at said modified electrode. In a second aspect the invention provides an amperometric biosensor comprising a cell for receiving an analyte, and electrodes for contacting analyte in the cell, said electrodes comprising a sensing electrode, a standard electrode and, optionally, a counter electrode, and wherein said sensing electrode comprises a modified electrode comprising:
(a) a conductive element having a surface; and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface; said biosensor including an enzyme selected such that a substrate or product thereof is capable of being electrochemically oxidised or reduced at said modified electrode; said enzyme being disposed in relation to the modified electrode so that, in the operation of the biosensor, the enzyme affects the amount of said substrate or product and thereby affects a signal current of said cell.
The enzyme may be retained on or adjacent said coating of the modified electrode which thus constitutes an enzyme electrode.
The biosensor may include means defining a fluid flow path through said cell, and wherein said enzyme is
disposed in the flow path upstream of the cell so as to affect the composition of the fluid flow reaching the cell.
A preferred type of embodiment is adapted for determining glucose in whole blood, serum or plasma.
In a third aspect the invention provides a method of determining the amount of an analyte in a sample comprising contacting a solution comprising said analyte with an enzyme electrode according to the first aspect and with a standard electrode, applying a potential between said electrodes, and monitoring the electrical current. The analyte may be a substrate for the enzyme, or an inhibitor or an activator thereof.
In a fourth aspect the invention provides a method of determining hydrogen peroxide in an analyte solution in the presence of one or more potentially interfering substances selected from ascorbate, uric acid and 4- acetamidophenol ("paracetamol" or "acetaminophen"), comprising contacting said analyte solution with a modified electrode comprising:
(a) a conductive element having a surface and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface; and with a standard electrode, applying a potential between said electrodes, and monitoring the electrical current. In a fifth aspect the invention provides a method of determining an analyte by means of an affinity
reaction using an enzyme label, wherein the amount of enzyme label is detected amperometrically by determining a substrate or product thereof by means of a modified electrode comprising: (a) a conductive element having a surface and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface.
An electrode as used in preferred embodiments of the invention can be much cheaper than a platinum electrode (e.g. using carbon as the underlying conductor) and can offer excellent resistance to interfering substances.
A modified electrode for use in the present invention may be a conductor with a PB coating applied as disclosed by Itaya in the papers referred to above. Alternatively the conductor, preferably of carbon, may be placed in a solution of hexacyanoferrate ( "HCF" ) II and/or III and connected into an electrolytic circuit with another electrode and a source of potential.
Preferably the potential of the conductor is cycled between a low or zero value and a positive value. Electrochemical deposition can provide suitable reaction kinetics to allow the formation of the complex. Prussian blue analogues display characteristic cyclic voltammagrams, hence cyclic voltammetry can be used to determine if film deposition has been successful. A simple test to see if the
deposited layer is suitable for biosensor application would be to poise the electrode at a relevant operating potential ( amperometry ) and immerse it in a solution containing the biological element. Once the background current has stabilised, aliquots of the substrate for the biological element can be introduced into the cell and the change in current as a result of this addition can be recorded. If current change is proportional to the substrate concentration then the modified electrode is suitable.
Some embodiments of the invention will now be described in greater detail with reference to the accompanying drawings.
Brief Description of Drawings Fig. la and b are schematic sectional views of two embodiments of enzyme electrodes of the invention.
Fig. 2 is a schematic sectional view on a smaller scale of an analytical cell including the electrode of Fig. la. Fig. 3 is a cyclic voltammogram of a HCF-modified graphite electrode.
Fig. 4 is a calibration graph of glucose concentration versus current for the cell of Fig. 2. Figs. 5-7 are bar charts showing the response of bare and HCF-modified electrodes to various circumstances.
Figs. 8 and 9 are graphs showing the effects on glucose determination, using modified and unmodified
electrodes, of ascorbate and 4-acetamidophenol in concentrations typically found in the blood of persons taking therapeutic doses.
Fig. 10 is a bar chart showing the effects of high concentrations of ascorbic acid and 4-acetamidophenol on glucose determination using modified and unmodified electrodes.
Fig. 11 is a cyclic voltammogram for demonstrating electrode stability. Modes for Carrying Out the Invention Materials and Methods
Glucox PS (E.C.I.1.3.4., 35000 International Units/g from As erqrillus Nlcrer ) was obtained from Rhone Poulenc Chemicals (Stockport, Cheshire, UK). Glucose, dipotassium hydrogen phosphate, potassium dihydrogen orthophosphate, potassium chloride, potassium hexacyanoferrate III and 1-ascorbic acid were all of analytical grade and purchased from BDH (Poole, Dorset, UK). l-Cyclohexyl-2-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate for enzyme immobilisation was purchased from Sigma (Dorset, Poole, UK). Uric Acid 99%, 4-acetamidophenol 98% from Aldrich Chemical Co., (Gillingham, Dorset). Platinum s.w.g.26, 0.44mm wire was purchased from BDH (Poole, UK). Spectrotech purity graphite rod 4.572mm diameter X 304.8mm long was purchased from Johnson Matthey, Materials Technology (Royston, UK).
The autolab and General Purpose Electrochemical
System software package supplied by Windsor Scientific Limited, (Berkshire, UK) was employed for all voltammetric experiments. A Ministat potentiostat and CR 600 JJ Instruments chart recorder were used in all amperometric measurements. In both cases a three electrode cell was used. All potentials quoted are with respect to a saturated calomel electrode (S.C.E). Platinum wire was used as the counter electrode.
Electrodes 10 as shown in Fig. la were prepared as follows.
Graphite rods 12 (1cm in length) were washed in a large stirred volume of boiling deionised water for 15 minutes. The rods were then rinsed in acetone and left to air dry in a drying cabinet at 80 degrees Celsius for approximately two hours. The rods were sealed in plastic capillary pipettes 14 and wire 16 was threaded through one end and bonded with silver loaded epoxy resin 18 to form a contact. Araldite05™' epoxy resin 20 was used to insulate the sides of the electrodes. All electrodes were polished prior to use.
The working electrode was cycled fifteen times between 0-2.5V vs SCE at a scan rate of 0.2V/s in potassium hexacyanoferrate (III) dissolved in deionised water (0.1M, 5ml) to deposit a layer 22. The ferricyanide solution was continually stirred during cycling. The modified electrodes were washed in a large, stirred, volume of water until the initial pale blue colour was no longer observed. (These electrodes
were used for experiments not requiring enzyme activity. )
A cyclic voltammogram of the modified electrode in O.IM potassium chloride was obtained, at a scan rate of lOmV/S (Figure 3).
Glucose oxidase was immobilised onto the surface of the modified carbon electrodes using carbodimide immobilisation. A modified electrode was placed in a beaker containing stirred l-cyclohexyl-3-(2- morpholinoethyl) carbodiimide (0.15M, 5ml) in sodium acetate buffer (O.IM, pH5.5) for ninety minutes. The electrodes were washed thoroughly with deionised water. Glucose oxidase (lOμl 200mg/ml) in sodium phosphate buffer (0.02M, pH7) containing potassium chloride (O.IM) was deposited onto the electrode surface and left to dry for four hours, to produce an immobilised enzyme layer 24. A semipermeable membrane 24' coating the enzyme layer 24 was produced as follows. Using micropipettes, two layers of Nafion solution and two layers of polyurethane solution were applied. The Nafion solution was 5% in aliphatic alcohols plus water, as supplied by Aldrich. The electrode was dried for 5 minutes after the first layer, and for 1 hour after the second layer. The polyurethane solution was 10% in 9:1 w/v THF/DMF. The coated electrode was stored at 4°C overnight to dry. The dried electrodes were stored in potassium phosphate buffer at 4 degrees Celsius until use.
Type 2 'minature' electrodes as shown in Fig lb were prepared by a similar process, starting from "pencil lead" carbon rods. Each rod 112 was first modified with HCF (III), producing a film 122 over an end region. To produce enzyme electrodes, layers of enzyme 124 and (preferably) semipermeable membrane were also applied, over the HCF layer. Supports for the rods were produced by cutting about 5cm of the narrow end off a "CIO Pipetteman" tip. A rod 112 was fed (modified end first) into the truncated tip 114, from the wide end. Wire 116 was fed part way, just into the well defined in the tip. A small plug of epoxy resin 120 was placed near the bottom of the well, for sealing. A larger plug 118 of silver-loaded epoxy resin closed off the top of the device and connected the wire 116 to the rod 112.
Amperometric Determination of Glucose The enzyme electrode response to glucose was determined by immersing the electrode in 10ml of stirred potassium phosphate buffer 25 (0.02M, pH7) containing potassium chloride (0.1M) in a water- jacketed (26) cell, thermostated at 25 degrees Celsius. The cell contained a saturated calomel electrode (SCE) 28 and a platinum wire counter-electrode 30. A potential of +450mV vs SCE was applied to the electrode. Once the background current had stabilised, successive 2μl injections of glucose (IM) in potassium phosphate buffer (0.02M, pH7) containing potassium
chloride (O.IM) were introduced into the cell giving a concentration range of up to 2.8mM. The steady state response after each addition was recorded. A calibration plot for the glucose sensor is shown in figure 4.
Amperometry was also used to investigate the effect of hydrogen peroxide (Figures 5 and 6), ascorbate, uric acid and 4-acetamidophenol (Figure 7) at a HCF (III) modified electrode (with no enzyme) and at an unmodified electrode.
A typical cyclic voltammogram of these modified electrodes (Figure 2) showed two redox couples, the first at about 0.224V and 0.148V and the second at 0.923V and 0.798V. Similar electrochemistry was observed with electrodes which were modified using solutions of HCF(II) and HCF( II )/HCF( III) . The redox potentials of the modified electrodes concurred with those cited in the literature for Prussian blue (Itaya et al., 1982) and therefore leads us to conclude that the modified electrodes may bear layers of a Prussian blue analogue.
In one application, glucose oxidase was immobilised on to the surface of these modified electrodes and the resulting enzyme electrode was used to monitor glucose. A typical sensor of this type exhibited a linear range up to 1.5mM glucose and sensitivity of 4.97μA mmolar ^cm"1* The use of outer membranes such as the polyurethane coating used herein,
was found to extend the linearity. The membranes act to restrain diffusion.
Two experiments were performed to determine whether the amperometric glucose-generated signal was a mediated response or oxidation of hydrogen peroxide. Firstly, the direct oxidation of hydrogen peroxide at 450mV vs SCE at an unmodified electrode was compared to that at an HCF(III) modified electrode. The response of the unmodified graphite electrodes ("-HCF") to hydrogen peroxide (3.32mM) was negligible relative to the response at a modified electrode ( "+HCF" )(Figure 5). Additionally, the glucose sensors displayed a reduced response to glucose (3.32mM) in a nitrogen saturated environment ( "N2" ) relative to an oxygen saturated environment ( "02" ) (Figure 6). (To achieve saturation, nitrogen or oxygen was bubbled through the liquid in the cell to displace other gases, eg for 1 hour. ) Both these findings lead us to propose that the glucose response of the sensor is via electrocatalytic oxidation of hydrogen peroxide by the modified electrode.
The response of common interferents (lOOμM) such as ascorbic acid and 4-acetamidophenol at a modified electrode ("+HCF") was similar to that observed at an unmodified electrode ("-HCF") (Figure 7). The difference in response of uric acid (lOOμM) at unmodified and modified electrodes was slightly more difficult to distinguish because of the large errors
incurred in this particular determination (Figure 7). However, from Figure 7 we deduce that any electrocatalytic effect the modified carbon electrode has on uric acid is negligible. Ascorbic acid/ ascorbate and 4-acetamidophenol are very important potential interferents in areas of great commercial importance. Their effect at both physiological and pharmacological levels (that is, levels as might occur in blood fluids of patients taking normal doses or excessive amounts, respectively) was also investigated at the miniature unmodified and modified carbon base electrodes (ie electrodes as shown in Fig 16). The electrodes were operated at the poised potential in 5mM buffered glucose (15ml) until the current reached steady state ("100%"). Three successive additions of either 0.IM ascorbic acid or O.IM 4-acetamidophenol (7.8μl) were introduced into the cell giving a 50μM increment at each addition. For concentrations representative of pharmacological levels 120μl of the interferent stock solution was added to the cell giving a final concentration of 800μM. The increase in steady state current was noted and the percentage change in current as a result of addition to the interfering substance was calculated as follows:
Increase in Current X 100
% change in current =
Current in 5mM Glucose
Figures 8-10 show the percentage changes in current caused by interferents.
Figure 8 shows that physiological levels of ascorbic acid produced no significant interference in sensor output when added to 5mM glucose at miniature modified carbon base electrodes. However, an approximately 10-fold increase in current was observed at miniature unmodified carbon base electrodes operated under similar conditions. Fig. 9 shows that a 1-2-fold increase in sensor output was observed when normal levels of 4-acetamidophenol were added to 5 millimolar glucose at miniature modified carbon-base electrodes The same effect was observed at pharmacological levels (800μM) of ascorbic acid and paracetamol (Fig. 10). Itaya et al . , 1984, observed that oxygen reduction at a Prussian blue derivatised electrode produces water (four electron reduction), as opposed to hydrogen peroxide (two electron reduction) which is the product typically observed at a base metal electrode. On the basis of this observation they have hypothesised that the local three dimensional distribution of iron centres within a Prussian blue derivative layer might act as a multi-electron source which is the reverse of the one electron nature of ferricyanide reactions in solution.
Furthermore these workers have suggested that this electrocatalytic effect might be observed only with substrates small enough to penetrate the Prussian blue
lattice where electron transfer reactions can occur.
Our results appear to conform to this hypothesis.. Hydrogen peroxide molecules may by virtue of their small size be able to penetrate the modified lattice and undergo subsequent oxidation whereas larger molecules such as ascorbic acid may be hindered from penetrating the lattice. Additionally in the case of anions such as ascorbic acid, charge repulsion may also contribute to the failure of such ions to reach the iron centres.
The modified electrodes were surprisingly stable and offer the commercially important advantages of operation at low potential and selectivity. The apparent absence of leaching will have important implications for In vivo monitoring of analytes such as glucose, where stable, continuous output of the sensor is essential. This invention may also find general applications in biosensors and chemical sensors.
Evidence of the electrode stability is provided by Fig. 11. HCF(III) modified graphite disc electrodes were repeatedly cycled at 200 mV/s in O.IM potassium chloride. Traces are shown for scan nos 2, 15 and 30. It can be seen that there is remarkably little change. Different embodiments may use different enzymes. Thus a wide range of analytes could be measured e.g. glucose, lactase, alcohol and many more.
Carbon is inexpensive and particularly amenable to mass production technology e.g. screen printing, thus
improving the electrochemistry of H202 at carbon so that it is as good as at platinum is useful.
Mediators may also exhibit good electrochemistry at this surface, so that the utility of such electrodes is not restricted to systems generating H202
Claims
1. An enzyme electrode comprising: (i) a modified electrode comprising:
(a) a conductive element having a surface; and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface; and
(ii) an enzyme retained on or adjacent said coating, said enzyme being selected such that a substrate or product thereof is capable of being electrochemically oxidised or reduced at said modified electrode.
2. An enzyme electrode according to claim 1 wherein said enzyme is an oxidoreductase enzyme which produces or consumes hydrogen peroxide, and said modified electrode is capable of oxidising hydrogen peroxide.
3. An enzyme electrode according to claim 2 wherein said enzyme is a glucose oxidase.
4. An enzyme electrode according to any preceding claim wherein said enzyme is immobilised on said coating of said modified electrode.
5. An enzyme electrode according to any preceding claim wherein said conductive element comprises carbon.
6. An enzyme electrode according to claim 5 wherein said conductive element comprises graphite or glassy carbon.
7. An enzyme electrode according to any preceding claim wherein the conductive element is provided by a conductive coating on a substrate.
8. An amperometric biosensor comprising a cell for receiving an analyte, and electrodes for contacting analyte in the cell, said electrodes comprising a sensing electrode, a standard electrode and, optionally, a counter electrode, and wherein said sensing electrode comprises a modified electrode comprising:
(a) a conductive element having a surface; and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said, surface; said biosensor including an enzyme selected such that a substrate or product thereof is capable of being electrochemically oxidised or reduced at said modified electrode; said enzyme being disposed in relation to the modified electrode so that, in the operation of the biosensor, the enzyme affects the amount of said substrate or product and thereby affects a signal current of said cell.
9. An amperometric biosensor according to claim 8 wherein said enzyme is retained on or adjacent said coating of the modified electrode which thus constitutes an enzyme electrode.
10. An amperometric biosensor according to claim 8 wherein said enzyme electrode is according to any of claims 1-7.
11. An amperometric biosensor according to claim 8 which includes means defining a fluid flow path through said cell, and wherein said enzyme is disposed in the flow path upstream of the cell so as to affect the composition of the fluid from reaching the cell.
12. An amperometric biosensor according to any of claims 8-11 adapted for determining glucose in whole blood, serum or plasma.
13. A method of determining the amount of an analyte in a sample comprising contacting a solution comprising said analyte with an enzyme electrode according to any of claims 1-7 and with a standard electrode, applying a potential between said electrodes, and monitoring the electrical current.
14. A method according to claim 13 wherein said analyte is a substrate or an inhibitor for said enzyme.
15. A method according to claim 13 or 14 wherein the analyte gives rise to hydrogen peroxide which is oxidised by the modified electrode to give rise to a signal current, and wherein the analyte contains one or more potentially interfering substances selected from ascorbate, uric acid and paracetamol.
16. A method of determining an analyte in an analyte solution in the presence of one or more potentially interfering substances selected from ascorbate, uric acid and 4-acetamidophenol, comprising contacting said analyte solution with a modified electrode comprising:
(a) a conductive element having a surface and
(b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface; and with a standard electrode, applying a potential between said electrodes, and monitoring the electrical current.
17. A method of determining an analyte by means of an affinity reaction using an enzyme label, wherein the amount of enzyme label is detected amperometrically by determining a substrate or product thereof by means of a modified electrode comprising:
(a) a conductive element having a surface and (b) a coating of a hexacyanoferrate-derived material or Prussian blue provided on said surface.
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GB9616824A GB2301441B (en) | 1994-02-10 | 1995-02-10 | Hexacyanoferrate modified electrodes |
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GB9402591A GB9402591D0 (en) | 1994-02-10 | 1994-02-10 | Hexacyanoferrate (III) modified carbon electrodes |
GB9402591.3 | 1994-02-10 |
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US9938555B2 (en) | 2006-09-18 | 2018-04-10 | Alexander Adlassnig | Determination of hydrogen peroxide concentrations |
CN114609205A (en) * | 2022-03-17 | 2022-06-10 | 苏州中星医疗技术有限公司 | Preparation method of reference electrode for implanting electrochemical biosensor |
CN114609205B (en) * | 2022-03-17 | 2024-01-30 | 苏州中星医疗技术有限公司 | Preparation method of reference electrode for implanting electrochemical biosensor |
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GB2301441B (en) | 1998-03-04 |
GB9402591D0 (en) | 1994-04-06 |
GB9616824D0 (en) | 1996-09-25 |
GB2301441A (en) | 1996-12-04 |
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