BIOSENSORS. Modern and future approaches to medical diagnostics. J. F. Rusling Dept. of Chemistry Dept. of Pharmacology, Univ. of CT Health Center

Transcription

1 BIOSENSORS Modern and future approaches to medical diagnostics J. F. Rusling Dept. of Chemistry Dept. of Pharmacology, Univ. of CT Health Center

2 Medical Diagnostics Doctors increasingly rely on testing Needs: rapid, cheap, and low tech Done by technicians or patients Some needs for in-vivo operation, with feedback

3 Principle of Electrochemical Biosensors substrate product electrode Enzyme Apply voltage Measure current prop. to concentration of substrate Figure 9

4 Equipment for developing electrochemical biosensors potentiostat insulator electrode material reference N 2 inlet counter Protein film working electrode E, V E-t waveform Cyclic voltammetry Electrochemical cell time

5 Cyclic voltammogram(cv) at 100 mvs -1 and25 o Cof Mycobac terium TuberculosisKatG catalase-peroxidasein a thin filmof dimyristoylphospha tidylcholineonbasal plane PG electrode, in anaerobic ph6.0buf fer. Reversible Peaks for Direct electron transfer I, µa Reduction Of Fe III Oxidation Of Fe II E, V vs SCE

6 A lipid-enzyme film enzyme Electrode

7 Catalytic enzyme electrochemistry a basis for biosensor - glucose oxidase I = f [glucose] oxidation Fc + glucose + enzyme Mediator shuttles Electrons between Enzyme and electrode Fc mediator A. Cass, G. Dav is, G. D. Francis, H.O.A. Hill, W. J. Aston,I. J. Higgins, E. V. Plotkin,L. D. L. Scott, A.P. F. Turner, Anal. Chem. 56, (1984).

8 Mechanism for catalytic oxidation of glucose With Glucose oxidase (GO) and Fc mediator Scheme 2 Glucose + GO(FAD) +2 H + Ÿ gluconol actone +GO(FADH 2 ) (1) GO(FADH 2 ) + 2 Fc + Ÿ GO( FAD) +2 Fc + 2H + (4) Fc Ÿ Fc e - (at electrode ) (5) Fc = ferrocenecarboxylate Signal can also be measured by amperometry: Hold const. E where oxidation occurs, measure I vs time

9 Commercial Glucose Sensors Biggest biosensor success story! Diabetic patients monitor blood glucose at home First made by Medisense (early 1990s), now 5 or more commercial test systems Rapid analysis from single drop of blood Enzyme-electrochemical device on a slide

10 Patient Diabetes Management Insulin secretion by pancreas regulated by blood glucose, 4.4 to 6.6 mm normal In diabetes, regulation breaks down Wide swings of glucose levels Glucose tests tell patient how much insulin to administer

11 Most sensors use enzyme called glucose oxidase (GO) Most sensors are constructed on electrodes, and use a mediator to carry electrons from enzyme to GO Fc = mediator, ferrocene, an iron complex These reactions occur in the sensor: Fc Fc + + e- (measured) GO R + 2 Fc + --> GO ox + 2 Fc GO ox + glucose --> GO R + gluconolactone Reach and Wilson, Anal. Chem. 64, 381A (1992) G. Ramsay, Commercial Biosensors, J. Wiley, 1998.

12 Glucose biosensor test strips (~$ ea.) Dry coating of GO + Fc Meter Read glucose e s electrodes Output: amperometry I Patient adds drop of blood, then inserts slide into meter Patient reads glucose level on meter t

13 Research on glucose sensors Non-invasive biosensors - skin, saliva Implantable glucose sensors to accompany artificial pancreas - feedback control of insulin supply Record is 3-4 weeks for implantable sensor in humans

14 Other biosensors Cholesterol - based on cholesterol oxidase Antigen-antibody sensors - toxic substances, pathogenic bacteria Small molecules and ions in living things: H +, K +, Na +, CO 2, H 2 O 2 DNA hybridization and damage Micro or nanoarrays, optical abs or fluor.

15 Layer by layer Film construction: Negative surface Protein layer Polycation soln., then wash soln. of negative protein then wash Polycation soln., then wash Repeat steps for desired number of layers Protein layer Polycation layers Figure 19

16 Detection of hydrogen peroxide Conductive polymers efficiently wire peroxidase enzymes to graphite Enzyme layer PSS layer SPAN layer (sulfonated polyaniline) e s Xin Yu, G. A. Sotzing, F. Papadimitrakopoulos, J. F. Rusling, Highly Efficient Wiring of Enzymes to Electrodes by Ultrathin Conductive Polyion Underlayers: Enhanced Catalytic Response to Hydrogen Peroxide, Anal. Chem., 2003, 75,

17 Horseradish Peroxidase (HRP) 100nm 50nm Tapping mode atomic force microscopy (AFM) image of HRP film

18 Electrochemical Response of Peroxidases H 2 O 2 O 2 +e - -e - 2e -, 2H + PFe III PFe II PFe II -O 2 PFe IV =O active oxidant H 2 O 2 + PFe II H 2 O 2 PFe III + H2 O + O 2 Possible reduced species in red

19 Catalytic reduction of H 2 O 2 by peroxidase films Catalytic cycles increase current 60 I,µA a with SPAN µm H E, V vs SCE Fe III /Fe II -0.6 reduction -0.8

20 Rotating electrode amperometry at 0 V HRP, 50 nmol H 2 O 2 additions I, µa span with PAPSA reduction 0 No span without PAPSA t, s

21 Rotating electrode amperometry at 0 V I, µa Span/HRP PAPSA/HRP Span/Mb PAPSA/Mb HRP Mb [H 2 O 2 ], µm Sensitivity much higher with conductive polymer (SPAN); Electrically wires all the protein to electrode

22 Biosensors Promising approach to medical diagnostics by patients or in doctors offices Other important applications: pathogens, disease biomarkers, DNA, peroxide, etc. Method of choice for blood glucose in diabetics Rapid diagnostics may lead to more timely and effective treatment