Plamen Atanasov

Transient response of electrochemical biosensors with asymmetrical sandwich membranes

Abstract A mathematical model of a sandwich membrane biosensor operating in the diffusion-limited regime is proposed. The enzyme (oxidase) is immobilized between two diffusion membranes with different thicknesses. The electrochemically active product of the enzymatic reaction (H2O2) is detected on a catalytic electrode. The exact transient solution of the model is obtained under the assumptions of diffusion-limited enzymatic and electrochemical reactions, a stepwise increase of the substrate concentration (from 0 to CG°) and zero concentration of the electrochemically active product (H2O2) in the bulk solution. The thickness of the enzyme layer in the sandwich is assumed to be negligibly small in comparison with that of the diffusionn membranes. The numerical values of the transient concentration distribution C(x, t), of the transient current i(t) and its time derivative di(t)/dt are computed and presented in dimensionless form for different sets of parameters of the model. The influence of the enzyme layer position in the sandwich membrane and of the ratio of the effective diffusion coefficients of the substrate and the electrochemically active product on the transient behaviour of the sensor is discussed. The model gives some hints for the design of amperometric biosensors.

Glucose biosensor based on carbon black strips

Amperometric biosensors for the determination of beta-D-glucose have been constructed. They were based on a porous matrix of carbon blacks--Ketjenblack (KB) and Shawinigan black (SB) wet-proofed with polytetrafluorethylene. Glucose-sensitive elements were prepared by subsequent adsorptional immobilization of 1,1-dimethylferrocene (DMFc) and nickel-ocene (Nc) on Shawinigan black or tetracyanoquinodimethane (TCNQ) on Ketjenblack together with Penicillium chrysogenum glucose oxidase. Maximum surface concentrations of DMFc, Nc and TCNQ on carbon black electrodes were 95, 116 and 151 nmol cm-2. The biosensor based on KB and TCNQ (KB-TCNQ biosensor) could be used at a potential of 0.5 V (vs. Ag/AgCl reference electrode) in the concentration range up to 7 mM. This biosensor possessed an approximately ten times higher sensitivity than the ones based on SB and DMFc (SB-DMFc biosensor) and on SB and Nc (SB-Nc biosensor) which acted at 0.3 V and 0.05 V, respectively. The biosensors were suitable for practical use longer than one week.

Amperometric biosensor for glucose and lactate

Abstract Amperometric membrane glucose and lactate biosensors are investigated. Sandwich-type membranes are used with an enzyme (glucose oxidase or lactate oxidase) immobilized between two membrane layers. A new type of catalytic electrode made from pyrolysed CoTMPP (cobalt-tetramethoxyphenylporphyrin) is used for detection of H 2 O 2 generated by the enzymatic reaction. The glucose biosensor is used for the determination of glucose concentrations up to 2 mM/l in water solutions and in diluted blood serum samples. The biosensor can be used for more than 100 days. Concentrations of Li-lactate up to 1.5 mM/l in water solutions are determined with the lactate biosensor.

Metallocene-mediated amperometric biosensors for one-shot glucose determination

Abstract Amperometric biosensors for the determination of glucose based on carbon black screen-printed on ceramics are described. The mediators, nickelocene, ferrocene and their derivatives, are used for the conjunction of glucose oxidase-catalysed oxidation of glucose and electrochemical reaction at the applied potential. It is shown that the nickelocene-mediated glucose oxidase electrode exhibits a similar behaviour to that mediated with ferrocene. However, the quasi-redox potential of nickelocene/nickelocenium cation, which is by 0.3 V more negative than that of any of the investigated ferrocene derivatives, significantly lowers the operating potential of the biosensor to ≈0.00 V versus an Ag/AgCl electrode.

ENZYME ELECTRODES WITH PTFE MODIFIED CARBON BLACK MEDIATOR MATRIX AND THEIR APPLICATION IN GLUCOSE BIOSENSORS

Publisher Summary nThis chapter focuses on enzyme electrodes with PTFE modified carbon black mediator matrix and their application in glucose biosensors. PTFE modified carbon blacks are prepared as a powder material by a special technology that allows the use of different carbon blacks and a controlled carbon black/PTFE ratio. This material possesses an electronic conductivity combined with hydrophobic surface properties, and enzymes can be immobilized on it by adsorption. Mediators are mixed with the PTFE modified carbon blacks to form a powdered composite material. Glucose oxidase electrode is prepared by coating of the porous matrix from composite material with enzyme solution and further evaporation of the solvent. The use of a PTFE modified carbon black-mediator matrix coated with enzyme allows standardizing the production of biosensors with reproducible performance.