Amperometric enzyme electrodes

The final method of coupling enzyme reactions to electrochemistry is to immobilize an enzyme directly at the electrode surface. Enzyme electrodes provide the advantages already discussed for immobilization of enzymes. In addition, the transport of enzyme product from the enzyme active site to the electrode surface is greatly enhanced when the enzyme is very near to the electrode. The concept of combining an enzyme reaction with an amperometric probe should offer all of the advantages discussed earlier for ion-selective (potentiometric) electrodes with a much higher sensitivity. In addition, since the response of amperometric electrodes is linear, background can be selected. 

Fig. 7. Schematic diagram of an enzyme electrode. A, B and C comprise the membrane system, while D is the detector (either amperometric or potentiometric)...

Good accuracy and precision were obtained in connection to 100 pL blood samples. A wide range of amperometric enzyme electrodes, differing in the electrode design or material, membrane composition, or immobilization approach have since been described. 

G. Guilbault and G. Lubrano, An enzyme electrode for the amperometric determination of glucose. Anal. Chim. Acta 64, 439-455 (1973). 

A. Cass, G. Davis, G. Francis, H.A. Hill, W. Aston, J. Higgins, E. Plotkin, L. Scott, and A.P. Turner, Ferrocene-mediated enzyme electrode for amperometric determination of glucose. Anal. Chem. 56, 667-671 (1984). 

G.G. Guilbault and G.J. Lubrano, Amperometric enzyme electrodes. Amino acid oxidase. Anal. Chim. Acta 69, 183-185 (1974). 

J.G. Zhao, J.R O Daly, R.W. Henkens, J. Stonehuemer, and A.L. Crumbliss, Axanthine oxidase/colloi-dal gold enzyme electrode for amperometric biosensor applications. Biosens. Bioelectron. 11, 493—502 (1996). 

Diffusion Currents. Half-wave Potentials. Characteristics of the DME. Quantitative Analysis. Modes of Operation Used in Polarography. The Dissolved Oxygen Electrode and Biochemical Enzyme Sensors. Amperometric Titrations. Applications of Polarography and Amperometric Titrations. 

Construction of enzyme-based amperometric biosensors usually involves coating the electrode surface with both the enzymes and the mediator. The method adopted and concentrations used are important factors in the performance of the device. For extended use, covalent immobilization is the most satisfactory method. 

Equations 2.26 and 2.27 carmot be solved analytically except for a series of limiting cases considered by Bartlett and Pratt [147,192]. Since fine control of film thickness and organization can be achieved with LbL self-assembled enzyme polyelectrolyte multilayers, these different cases of the kinetic case-diagram for amperometric enzyme electrodes could be tested [147]. For the enzyme multilayer with entrapped mediator in the mediator-limited kinetics (enzyme-mediator reaction rate-determining step), two kinetic cases deserve consideration in this system in both cases I and II, there is no substrate dependence since the kinetics are mediator limited and the current is potential dependent, since the mediator concentration is potential dependent. Since diffusion is fast as compared to enzyme kinetics, mediator and substrate are both approximately at their bulk concentrations throughout the film in case I. The current is first order in both mediator and enzyme concentration and k, the enzyme reoxidation rate. It increases linearly with film thickness since there is no... 

Enzyme electrodes with amperometric indication have certain advantages over potentiometric sensors, chiefly because the product of the enzymic reaction is consumed at the electrode and thus the response time is decreased. For this reason, the potentiometric glucose enzyme electrode, based on reaction (8.1) followed by the reaction of HjO, with iodide ions sensed by an iodide ISE [39], has not found practical use. 

Hall GF, Best DJ, Turner APF. 1988. Amperometric enzyme electrode for thedetermination of phenols in chloroform. Enzyme Microb Technol 10(9) 543- 546. 

Besides the broad applications of electrically contacted enzyme electrodes as amperometric biosensors, substantial recent research efforts are directed to the integration of these functional electrodes as biofuel cell devices. The biofuel cell consists of an electrically contacted enzyme electrode acting as anode, where the oxidation of the fuel occurs, and an electrically wired cathode, where the biocatalyzed reduction of the oxidizer proceeds (Fig. 12.4a). The biocatalytic transformations occurring at the anode and the cathode lead to the oxidation of the fuel substrate and the reduction of the oxidizer, with the concomitant generation of a current through the external circuit. Such biofuel cells can, in principle, transform chemical energy stored in biomass into electrical energy. Also, the use... 

Many problems involving competitive reaction kinetics may be treated by invoking the steady-state assumption within the digital simulation this has been done in at least two instances [29-34]. The first of these involves the development of a model for enzyme catalysis in the amperometric enzyme electrode [29-31]. In this model, the enzyme E is considered to be immobilized in a diffusion medium covering an electrode that is operated at a fixed potential such that the product (P) of enzyme catalysis is electroactive under diffusion-controlled conditions. (This model has also served as the basis for the simulation of the voltammetric response of the enzyme electrode [35].) The substrate (S) diffuses through the medium that contains the immobilized enzyme and is catalyzed to form P by straightforward enzyme kinetics ... 

The three types of glucose electrode discussed here illustrate the major facets of design and operation of enzymatic amperometric sensors. Examples of amperometric enzyme electrodes for other substrates are shown in Table 7.3. The actual design details of these sensors depend on the enzyme kinetics involved and on the operating conditions under which they are used. 

C. Loechel, A. Basran, J. Basran, N. S. Scrutton and E. A. Hall, Using trimethylamine dehydrogenase in an enzyme linked amperometric electrode. Part 1. Wild-type enzyme redox mediation, Analyst, 128(2) (2003) 166-172 Part 2. Rational design engineering of a wired mutant, Analyst, 128(7) (2003) 889-898. 

M.J. Lobo Castanon, A.J. Miranda Ordieres and P. Tunon Blanco, Amperometric detection of ethanol with poly-(o-phenylenediamine)-modified enzyme electrodes, Biosens. Bioelectron., 12(6) (1997) 511-520. 

E. Maestre, I. Katakis and E. Dominguez, Amperometric flow-injection determination of sucrose with a mediated tri-enzyme electrode based on sucrose phosphorylase and electrocatalytic oxidation of NADH, Biosens. Bioelectron., 16(1-2) (2001) 61-68. 

N.F. Almeida and A.K. Mulchandani, A mediated amperometric enzyme electrode using tetrathiafulvalene and L-glutamate oxidase for the determination of L-glutamic acid, Anal. Chim. Acta, 282(2) (1993) 353-361. 

A. Guzman-Vazquez de Prada, N. Pena, C. Parrado, A.J. Reviejo and J.M. Pingarron, Amperometric multidetection with composite enzyme electrodes, Talanta, 62(5) (2003) 896-903. 

Vegetable tissue based electrochemical sensors can be divided into two groups according to their principle of operation potentiometric and amperometric. Such devices are usually prepared in a manner similar to that of conventional enzyme electrodes, with the detection of an electroactive species that is consumed or produced by the enzyme present in the vegetable tissue. 

Amperometric Transduction of Optical Signals Recorded by Photoisomerizable Enzyme Electrodes... 

---