Enzyme electrodes platinum surface

Carbonaceous substrates (graphite and glassy carbon) are generally preferred because of their mechanical, chemical, and electrochemical properties. Excellent results are also obtained by chemically modified platinum (154,156,179) and tin(IV) oxide electrodes (155). For example, glucose oxidase has been successfully immobilized by cross-linking the enzyme with BSA and GA onto an electrochemically oxidized platinum surface, with silanization using 3-amino-propyltriethoxysilane ... 

An example of a sensor utilizing these three components is illustrated in figure 1.2, which shows a schematic of a typical enzyme electrode for the detection of glucose (also see chapter 17 of this text). The bioactive surface consists of immobilized glucose oxidase (GOD) sandwiched between a polycarbonate and cellulose acetate membrane. The transducer is a platinum electrode and the electronics are those typically found in any polarograph, i.e. an electronic system to measure low currents (on the order of microamperes) at a fixed voltage bias on the platinum electrode. The action of glucose... 

Enzymes are often employed in the chemical layer to impart the selectivity needed. We saw an example of this in Chapter 13 when discussing potentiometric enzyme electrodes. An example of an amperometric enzyme electrode is the glucose electrode, illustrated in Figure 15.4. The enzyme glucose oxidase is immobilized in a gel (e.g., acrylamide) and coated on the surface of a platinum wire cathode. The gel also contains a chloride salt and makes contact with silver-silver chloride ring to complete the electrochemical cell. Glucose oxidase enzyme catalyzes the aerobic oxidation of glucose as follows ... 

Proctor, A., Castner, J. F., Wingard Jr., L. B., Hercules, D. M., Electron Spectroscopic (ESCA) Studies of Platinum Surfaces Used for Enzyme Electrodes , AnaL Chem. 57 (1985) 1644-1649. 

Cross-linking an Os-polymer containing 20 PVP (Fig. 11.5) and GOx on a platinum or glassy carbon electrode (GCE) surface with glutaraldehyde, produces biosensors that are very sensitive and stable in organic phases. The CV of the enzyme electrode shows that complexing the polymer with GOx does not change... 

Regarding the electrocatalyst, the similar concepts about the catalytic activity can be defined in the similar ways as Eqns (3.1)—(3.4). Actually, electrocatalysts are a specific form of catalysts that function at electrode surfaces or may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinum surface or nanoparticles, or homogeneous like a coordination complex or enzyme. However, in this book, we are only focused on the heterogeneous electrocatalysts. The role of electrocatalyst is to assist in transferring electrons between the electrode catalytic active sites and reactants, and/or facilitates an intermediate chemical transformation. One important difference between catalytic chemical reaction and electrocatalytic reaction is that the electrode potential of the electrocatalyst can also assist in the reaction. By changing the potential of the electrocatalyst, which is attached onto the electrode surface, the electrocatalytic activity can be enhanced or depressed significantly. 

Matsumaea et al. [110] worked out an SECM method for detecting the intracellular NQO enzyme activity of a single cell. They employed menadione mediator for shuttling electrons through the cell membrane and ferticyanide as hydrophilic second mediator for increasing the electron exchange rate at the platinum surface of the microtip. In this study HeLa cells cultured on plastic Petri dish were tested and disc-type Pt electrode with a diameter of 20 pm (RG = 2) was used as SECM tip. 

Fortier [6] found that AQ polymer from Eastman was not deleterious for the activity of a variety of enzymes such as L-amino acid oxidase, choline oxidase, galactose oxidase, and GOD. Following mixing of the enzyme with the AQ polymer, the mixture was cast and dried onto the surface of a platinum electrode. The film was then coated with a thin layer of Nafion to avoid dissolution of the AQ polymer film in the aqueous solution when the electrode was used as a biosensor. These easy-to-make amperometric biosensors, which were based on the amperometric detection of H202, showed high catalytic activity. 

A platinum disk electrode was electrolytically platinized in a platinum chloride solution to increase the surface area and enhance the adsorption power. The platinized platinum electrode was then immersed in a solution containing 10 mg ml l ADH. 0.75 mM and 6.2 mM NAD. After sufficient adsorption of these molecules on the electrode surface, the electrode was transferred into a solution containing 0.1 M pyrrole and 1 M KC1. Electrochemical polymerization of pyrrole was conducted at +0.7 V vs. Ag/AgCl. The electrolysis was stopped at a total charge of 1 C cm 2. An enzyme-entrapped polypyrrole membrane was deposited on the electrode surface. 

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