Electrode construction procedure

Molecular recognition between biomolecules is another strategy that has been used to deposit assemblies of redox enzyme on electrodes. It has led to the construction of true monomolecular layers and of spatially defined multimonomolecular structures. The dynamics of these systems has been fully characterized and the activity of the deposited enzyme tested quantitatively, which has been very seldom the case with the systems depicted in the preceding text. For this reason, the following sections focus on these structures. Besides describing the construction procedures, emphasis is laid on the detailed analysis of the catalysis responses and on the mechanisms it allows one to uncover. As a prelude to such kinetic analyses, the catalytic responses of a redox enzyme with a one-electron mediator in solution are first examined. 

Scheme 16.2 Schematic representation of the construction procedure for the PEI functionalized GO-COOH sheets and the electrochemical oxide of ammonia on the surface of the relative electrode. Reproduced from reference (71) with permission from Wiley...

Procedure 3 We construct cell (V) using the HA type acid under study and its conjugate base and measure the emfs by varying the ratio Ca/Cs. The procedure to vary the ratio Cs/Ca can be replaced by the titration of the acid HA with a strong base (BiuNOH in MeOH, toluene-MeOH, or 2-PrOH), but the alcohol introduced with the base may have some influence on the results. Because the glass electrode has been calibrated in Procedure 2, the emf values can be converted to pH values. 

Procedure 1 Cell (VI) is constructed using a univalent cation-sensitive glass electrode (Ag electrode for Ag+) and the emf is measured by titrating metal ion M+ with ligand L ... 

The second apparatus was constructed by Monte si (JRef 31) to provide a faster testing procedure. It was designed with simplicity and reproductivity in mind to determine relative sensitivity only. A fixed electrode configuration was used for all tests. Additional details are given in Ref 35,pp 27-8... 

Herbicides, like demestryn, have been determined using a chemosensor based on the MIP film recognition and capacitive transduction [193, 194]. In this determination, photografting polymerization has been demonstrated as an efficient procedure for fabrication of a capacitive chemosensor. This procedure involved immobilization of an initiator on the electrode. In this case, first, an alkanethiol monolayer was self-assembled on the gold electrode. This monolayer was perfectly dielectric. Then, an MIP film was deposited on top of this monolayer by photo-radical polymerization in the acetone solution with benzophenone, 2-acrylamido-2-methyl-1-propane sulphonic acid, /V./V -iriethylenediacrylamide and demestryn used as the initiator, cross-linker, functional monomer and template, respectively. Subsequently, the template was extracted with methanol. The capacitance decreased by 20% upon binding the demestryn analyte by the MIP film. Similarly, a creatine chemosensor was constructed [194],... 

Scheme of the construction of ultramicro electrodes according to a procedure described in the text. 

The construction of the m-GEC electrode is explained in Procedure 31 (see CD accompanying this book). The steps are schematically explained in Fig. 31.1 therein. 

As many physicochemical characteristics as possible of reactants, possible intermediates and products should be considered. These might include spectral features (IR, UV-vis, NMR), ion conductivities (if ions participate in the reaction), optical activity, etc. If such data are not available in the literature, they should be investigated early on as they may lead to a monitoring procedure for the kinetic study. Although physicochemical properties which are directly proportional to concentration are most convenient, others such as pH or electrode potentials may be used as their relationship to concentration is well understood. When the relationship between an observed property or measured signal and concentration of a component in the reaction mixture is not theoretically derived, e.g. GLC signals from analysed samples of the reaction mixture, calibration curves may be used. These are constructed by analysis of standard solutions of a reaction component (see Chapter 2). 

Fluorescence burst analysis, a variation of FCS procedures that has an optimum configuration for simple presentation, uses a uniform nanoscopic flow channel with an optically perfect ceiling, uniform cross section, and periodic electrodes that can now be constructed by careful electron lithography techniques.55 By application of controlled electric fields, uniform plug flow of solution through... 

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