Electrochemical cell electron transfer resistance

A label-free electrochemical impedance immunosensor for the rapid detection of E. coli 0157 H7 consists of immobilized anti- . coli antibodies on an indium-tin oxide IDA microelectrode [123]. The binding of E. coli cells to the IDA microelectrode surface increases the electron-transfer resistance, which is directly measured with electrochemical impedance spectroscopy in the presence of [Fe(CN)(6)] as a redox probe. The electron-transfer resistance correlates with the concentration of E. coli cells in a range from 4.36 X 10 to 4.36 X 10 cfu ml with a detection Umit of 10 cfu ml . ... 

A very interesting biosensor was developed based on a similar principle for the detection of cancer cells [34]. The aptamer selected for acute leukaemia cells was fixed onto a gold electrode and electrochemical impedance spectroscopy (EIS) technique was used to characterize the surface with [Fe(CN)6] as a redox probe. Upon binding of the aptamer-modified electrode with leukaemia cells, the electron-transfer resistance of [Fe(CN)6] on the sensor surface increased substantially. A linear relationship was observed between the electron-transfer resistance and the concentration of the leukaemia cells in a range 1 x lO to 1 x 10 cells/mL with a detection limit of 6 x 10 cells/mL and high selectivity. 

Figure 7 shows the detection principle of an impedimetric IME biosensor for bacterial detection [8]. It is based on measurements of electrochemical faradic impedance in the presence of [Fe(CN)6] " as a redox probe. When a bare interdigitated microelectrode is immersed into an electrolyte solution containing the redox couple and a small-amplitude AC potential (5 mV) is applied to the electrode, the faradic process of oxidation and reduction of the redox couple occurs, and then electrons are transferred between the two sets of array electrodes through the redox couple (Fig. 7a). When antibodies are immobilized onto the electrode surface (Fig. 7b) they form a layer that can inhibit the electron transfer between the electrodes, and thus an increase in the electron transfer resistance can be expected. If bacterial cells attach to the antibody-modified electrode surface (Fig. 7c), the intact cells can create a further barrier for...

In studies of molecular charge transfer systems a transient method is generally used to determine an electron transfer rate constant from the variation of the concentration of a reactant or product as a function of time. By contrast, in characterizing charge transfer processes in electrochemical cells or at metal-molecule- metal junctions the parameter of interest is usually the resistance or conductance (reciprocal of resistance) of the cell or junction. The conductance of the cell or junction is generally determined from the variation of the current through the system as a function of applied voltage. Here we briefly consider the relationship between electron transfer rate constants and conductances. 

The electrochemical kinetics study involves the study of electrochemical reaction rates and the key factors that determine whether a reaction will be fast or slow, and how the reaction rate may be changed. The study of kinetics is important in the design and operation of a fuel cell. The rate of electron transfer at the electrodes or the current produced by the fuel cell depends on the rate of electrochemical reaction. The key factors that affect the electron transfer are ionic and electronic resistances in electrolyte and in electrodes and the rate of mass transport through the electrodes. In order to understand how these factors affect reaction rates, phenomena at molecular level during a chemical reaction need to be imderstood. The processes at the electrode and electrolyte interface are illustrated in Figure 5.1. 

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