Ion-to-electron transduction

An ISE is composed of an ion-selective membrane and an ion-to-elec-tron transducer. In the conventional ISE, the ion-to-electron transduction takes place at the internal reference electrode that is immersed in the inner filling solution. In the case of the commonly used Ag/AgCl reference electrode immersed in an electrolyte solution containing Cl anions, the ion-to-electron transduction process can be written as follows ... 

Principle of ion-to-electron transduction in conducting polymer-based ISEs... 

Conducting polymers have already been well documented in conjunction with the classical ionophore-based solvent polymeric ion-selective membrane as an ion-to-electron transducer. This approach has been applied to both macro- and microelectrodes. However, with careful control of the optimisation process (i.e. ionic/electronic transport properties of the polymer), the doping of the polymer matrix with anion-recognition sites will ultimately allow selective anion recognition and ion-to-electron transduction to occur within the same molecule. This is obviously ideal and would allow for the production of durable microsensors, as conducting polymer-based electrodes, and due to the nature of their manufacture these are suited to miniaturisation. There are various examples of anion-selective sensors formed using this technique reported in the literature, some of which are listed below. 

PEDOT PSS-Based Electrochemical Transistors for Ion-to-Electron Transduction and Sensor Signal Amplification... 

The PEDOT PSS-based electrochemical transistor balance at the boundary between amperometric and potentiometric sensor functionality. Its device architecture is simple and robust and these PEDOT PSS sensors can easily be manufactured using standard printing technologies. In addition, its proper ion-to-electron transduction characteristics and the possibility to integrate biologically active substances promise for simple and sensitive sensors in the... 

Berggren, M., Forchheimer, R., Bobacka, J., Svensson, P.O., Nilsson, D., Larsson, O., Ivaska, A., 2008. PEDOT PSS-Based electrochemical transistors for ion-to-electron transduction and sensor signal amplification. In Bernards, D., MaUiaras, G., Owens, R. (Eds.), Organic Semiconductors in Sensor Applications. Springer Berhn Heidelberg. 

The internal solution in conventional ion-selective membrane (ISE) and reference electrodes has two roles. One is to support ion-to-electron transduction, or ion-to-electron current, between the internal solution and the electronically conducting substrate, e.g., metal, which is (or is a part of) the lead to the meter. For instance, in a silver-silver chloride reference electrode, it is the chloride ion in the potassium chloride solution that makes the transduction process possible, according to the reaction (see Sect. 5.2 and Chapter 6) ... 

Electron-ion transduction allows local modulation of the ionic concentration in a solution at a distance from the electrode that is less than the thickness of the diffusion layer.171-173 The solution volume can be modified through the hydrodynamic conditions or the viscosity of the polymeric surrounding in order to reduce or enlarge the thickness of the diffusion layer. 

Apart from individual sites, series of metal ion sites provide electron conduction paths, vital in energy transduction in all organisms and leading to proton transfer, and Mg2+ in chlorophyll is essential for light capture (see Section 4.17). 

We next focus on the use of fixed-site cofactors and coenzymes. We note that much of this coenzyme chemistry is now linked to very local two-electron chemistry (H, CH3", CH3CO-, -NH2,0 transfer) in enzymes. Additionally, one-electron changes of coenzymes, quinones, flavins and metal ions especially in membranes are used very much in very fast intermediates of twice the one-electron switches over considerable electron transfer distances. At certain points, the chains of catalysis revert to a two-electron reaction (see Figure 5.2), and the whole complex linkage of diffusion and carriers is part of energy transduction (see also proton transfer and Williams in Further Reading). There is a variety of additional coenzymes which are fixed and which we believe came later in evolution, and there are the very important metal ion cofactors which are separately considered below. 

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