Mediated ET Employed for Biosensors and Biofuel Cells

As aheady described in Sections 1.1.4 and 1.1.6 (mobile or immobihzed) mediators and/or conducting polymers can also be employed to shuttle electrons between a redox enzyme and an electrode surface [11, 12, 16, 20, 21, 24, 25, 28, 270-273]. This approach is called mediated ET (see also Eigure 1.6). Efficient ET throughout the entire sensing layer is envisaged in order to avoid only the enzyme layer in close vicinity to the electrode surface contributing to the overall current signal. 

The approach of employing redox hydrogels helps one to obtain higher current densities which are not only advantageous for, for example, long-term glucose 

For a rational design of biosensor devices, it is advantageous to aim for non-manual fabrication processes. Electrochemical techniques provide advantages as many polymers can be electrochemically formed or deposited such as conduchng 

One successful strategy to improve ET rates between enzyme and electrode is the modification of conducting polymers with redox mediators in order to obtain reagentless biosensors [11, 270, 271, 292-299]. The drawback of electropolymerization of conducting polymers is that the reaction is sensitive to oxygen, which complicates fabrication at the industrial scale. 

Mediated enzyme electrodes were also realized on combined microscale and nanoscale supports [300]. Bioelectrocatalytic hydrogels have also been realized by co-assembling electron-conducting metallopolypeptides with bifunctional building blocks [301]. More recently, redox-modified polymers have been employed to build biofuel cells [25, 70, 302, 303]. In 2003, an enzymatic glucose/02 fuel cell which was implanted in a living plant was introduced [147]. 

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