Non-mediated biosensors

Electrochemical biosensors can be divided into mediated and non-mediated biosensors. Biosensors that do not require the participation of redox molecules with reversible electrochemistry are referred to as non-mediated biosensors, whereas the participation of redox mediators in signal transduction generates a category of mediated biosensors. 

In contrast, Boguslavsky and co-workers used a flexible polymer chain to put electron relays [15]. Their polymers provide communication between redox centres in glucose oxidase (GOD) and the electrode. No mediation occurred when ferrocene was attached to a non silicone backbone. Their ferrocene-modified siloxane polymers are stable and non diffusing. Therefore, biosensors based on these redox polymers give good response and stability. 

Not surprisingly, ferrocenyl (Fc) derivatives have been widely used either as diffusional or non-diffusional charge transfer mediators because of their almost ideal electrochemical properties, i.e. fast ET rate, low redox potentials and high chemical stability of both the oxidized and the reduced forms. Examples of protein labeling with ferrocene redox probes in the field of amperometric biosensors are reviewed below. 

Electrochemistry is a cheap analytical method that can be used with cloudy test samples and works well with miniaturization. It was thus adopted early as an ideal analytical method when novel reliable and sensitive non-isotopic immunoassays were developed [79]. In addition, ferrocene has long been known as an excellent redox mediator, used in many applications some of which are discussed in this book (cf. Chapters 6 and 9). One example is in commercial biosensor devices, such as the hand-held Medisense Precision QID glucose meter for use by diabetics to determine their sugar levels in whole blood [80]. It is therefore unsurprising to find that some of the oldest and best developed MIAs employ electrochemical methods to quantify the tracer. 

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