Traditional biosensors rely on redox enzymes to turnover the analyte. In this case, it is the by-products of these reactions, or mediator substituents, rather than the analyte itself that is detected. The thrust behind this work is to design a biosensor that allows direct detection of the analyte, utilising a recognition element without turning over the analyte.

The sensor is based upon a redox scaffold, which is functionalised with an analyte recognition site. The analyte binding event is detected by a shift in the redox potential of the scaffold. The scaffold is bound to an electrode to allow direct electron transfer between it and the redox centre. This concept has been tested using a tyramine antibody as the analyte and tyramine as the analyte recognition site.

1,4,7,10-tetraazacyclotetradecane (cyclam) is presented as the scaffold, as it forms kinetically and thermodynamically stable complexes with a wide variety of transition metals and is readily functionalised. Introduction of pendant arms on the macrocyclic scaffold lead to a significant (anodic) shift in redox potential.

A model redox-recognition scaffold is proposed (shown above), and the results presented, to test cyclam as a core biosensor reagent. The scaffold is immobilised via amino-phenanthroline through diazo groups on to a mixed SAM on a gold electrode, thereby permitting direct electron transfer from scaffold to electrode.

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