Stable mediated amperometric biosensors using a graphite electrode embedded with tetrathiafulvalene in silicone oil

A new method has been developed to incorporate the mediator, tetrathiafulvalene (TTF), to the electrode/solution interface of an amperometric biosensor. TTF was dissolved in methylphenyl polysiloxane (silicone oil) and embedded in a graphite disc electrode. The mediator was able to diffuse to the electrode surface at an electrocatalytically significant speed. The storage of TTF in the inert polysiloxane provided a long-lasting and stable mediator supply. TTF-silicone oil electrodes with immobilized glucose oxidase, xanthine oxidase, or amino acid oxidase exhibited sensitive, fast and reproducible responses. The glucose oxidase electrode was very stable for at least 2 months when stored at 4°C. Together with flow injection analysis (FIA), the enzyme electrodes were reused for at least 500 repeated analyses during a 25 h operation without losing their initial activity.