Ferrocene-Mediated Amperometric Glucose Sensor

Sensors for home use glucose sensor operating with a mediator. In the second type of sensor, the amount of glucose is monitored amperometrically via the current. At the heart of the assay is enzymatic oxidation of glucose by glucose oxidase (GOD). The enzyme itself is not electroactive, so a mediator will oxidize it. The mediator of choice is ferrocene (Felcplj), which can readily oxidize to form a stable radical cation (Fe(cp)J ) (see Figure 6.31). 

Plotkin E V, Scott L D L and Turner A P F 1984 Ferrocene-mediated enzyme electrode for amperometric determination of glucose Anal. Chem. 56 667-1 Higgins 1 J, Hill H A O and Plotkin E V 1987 Sensor for components of a liquid mixture US Patent 4711 245... 

Long Term Performance of Sensors. The sensors showed excellent long term stability stored in buffer at 4 °C. Table 1 shows the long term performance of four typical biosensors. The usual current response to 6 mM glucose for a new biosensor is about 2 fiA. The precision of the absolute current response to 6 mM glucose remains within 15 % for up to four months. This level of precision is unusual for amperometric biosensors. Normally, variations in current are compensated by calibration. The sensitivity of the biosensors, as indicated by the slope of the response, is also stable. This stability is due to the film which maintains the ferrocene within the sensing layer. Biosensors with adsorbed mediator and immobilized enzyme but without film are not stable for any period of... 

Polysiloxane random copolymers (with molecular weights of 5000 to 10,000) with pendant ferrocene groups have been synthesized (2.26) by hydrosUylation of vinylferrocene or 9-ferrocenyl-l-nonene with a poly(methylhydrosiloxane)-r-poly(dimethylsiloxane) random copolymer (Eq. 2.11). These materials were used as amperometric biosensors for the detection of glucose [59]. In this application, the polymers effectively mediated electron transfer between reduced glucose oxidase and a conventional carbon paste electrode. The response of the sensor to glucose was dependent upon the nature of the polymeric backbone. The optimal response was achieved by finding a compromise between increased polymer flexibility and decreased spacing between individual relay (i.e. ferrocene) sites. 

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