Dawson-type polyoxometalate nanoclusters confined in a carbon nanotube matrix as efficient redox mediators for enzymatic glucose biofuel cell anodes and glucose biosensors.

Two new inorganic-organic hybrid materials based on heteropolyoxometalates (POMs): (C4H10N)6[P2Mo18O62]·4H2O (P2Mo18) and (C6H8NO)4[H2P2W18O62]·6H2O (P2W18) are reported as mediators for electron transfer between FAD-dependent glucose dehydrogenase (FAD-GDH) and a multiwalled carbon nanotube (MWCNT) matrix for glucose biofuel cell and biosensor applications. These polyoxometalates were chosen due to their promising redox behavior in a potential range for mediated electron transfer with the glucose oxidizing enzyme, FAD-GDH. P2Mo18 and P2W18 were immobilized on 1-pyrenemethylamine (PMA) functionalized MWCNT deposits. After immobilization of FAD-GDH, the P2W18-modified MWCNT electrode demonstrated mediated electron transfer and provided a catalytic current density of 0.34 mA cm-2 at 0.2 V vs SCE with an open circuit potential (OCP) of -0.08 V vs SCE. A 10-fold increase in catalytic current to 4.7 mA cm-2 at 0.2 V vs SCE and a slightly lower OCP of -0.10 V vs SCE was observed for an equivalent electrode modified with P2Mo18.The apparent superiority of P2Mo18 is related, at least in part, to its improved incorporation in the MWCNT matrix compared to P2W18. Both POM-modified bioanodes showed exceptional stabilities with 45% of their initial performances remaining after 15 days. The mediated electron transfer capacities of the POMs were also evaluated in a glucose sensor setup and showed very satisfying performances for glucose detection, including a sensitivity of 0.198 mA mol L-1 cm-2, a satisfying linear range between 1 mmol L-1 and 20 mmol L-1, and good reproducibility for the P2Mo18 electrode.