Construction of an amperometric biosensor for xanthine via supramolecular associations

Xathine oxidase was chemically modified with β-cyclodextrin-branched carboxymethylcellulose and further supramolecularly immobilized on a gold electrode, previously coated with a monolayer of 1-adamantanyl residues. The electrode was employed for constructing an amperometric biosensor device, which showed linear response (poised at +700 mV vs. Ag/AgCl) toward xanthine concentration between 300 μM and 10.4 mM at pH 7.0. The biosensor reached 95% of steady-state current in about 14 s and its sensitivity was 8.2 mA/M cm2. The enzyme electrode retained 93% of its initial activity after 3 weeks of storage at 4 °C in 50 mM sodium phosphate buffer, pH 7.0. The supramolecular nature of the immobilization approach was confirmed by cyclic voltammetry.