Biosensor based on laccase immobilized on microspheres of chitosan crosslinked with tripolyphosphate

A novel biosensor based on laccase immobilized on microspheres of chitosan crosslinked with tripolyphosphate was developed for rutin determination in pharmaceutical formulations by square wave voltammetry. In the biosensor, laccase catalyzes the oxidation of rutin to the corresponding o-quinone, which is electrochemically reduced back to rutin at +0.35 V vs. Ag/AgCl. The resultant reduction current is used as the analytical response. Under the optimum conditions established (laccase 0.55 units mg−1; pH 4.0; frequency 30 Hz; pulse amplitude 30 mV; and scan increment 2.0 mV), the analytical curve showed two linear ranges: 5.99 × 10−7 to 3.92 × 10−6 mol L−1 and 5.82 × 10−6 to 1.31 × 10−5 mol L−1 rutin with detection limits of 6.23 × 10−8 and 7.12 × 10−7 mol L−1, respectively. The recovery of rutin ranged from 90.7 to 105.0% and the relative standard deviation was 3.1% for a solution containing 2.0 × 10−6 mol L−1 rutin (n = 9). The lifetime of this biosensor was 320 days (at least 930 determinations). The results obtained for rutin in pharmaceutical formulations using the proposed biosensor were in agreement with those obtained with the standard method at the 95% confidence level.