Pulsed electrochemical detection of orotic acid by an activated potential waveform at a gold working electrode following anion-exchange chromatography

An improved L-lysine amperometric biosensor based on lysine oxidase immobilised onto a platinum electrode by glutaraldehyde co-crosslinking with bovine serum albumin is described. A thoroughly optimization of the enzyme immobilization procedure permitted the fabrication of a fast-response biosensor with high sensitivity and improved stability. Moreover, the relevant electrochemical study showed the possibility to tune the overall kinetic control of biosensor from merely diffusive to enzymatic or mixed by switching the pH from weakly alkaline to weakly acid values, respectively, as well as by controlling its hydrodynamic behaviour. The response time, t(0.95), evaluated in batch addition experiments, was lower than 6 s. Linear lysine responses up to 0.6 M were observed with a sensitivity of 4.4 mu A mM(-1), while detection limit at S/N = 3 was 1 mu M. The sensor has been tested for lysine determination of a pharmaceutical sample obtaining a good agreement with the expected values.