Flow injection analysis system for L-lysine estimation in foodstuffs using a biosensor based on lysine oxidase immobilization on a gold-poly(m-phenylenediamine) electrode

The development and the evaluation of an amperometric FIA bio-sensing system for L-lysine determination in foodstuffs is described. The system employs a home-made flow-cell with an amperometric biosensor, prepared by immobilization of lysine oxidase on a gold-poly(m-phenylenediamine) electrode. A peristaltic pump is connected to the flow-cell via a 2-position 6-port sample injector/switching valve for the on-line transfer of the samples. The analytical procedure is based on the oxidation of L-lysine by L-lysine alpha-oxidase. The produced H2O2 is monitored amperometrically at 650 mV in FIA set-up. The lysine biosensor construction procedure comprises: a) the electropolymerization of m-phenylenediamine on a Si-gold strip electrode and b) the immobilization Of L-lysine a-oxidase on the poly(m-phenylenediamine) membrane with glutaraldehyde in the presence of bovine serum albumin. Parameters, such as, flow rate, enzyme amount, monomer concentration, matrix effect, effect of interference's, etc., were studied. The flow-cell biosensor system provides a linear response from 1 x 10(-3) to 5 x 10(-5) M of lysine, with excellent characteristics of reproducibility, stability, and life-time. The system was further applied and evaluated for the estimation of lysine in various hydrolysate food samples (e.g., pasta, milk, wheat flour, etc.) without any pretreatment with an average recovery of 97.3%.