Development of L-phenylalanine biosensor and its application in the real samples

Electrochemical biosensor based on boron-doped diamond (BDD) electrode modified with the enzyme tyrosinase (Ty), obtained from mushrooms (Sigma-Aldrich), immobilized on polyaniline (PANI) doped with polyvinyl sulfonate (PVS) composite films.The biosensor offered a new possibility to detect L-phenylalanine in real samples.The biosensor response to its natural substrate, L-tyrosine, was compared to its response to Lphenylalanine using voltammetric methods and the results obtained were plotted as Lineweaver-Burk plots in order to determine apparent Michaelis-Menten constants.The biosensor was also applied to certain commercially available real sample to assess its performance.The enzyme catalysed oxidation of L-phenylalanine was measured as the formation of L-3,4-dihydroxyphenylalanine (L-dopa) at peak potential +800 mV (vs.Ag/AgCl).The linearity response of the biosensor to L-phenylalanine (L-Phe) compared to L-Tyrosine (L-Tyr) was demonstrated, in the concentration range between 2-10 µM (r = 0.998, n = 6).The apparent Michaelis-Menten constants (K m ) of the immobilized tyrosinase for L-phenylalanine and L-tyrosine were 1.39 µM and 2.83 µM, respectively.The detection limits for L-phenylalanine was 1.0x10 -2 µM and for L-tyrosine was 1.0x10 -2 µM.Biosensor performance analysis on lipoprotein standard material and commercial lemonade sample were respectively found to be (1.0x10-3 ±0.1 µM).The sensitivity of the biosensor towards Insciences Journal | SensorsISSN 1664-171X L-phenylalanine as a substrate was 7.19 Amol -1 .dm 3 compared to 3.53 Amol -1 .dm 3 for Ltyrosine..