Insciences J. 2013, 3(1), 1-23;doi:10.5640/insc.030101
Full Research Paper, Section: Sensors
Development of L-phenylalanine biosensor and its application in the real samples
Z A Mangombo1,2, D Key1, E I Iwuoha1, P G L Baker1,2
1 Chemistry Department, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
2 Forensic Science Laboratory, Chemistry Section, Western Cape, Private Bag X3, Plattekloof 7441, South Africa
* Author to whom correspondence should be addressed.
Published: April 25, 2013
Complete Article
Abstract
Electrochemical biosensor based on boron-doped diamond (BDD) electrode modified with the enzyme tyrosinase (Tyr), obtained from mushrooms (Sigma-Aldrich), immobilized in polyaniline (PANI) doped with polyvinyl sulfonate (PVS) composite films were studied and offered many advantages for new possibilities to be used as biosensors to detect L-phenylalanine in real samples. The biosensor response to its natural substrate, L-tyrosine, was compared to its response to L- phenylalanine 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 (Km) 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 1.0×10-2 µM and for L-tyrosine was 1.0×10-2 µM. Biosensor performance analysis on lipropotein standard material and commercial lemonade sample were respectively found to be (1.0×10-3±0.1 µM). The sensitivity of the biosensor towards L-phenylalanine as a substrate was 7.19 Amol-1.dm3 compared to 3.53 Amol-1.dm3 for L-tyrosine.
biosensor, boron-doped diamond, L-phenylalanine, real samples, tyrosinase
