Dual Enzyme Electrode with Optical Specificity for L- and D-Amino Acids

Toshio YAO, Kazuyoshi TAKASHIMA, Youko NANJYO
2002 Analytical Sciences  
Amino acid oxidases are selective for amino acids, but not for particular amino acids. That is, they act on a considerable number of amino acids. In addition, amino acid oxidases have an optical specificity for D-or L-isomers; L-amino acid oxidase (L-AAO) is specific for L-amino acids and D-amino acid oxidase (D-AAO) is specific for D-amino acids. The general enzyme reaction is Amino acids + O2 + H2O AAO → 2-oxo acids + NH3 + H2O2. Many research groups have proposed the enzyme sensors for the
more » ... me sensors for the specific detection of L-1-7 or D-3,8,9 isomers of amino acids. Most of the enzyme sensors proposed are based on the amperometric 1,2,4-6,8 and potentiometric 7 detections or chemiluminometric 3,9 detection of hydrogen peroxide or ammonia produced by the amino acid oxidases. In addition, the development of new biosensors which may enable the simultaneous determination of L-and D-isomers of amino acids is also important, but it had not been achieved except for the successive detection 3,10 of both isomers. In this note, a dual enzyme electrode suitable for the simultaneous amperometric detection of D-and L-amino acids is described. The proposed dual electrode consists of two platinum disks modified by an L-AAO or D-AAO membrane cross-linked by glutaraldehyde. Furthermore, the electropolymerization to coat with a thin film of poly(1,2diaminobenzene) was subsequently carried out to protect the electrode from direct (nonenzymatic) oxidation of electroactive amino acids such as methionine and tyrosine or electroactive interferents such as L-ascorbate, urate, and cysteine, which may otherwise cause electrode fouling. The analytical performance of the dual enzyme electrode is assessed under flow-injection conditions, particularly on substrate selectivity within a group of amino acids and on optical specificity for D-and L-isomers of amino acids. Experimental Reagents D-AAO (EC, 9.9 U mg -1 of solid from porcine kidney), L-AAO (EC, 4 U mg -1 of solid from Crotalus adamanteus), and the D-and L-forms of alanine, arginine, histidine, leucine, lysine, methionine, phenylalanine, proline, serine, tyrosine, and valine were obtained from Sigma. Bovine serum albumin (BSA, 96 -99 % albumin), glutaraldehyde (20%
doi:10.2116/analsci.18.1039 pmid:12243401 fatcat:27do3xudhnho7fejexsqzmjpwe