Rapid measurement of transaminase activities using an amperometric L-glutamate-sensing electrode based on a glutamate oxidase-polyion complex-bilayermembrane

An amperometric L-glutamate-sensing electrode was prepared by immobilizing glutamate oxidase (GlOx) on a polyion complex layer-modified electrode. Fir st, a monolayer of 3-mercaptopropionic acid was made on the surface of a go ld electrode by immersing it in an ethanol solution containing the modifier . Next, aqueous solutions of poly-L-lysine and poly(4-styrenesulfonate) wer e successively placed on the electrode surface and allowed to dry. Finally, a GlOx layer was formed on the poly-L-lysine/poly(4-styrenesulfonate)-comp lex layer by crosslinking the enzyme by the addition of a glutaraldehyde so lution. The use of thin bilayer system with the inner, polyion complex memb rane, which showed permselectivity based on the solute size with the molecu lar cut-off of approximate to 100, brought high performance characteristics to the L-glutamate-sensing electrode; it showed high sensitivity (detectio n limit, 20 nM), rapid response (100% response time, 3 s), low interferenti al level (the ratio of response for L-ascorbic acid to that for the same co ncentration of L-glutamic acid, 8 x 10(-2)), and high stability (usable for more than a month). The bilayer-based electrode was useful for the rapid m easurement of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruv ate transaminase (GPT) in serum sample: each transaminase (0.2-1000 U l(-1) ) could be determined within 10 s. (C) 1998 Elsevier Science S.A. All right s reserved.