Prussian blue-glutamate oxidase modified glassy carbon electrode: A sensitive l-glutamate and β-N-oxalyl-α,β-diaminopropionic acid (β-ODAP) sensor

A sensitive biosensor has been developed for the neurotoxin β-N-oxalyl-α,β-diaminopropionic acid (β-ODAP) contained in the seeds of grass pea (Lathyrus sativus) and for l-glutamate based on glutamate oxidase (GlOx) and a Prussian blue (PB) modified glassy carbon (GC) electrode. The configuration of the system is so as to detect the hydrogen peroxide released during the enzymatic cycle at a low applied potential, −50 mV versus Ag|AgCl, in the flow injection mode. For this purpose GlOx was coupled to PB electrodeposited onto a glassy carbon electrode and stabilised by treatment with tetrabutylammonium toluene-4-sulfonate (TTS) during one of the steps in the electrodeposition. GlOx was cross-linked with glutaraldehyde (GA), bovine serum albumin (BSA) and Tween-20 on the surface of the PB modified GC electrodes. Addition of 0.01% and 0.001% polyethyleneimine (PEI) to the immobilisation mixture resulted in an enhancement of the response signal with about 35% and 62% for glutamate and β-ODAP, respectively, when using 0.01% PEI and with 164% and 200% for glutamate and β-ODAP, respectively, when using 0.001% PEI. The linear response range for β-ODAP was extended from 0.05–0.5 mM to 0.01–1 mM, when 0.001% PEI was used. However, a higher concentration of PEI, 0.1%, caused a decrease in the sensitivity of the biosensor.