A novel optical procedure for measuring L-glutamate concentrations is described that exploits the quenching of thionine fluorescence by NADH, the latter being generated due to the reduction of NAD+ in an enzymatic reaction between L-glutamate dehydrogenase (GlDH) and L-glutamate. A substrate induced quenching (SIQ) constant of 660 (+/- 140) M-1 at 200 s is obtained. The reported method was investigated over the L- glutamate concentration range of 0 - 800 (mu) M and offers a detection limit of 6 (mu) M.
Nigel S. M. Quantrill,
"Novel L-glutamate assay based on fluorescence quenching", Proc. SPIE 2131, Biomedical Fiber Optic Instrumentation, (28 July 1994); doi: 10.1117/12.180765; https://doi.org/10.1117/12.180765