Development of a Disposable Screen Printed Amperometric Biosensor Based on Glutamate Dehydrogenase, for the Determination of Glutamate in Clinical and Food Applications

A screen printed carbon electrode (SPCE) containing the electrocatalyst Meldola’s Blue (MB) has been investigated as the base transducer for a glutamate biosensor. The sandwich biosensor was fabricated by firstly depositing a chitosan (CHIT) layer onto the surface of the transducer (MB-SPCE), followed by glutamate dehydrogenase (GLDH): this device is designated GLDH-CHIT-MB-SPCE. NAD+ was added to buffer solutions prior to the measurement of glutamate. This biosensor was used in conjunction with amperometry in stirred solution at an applied potential of +0.1 V (vs. Ag/AgCl). Optimum conditions for the analysis of glutamate were found to be as follows: temperature, 35 °C; buffer, pH 7; ionic strength, 75 mM; NAD+, 4 mM; CHIT 0.05% in 0.05 M HCl; GLDH, 30 U. The linear range of the biosensor was found to be 12.5 ?M to 150 ?M, the calculated limit of detection (based on three times signal to noise) was 1.5 ?M and the sensitivity was 0.44 nA/?M. The proposed biosensor was used to measure glutamate in serum before and after fortification with glutamate. The endogenous concentration of glutamate was found to be 1.68 mM and the coefficient of variation (CV) was 4.1%. The serum was then fortified with 2 mM of glutamate, and the resulting mean recovery was 96% with a CV of 3.3% (n=6). An unfiltered beef OXO cube was analysed for monosodium glutamate (MSG) content. The endogenouscontent of MSG was 125.43 mg/g with a CV of 8.98%. The OXO cube solution was fortified with 0.935 g (100 mM) of glutamate, the resulting mean recovery was 91% with a CV of 6.39%.