Glutamate optical biosensor based on the immobilization of glutamate dehydrogenase in titanium dioxide sol–gel matrix

A simple and novel titania sol–gel derived optical biosensor coupled with carboxy seminaphthorhodamine-1-dextran (SNARF-1-dextran) as the fluorescent dye was fabricated for the determination of glutamate in water and biological samples. The NADH-dependent glutamate dehydrogenase (GLDH) was trapped in titania sol–gel derived matrix prepared by vapor deposition method. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the surface morphology of the spots. SEM and AFM images showed that the deposition of titania precursor at 27 °C for 6.5 h was found to be suitable to form transparent titania sol–gel matrix to encapsulate GLDH and fluorescent probe. AFM images showed that the roughness of TiO2 surface increased from 2.16 nm in the absence of GLDH and SNARF to 37.8 nm after the immobilization. The developed titania biosensor has good analytical performance with water samples. A dynamic range between 0.04 and 10 mM with the detection limit of 5.5 μM were observed. The responses to glutamate in biological samples also showed good performances, and the dynamic range and detection limit were 0.02–10 mM and 6.7 μM, respectively. High precision with relative standard deviations of 4.2 and 10.7% in water and biological samples, respectively, were also demonstrated. In addition, the biosensor showed a relatively high storage stability over more than 1 month. Results obtained in this study clearly demonstrate that this simple vapor deposition method can be successfully used to form transparent titania sol–gel film for the fabrication of glutamate biosensors that are suitable for optical detection of glutamate in water and biological samples.