Glutamate detection by amino functionalized tetrahedral amorphous carbon surfaces

In this paper, a novel amperometric glutamate biosensor with glutamate oxidase (GlOx) immobilized directly on NH2 functionalized, platinum doped tetrahedral amorphous carbon (ta-C) film, has been successfully developed. First, we demonstrate that direct GlOx immobilization is more effective on amino-groups than on carboxyl- or hydroxyl-groups. Second, we show that anodizing and plasma treatments increase the amount of nitrogen and the proportion of protonated amino groups relative to amino groups on the aminosilane coating, which subsequently results in an increased amount of active GlOx on the surface. This effect, however, is found to be unstable due to unstable electrostatic interactions between GlOx and NH3+. We demonstrate the detection of glutamate in the concentration range of 10 mu M - 1 mM using the NH2 functionalized Pt doped ta-C surface. The biosensor showed high sensitivity (2.9 nA mu M-1 cm(-2)), low detection limit (10 mu M) and good storage stability. The electrode response to glutamate was linear in the concentrations ranging from 10 mu M to 500 mu M. In conclusion, the study shows that GlOx immobilization is most effective on aminosilane treated ta-C surface without any pre-treatments and the fabricated sensor structure is able to detect glutamate in the micromolar range. (C) 2015 Elsevier B.V. All rights reserved.