Search

In this work the preparation and electrochemical characterisation of a new glutamate amperometric sol-gel biosensor is described. A carbon paste electrode was electrochemically modified with the phenothiazine dye methylene green (MG). The NADP+ and glutamate dehydrogenase were co-immobilised in a sol-gel matrix. When coupled to a flow injection system (FIA) the biosensor showed good electrocatalytic activity towards NADPH oxidation at the potential of + 0.3 V vs. Ag/AgCl; KCl sat., which represents a strong overpotential reduction. The biosensor yielded a linear response from 5.0 × 10−5 to 1.0 × 10−2 M glutamate concentration, with a detection limit of 5 × 10−6 M and reproducibility of results better than 2.3% (RSD). Moreover, the implemented biosensor showed to be still useful after 7 months, 500 determinations.

In this paper we propose the construction of a new non-mediated electrochemical biosensor for nitrite determination in complex samples. The device is based on the stable and selective cytochrome c nitrite reductase (ccNiR) from Desulfovibrio desulfuricans, which has both high turnover and heterogeneous electron transfer rates. In opposition to previous efforts making use of several redox mediators, in this work we exploited the capacity of ccNiR to display a direct electrochemical response when interacting with pyrolytic graphite (PG) surfaces. To enable the analytical application of such bioelectrode the protein was successfully incorporated within a porous silica glass made by the sol-gel process. In the presence of nitrite, the ccNiR/sol-gel/PG electrode promptly displays catalytic currents indicating that the entrapped ccNiR molecules are reduced via direct electron transfer. This result is noteworthy since the protein molecules are caged inside a non-conductive silica network, in the absence of any mediator species or electron relay. At optimal conditions, the minimum detectable concentration is 120 nM. The biosensor sensitivity is 430 mA M(-1) cm(-2) within a linear range of 0.25-50 microM, keeping a stable response up to two weeks. The analysis of nitrites in freshwaters using the method of standard addition was highly accurated.

This work describes the construction and evaluation of lactate sol–gel biosensors to accomplish the determination of lactate in pharmaceutical products. Lactate oxidase was incorporated in a porous sol–gel film placed onto a platinum-based electrode. Acid and basic catalysis were assessed. When coupled to a sequential injection system (SIA) the biosensor, based on (3-aminopropyl)trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane, deionised water, polyethylene glycol 6000 and acid catalyst, presented a range of linearity of 5 × 10 −5 to 5 × 10 −3 M. The analytical usefulness of the developed biosensor was evaluated through analysis of commercial pharmaceutical products containing lactate with a sampling rate of 40 samples h −1 . The enzyme remained active for at least 30 days, enabling about 700 determinations without sensitivity decrease.