Evaluation of different strategies for the development of amperometric biosensors for l-lactate

Two strategies were investigated for the development of lactate biosensors based on sol-gel matrixes and polysulfone composite films, both containing l-lactate dehydrogenase (LDH). Firstly, reagentless disposable screen-printed electrodes (SPE's) with Meldola's Blue (MB) and the cofactor NAD⁺ inside a sol-gel matrix were prepared. These showed relatively low sensitivities (260 μA/M). Secondly, mediator-modified-polysulfone-graphite composite films deposited over both cylindrical epoxy-graphite and SPE's. These electrodes showed enhanced performance characteristics: improved sensitivity (80 mA/M), detection limit (0.87 μM) and reproducibility (2%). Reagentless electrodes, incorporating NAD⁺ in the polysulfone film, had a decreased sensitivity, although better than that achieved by the sol-gel electrodes. While sol-gel electrodes showed a linear range between 1.25 × 10^-4 and 2.48 × 10^-3 M, the epoxy-graphite composite electrodes based on polysulfone composite films allowed the detection of lactate at a linear range of lower concentrations from 1 × 10^-6 to 1.2 × 10^-5 M. Finally, the performance of the LDH-MB-polysulfone-composite film-based SPE's in a flow system was studied. Short response times were obtained (t < 30 s). Furthermore, repeatability and reproducibility values were notably improved, especially when working with electrodes covered with a polyamide layer prepared with N-(2-aminoethyl)-piperazine.