Synergistic effect of mediator–carbon nanotube composites for dehydrogenases and peroxidases based biosensors

Very sensitive, low cost and reliable NADH and H2O2 sensors were realised and used for development of enzyme based biosensors. The active surface of the electrodes was modified with a nanocomposite obtained by modification of SWNT with a proper mediator: Meldola Blue (for NADH) and Prussian Blue (for H2O2). Low applied potential of − 50 mV vs. Ag/AgCl reference electrode proved the synergistic effect of nanocomposite materials towards NADH and H2O2 detection. Biosensors for malic acid and alkylphenols have been developed, using mediator-functionalised-SWNT-based electrodes and two different classes of enzymes: NAD+-dependent dehydrogenases and peroxidases. Immobilization of the enzymes was realised using a series of different procedures — adsorption, Nafion membrane, sol–gel and glutaraldehyde, in order to find the best configuration for a good operational stability. A higher sensitivity comparing with other reported biosensors of about 12.41 mA/M·cm2 was obtained for l-malic acid biosensor with enzyme immobilised in Nafion membrane. Phenol, 4-t-octylphenol and 4-n-nonylphenol were used as standard compounds for HRP based biosensor. Fast biosensor response and comparable detection limit with HPLC methods were achieved.