Biosensors based on nanostructured electrochemical transducers have a great interest because of their particular advantages. Carbon nanotubes (CNTs) and conducting polymers have been used successfully for the preparation of hybrid electrodes which exhibit special properties due to the synergic effect from both components. However, poly(3-methylthiophene) P3MT has been scarcely applied for the fabrication of composite materials. In a previous report, we synthesized a P3MT/ CNTs hybrid composite onto a glassy carbon electrode (GCE)1. Recent investigations in our lab have revealed that this type of hybrid electrodes possess the ability to decrease significantly, the overpotential for electrochemical oxidation of H2O2 and NADH.
In this communication, a lactate biosensor in which the enzyme lactate dehydrogenase (LDH) was immobilized onto a CNTs-P3MT-GCE has been developed. The resulting design is very attractive because of its simplicity, high sensitivity and low potential without using redox mediators.
The influence of experimental variables that could affect the performance of the biosensor: enzyme immobilization procedure, CNTs loading, applied potential, pH and NAD+ concentration, were investigated in order to optimize the electroanalytical characteristics of the amperometric detection.
A good electroanalytical behaviour of the hybrid electrode was observed. The NADH analytical signal obtained by CV in 0.1 M PBS at pH 7.4 was approximately, three times higher at CNTs-P3MT-GCE than those at CNTs-GCE or P3MT-GCE. Furthermore, amperometric measurements at the LDH biosensor in stirred 0.1 M PBS pH 8.0 in the presence of 2.5 mM NAD+, using 300 mV as the potential value, allowed the achievement of a quantification limit of 1ìM lactate. A good electrode-to-electrode reproducibility (RSD: 7.4 %, n = 5) was also obtained. The influence of other species: ethanol, citric, malic, tartaric, uric (UA) and ascorbic (AA) acids was also investigated. Only UA and AA interferred, but this effect can be drastically reduced by casting a Nafion film over the working electrode.