Lactate Dehydrogenase Biosensor Based on an Hybrid Carbon Nanotube-Conducting Polymer Modified Electrode

A lactate biosensor constructed by immobilization of the enzyme lactate dehydrogenase (LDH) on a glassy carbon electrode modified with a hybrid material composed of the conducting polymer poly (3-methylthiophene) (P3 MT) electrodeposited on the electrode surface, and multiwalled carbon nanotubes (MWCNTs), is reported. The excellent characteristics of the electrode modified with the hybrid material toward the electrochemical oxidation of NADH allowed the construction of a robust LDH electrochemical biosensor able to operate at a working potential as low as +300 mV without the need for redox mediator. Experimental variables affecting the performance of the biosensor: amount of LDH immobilized on the modified electrode surface, buffer composition and working pH value, MWCNTs loading in the hybrid material and NAD(+) concentration were optimized. Under the optimized conditions, a linear calibration graph for lactate was obtained over the 1.0 x 10(-6) - 5.0 x 10(-4) M (r=0.9993) concentration range, with a detection limit of 5.6 x 10(-7) M. The biosensor design showed good repeatability of the measurements, good reproducibility in the inter-biosensor assays and a good selectivity against other organic acids, especially when the biosensor is coated with a Nafion film.