Amperometric Detection of L-Lactate Using Nitrogen-Doped Carbon Nanotubes Modified with Lactate Oxidase

Nitrogen-doped carbon nanotubes (N-CNTs) provide a simple, robust, and unique platform for biosensing. Their catalytic activity toward the oxygen reduction reaction (ORR) and subsequent hydrogen peroxide (H2O2) disproportionation creates a sensitive electrochemical response to enzymatically generated H2O2 on the N-CNT surface, eliminating the need for additional peroxidases or electron-transfer mediators. Glassy carbon electrodes were modified with 7.4 atom % N-CNTs, lactate oxidase (LOx), and a tetrabutylammonium bromide (TBABr)-modified Nafion binder. The resulting amperometric L-lactate biosensors displayed a sensitivity of 0.040 +/- 0.002 AM(-1) cm(-2), a low operating potential of -0.23 V (vs Hg/Hg2SO4), a repeatability of 1.6% relative standard deviation (RSD) for 200 mu M samples of lactate, a fabrication reproducibility of 5.0% (RSD), a limit of detection of 4.1 +/- 1.6 mu M, and a linear range of 14-325 mu M. Additionally, over a 90 day period, the repeatability for 200 mu M samples of lactate remained below 3.4% (RSD). Direct electron transfer was observed between the LOx redox-active center and the N-CNTs with the electroactive surface coverage determined to be 0.27 nmol cm(-2).