The promotion effect of titania nanoparticles on the direct electrochemistry of lactate dehydrogenase sol–gel modified gold electrode

The promotion effect of titania nanoparticles (nano-TiO2) on the direct electron transfer between lactate dehydrogenase (LDH) and the silica sol–gel modified gold electrode was investigated by adding nano-TiO2 (50 nm) in the modification process. This nano-TiO2–LDH electrode showed a pair of quasi-reversible cyclic voltammetry peaks with the formal potential of 70 mV (vs. SCE). Compared to the previous result of LDH modified electrode with only an irreversible cathodic peak, an anodic peak appeared and the cathodic peak potential shifted to the positive direction on this nano-TiO2–LDH electrode, which demonstrated that the direct electrochemistry of LDH was enhanced by nano-TiO2. We supposed that the direct electrochemistry of LDH may be due to the redox reaction of some electroactive amino acids in the LDH molecule. The surface morphologies of electrodes characterized by SEM indicated that LDH was successfully immobilized on the sol–gel matrix and also had some interactions with nano-TiO2. This electrode can be used as a biosensor for the determination of lactic acid. The calibration range of lactic acid was from 1.0 to 20 μmol L−1 and the detection limit was 0.4 μmol L−1. Meanwhile, the small K m app value (2.2 μmol L−1) suggested that LDH possessed high enzymatic activity and good affinity to lactic acid owing to the promotion effect of nano-TiO2.