Designing Bimetallic Ni-based Layered Double Hydroxides for Enzyme-Free Electrochemical Lactate Biosensors

Lactate concentration in the human body is the crucial index to be monitored for evaluating exercise levels under anaerobic metabolism conditions. To solve the unstable nature of enzymes in biosensors for lactate detection, in this study, Ni-based layered double hydroxide (LDH) with various secondary transition metals (Fe and Co) was proposed as electrocatalysts in an enzyme-free electrochemical lactate sensor. According to the mechanism of lactate oxidation on the transition metal-based electrocatalyst, secondary transition metal of Co could serve as the active site for lactate oxidation and facilitate the adsorption of OH- in the alkaline electrolyte. After exploring the influence of secondary metal in Ni-based LDH, NiCo LDH modified screen-printed carbon electrodes (SPCEs) reached the high sensitivity of 30.59 +/- 0.34 mu A mM(-1) cm(-2) at an applied potential of 0.55 V (vs. Ag/AgCl KCl sat'd) in the concentration range from 5 to 25 mM, which is relatively higher than pristine Ni LDH (23.51 +/- 0.45 mu A mM(-1) cm(-2)) and NiFe LDH (3.03 +/- 0.06 mu A mM(-1) cm(-2)). This study proposes a new category of electrocatalyst to be utilized in enzyme-free electrochemical lactate sensors with reliable and stable performance as one of the non-invasive biosensors.