Hollow sphere nickel sulfide nanostructures-based enzyme mimic electrochemical sensor platform for lactic acid in...

An enzyme-free electrochemical sensor platform is reported based on hollow sphere structured nickel sulfide (HS-NiS) nanomaterials for the sensitive lactic acid (LA) detection in human urine. Hollow sphere nickel sulfide nanostructures directly grow on the nickel foam (NiF) substrate by using facile and one-step electrochemical deposition strategy towards the electrocatalytic lactic acid oxidation and sensing for the first time. The as-developed nickel sulfide nanostructured electrode (NiF/HS-NiS) has been successfully employed as the enzyme mimic electrode towards the enhanced electrocatalytic oxidation and detection of lactic acid. The NiF/HS-NiS electrode exhibits an excellent electrocatalytic activity and sensing ability with low positive potential (~ 0.52 V vs Ag/AgCl), catalytic current density (~ 1.34 mA), limit of detection (LOD) (0.023 μM), linear range from 0.5 to 88.5 μM with a correlation coefficient of R² = 0.98, sensitivity (0.655 μA μM^-1 cm^-2), and selectivity towards the lactic acid owing to the ascription of high inherent electrical conductivity, large electrochemical active surface area (ECASA), high electrochemical active sites, and strong adsorption ability. The sensors developed in this work demonstrate the selectivity against potential interferences, including uric acid (UA), ascorbic acid (AA), paracetamol (PA), Mg²⁺, Na⁺, and Ca²⁺. Furthermore, the developed sensors show practicability by sensing lactic acid in human urine samples, suggesting that the HS-NiS nanostructures device has promising clinical diagnostic potential. Graphical abstract.