N, S-co-doped carbon/Co1-xS nanocomposite with dual-enzyme activities for a smartphone-based colorimetric assay of total cholesterol in human serum

We fabricated a novel N,S-co-doped carbon/Co 1-x S nanocomposite (NSC/Co 1-x S) using a facile sol-gel approach, which featured a multiporous structure, abundant S vacancies and Co-S nanoparticles filling the carbon-layer pores. When the Co 1-x S nanoparticles were anchored onto the surface of N,S-co-doped carbon, a synergistic catalysis action occurred. The NSC/Co 1-x S nanocomposites possessed both peroxidase-like and oxidase-mimetic dual-enzyme activities, in which the oxidase-mimetic activity dominated. By scavenger capture tests, the nanozyme was demonstrated to catalyze H 2 O 2 to produce h + , •OH and •O 2 − , among which the strongest and weakest signals were h + and •OH, respectively. The multi-valence states of Co atoms in the NSC/Co 1-x S structure facilitated electronic transfer that enhanced redox reactions , thereby improving the resultant color reaction. Based on the NSC/Co 1-x S's enzyme-mimetic catalytic reaction, a visual colorimetric assay and Android “Thing Identify” application (app), installed on a smartphone, offered detection limits of 1.93 and 2.51 mg/dl, respectively, in human serum samples. The selectivity/interference experiments, using fortified macromolecules and metal ions , demonstrated that this sensor had high selectivity and low interference potential for cholesterol analysis. Compared to standard assay kits and previously reported visual detection, the Android smartphone-based assays provided higher accuracy (recoveries up to 93.6–104.1%), feasibility for trace-level detection, and more convenient on-site application for cholesterol assay due to the superior enzymatic activity of NSC/Co 1-x S. These compelling performance metrics lead us to posit that the NSC/Co 1-x S-based nanozymic sensor offers a promising methodology for several practical applications, such as point-of-care diagnosis and workplace health evaluations.