Template-Regulated Bimetallic Sulfide Nanozymes with High Specificity and Activity for Visual Colorimetric Detection of Cellular H₂O₂

For the past several decades, most of the research studies on nanozymes have been aimed at improving their catalytic activity and diversity; however, developing nanozymes with strong catalytic activity and great specificity remains a challenge. Herein, a simple and efficient template synthesis method was used to synthesize bimetallic sulfide nanoparticles, NiCo2S4 NPs, and prove that they have excellent peroxidase-like activity with good specificity. By regulating polyvinyl pyrrolidone (PVP) and hexadecyl trimethyl ammonium bromide as the templating agent, we have obtained the NiCo2S4 (PVP) NPs with a high Ni/Co ratio, thus exhibiting superior peroxidase activity. In addition, the NiCo2S4 NPs selectively catalyzed and oxidized colorless 3,3,5,5-tetramethylbenzidine (TMB). On being treated with H2O2, TMB turns blue while other substrates did not undergo the oxidation reaction under the same conditions, such as 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) and dopamine. The high specificity of NiCo2S4 NPs is due to the strong electrostatic driving coordination between negatively charged NiCo2S4 NPs and positively charged TMB. Due to the peroxidase activity of the developed NiCo2S4 NPs, a simple, low-cost, and reliable colorimetric method was established. Simultaneously, this method for in situ quantitative monitoring of H2O2 produced by MDA-MB-231 cells was also achieved. This study has provided a theoretical basis for the improvement of the activity and specificity of bimetallic sulfide nanozymes and may offer guidance for the further reasonable design of related materials.