Optimizing single-atom cerium nanozyme activity to function in a sequential catalytic system for colorimetric biosensing

Ever-increasing attention is being drawn towards single-atom nanozymes (SAzymes) for colorimetric biosensing applications. A series of atomically dispersed cerium (Ce) nanozymes are synthesized with different feeding molar ratios of Ce/Zn or under various pyrolysis temperatures, and their enzymatic performance, including peroxidase-, oxidase-, and catalase-activities, is explored. Both theoretical and experimental results demonstrate that Ce species symmetrically coordinate with nitrogen atoms to form CeN4 moieties which exhibit peroxidase-like activity. The best Ce-based SAzyme achieves remarkable peroxidase-like specificity and enables the colorimetric sensing of H2O2. This sensitivity provides a versatile reporter platform for detecting the activities of natural enzymes involved in H2O2 generation and further monitoring their substrates as well as inhibitors, for example, organophosphorus pesticides (OPs) when integrating with the acetylcholine esterase-choline oxidase biocatalyzed cascade. More importantly, this proposed sequential catalytic biosensor exhibits the capability to monitor trace OPs in the real samples with high sensitivity yet insignificant interference. This work sheds new light on further design of highly active lanthanide-based SAzymes to boost enzyme-mimicking reactions for the applications in rapid on-site colorimetric analysis of emerging contaminants in environmental and food samples.