Microbe-mediated synthesis of defect-rich CeO2 nanoparticles with oxidase-like activity for colorimetric detection of L-penicillamine and glutathione.

To enhance production efficiency, curtail costs, and minimize environmental impact, developing simple and sustainable nanozyme synthesis methods has been the focus of relevant research. In this report, graphite-coated CeO2 nanoparticles (CeO2 NPs) with multiple defects (Ce3+ defects, oxygen vacancies and carbon defects) were synthesized via the culture filtrate of the extremely radioresistant bacterium Deinococcus wulumuqiensis R12 (D. wulumuqiensis R12). The as-prepared CeO2 NPs exhibit remarkable oxidase (OXD)-like activity, efficiently catalyzing the oxidation of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to form oxTMB, even in the absence of H2O2. The electron-rich bioactive substances in the supernatant were demonstrated to modulate the electronic state of the Ce atom and played a key role in the formation of multiple defects, thereby enhancing the OXD-like activity of CeO2 NPs. Based on the inhibitory effect of sulphydryl groups (-SH) on the TMB-CeO2 system, a colorimetric strategy for the detection of both L-penicillamine (L-PA) and glutathione (GSH) was devised and successfully applied in real sample analysis. The linear ranges of L-PA and GSH detection were found to be 10-500 μM and 9-200 μM with the limits of detection (LODs) at 8.53 and 5.19 μM, respectively. This work provides a straightforward, eco-friendly and nontoxic method for the synthesis and defect construction of CeO2 NPs with OXD-like activity.