Microbe-mediated synthesis of defect-rich CeO₂ nanoparticles with oxidase-like activity for colorimetric detection of <scp>l</scp>-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 <i>via</i> the culture filtrate of the extremely radioresistant bacterium <i>Deinococcus wulumuqiensis</i> R12 (<i>D. wulumuqiensis</i> 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.