Ultrasmall Rh‐Mo Nanoparticles with Prominent Peroxidase Activity for Colorimetric Sensing of L‐Cysteine

Nanozymes with peroxidase-mimicking properties have emerged as attractive candidates for diverse biomedical applications. In this study, we first prepared ultrasmall rhodium-molybdenum nanoparticles (Rh-Mo NPs) via a straightforward hydrothermal method, which exhibited remarkable peroxidase (POD)-like catalytic activity. These nanoparticles effectively catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate blue oxidized TMB (ox-TMB), demonstrating superior catalytic performance and substrate specificity. Leveraging this exceptional enzymatic activity, we established a novel colorimetric biosensing platform for sensitive determination of L-cysteine (L-Cys). Experimental data confirmed dual linear absorbance-concentration correlations for L-Cys (0.01-10.0 µM, limit of detection (LOD) = 3.3 nM; 10.0-40.0 µM, LOD = 26.5 nM), exhibiting a segmented dose-response pattern over the 0.01-40.0 µM detection range. The sensing system has three significant advantages: (1) intuitive operation requiring minimal technical expertise, (2) accelerated analysis completion within 5 min, and (3) exceptional sensitivity with low LOD. Notably, the Rh-Mo NPs-based sensing platform could successfully detect endogenous L-Cys in complex biological matrices, including serum and milk samples, confirming their practical applicability in real-sample analysis.