Yun Zhang

This work describes a label-free colorimetric immunoassay by integrating rolling circle amplification (RCA) with intrinsic Tyndall effect (TE) characteristics of nucleic acid colloids.

A novel colorimetric sensing platform was developed for rapid detection of L-cysteine (L-Cys) in human serum and milk samples, utilizing L-glutamic acid-coated Fe₃O₄ quantum dots (Glu-Fe₃O₄ QDs) with enhanced peroxidase-like activity. The Glu-Fe₃O₄ QDs were synthesized via a two-step hydrothermal method, where L-glutamic acid modification significantly improved both catalytic performance and stability compared to unmodified Fe₃O₄ nanoparticles. Characterization by TEM, XPS, and FTIR confirmed the ultrasmall size (2.57 ± 0.78 nm) and successful surface functionalization with carboxyl/amino groups. The nanozymes catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂, generating a blue color change measurable at 652 nm. L-Cys suppressed this reaction by competitively consuming hydroxyl radicals, enabling quantitative detection with a linear range of 5-50 µM (R² = 0.997) and a low detection limit of 0.73 µM. The method exhibited high selectivity against interfering amino acids and ions, and achieved recoveries of 96.99-107.59% in spiked serum and milk samples with RSDs < 3.86%. This work provides a simple, cost-effective tool for monitoring L-Cys in complex biological matrices, with potential applications in food safety and clinical diagnostics.

Biothiol analysis holds critical importance in disease diagnosis, but the highly similar structures of biothiols pose a major obstacle to their practical detection. Herein, a straightforward yet efficient CoOOH nanoflake (CoOOH NF)-triggered dual-color fluorescence sensor array has been developed for the discrimination of biothiols. Owing to their high oxidase-like activity, CoOOH NFs efficiently catalyze the oxidation of fluorometric signal indicators, generating diverse fluorescence signals. However, the presence of biothiols induced structural degradation of CoOOH NFs via redox etching, thereby inhibiting the fluorescence reactions. Based on the differential reducing capacities of biothiols, the sensor array produced unique fluorescence response patterns, which were further analyzed using principal component analysis (PCA) and hierarchical cluster analysis (HCA). The results demonstrated that the sensor array could reliably discriminate three biothiols (glutathione (GSH), cysteine (Cys), and homocysteine (Hcy)) across a broad concentration range (0.5–100 μM), as well as their mixtures with varying molar ratios. Importantly, this strategy was successfully applied to distinguish cancer cells from normal cells and to analyze clinical serum samples, highlighting its potential for medical diagnostics.