Nanocrystals (NCs) of cesium lead halide perovskites are optically unstable, which prevents their use in optical sensors. The combination of perovskite NCs and metal single atoms (SAs) may be a good solution to this issue. Unfortunately, depositing metal SAs on perovskite NCs remains a challenge due to relative weak metal–halide bonds. Herein, we present that, via a photo assisted method using cesium lead halide perovskite NCs as host material to anchor Y single atoms, we successfully synthesize Y SA anchored CsPbBr₃ NCs (Y-SA/CsPbBr₃ NCs) with outstanding fluorescence stability through the formation of two Y–O bonds and two Y–Br bonds. In comparison to bare CsPbBr₃ NCs, Y-SA/CsPbBr₃ NCs possess more stable optical characteristics. The as-synthesized Y-SA/CsPbBr₃ NCs can be employed as a colorimetric platform to perform rapid CH₃I sensing. Detection limit of 0.044 ppm is exhibited in this approach with excellent anti-interference performance. The Y-SA/CsPbBr₃ NCs-based system has been applied to the detection of CH₃I in sweet potato samples with satisfying results.

Owing to the unique coordination environment and high atom utilization efficiency, single atom catalysts have been considered as an ideal artificial enzyme to mimic natural enzymes. Herein, single-atom Fe nanozyme anchored on N-doped Ti₃C₂T_x (Fe SA/N-Ti₃C₂T_x) with asymmetrically coordinated Fe-N₁C₂ configuration is synthesized by vacancy capture and heteroatom doping strategy, which exhibits excellent peroxidase-like activity. Based on the results of peroxidase catalytic kinetics and X-ray adsorption fine spectroscopy, the Fe-N₁C₂ active sites in Fe SA/N-Ti₃C₂T_x are responsible for the excellent performance. Furthermore, the developed Fe SA/N-Ti₃C₂T_x can be employed to quantitative detection of melatonin (MT), which shows a wide linear detection range (0.01–100 μM) and an excellent detection limit (7.3 nM) in buffer, 0.01–100 μM and 7.8 nM in serum samples. Our work proves that MXene-based single atoms can be promising nanozyme in the field of bioassays.