Smartphone-based colorimetric sensor using Fe-N-P-C single-atom nanozymes with boosted activity for sensitive detection of S2−

Abnormal sulfur ion (S2−) concentration poses a serious threat to human health and the environment, and there is an urgent need to develop an S2− detection platform with good selectivity, sensitivity and portability. In this study, we synthesized Fe-P/N-C single-atom nanozymes using sweet potato as carbon, nitrogen, and phosphorus sources. Higher metal loading and heteroatom doping (P, N) increased the number of active sites, which resulted in excellent peroxidase activity of the prepared Fe-N-P-C SAzyme. In addition, Fe-P/N-C has higher substrate affinity and higher catalytic performance, which will be beneficial for improving the sensitivity of colorimetric sensing. An S2− detection method with good selectivity and sensitivity was constructed based on Fe-N-P-C SAzyme, with a wider detection range (1–800 μM) and a low detection limit of 0.23 μM. Meanwhile, a smartphone platform for signal readout was integrated, which enables accurate visual detection of S2− with the help of the color-value conversion function of smartphones. The method can be applied to the detection of S2− in real water samples, and the spiked recoveries ranged from 87.69 % to 109.53 % with good accuracy and acceptable reliability. This work provides a new pathway for single-atom nanozymes synthesis and expanding its application in water environment safety monitoring.