A dual-mode biosensor featuring single-atom Fe nanozyme for multi-pesticide detection in vegetables.

The single-atom iron nanozyme (SA-Fe-NZ) exhibits high catalytic activity and excellent electron transfer efficiency in biosensors. However, the binding of bioreceptors to the surface of SA-Fe-NZ results in a decrease in the catalytic activity of the nanozyme due to its toxic effects. We utilized the toxic effects and excellent electrochemical properties of the SA-Fe-NZ to successfully construct a smartphone-assisted dual-mode biosensor. The complex formed by the binding of organophosphorus pesticides (OPs) to the aptamer exhibited toxic effects and inhibited the catalytic activity of the nanozyme, preventing the colorimetric substrate from being catalyzed. Simultaneously, the aptamers labeled with electrochemical signal molecules approached the electrode surface, causing a change in the electrochemical signal. The results demonstrated that the constructed broad-spectrum aptamer biosensor exhibited a low limit of detection of 3.55 fM and a wide linear range of 10-13-10-2 M, allowing for qualitative and quantitative detection of multiple OPs in vegetables.