A novel signal amplification strategy based on the competitive reaction between 2D Cu-TCPP(Fe) and polyethyleneimine (PEI) in the application of an enzyme-free and ultrasensitive electrochemical immunosensor for sulfonamide detection.

Nanozymes with peroxidase-like activity have been widely used as signal labels in electrochemical immunosensors. However, these sensors always suffer from some shortcomings during the processes underlying nanozyme labeling, including complex reactions, nanozyme inactivation after being decorated on the antibodies. To solve these problems, a novel electrochemical immunosensor was designed for ultrasensitive detection of sulfonamides (SAs), in which the synthesized 2D Cu-TCPP(Fe) with peroxidase-like property was used as a nanozyme that was directly modified on the electrode surface. Meanwhile, the structure of 2D Cu-TCPP(Fe) could be destroyed by the polyethyleneimine (PEI) from PEI-GO@Ab2 due to the stronger affinity between PEI and Cu2+, leading to an activity change of the prepared nanozyme. When H2O2 was introduced to the system, the electrochemical current was significantly declined owing to the peroxidase activity of 2D Cu-TCPP(Fe) decreased, which led to signal amplifications. Under the optimized conditions, this strategy had a wide detection range (1.186-28.051 ng/mL), satisfactory accuracy and precision (recoveries, 64-118%; CV, 2.16-7.27%) with a low detection limit of 0.395 ng/mL. The findings of this study indicate that the electrochemical immunosensor we developed has great potential and can be used for enzyme-free detection of SAs in environmental samples.