Photocurrent-Polarity-Switching Aptasensor Based on SnS Nanoparticles and G4-Hemin Nanospheres for Ampicillin Detection

In this work, taking SnS nanoparticles as the photoactive material, a photoelectrochemical (PEC) aptasensor was developed for ampicillin detection based on G4-hemin nanosphere-induced switching of the photocurrent direction. Herein, an n-type semiconductor SnS was used as a photoelectric substrate material to generate anodic photocurrent. Au nanoparticles (NPs) were used as carriers to synthesize the S0–Au NPs-S1 complex and were immobilized on the electrode surface to form G-rich DNA nanospheres, which were obtained by the terminal polymerization of terminal deoxynucleotidyl transferase (TdT). These G-rich DNA nanospheres can load with large amounts of hemin; due to the matched energy level between SnS and hemin, the photocurrent of the SnS/S0–Au NPs-G4-hemin electrode was switched from anodic photocurrent to cathodic photocurrent. At the same time, the signal was amplified, and a relatively large cathodic photocurrent was produced. This PEC aptasensor had good analytical performance for the target ampicillin, with a wide linear range from 100 fM to 500 nM and a limit of detection of 1.69 fM.