Amplified photocurrent signal for fabricating photoelectrochemical sulfadimethoxine aptasensor based on carbon nitride photosensitization with visible/near-infrared light responsive zinc phthalocyanine

Developing effective analytical method for sulfadimethoxine (SDM) detection is highly desirable and vitally crucial for protecting environment safety and human health. Herein, a highly selective and sensitive photoelectrochemical (PEC) aptasensor for accurate detection of SDM was proposed, which employed zinc phthalocyanine/graphitic carbon nitride (ZnPc/CN) nanocomposite as photosensitive material. The ZnPc/CN nanocomposite was constructed by modification of CN nanosheet with visible/near-infrared light responsive photosensitizer ZnPc. The introduction of ZnPc into CN exhibited amplified PEC response, which was 5.7 and 18.3 times than pure ZnPc and CN, attributed to the enhanced light harvesting ability and improved photoelectric conversion efficiency of such nanocomposite. By using ZnPc/CN and sulfadimethoxine (SDM) aptamer as PEC response material and specific probe, a PEC aptasensor was established for SDM detection. The aptamer was connected to the surface of chitosan/ZnPc/CN/ITO through the formation of phosphoramidate bonds between the amino group of the chitosan and phosphate group of the aptamer at 5′ end. The fabricated aptasensor displayed good detection linearity of 0.1 ~ 300 nM and low detection limit of 0.03 nM (S/N = 3) under optimized conditions, and the potential applicability of the PEC aptasensor was confirmed by detecting SDM in milk powder samples.