Target-induced photoelectrochemistry and colorimetric dual-mode platform for HIgG based on Ag2S/SnO2 composites and CoOOH nanoflakes

Human immunoglobulin G (HIgG) plays a significant role in diagnosing infections and monitoring autoimmune diseases. However, the development of sensitive and reliable sensing platforms remains a challenge. Based on the Ag2S/SnO2 composites, a dual-mode sensing platform was developed using multifunctional CoOOH nanoflakes for the sensitive detection of HIgG through photoelectrochemistry (PEC) and colorimetry. In the PEC mode, Ag2S QDs boost the PEC activity of SnO2 NFs and facilitate the subsequent antibody immobilization. Ascorbic acid (AA) captures holes in Ag2S/SnO2 to enhance the photocurrent. CoOOH, acting as a secondary antibody label, forms a sandwich structure with the electrode. The loading of HIgG and CoOOH-Ab2 due to specific recognition of antigen-antibody, leads to the quenching of PEC signal. Various amounts of HIgG will bind with different amounts of CoOOH-Ab2, displaying a linear response within the range of 100 pg/mL~10 μg/mL, with the detection limit of 2.2 pg/mL. In the colorimetric mode, CoOOH efficiently catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), and various amount of the sandwich biocomplexes formed with different HIgG levels lead to distinct color changes for visual detection. The linear response range is 500 pg/mL~9.375 μg/mL with a lower detection limit of 0.29 ng/mL. The two independent modes with different mechanisms, based on the same PEC electrode, can validate each other and provide more scientific and reliable results in response to the targets. Thus, this dual-mode sensing platform for targets-induced signaling changes presents a novel strategy for bioanalysis and detection.