Dual-mode detection of human immunoglobulin via copper oxide nanozyme catalysis fluorescent species generation and photoelectrochemical alteration in ZnIn2S4/SnO2-based system

Human immunoglobulin (HIgG) has gained recognition as a crucial biomarker diagnosing and treating various diseases, particularly in identifying elevated serum levels in conditions like measles and pneumococcal disease. Traditional detection methods, however, are often hindered by inefficiencies, high costs, and potential inaccuracies, underscoring the urgent need for more sensitive, efficient, accurate, and self-calibration methods for HIgG. Here, a novel ZnIn₂S₄/SnO₂ composites was synthesized, featuring uniformly dispersed SnO₂ nanoparticles on the flower-like ZnIn₂S₄ structure, resulting in a type II heterojunction that promotes the separation and transfer of photogenerated carriers. Under optimized conditions, this composite demonstrated remarkable photocurrent enhancements 52 and 195 times greater than that of the individual ZnIn₂S₄ or SnO₂, respectively. A novel dual-mode biosensing platform was subsequently developed, employing the ZnIn₂S₄/SnO₂ composites as both as the photoelectrochemical (PEC) signal generator and antibody carrier. This system utilizes multifunctional CuO NPs with ascorbic acid oxidase-like properties, serving as a secondary antibody label. Upon specific binding to HIgG, a notable decrease in the PEC response occurs due to the catalytic activity of CuO NPs and the antigen-antibody interactions. The introduction of o-phenylenediamine (OPD) further enhances detection by facilitating the formation of a fluorescent substance DHAA. This dual-signal approach yielded excellent linear correlations between both PEC and fluorescence signals and HIgG concentration, achieving low detection limits of 22.5 pg/mL or 8.6 pg/mL. These two signals originated from the same PEC electrode with continuous detection in the absence and presence of OPD, simplifying experimental procedures and enhancing the reliability of detection. The non-toxic, chemically stable ZnIn₂S₄/SnO₂ composites ensures reliable and sensitive detection through photocurrent output after incubation with biomolecules. The integration of nanozyme catalysis, biospecific reactions, and in situ fluorescent products generation promise high selectivity across diverse immunosensing applications.