Asymmetric Sulfur Vacancy-Engineered Cu-Co₉S₈ Nanozyme: A High-Performance Signal Label for Chemiluminescence...

Sulfur vacancy (S_V) is known to promote the catalytic activity of metal sulfides. However, in pure metal sulfides, the highly symmetric cation arrangement around an S_V tends to localize electrons within the vacancy, limiting the electron transfer efficiency. Here, we engineered asymmetric S_V sites in Co₉S₈ nanowires through a simple copper doping strategy. Compared with pristine Co₉S₈, Cu-Co₉S₈ achieved a 4.1-fold increase in catalytic activity for the chemiluminescence (CL) reaction between luminol and H₂O₂. The outstanding activity stemmed from the Cu-S_V-Co sites. The asymmetric S_V (Cu-S_V-Co) sites break the electron cloud symmetry around the vacancy, creating a localized internal electric field that significantly enhances H₂O₂ adsorption, polarization, and activation. More importantly, the Cu-Co₉S₈ nanowires retained approximately 93% of their catalytic activity after modification with the antibody. A sandwich-type CL immunoassay for alpha-fetoprotein was constructed through labeling the secondary antibody with Cu-Co₉S₈ nanowires. The assay achieved a detection limit of 0.32 ng/mL. This work not only presents a highly active CL catalyst but also offers a simple and effective strategy for enhancing the catalytic performance of metal sulfides through rational vacancy engineering.