Single-atom nanozymes (SANs) possess unique features of maximum atomic utilization and present highly assembled
enzyme-like structure and remarkable
enzyme-like activity. By introducing SANs into immunoassay, limitations of ELISA such as low stability of
horseradish peroxidase (HRP) can be well addressed, thereby improving the performance of the immunoassays. In this work, we have developed novel Fe-N-C single-atom nanozymes (Fe-Nx SANs) derived from Fe-doped
polypyrrole (PPy) nanotube and substituted the
enzymes in ELISA kit for enhancing the detection sensitivity of
amyloid beta 1-40. Results indicate that the Fe-Nx SANs contain high density of single-atom active sites and comparable
enzyme-like properties as HRP, owing to the maximized utilization of Fe atoms and their abundant active sites, which could mimic natural
metalloproteases structures. Further designed SAN-linked
immunosorbent assay (SAN-LISA) demonstrates the ultralow limit of detection (LOD) of 0.88 pg/mL, much more sensitive than that of commercial ELISA (9.98 pg/mL). The results confirm that the Fe-Nx SANs can serve as a satisfactory replacement of
enzyme labels, which show great potential as an ultrasensitive colorimetric immunoassay.