A sandwich ECL immunoassay system for tau protein detection using Ru(II)-AuNP signal probes integrated with copper nanoclusters.

Tau protein is an important biomarker which is associated with neurodegenerative disorders, particularly Alzheimer's disease, where abnormal tau aggregation and hyperphosphorylation contribute to neuronal dysfunction and cognitive decline. The sensitive and early detection of tau protein is therefore crucial for the diagnosis, prognosis and therapeutic monitoring of neurodegenerative diseases. Owing to its clinical significance, the development of rapid, highly sensitive and reliable analytical platforms for tau detection has gained considerable attention in biomedical diagnostics. In this work, a Ru(II) based homogeneous sandwich ECL immunosensor was developed for the turn-on detection of tau. A polyclonal antibody was conjugated with Ru(II)@AuNP, which served as the ECL signal probe, and further integrated with monoclonal antibody conjugated L-Cys-CuNC to construct the ECL immunoassay system. Upon the addition of tau protein, the ECL intensity was enhanced due to the specific antigen-antibody interaction. The probe is selective and sensitive towards tau with a limit of detection of 0.23 pg mL-1. Also, the probe is validated with spiked human serum samples with a recovery percentage of 90 to 104%.