Carbon Dot-Encapsulated Plasmonic Core-Satellite Nanoprobes for Sensitive Detection of Cancer Biomarkers via Dual-Mode Colorimetric and Fluorometric Immunoassay

The enzyme-linked immunosorbent assay (ELISA) commonly used for the detection of cancer biomarkers suffers from low sensitivity. Although emerging plasmonic ELISA has become a candidate owing to unprecedented sensitivity and operation convenience, the single-mode colorimetric readout mainly dependent on the monodisperse or aggregated state of gold (Au) or silver (Ag) nanoparticles remains limited in clinical applications because of poor accuracy from uncertain experimental and environmental factors. Herein, we presented a carbon dot (CD)-encapsulated plasmonic core-satellite single nanoprobe, CDs/Ag–Au, prepared by a simple sequential in situ reduction strategy without needing additional reducing agents. The developed nanoprobe could simultaneously generate notable colorimetric and fluorometric signals triggered by H2O2 due to its selective etching to the Ag core accompanied by the release of CDs. Inspired by this dual responsiveness, we further utilized this integrated nanoprobe as the signal reporter in the glucose oxidase-involved immunoassay for prostate-specific antigen (PSA), a model cancer biomarker. Both the clear changes in the localized surface plasmon resonance peak and remarkable fluorescence enhancement were closely correlated with the target concentration, thus achieving highly sensitive and reliable dual-mode detection of PSA in a simple manner. This approach also enabled dual-mode visual detection and evaluation of the PSA level in human serum samples.