PEI-Mediated Assembly of FeO onto SiO-Encapsulated CsPbBr for Highly Sensitive Fluorescent Lateral Flow Immunoassay.

The conventional lateral flow immunoassay (LFIA) method using colloidal gold nanoparticles (Au NPs) as labeling agents faces two inherent limitations, including restricted sensitivity and poor quantitative capability, which impede early viral infection detection. Herein, we designed and synthesized CsPbBr perovskite quantum dot-based composite nanoparticles, CsPbBr@SiO@FeO (CSF), which integrated fluorescence detection and magnetic enrichment properties into LFIA technology and achieved rapid, sensitive, and convenient quantitative detection of the SARS-CoV-2 virus N protein. In this study, CsPbBr served as a high-quantum-yield fluorescent signaling probe, while SiO significantly enhanced the stability and biomodifiability of CsPbBr. Importantly, the SiO shell shows relatively low absorption or scattering toward fluorescence, maintaining a quantum yield of up to 74.4% in CsPbBr@SiO. Assembly of FeO nanoparticles mediated by PEI further enhanced the method's sensitivity and reduced matrix interference through magnetic enrichment. Consequently, the method achieved a fluorescent detection range of 1 × 10 to 5 × 10 pg·mL after magnetic enrichment, with a limit of detection (LOD) of 58.8 pg·mL, representing a 13.3-fold improvement compared to nonenriched samples (7.58 × 10 pg·mL) and a 2-orders-of-magnitude improvement over commercial colloidal gold kits. Furthermore, the method exhibited 80% positive and 100% negative detection rates in clinical samples. This approach holds promise for on-site diagnosis, home-based quantitative tests, and disease procession evaluation.