PEI-Mediated Assembly of Fe₃O₄ onto SiO₂-Encapsulated CsPbBr₃ for Highly Sensitive Fluorescent Lateral Flow...

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 CsPbBr₃ perovskite quantum dot-based composite nanoparticles, CsPbBr₃@SiO₂@Fe₃O₄ (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, CsPbBr₃ served as a high-quantum-yield fluorescent signaling probe, while SiO₂ significantly enhanced the stability and biomodifiability of CsPbBr₃. Importantly, the SiO₂ shell shows relatively low absorption or scattering toward fluorescence, maintaining a quantum yield of up to 74.4% in CsPbBr₃@SiO₂. Assembly of Fe₃O₄ 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 × 10² to 5 × 10⁶ pg·mL^-1 after magnetic enrichment, with a limit of detection (LOD) of 58.8 pg·mL^-1, representing a 13.3-fold improvement compared to nonenriched samples (7.58 × 10² pg·mL^-1) 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.