Polyethyleneimine-interlayered silica-core quantum dot-shell nanocomposites for sensitive detection of Salmonella typhimurium via a lateral flow immunoassay

Herein, we synthesized high-performance SiO2–core quantum dot (QD)–shell nanocomposites (SiO2@PEI-QDs) using the polyethyleneimine (PEI)-mediated adsorption method. Cationic PEI was used to form a positively charged interlayer on the SiO2 core, which achieved a dense adsorption of carboxylated QDs to form a shell of QDs and maintained a good dispersibility of the nanocomposite. The SiO2@PEI-QDs showed excellent stability and high luminescence, and served as high-performance fluorescent labels for the detection of bacteria when used with the lateral flow immunoassay (LFA) technique. An SiO2@PEI-QD-based LFA strip was successfully applied to rapidly detect Salmonella typhimurium in milk samples with a low limit of 5 × 102 cells per mL.