Layer-by-Layer Assembly of Magnetic-Core Dual Quantum Dot-Shell Nanocomposites for Fluorescent Lateral Flow Detection of Bacteria
Lateral flow immunoassay (LFA) strips are extensively used for rapid tests of various biochemical molecules, but these strips still have some limitations in bacteria detection due to their low sensitivity and poor stability for complex samples. In this study, we reported a highly sensitive and quantitative fluorescent LFA strip for bacteria detection by using novel magnetic-core@dual QD-shell nanoparticles (Fe3O4@DQDs) as multifunctional fluorescent labels. The Fe3O4@DQDs were prepared through a polyethyleneimine-mediated layer-by-layer assembly method, which possess monodispersity, high magnetic responsiveness, good stability, and superior fluorescence properties. Based on these merits, the Fe3O4@DQDs were used to capture and enrich bacteria from complex samples and then acted as advanced fluorescent labels of LFA strip for the quantitative detection of bacteria. Under optimal conditions, the assay ultra-sensitively detected Streptococcus pneumoniae with a low limit of detection of 8 cells/mL and a wide dynamic linear range of 10 cells/mL to 107 cells/mL. Systematic comparison revealed that the fluorescence detection limit of the Fe3O4@DQD-based strip was 55 and 1000 times higher than those of Fe3O4-QDs particle-based and conventional QD microsphere-based strips, respectively. The proposed method also exhibited high specificity and selectivity for biological samples (human whole blood and sputum) and is thus a promising tool for real bacterial sample testing.