Electropositive Magnetic Fluorescent Nanoprobe-Mediated Immunochromatographic Assay for the Ultrasensitive and Simultaneous Detection of Bacteria.

Immunochromatographic assays (ICAs) provide simple and rapid strategies for bacterial diagnosis but still suffer from the problems of low sensitivity and high dependency on paired antibodies. Herein, the broad-spectrum capture and detection capability of the antibody-free electropositive nanoprobe are clarified for bacteria for the first time and an ultrasensitive fluorescent ICA platform is constructed for the simultaneous diagnosis of multiple pathogens. A magnetic multilayer quantum dot nanocomposite with an amino-embedded SiO shell (MagMQD@Si) is designed to enrich bacteria from solutions effectively, offer high luminescence, and reduce background signals on test strips, thus greatly improving the sensitivity and stability of ICA technique for pathogen. The superior performance of the MagMQD@Si-based ICA through the multiplex detection of three common pathogens is demonstrated, namely, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Salmonella typhimurium, showing that this ICA possesses high sensitivity (8-40 cells mL), good reproducibility (relative standard deviation <5.4%), and high specificity for the three target bacteria. The clinical utility of the proposed method is verified through the detection of 30 real sputum samples from patients with bacterial respiratory infections, revealing that the MagMQD@Si-based ICA has massive potential as a powerful inspection tool for the rapid, sensitive, and ultrasensitive diagnosis of bacterial infections. [Correction added on 29 January 2025, after first online publication: Streptococcus typhi was corrected to Salmonella typhimurium.].