Ultrabright magneto-fluorescent nanoparticles-enhanced lateral flow immunoassay for ultrasensitive detection of Escherichia coli O157:H7

Rapid and sensitive detection of Escherichia coli O157:H7 in complex food matrices is critical for ensuring food safety and public health. Herein, an innovative lateral flow immunoassay (LFIA) platform was developed for detecting E. coli O157:H7, utilizing a probe of magneto-fluorescent nanoparticles and smartphone interpretation. An ultrabright magneto-fluorescent nanoparticle, Fe₃O₄@mSiO₂@rQDs, was first prepared by high-density loading of red-emitting quantum dots (rQDs) in a core-shell template of Fe₃O₄ with a dendritic mesoporous silica shell. Subsequently, a metal-polyphenol network coating composed of Zr⁴⁺ and tannic acid (TA) was applied to enhance the fluorescent stability and water dispersibility of Fe₃O₄@mSiO₂@rQDs, as well as to facilitate efficient and repeatable antibody immobilization. By leveraging immunomagnetic separation-based target enrichment and the high-intensity fluorescent signal output of Fe₃O₄@mSiO₂@rQDs@TA, the developed LFIA achieved rapid and sensitive detection of E. coli O157:H7, with a detection limit as low as 2.12 × 10² CFU mL⁻¹. Notably, the FSQT-LFIA demonstrated the capability to detect bacterial concentrations down to single-cell levels following a brief pre-enrichment period. Moreover, the FSQT-LFIA exhibited excellent accuracy and high reliability in detecting E. coli O157:H7 across diverse food matrices, including skimmed milk, lettuce, apple juice, and chicken meat, with average recovery rates ranging from 85 % to 110 %. Collectively, our FSQT-LFIA platform presents a promising alternative for ultrasensitive and rapid screening of foodborne pathogens in a variety of complex food samples.