Quantum Dot Nanobeads-Labelled Lateral Flow Immunoassay Strip for Rapid and Sensitive Detection of Salmonella Typhimurium Based on Strand Displacement Loop-Mediated Isothermal Amplification

Abstract

Rapid, sensitive, point-of-care detection of pathogenic bacteria is important for food safety. In this study, we developed a novel quantum dot nanobeads-labelled lateral flow immunoassay strip (QBs-labelled LFIAS) combined with strand displacement loop-mediated isothermal amplification (SD-LAMP) for quantitative Salmonella Typhimurium (ST) detection. Quantum dot nanobeads (QBs) served as fluorescence reporters, providing good detection efficiency. The customizable strand displacement (SD) probe was used in LAMP to improve the specificity of the method and prevent by-product capture. Detection was based on a sandwich immunoassay. A fluorescence strip reader measured the fluorescence intensity (FI) of the test (T) line and control (C) line. The linear detection range of the strip was 102–108 colony forming units (CFU)·mL−1. The visual limit of detection was 103 CFU·mL−1, indicating that the system was ten-fold more sensitive than AuNPs-labelled test strips. ST specificity was analyzed in accordance with agarose gel outputs of polymerase chain reaction (PCR) and SD-LAMP. We detected ST in foods with an acceptable recovery of 85%–110%. The method is rapid, simple, almost equipment-free, and suitable for bacterial detection in foods and for clinical diagnosis.

Keywords

• Salmonella Typhimurium
• Quantum dot nanobeads
• Lateral flow immunoassay strip
• Loop-mediated isothermal amplification
• Strand displacement probe