An Enhanced Lateral Flow Assay Based on Aptamer–Magnetic Separation and Multifold AuNPs for Ultrasensitive Detection of <i>Salmonella</i> Typhimurium in Milk

• Main Authors: Pingping Gao, Lihan Wang, Yang He, Yitian Wang, Xinyan Yang, Shiqian Fu, Xue Qin, Qing Chen, Chaoxin Man, Yujun Jiang
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Foods
• Subjects: enhanced lateral flow assay; multifold AuNPs; magnetic separation; <i>S.</i> Typhimurium
• Online Access: https://www.mdpi.com/2304-8158/10/7/1605

In this paper, a novel and ultrasensitive lateral flow assay (LFA) based on aptamer–magnetic separation, and multifold Au nanoparticles (AuNPs) was developed for visual detecting <i>Salmonella enterica ser.</i> Typhimurium (<i>S.</i> Typhimurium). The method realized magnetic enrichment and signal transduction via magnetic separation and achieved signal amplification through hybridizing AuNPs–capture probes and AuNPs–amplification probes to form multifold AuNPs. Two different thiolated single-strand DNA (ssDNA) on the AuNPs–capture probe played different roles. One was combined with the AuNPs–amplification probe on the conjugate pad to achieve enhanced signals. The other was connected to transduction ssDNA1 released by aptamer–magnetic capture of <i>S.</i> Typhimurium, and captured by the T-line, forming a positive signal. This method had an excellent linear relationship ranging from 8.6 × 10² CFU/mL to 8.6 × 10⁷ CFU/mL with the limit of detection (LOD) as low as 8.6 × 10⁰ CFU/mL in pure culture. In actual samples, the visual LOD was 4.1 × 10² CFU/mL, which did not carry out nucleic acid amplification and pre-enrichment, increasing three orders of magnitudes than unenhanced assays with single–dose AuNPs and no magnetic separation. Furthermore, the system showed high specificity, having no reaction with other nontarget strains. This visual signal amplificated system would be a potential platform for ultrasensitive monitoring <i>S.</i> Typhimurium in milk samples.