An aptamer magnetic capture based colorimetric method for rapid and sensitive detection of Listeria monocytogenes

Listeria monocytogenes (L. monocytogenes) is a ubiquitous foodborne pathogens responsible for listeriosis, which is associated with high morbidity and mortality. Development of simple and fast methods for L. monocytogenes detection is of great needed. In this study, we present a simple method for L. monocytogenes detection combined aptamers decorated magnetic beads for selective capture and gold nanoparticles (AuNPs) mediated signal amplication. A NH₂ labeled aptamer specific to L. monocytogenes was decorated on magnetic beads for selective capture and isolation of L. monocytogenes from food sample. AuNPs was functionalized with sulfhydryl modified primers specific to hly gene of L. monocytogenes in acidic environments. The AuNP@primers could catalyze TMB-H₂O₂ to TMB²⁺ and generate a significant blue color, this reaction was found to be enhanced by DNA. AuNP@primers was used as a signal indicator for the presence of L. monocytogenes DNA by enhancing the catalytic reaction of TMB-H₂O₂. The colour change was observed by naked eye and the optical density of TMB^2 + was analyzed to quantify the result. The developed assay was highly specific and the limit of detection was 10¹ CFU/mL of L. monocytogenes. For the detection of L. monocytogenes in spiked food samples, the recoveries were ranging from 73.63 to 84.21% with the coefficient of variation less than 2.41% in meat, and ranged from 94.13 to 100.71% with the coefficient of variation less than 2.82% in milk, respectively. Therefore, the developed colorimetric assay is suitable for food sample testing, the detection takes less than 1.5 h, which enables on-site screening. This study offers a promising approach for rapid, sensitive and accurate detection of L. monocytogenes in food.