RAPID LISTERIA MONOCYTOGENES ASSAY BASED ON HELICASE DEPENDENT AMPLIFICATION (HDA) AND NUCLEIC ACID HYBRIDIZATION IN BLUE SILVER NANOPLATES

Listeria monocytogenes, a foodborne pathogen, is considered as one of the major problems in food safety. With strong safety regulations, a monitoring measure is essential for protecting the health and safety of consumers. Thus, a reliable monitoring method is required. In this study, a rapid assay based on a combination of helicase dependent amplification (HDA) and DNA signal detection via nucleic acid hybridization in blue silver nanoplates (AgNPls) was established. The assay started directly after short term enrichment in terrific broth using cotton ball swapping technique on seafood surface. A HDA amplification of hly gene of L. monocytogenes at 65 °C allowed DNA signals to be increased, whereas the rendered DNA products were detected via nucleic acid hybridization with an oligonucleotide probe in AgNPls solution. The positive specimens induced blue silver nanoplates' aggregation resulting in pale gray change to colorless, while the negative specimens showed the blue color of non-aggregated nanoplates. The method had a detection limit at 100 copies of L. monocytogenes DNA per 50 g of sample. This method was rapid, simple, did not require laboratory facilities and was suitable for field food safety monitoring.