Construction Of Novel PH Colorimetric Nanoprobes And Their Application In The Detection Of Microbial Contamination In Food

Foodborne diseases（FBDs）have always been the top issue of food safety and a major issue of global public health security,which not only seriously threatens people’s health and safety,but also brings a heavy burden to the economies of various countries.In the list of various foodborne pathogenic factors,microbial pathogenic factors are one of the important causes of foodborne diseases,especially the two categories of pathogens and mycotoxins,which are still the focus of people’s attention.In recent years,researchers have continuously developed various biosensors for the accurate detection of these pathogenic factors.Among many sensors,the sensor based on the principle of colorimetric analysis are favored by researchers.Compared with other sensing methods,the colorimetric sensing method doesn’t require sophisticated equipment and trained professionals,and is especially suitable for on-site instant detection.So far,some colorimetric sensors have been developed for the rapid detection of pathogens and mycotoxins,but there are still some problems,such as insufficient detection sensitivity,insufficient detection time,expensive identification components and so on.Based on this,two pH-responsive color-changing nanoprobes were synthesized in this paper.Combined with magnetic separation and enrichment technology,two colorimetric sensing analysis methods were constructed for the rapid and sensitive colorimetric analysis of Gram-negative bacteria and zearalenone toxin in food.The specific research contents are as follows:1.A colorimetric assay based on pH-responsive nanoprobes and antimicrobial peptides for point-of-care detection of Gram-negative bacteria in food.In this work,we prepared two targeted probes:firstly,a pH-responsive colorimetric nanoprobe（PDA@TP-AMP）was prepared.By introducing antimicrobial peptide（AMP）,the colorimetric probe could be It binds to bacteria in a short time and acts as a direct amplification source of bacterial detection signals;then we prepared a magneti c nanocapture probe（Fe₃O₄@PMB）,the modification of polymyxin B molecule,which enables the magnetic probe to selectively capture Gram-negative bacteria.Subsequently,the magnetic capture probe Fe₃O₄@PMB and the nano-colorimetric probe PDA@TP-AMP were co-acted on the sample solution containing Gram-negative bacteria.After separation by magnetic separation,pH solution（alkaline）was added dropwise,so that the TP molecules on the PDA@TP-AMP colorimetric nanoprobe were rapidly converted into TP^2-ions,resulting in a significant blue signal.Thus,the rapid visual detection of Gram-negative bacteria in food is realized.2.A colorimetric assay based on pH-responsive nanoprobes and aptamers was used for the specific detection of zearalenone（ZEA）.In this work,we constructed a colorimetric nanoassembly consisting of an aptamer-functionalized magnetic probe（MNP@_PD-Apt）and a complementary strand-modified colorimetric probe（PDA@TP-c DNA）constitute.When ZEA is present,the aptamer on the MNP@_PD-Apt probe is more inclined to bind to ZEA,which leads to the disassembly of the assembly（MNP@_PD-Apt/PDA@TP-c DNA）.After magnetic separation,the supernatant solution containing the PDA@TP-c DNA colorimetric probe was collected,and the alkaline solution was added dropwise,and the blue intensity changes were recorded by ultraviolet-visible absorption spectrum test or by taking pictures with a smartphone,so as to achieve specific colorimetric assay for ZEA.