T₂ Mode Low-field Magnetic Resonance Detection Method Of S.aureus

"The people depend on food,and food safety is the first concern”.With the advancement of building a well-off society in an all-round way,people's food safety issues have also received more and more attention from the state.And comprehensively improving food safety has become a strategic task in China.Staphylococcus aureus is a common food-borne pathogen.The bacteria can secrete a variety of toxic proteins,among which staphylococcal enterotoxin can cause human gastrointestinal inflammation and other diseases.For the detection of S.aureus in food,we obey the current national standard: "National Food Safety Standard,Food Microbiological Inspection of Staphylococcus Aureus"(GB 4789.10-2016).This method uses agar plate counting method to count S.aureus.It still has a lot of limitation such as time consuming and unstable.So a quick and accurate method is needed in S.aureus counting.In this paper,we use bio-functionalized specific superparamagnetic nano-beads,based on the principle of magnetic relaxation conversion,and use low-field magnetic resonance technology to quickly count the number of S.aureus in the sample.The main indicator of low-field magnetic resonance detection is the change of T2.In the first part,a magnetic nanoprobe with immunofunctionality was successfully synthesized.First,the superparamagnetic and oil-soluble magnetic nanoparticles Au-Fe3O4 were prepared by high-temperature pyrolysis.The particles were flower-like,with good dispersibility,and the particle size was about 24.73 nm.Then,a water-soluble,carboxyl group was prepared by the ligand exchange method.Au-Fe3O4,with good particle dispersibility and average particle size of about 24.92nm;finally,antibody was successfully connected to Au-Fe3O4,because the principle of amino carboxyl specific binding.The maximum antibody load of 5mg magnetic beads is 0.85 mg;after immunofunctionalization,it still has superparamagnetism,which can be used for subsequent low-field magnetic resonance detection.In the second part,S.aureus was selected as the research object,and the optimal growth medium was determined to be 75% sodium chloride broth by measuring the growth curve.It is clear that the lag periods are much higher than the time required for low-field magnetic resonance detection.Therefore,the number of bacteria does not significantly increase during the detection process.In the last part,a fast detection method of LF-NMR for S.aureus was constructed with Au-Fe3O4.The experiment showed that the method has strong specificity.To avoid interference of non-specific factors,a standard was set:?T2 / T2<0.014,identified as non-detection level.The most ideal stabilizer is 1% skim milk;the optimal incubation time is 40 minutes;the optimal reaction concentration of magnetic nanoparticles is 0.50 mg / m L;the detection linear range is 1 ~ 1000 CFU /m L.In summary,by preparing superparamagnetic nanobeads and constructing specific biofunctional nanoprobes,a high-sensitivity and specific quantification method for S.aureus based on low-field magnetic resonance technology has been established.Provide a new method for the rapid and economical detection of microorganisms.Compared with the existing detection methods(such as colloidal gold method,multiplex PCR,etc.),it has the characteristics of lower detection target concentration and higher detection sensitivity.