Preparation Of NMR Long Arm Functionalized Nanoprobe And Its Application In Food Microbial Detection

The development of nuclear magnetic resonance(NMR)from theory to application has become increasingly mature and popular.According to high and low field,it can be applied to disease diagnosis,oil exploration,and food quality analysis.Medical nuclear magnetic resonance imaging technology requires appropriate contrast agents and professional medical personnel to diagnose and treat diseases.In this study,based on the medical nuclear magnetic resonance tumor targeting technology,a new structure of targeted contrast agent was designed to detect Salmonella in food.On the basis of magnetic nanoprobe as the output signal,combined with antigen-antibody reaction,and using SA-Bio as the bridge,the detection signal was further amplified to realize the detection of pathogenic microorganisms in food.This is a research direction with social and economic value in the field of food safety,which provides impetus for the development of portability and miniaturization of low-field NMR.The main research contents are as follows:Firstly,in order to obtain monodisperse and stable long arm biotinylated magnetic nanoparticles(Bio-PEG-MNPs),PEG chain was used as a molecular gripper to increase the water solubility and biocompatibility of Bio-PEG-MNPs.Then,dynamic light scattering(DLS)was used to evaluate the effect of MNPs/PEG molar ratio on the particle size of magnetic beads,including PEGization and biotinization.The results showed that Bio-PEG-MNPs were monodisperse and stable when the MNPs/PEG molar ratio was 1:15.The probe characterization experiment included particle size distribution,Zeta potential change,scanning electron microscope(SEM)morphology and dispersion state,Fourier transform infrared characteristic peak,confirming that the synthesized Bio-PEG-MNPs were stably dispersed.In addition,the magnetic relaxation properties of magnetic nanoparticles with different MNPs/PEG molar ratios were compared,and the results showed that the magnetic nanoparticles still showed good magnetic relaxation properties after PEGylation.NMR detection system was constructed and applied to rapid detection of Salmonella in food.Firstly,the target bacteria were fixed according to the double antibody sandwich,and then the biotinylated antibody was connected with the biotinylated probe through SA as a bridge.Finally,the corresponding transverse relaxation time T₂ was measured by low-field magnetic resonance instrument.In order to obtain a stable,sensitive and rapid Salmonella detection system,the key detection conditions were optimized.The results showed that the detection signal?T₂was the best when the molar ratio of MNPs/PEG was 1:15 and the molar ratio of MNPs/Bio was 1:21.The optimal concentration of biotinylated antibody was 1?g/mL,the optimal incubation time of Salmonella was 60min,the optimal incubation time of probe was 60min,and the optimal dosage of SA was 1?g/mL.Finally,the sensitivity and specificity of the detection system were evaluated under the optimal conditions.The results showed that the NMR sensor could specifically detect Salmonella in PBS system with a detection limit of 10⁰CFU/mL and a detection range of 10⁰?10⁷CFU/mL.In order to achieve the purpose of practical sample detection,milk samples and pork samples contaminated by Salmonella were used as the detection objects,and the detection limits in milk samples and pork samples were10²CFU/mL and 10²CFU/g,respectively.Therefore,the innovative NMR detection system can rapidly and sensitively detect Salmonella.