Synthesis of multifunctional fluorescent magnetic nanoparticles for the detection of Alicyclobacillus spp. in apple juice

An approach based on multifunctional fluorescent magnetic nanoparticles was proposed for the enrichment and identification of Alicyclobacillus spp. in apple juice simultaneously. The prepared Fe 3 O 4 magnetic particles (MNPs) were modified by the sol-gel process and a silica shell was formed to improve the reactivity, and then the obtained MNPs@SiO 2 -SH nanoparticles were conjugated with Thioglycolic acid functionalized CdTe/CdS QDs via thiols chemistry. The characteristic evaluation results indicated that the MNPs-QD nanocomposites exhibited good magnetic properties and optical characterization. The polyclonal anti- Alicyclobacillus IgG antibody was immobilized onto the surface of MNPs-QD materials via esterification reactions. The maximum antibody immobilization capacity was 119.62 μg/mg and the adsorption reaction could be accomplished in 60 min. The adsorption process could be represented by Langmuir model and pseudo-second order kinetics equation, respectively. Based on the high immunocapture efficiency and sensitive fluorescence characteristics, the obtained MNPs-QDs-antibody conjugates could be applied to recognize the contamination of Alicyclobacillus spp. and a quantitative analysis method was established for target cells detection. The minimum quantitative limit was 10 4  CFU (colony forming unit)/mL and the testing process could be completed in 90 min. The results indicated that the MNPs-QDs-antibody conjugates can be successfully applied for immunocapture and detection of Alicyclobacillus spp. in apple juice. That is to say, the developed MNPs-QDs-antibody conjugates have exhibit more attractive and great potential for the immunocapture and recognition of target bacteria, fully demonstrated a new method for enrichment and rapid detection of Alicyclobacillus spp. in fruit juices.