Synthesis Of Upconversion Nanoparticles And Their Applications In Oxytetracycline Detection

Oxytetracycline(OTC) is one of the common broad-spectrum antibiotics. The OTC residue from animal-derived foods poses a great risk towards human health, and methods of detection of OTC were very important to food safety analysis. Rare earth doped upconversion nanoparticles(UCNPs) can emit ultraviolet or visible light under excitation by near-infrared light or infrared light, and the autofluorescence of biosamples could be effectively avoided due to the unique property. In the study, OTC aptamer with high specificity identification function combined with Na YF4 nanoparticles are used to construct aptasensor for OTC.Firstly, based on the solvothermal technology, both hexagonal-phase nanocrystals and cubic-phase nanocrystals with good fluorescent property and uniform morphology were synthesized. Furthermore, the UCNPs were coated with a layer of silica by the microemulsion method, and ways to get different thickness of silica was studied.Secondly, a novel sensitive aptasensor was constructed for the quantification of oxytetracycline(OTC) in this study. Under the optimal conditions, the limits of detection(LOD) were as low as 0.036 ng/m L, benefiting largely from UCNPs labeling, aptamer affinity and magnetic separation. The aptasensor achieved a linear range between 0.05 to 100 ng/m L and the calibration curve was y=-273.8x+2620.63(R2=0.9969). The spiked recovery experiments and the specificity analysis proved this method could be used for actual sample detection.Thirdly, a new aptasensor for OTC based on luminescence resonance energy transfer(LRET)between upconversion conversion nanoparticles(UCNPs)and SYBR Green I was fabricated. Under the optimal conditions, the proposed method achieved a linear range between 0.1 to 10 ng/m L, and the calibration curve was y=-0.1169x+0.2062(R2=0.9925). The limit of detection(LOD) was as low as 0.054 ng/m L. The spiked recovery experiments and the specificity analysis proved this method could be used for actual sample detection.Fourthly, core/shell silica/Na YF4 with uniform silica coating on the surface were synthesized, and multicolor spheres were produced by encapsulating organic dyes into the silica shell. And the commonly used fluorescein isothiocyanate(FITC) was used to prove the concept.