Study On The Detection Methods Of Ochratoxin A Based On Upconversion Nanoparticles

Attention has been attracted on the problems of food safety caused by mycotoxins. Ochratoxin A(OTA), known as one kind of mycotoxins which causes contamination in the world widely and has great significance on food safety. Currently, the detection methods for OTA need special equipments and operators, which not only require expensive equipment investment and personal training, but also hard to meet the needs of on-site rapid detection. Although some rapid detection methods have been reported, sometimes they can’t have an accurate result influenced by external factors. So developing rapid, cheap and stable methods for OTA detection will make a great realistic sense on food safety.Upconversion nanoparticles(UCNPs) can make use of metastable energy level of rare elements. They can absorb long wavelength near-infrared photos and emitte short wavelength ultraviolet light photos. They have advantages of narrowband emission, large stokes wavelength shift, stable photochemical property, no biological background interference, high signal-to-noise ratio, no light bleaching effect and have great application prospect in biological analysis and so on. Howerver, there also exist some drawbacks, such as poor biocompatibility and low quantum yield. In this study, we prepared upconversion nanoparticles by thermal decomposition, using the aptamer as specific molecular recognition, combined with magnetic separation and luminescence resonance energy transfer, constructed highly specific and sensitive aptasensors for OTA.Firstly, a near-infrared magnetic aptasensor was constructed for the quantification of OTA based on near-infrared upconversion nanoparticles labeled and magnetic separation in this study. Our previous studies have shown that the emission peaks of upconversion luminescence can be well-separated, so in the vision of attempting to broaden the single emission of upconversion nanoparticles, we synthesized NaYF4: Yb0.2, Tm0.02 nanoparticles with a strong emission at 804 nm using as a limiescent label. Near-infrared UCNPs and magnetic nanoparticles(MNPs) were modified with OTA aptamer and cDNA, respectively. The nano-composites were established by the hybridization reaction of the two nanoprobes. When the target OTA was introduced, the aptamer tended to preferentially combine with OTA and the cDNA-MNPs were replaced. Under the optimal conditions, the proposed method achieved a linear range between 0.01 and 100 ng/mL(R2=0.9958) with a detection limit as low as 0.005 ng/mL. Then, we successfully applied this method to measure OTA in beer samples.Secondly, we constructed a turn-on luminescence resonance energy transfer(LRET) aptasensor for the detection of OTA based on upconversion nanoparticles and gold nanorods. Gold nanorods have been arised a lot of attention due to its adjustable longitudinal plasma peak. We assumed to regulate the longitudinal plasma peak of gold nanorods inorder to overlap well with the upconversion luminescence spectra of Er doped UCNPs and fabricate a homogeneous detection model based on luminescence resonance energy transfer. Then we synthesized Er doped upconversion nanoparticles modified with aptamer as energy donor and gold nanorods with an aspect ratio of about 2.5 modified with cDNA as energy acceptor, and fabricated luminescence resonance energy transfer OTA aptasensor successfully. The calibration plot was linear in the 0.05 to 100 ng/mL OTA concentration range(R2= 0.9951) and the limit of detection was 0.027 ng/mL. The method was successfully applied to the determination of OTA in beer.Finally, we constructed a LRET aptasensor for the detection of OTA based on Core/Shell UCNPs and graphene oxide(GO). The Core/Shell NaYF4: Yb0.18, Er0.02@ NaYF4 was prepared by Layer By Layer strategy using thermal decomposition method. The luminescence intensity of Core/Shell UCNPs is 2.74 times than the Core UCNPs. The Core/Shell UCNPs were modified with OTA aptamer and acted as energy donor, while GO acted as energy acceptor, which has strong absorption in the ultraviolet visible light area and can absord aptamer on its surface based on stacking force and hydrogen bond, making the luminescence quench. When the energy donor was combined with OTA, it can’t be absorb on the surface of GO, and the luminescence of energy donor was retained. The luminescence intensity was positively correlated with the concentration of OTA. The calibration plot was linear in the 0.001 to 250 ng/mL OTA concentration range(R2=0.9928) and the detection limit was 0.001 ng/mL. The method was successfully applied to the determination of OTA in beer.