NaYF₄:Yb,Er Upconversion Nanoparticles: Synthesis And Application In Constructing A DNA Fluorescent Nanoprobe

With the development of nanotechnology, excellent optical property of upconversion nanoparticles?UCNPs? has been found, which could overcome many shortages presented in traditional luminescent materials. Especially, with near infrared light as excited resource, the nanoprobes based on UCNPs can avoid the autofluorescence of biological samples and light scattering effectively, which improve the detection sensitivity greatly. Since it has the ability of remarkable self-assembly and super molecular recognition, DNA molecules, belonging to nanomaterials, is very suitable in proposing nanometer devices. UCNPs combines with DNA molecules could propose a DNA fluorescent nanoprobe, which has great potential in the realm of biology. This paper study the preparation of NaYF₄:Yb,Er nanoparticles in detail.After combined it with DNA molecules, a new DNA fluorescent nanoprobe with the function of molecular recognition was proposed finally.Ochratoxin A?OTA? is a common natural pollutant in agricultural products,which arises easily in the process of growing, harvesting, post-processing and reserving, etc. Considering the toxicity, the maximum limits and quality control of OTA in agricultural products are very meaningful. As one kind of single DNA or RNA sequences, nucleic acid aptamer has shown broad application in biological field,particularly as molecular recognition elements used in the detection of small toxic molecules in food safety. When designed DNA molecules in this paper, OTA is the target material, and then we proposed the DNA fluorescent nanoprobe for the detection of OTA. The nanoprobe provides a new idea for the simple, cheap and fast detection of OTA or other materials.For the first part, the preparation of NaYF₄:Yb,Er nanoparticles has been explored in detail. We use thermal decomposition to synthesize the nanoparticles by using rare earth stearate as a precursor at the same time. We finally obtained small,uniform, monodisperse and ? phase NaYF₄:Yb,Er nanoparticles with good fluorescence, whose surface were covered with acid oleic. In the conditions of 315?,45 min, OA/ODE=12:8, NaF/RE=28:1, we got the best nanoparticles. Afterpreparation, we worked hard in characterization, including X-ray powder diffraction,transmission electron microscope, energy spectroscopy, Fourier transform infrared spectroscopy, luminescent spectroscopy, etc. All the characterization results confirm that we have successfully prepared good NaYF₄:Yb,Er nanoparticles.For the second part, after combined DNA molecules with NaYF₄:Yb,Er nanoparticles, we proposed a DNA fluorescent nanoprobe, and we verified the availability of the probe. Firstly, we use ligand exchange method to prepare the probe,and different Sp sequences which complement the sequences containing OTA nucleic acid aptamer were designed. According to ligand exchange method, Sp sequences could replace the oleic acid coated on the surface of NaYF₄:Yb,Er nanoparticles directly, thus a water-soluble and target-specific nanoprobe was obtained. The results show that the conditions of ligand exchange with 44.9 nm NaYF₄:Yb,Er, 25 nmol 36 bp sequence and reaction for 24 h were best effective. In the future, the prepared nanoprobe Sp3-UCNPs would be a new tool to realize the specific detection of OTA.In addition, the DNA fluorescent nanoprobe could be used to detect other materials when change the Sp sequences to other target DNA sequences.