Study On The Synthesis Of Upconversion Nanoparticles And Their Application In Detection Of Small Biomolecules And Ions

Trace analysis of small molecules and ions is very important in disease prevention anddiagnosis, food safety inspection and environmental monitoring. At the present time, detectionmethods for small molecules and ions are generally dependent on large-scale analyticalinstruments, such as gas chromatography, mass spectrometry and so on. These methods stillexhibit deficiencies in some extent, including complex sample preparation andtime-consuming detection process. With the development of nanotechnology, a variety ofsimple methods based on nanomaterials have been developed, such as colorimetry,fluorescence analysis, and electrochemical methods. Therefor, fluorescence analysis hasreceived most attention because it is simple, rapid and highly sensitivite. The commonly usednanomaterials-based fluorescent labels include dye-doped nanoparticles, quantum dots and soon. However, when these nanomaterials are used for assay of complex biological samples,they often show high background and low sensitivity as a result of the autofluorescenceinterference from biomolecules. Upconversion nanoparticles （UCNPs） have prominent opticalproperties that can convert the low-energy light （980nm NIR light） to the higher-energy light（UV or visible light）, and thus can effectively eliminate the interference of autofluorescence.Recenctly, UCNPs have become a research hotspot for the detection of biomolecules and ions,cell labeling and in vivo imaging. In this thesis, aiming at the development of novelultrasensitive detection methods of small biomolecules and ions, we synthesised chemicallystable UCNPs, and applied it to design simple, sensitive analysis methods to detection smallbiomolecules and environmental heavy metal ions. The main works are summarized asfollows:1. Study on the preparation of UCNPs based on hydrothermal synthesis methodUsing hydrothermal synthesis method, we prepared sodium yttrium fluoride crystalsdoped with ytterbium, erbium, germanium ions. At the same time, and the effects of differentconditions on the surface topography, size and fluorescence intensity of UCNPs have beeninspected. Results showed that the UCNPs doped with ytterbium and erbiums are much betterthan those doped with ytterbium, erbium and germanium in fluorescence properties. Byselecting to synthesize UCNPs doped with ytterbium and erbium, we further studied the influences of the low temperature preheating treatment with different temperature and time onthe synthesis of UCNPs. Results revealed that these factors could influence the crystal shape,size and fluorescence property of UCNPs. Finally, we obtained the UCNPs with appropriatesize and strong fluorescence intensity under the condition of preheating for30min at120℃firstly and then reacting for8h at200℃. In order to further improve the biocompatibility,dispersibility and modificability of UCNPs, the silica shell coating was further conductedthough the reverse microemulsion method. Results demonstrated that the coated silica shellwith controlled thickness made UCNPs more dispersive, easy to modify, and available for theapplication in biomedicine.2. Detection of ATP based on split aptamer fragments and UCNPsThrough the combination of UCNPs’ unique optical properties and aptemer’s high specificrecognition ability, we developed a simple, sensitive and specific method for detection ofAdenosine triphosphate（ATP）. The aptamer of ATP was split into two fragments. One wasmodified onto the UCNPs, and another was labeled with the quenching molecule BHQ1. Inthe absence of ATP, the UCNPs’ fluorescence emission at550nm was detected with theexcitatation of980nm laser. In the presence of ATP, the UCNPs’ emission was quenched byBHQ1due to the specific binding of the two split aptamer fragments. The effective ATP assaycould be achieved by measuring the fluorescence intensity of UCNPs. The linear responserange was2μM¹6μM, and the detection limit was1.70μM.3. Detection of mercury ion based on UCNPs fluorescence and magneticnanoparticles-mediated separation techniqueThrough the combination of UCNPs’ unique optical properties and the magneticnanoparticles （Mag NPs）-mediated separation technique, we developed a simple, sensitiveand specific method for detection of mercury ion based on the formation of specific and stable“T-Hg²⁺-T” structure. Three DNA sequences, S1, S2and S3, were designed, and S1could behybridized with S2and S3in the presence of Hg²⁺. S2and S3were modified onto UCNPs andMag NPs, respectively. In the absence of Hg²⁺, S1could not hybridize with S2and S3, andtherefore UCNPs were not conbined with Mag NPs, thus leading to no fluorescence wasdetected after magnetic separation. However, in the presence of Hg²⁺, the hybridization of S1with S2and S3occurred through “T-Hg²⁺-T” interaction, thus leading to the attachment of UCNPs with Mag NPs and a strong fluorescence was observed after magnetic separation. Theeffective Hg²⁺assay could be achieved by measuring the fluorescence intensity of UCNPs.The linear response range was30nM¹00nM, and the detection limit was24.1nM. Thismethod is expected to be used to detect other heavy metal ions.