A Study On The Preparation Of Upconversion Nanoparticles And The Application In Rapid Toxin Detection

Upconversion nanoparticles (UCNPs) are a new type of fluorescent materials capable of converting a long-wavelength radiation to a short-wavelength radiation through the two-photon or multi-photon mechanism. UCNPs give off anti-Stocks emissions and mostly belong to rare-earth doped inorganic materials. Excited by a980nm-infrared light, UCNPs can emit visible lights of different colors.Compared with conventional fluorophores and underconversion nanoparticles, UCNPs have a number of unique features. The important advantages of UCNPs include high-brightness fluorescence, narrow emission peaks, large anti-Stocks shifts, good chemical stability, high sensitivity for detection, no spontaneous upconversion fluorescence in organisms, and no photobleaching problem. UCNPs are thus a class of ideal fluorescence probes. In recent years, UCNPs have attracted the domestic and foreign widespread attentions because of their superior characteristics. UCNPs have found a wide range of applications in biology, clinical medicine, drug screening, food safety, and environment monitoring, especially in biological and biological analyses.In this thesis work, different methods were used to prepare two types of UCNPs, NaYF4:Yb, Er and Y2O3:Yb, Er, and the NaYF4:Yb, Er UCNPs was used to establish a fluorescence resonance energy transfer (FRET) immunoassay for detection of Staphylococcus enterotoxin B (SEB). Such a sensitive, specific and simple method for toxin detection was deveolped to overcome the limitations of existing approaches. The main contents of this thesis include:1. A review on the preparation methods, lumicescence mechanisms, and applications of UCNPs, including the applications in FRET.2. Coprecipitation and hydrothermal methods were chosen to prepare the NaYF4:Yb,Er UCNPs and optimize the experimental conditions for hydrothermal methods. The optimal preparation conditions were chosen through investigating the effects of solution pH, complexing agent, and concerntrations of Yb3+and Er3+. The NaYF4:Yb, Er UCNPs was characterized by Fluoscence Spectroscopy (FL), X-ray diffraction (XRD), Infrared Absorption Spectroscopy(IR), Scanning Electron Microscpe (SEM) and Transmission Electron Microscopy (TEM).3. A FRET immunoassay was developed for detection of SEB based on UCNPs. In the FRET system, anti-SEB antibody-conjugated NaYF4:Yb, Er UCNPs was used as energy donor, and SEB-conjugated gold nanoparticles (AuNPs) as energy accepter. The AuNPs were prepared using sodium citrate as a reducing agent. The energy transfer process was succesfully achived through specific bindings of SEB antigens and antibodies. Detection of SEB was performed in both borete buffer solution and milk. The lowest detection limit obtained in the borate buffer solution was0.01ng/mL, the detection range is0.01-500ng/mL, and the reaction time was2h. The sample matrix of milk did not interfere with the detection of SEB, also showing a detectable limit of0.01ng/mL4.A corprecipition method was used to prepare Y2O3:Yb, Er UCNPs. Through changing the molar ratio of Yb3+and Er3+UCNPs emitting strong fluorescence of different colors were obtained. The experimental conditions were optimized. The Y2O3:Yb, Er precursor and/or UCNPs were characterized by FL, IR, thermogravimetry (TG), differential thermal analysis (DTA), XRD, SEM and TEM. In addition, a wettability study revealed a super hydrophilicity for the Y2O3:Yb, Er UCNPs.