Synthesis Of Rare Earth Doped Upconversion Nanomaterials And Their Sensing Applications

In this thesis,upconversion core-shell nanoparticles with uniform size and strong luminescence efficiency were prepared by a solvothermal method,and the epitaxial growth direction was controlled to achieve precisely controlled shapes of nanoparticles.Then the surface of the prepared hydrophobic nanoparticles was functionalized via silanization and amphiphilic polymer coating to transfer the nanoparticles to the aqueous phase.We further systematically investigated the optical properties of hydrophobic and hydrophilic nanoparticles.Hydrophilic upconversion nanoparticles(UCNPs)worked as energy donors,other materials as energy receptors,we have designed a variety of high-efficiency sensors based on inner filter effect(IFE)or fluorescence resonance energy transfer(FRET)mechanisms for the detection of disease-related molecules and ions.And the designed systems were successfully applied in the real samples.The specific research contents are listed as follows:1.The inert NaYF4 shell was introduced into the surface of NaYF4:Yb,Er core nanoparticles through solvothermal method.The epitaxial growth direction of the nanoparticles was controlled by adjusting various parameters in the shell growth process to obtain nanoparticles with ideal shape.2.A nanosensor for rapid and sensitive antioxidant capacity assay based on IFE of UCNP/KMnO4 was designed.The absorption band of KMnO4 overlaps well with the green emission bands of Er3+-doped UCNPs,which causes the upconversion green emission to be reduced.It is mainly based on fluorescence absorption of KMnO4.Antioxidant capacity assay in organisms is a means of assessing the balance between free oxygen radicals and antioxidant defense systems.In this strategy,upconversion fluorescence can recover after the addition of antioxidants due to the redox reaction between antioxidants and KMnO4,which reduces MnO4-to Mn2+.This UCNP/KMnO4 system provides a low detection limit,wide detection range and fast detection speed for quantitative antioxidant detection.The nanosystem is highly selective and sensitive to antioxidants compared to interference species at 10-fold higher concentration.Taking advantage of negligible autofluorescent background of UCNPs,the nanosystem has successfully applied to evaluating the antioxidant capacity in human plasma samples with satisfactory repeatability and specificity.The proposed method shows great potential for antioxidant-related diseases research and clinical diagnosis.3.Dual-functional nanosensors based on small molecule regulation can be widely used due to their simplicity,high sensitivity and selectivity.Herein,glutathione(GSH)calibrated dual-functional system for GSH and cadmium ions(Cd2+)detection based on FRET between NH2-NaYF4:Yb,Er/NaYF4@Si02 UCNPs and gold nanoparticles(AuNPs)was designed.Unmodified AuNPs are easy to aggregate in high-salt solution and thereby quenching the red emission of UCNPs.The presence of GSH prevent the aggregation of AuNPs,so GSH can be detected by the changes in the color of solution and the recovery of red emission of UCNPs.However,Cd2+ could interact with GSH,which makes AuNPs easy to aggregate,resulting in a gradual decrease in red emission of UCNPs.Under the optimized conditions,the fluorescence response of the system is linear with the concentrations of GSH and Cd2+ in a wide range of concentrations,with low detection limits of 0.016 μM and 0.059 μM,respectively.Furthermore,the proposed nanosensor demonstrates high selectivity for GSH and Cd2+ detection and can be applied for the detection of GSH in human plasma and Cd2+ in drinking water.