Preparation Of NaYF₄:Yb,Er Upconversion Nanophosphors And The Application Of Fluorescence Sensors

Rare-earth doped up-conversion nanoparticles?UCNPs?is a novel material.UCNPs uses near-infrared light as excitation light and emits short-wavelength light.They have many advantages,such as high photochemical stability,good luminescence,and low background interference.Therefore,they are widely used in various fields.However,it is still a challenging issue to synthesize the UCNPs of high quality,pure phase and high fluorescence intensity.It needs constant exploration and summary.On the other hand,UCNPs can construct the highly sensitive fluorescence biosensors to detect the traces of small molecule compounds such as disease markers,environmental residues,by fluorescence resonance energy transfer?FRET?.It is also an important application of rare earth upconverting luminescent nanomaterials.In this dissertation,the preparation conditions of NaYF₄:Yb,Er?NaYF?based upconversion luminescent nanomaterials were explored,and the controllable preparation of these UCNPs was initially achieved.Based on the principle of fluorescence resonance energy transfer?FRET?,three high-sensitivity fluorescence sensors were constructed,which can be applied to the quantitative detection of trace amounts of glucose,cholesterol and coumarin,respectively,in complex systems.First,this paper adopts hydrothermal method to prepare NaYF,a rare earth upconversion luminescent nanomaterial.Orthogonal experimental system was used to investigate the effect of rare earth ion addition amount,reaction temperature and reaction time,as well as the ratio of additive,oleic acid and sodium oleate on the fluorescence properties,morphology,and phase of the material.It was found that higher fluorescence intensity can be obtained by increasing the reaction temperature,prolonging the reaction time,and increasing the content of F-.On the other hand,ordinary fluorescence spectrophotometers only have UV-visible light sources,but no near-infrared light sources.It is inconvenient to transform the instrument for upconversion material research.In order to increase the utilization of general fluorescence spectrophotometers and expand its application range,we have designed portable high-power lasers that can be commonly used in various types of fluorescence spectrophotometers,and can increase multiple wavelengths and more without any changes to the instrument.Second,the prepared NaYF nanoparticles was using for detection of trace glucose by a fluorescence resonance energy transfer?FRET?system.In this system,fluorescence resonance energy transfer occur when AuNPs-CS,as an energy accepter was added into NaYF-conA,as an energy donor.When FRET occurring,the AuNPs-CS quenches the NaYF fluorescence and the system switched to the“off”state.ConA and glucose has stronger binding energy than conA and CS.Therefore,when addding glucose to the NaYF-conA-CS-AuNPs system,the AuNPs-CS was removed from the NaYF-con A and the fluorescence of NaYF is recovered.The glucose content can be determined by measuring the fluorescence intensity.The detection limit of this method was 0.02?mol/L,and the concentration of glucose detected was in the range of 0.4-1.87?mol/L?R=0.98,n=7?.This method can be detected in serum samples.Third,the cholesterol level was determined on fluorescence resonance energy transfer between NaYF-Cit-?-CD and Rh6G.When FRET occurs,the fluorescence of NaYF is quenched by Rh6G and the system switched to the“off”state.Cholesterol and?-CD have strong binding sites.When cholesterol is added to theNaYF-Cit-?-CD-Rh6G system,Rh6G is removed from NaYF-Cit-?-CD,and NaYF fluorescence is recovered.The level of cholesterol can be determined by measuring the fluorescence intensity of the system.The detection limit of the method was 0.21?mol/L.The cholesterol detection curve was F=59.36c+310.The linear range was 0.25-9?mol/L?R=0.99,n=10?.Fourth,a new method for detecting the content of coumarin in cosmetics was proposed.The coumarin level was determined by fluorescence resonance energy transfer between NaYF-Cit-?-CD and Rh6G.The linear concentration range of coumarin was 2.5-32.5?mol/L.The working curve was?F=17.843c-47.44?R=0.98,n=5?.The detection limit was 0.74?mol/L.