Biosensing Technology Based On The Upconversion Fluorescence For The Detection Of Exosomes And Glutathione

Nowdays,as one kind of excellent luminescent materials,the rare earth doped upconversion nanoparticles(UCNPs)have attracted most attention and have been made great advances in various fields.Compared with organic dyes,semiconductor quantum dots,UCNPs have the intermediate state of real and continuous excitation process,which can make longwave radiation(such as NIR or IR)convert into shorter wavelengths(such as ultraviolet or visible light),as called a kind of anti-Stokes process.Because of this unique luminescent process,the UCNPs have superior optical properties such as sharp absorption and emission,long lifetime,excellent light stability,low background without autofluorescence etc.According to the characteristics of upconversion luminescence,we have designed different sensing strategies for exosome and L-glutathione detection.Then,according to the actual situation of luminescence properties,the core-shell structure of UCNPs has been improved optimally.In Chapter 1,a new technique based on fluorescence resonance energy transfer(FRET)of UCNPs was developed for the detection of the exosomes.With the presence of exosomes,due to the FRET between UCNPs and gold nanorods(Au NRs),the upconversion luminescence(UCL)of UCNPs was quenched,so the exosomes was quantified by the relationship between the quantities of exosomes and the degree of luminescence quenching.Under the optimum conditions,the linear range of the sensor is 1×104 ~ 1×108 particles/μL and the detection limit of exosomes is 1.1?103particles/μL.This kind of technique avoids the disadvantage that the UCNPs is not conducive to the biological detection in a heterogeneous system.Because of the detection on the solid interface,the superior performance of UCNPs has been broughtinto full application.In chapter 2,a UCL-based weak light detector was built for the dectcetion of the UCL of UCNPs.And on this basis,a simple sensor based on the FRET between UCNPs and MnO2 nanosheet for the GSH detection has been constructed in this paper.Because the UCNPs are likely to accumulate on the surface of MnO2 nanosheet,so the UCL of UCNPs will quench after MnO2 is added into UCNPs aqueous system.Actually,L-glutathione can reduce MnO2 into Mn2+ quickly,which causes to release UCNPs and make the UCL recover.Under the optimum conditions,the detection range is 0.5~100 μM and the LOD is 0.24 μM.In chapter 3,the core-shell UCNPs(NaYF4: Yb,Er,Nd@NaYF4: Nd)was synthesized by thermal decomposition with the rare earth stearate as precursor,which can be excited by the 808 nm infrared light.It avoids the absorption of water to the excitation light,so such as core-shell UCNPs can be better applied to the biological fields.And the influence of feed ratios and reaction time on the morphology of nanoparticles,core-shell thickness and the luminescence intensity has been studied carefully.