Fabricate The Luminescence Resonance Energy Transfer Biosensor Based On Upconversion Nanoparticles As Energy Donor/Acceptor

Upconversion Nanoparticles（UCNPs）are kinds of luminescent materials of lanthanide-ion doping with anti-Stokes emission.The characteristics of near-infrared excitation effectively reduce the interference of autofluorescence and scattered light in biological samples.At the same time,UCNPs can avoid co-excitation with other luminescent materials due to the feature of near-infrared excitation,so UCNPs are often used in luminescence resonance energy transfer（LRET）as energy donors.So far,most of the biosensors based on UCNPs have been constructed via LRET,in which the luminescence undergoes the process from quenching to recover.In these circumstances,the signal enhancement factor（SEF）of the detection depends on LRET efficiency.Although some methods have been proposed to improve the LRET efficiency,the highest efficiency of LRET reported currently is around 90%,which is difficult to be further improved.Therefore,it is urgent to find a new principle to fabricate upconversion sensor to extend the application of UCNPs in bioassay without the limitation of LRET efficiency.Dye-sensitized upconversion can effectively enhance upconversion luminescence through expending the light absorption capacity of UCNPs.There has a work concentrated on utilizing the dye as the recognition unit and sensitization switch of upconversion probe,geting rid of the dependence on LRET efficiency and breaking the limitation of SEF.However,most of the near-infrared dyes have some drawbacks such as low quantum yield,small Stokes shift,and poor water solubility.It is challenged to select and prepare a near-infrared dye as sensitizer.Therefore,two progressive strategies are proposed to fabricate LRET biosensors based on UCNPs in this dissertation:1)Ultilize polydopamine coated UCNPs（UCNPs@PDA）as energy donor and aptamer stabilized gold nanoparticles（AuNPs）as energy donor for bioassay.2)Use UCNPs as energy acceptors,semiconductor quantum dots（QDs）as sensitizers for UCNPs,and targets as switching to fabricate the biosensor.The details are as follows:1.A biosensor for carcinoembryonic antigen（CEA）based on LRET from（NaYF₄:Yb,Tm）@PDA to AuNPs is constructed.The water solubility of UCNPs is achieved by coating PDA on oleic acid capped UCNPs via microemulsion method.The CEA aptamer is covalently coupled to the surface of AuNPs,therefore,the aptamer is adsorbed on the surface of UCNPs@PDA byπ-πstacking,which narrows the distance between energy donor and receptor and triggers LRET process.At this time,the fluorescence of UCNPs is quenched by AuNPs.In the presence of CEA,the conformation of the aptamer is changed,leaving AuNPs away from UCNPs@PDA and destroying the LRET effect,so that the quantitative detection of CEA can be achieved by the degree of fluorescence recovery.2.A biosensor for thrombin based on QDs-sensitized UCNPs is constructed.The PAA-modified NaYF₄:Yb,Er endows the covalently conjugate to the TBA1,which is the aptamer of thrombin.TBA2,another aptamer of thrombin,is modified on the glutathione-stabilized Ag₂Se QDs.In the presence of thrombin,Ag₂Se QDs were assembled with UCNPs due to the interaction of aptamer and thrombin,enabling the nonradiative energy transfer from Ag₂Se QDs to UCNPs.Thus,the concentration of thrombin can be determined by the luminescence enhancement in the buffer and diluted serum.