Energy Transfer And Single-molecule Nanoprobe Construction In Highly Doped Tb³⁺ Upconversion Nanoparticles

Lanthanide-doped upconversion nanoparticles?UCNPs?have proven to be a promising fluorescent probe material in bioimaging and bio-detection.In particular,constructing fluorescence nanoprobes based on single nanoparticle is of great research significance as it helps to reveal single molecule properties inaccessible by ensemble observations.However,on the one hand,the traditional low doping UCNPs have weak response of existing nanoparticles to functional molecules due to the relatively large distance between dopants;on the other hand,although the high doping UCNPs can accelerate the energy transfer rate by narrowing the distance between lanthanide ions,they tend to transfer the energy to the surface quenching sites,leading to deleterious concentration quenching.Therefore,designing the optimal UCNPs as energy donors and applying them to probe single-molecular target through particle-to-molecule interactions is still a daunting challenge.In this thesis,to overcome the above scientific problems,the Tb³⁺ions have been chosen as activators to develop a series of core-shell upconversion nanoparticles with different content of Tb³⁺activators.Then we take these nanoparticles as energy donors,together with the acceptor molecule BODIPY TMR carboxylic acid?BDP TMR?,and have explored the concentration quenching mechanism,energy transfer rate and efficiency systematically in a high doping condition.Following are the main research results:?1?The upconversion nanoparticles with uniform phase and adjustbale size were synthesized by hot-injection method.Through analyzing the variation of luminescence spectra and lifetime diagram in the methanol solution by controlling experimental variables,it was found that energy transfer efficiency showed a positive correlation with Tb³⁺doping concentration and BDP TMR loading quantity.It also showed that high Tb³⁺concentration nanoparticles-NaYbF₄:Tb?40 mol%?@NaTbF₄ could significantly improve spectral response to fluorescence molecular targets and more efficiently sensitize organic fluorophores.?2?The theoretical calculation in an experienced model was carried out.By setting up comparison group of traditional low doping upconversion nanoparticles-NaYF₄:Yb/Er?18,2 mol%?@NaYF₄,the energy transfer rate and efficiency of NaYbF₄:Tb?40 mol%?@NaTbF₄ were demonstrated.The results showed that this non-radiative energy in high doping UCNPs can transfer by a rate over an order of magnitude faster than conventional compositions,suppressing the phonon relaxation dissipation.Moreover,it also predicted that high Tb³⁺doped nanoparticle had greater ability to sensitize ultra-low quantity of loading molecules,even for single molecule.?3?Single high Tb³⁺concentration doped nanoparticle was adopted as an effective nanoprobe to track single molecule dynamic decay process from a perspective of single-particle spectroscopy.Firstly,the single NaYbF₄:Tb?40 mol%?@NaTbF₄-BDP TMR nanoprobe was constructed,then the fluorescence of BDP TMR was detected by the confocal microscope.After that,a molecule counting method was raised by adjusting the loading concentration on a single nanoparticle in terms of photobleaching mechanism.Then,based on this method,we explored the decay kinetics of attached molecule to track molecular photoreaction dynamics in complex systems.This design provides an unprecedented opportunity to generate versatile single-molecule nanoprobes and paves a way for wider application.