Low Power Super-resolution Imaging Based On Saturated Luminescence Characteristics Of Upconversion Rare Earth Nanoparticles

Optical microscope is an indispensable tool in many fields such as modern medicines and molecular biology.However,the resolution of the confocal microscope can only reach 200-300nm in the visible light range due to the diffraction limit.This means that small molecules such as proteins or other features smaller than this range cannot be resolved.Since the 20th century,researchers have developed different kinds of super-resolution far-field fluorescence microscopy techniques to break the diffraction limit which can be divided into two major categories in principle.one of which is based on point spread function(PSF)regulation engineering,and the other is stochastic optical reconstruction technology.The concept of stimulated emission depletion microscopy(STED)was put forward by Professor Stefan W Hell in 1994 and realized for the first time in 1999.In the past few decades,STED technology has achieved great development in different dimensions,such as:high imaging speed,high imaging resolution,three-dimensional imaging,etc.However,a relatively high light intensity is required to obtain a high resolution in the ordinary STED technology,usually on the order of GW/cm².Intense laser power is likely to cause problems such as bleaching of fluorescent dyes and phototoxicity,which hinders the application of the STED in living organism imaging.Upconversion nanoparticles(UCNPs)are a new kind of multiphoton nanoprobe developed rapidly in recent years.UCNPs have the advantages of narrow emission spectrum,high chemical stability and photobleaching and large anti-Stokes spectral separation between excitation and emission spectra.Different from other multiphoton processes,UCNPs have many intermediate excited states which can absorb low-energy photons and convert them into high-energy photons.This makes the pump intensity of the rare-earth-doped upconversion nanocrystals several orders of magnitude lower than that of the traditional nonlinear optical technology.In order to further simplify the experimental system of the traditional STED technology and reduce the saturation power of the upconversion rare earth nanomaterials.In this paper,Yb³⁺/Tm³⁺/Tb³⁺-doped upconversion nanoparticles are combined with a 980 nm laser to demonstrated the ultra-low-power super-resolution microscopy imaging of a single-beam imaging system.Here are my creative jobs:1.Characterizations of upconversion emission from NaYF₄:Yb³⁺/Tm³⁺/Tb³⁺/Y nanoparticles were carried out systematically.It is experimentally verified that the higher the concentration of doped Tb³⁺ions,the greater the impact on the saturation characteristics of Tm³⁺ions,the lower saturation light intensity of the co-doped Tm³⁺ions can be achieved.Finally,the saturation light intensity is reduced to 0.04 MW/cm².The saturation power is reduced by about one order of magnitude compared with nanoparticles that undoped Tb³⁺ion.2.The energy level transition of rare earth ions is used to establish a kinetic model to solve the energy level rate equation and simulate the saturation emission characteristics.The simulation reveals the low-power saturation emission characteristics of upconversion nanoparticles theoretically.It shows that doping with Tb³⁺ions in the upconversion nanoparticles can further reduce the saturation emission intensity of the upconversion nanoparticles,which means that higher resolution can be obtained at lower power after Tb³⁺doped.3.A single-beam super-resolution imaging system based on saturation characteristics was built.980 nm continuous laser was used as the excitation light,a single-beam super-resolution microscopy experiment was performed on different doped up-conversion nanoparticles.Finally,the full width at half maximum of the vortex hollow spot reaches 32 nm when the excitation power of the 980 nm laser was 15 mw.