Construction Of Label-free Rare-earth Upconversion Nanoparticle-based Probes And Their Applications In Bioanalysis

Rare-earth upconversion luminescence is a process in which high-energy short-wave photons are emitted by absorbing multiple low-energy long-wave photons based on the rich electron-level structure in rare-earth ions.The lanthanide-doped upconversion luminescent nanomaterials have attracted much attention from researchers due to their large anti-Stokes shift,long luminescence lifetime,and the absence of autofluorescence under low energy near-infrared?NIR?excitation.The many properties of rare-earth upconversion luminescent nanomaterials determine their application in many fields,such as solar energy conversion,nanoprinting,NIR light security,as well as biosensing and imaging.In this dissertation,the upconversion luminescence of the rare-earth ion f-f transition process is used as the detection signal to carry out its application research in the field of biosensing and imaging.Due to their good biocompatibility and the unique optical frequency upconversion capability of NIR light,they are likely to achieve high detection sensitivity in biological systems.However,in most cases,the luminescence of upconversion nanomaterials are not directly related to biochemical properties of the system.Therefore,in order to achieve highly selective detection or imaging of the target in the biochemical identification process?the basic process in chemical sensing?,the upconversion nanomaterials must be used in conjunction with suitable recognition units such as organic dye.In this dissertation,we have combined recognition units such as organic dye and metal organic complexes with upconversion nanoparticles?UCNPs?to design a series of novel upconversion nanosensing platforms.The upconversion luminescence was used as the detection signal to carry out the biosensing and imaging research of target analytes.The main contents are as follows:Chapter 1.IntroductionThe introduction mainly summarizes the general introduction of upconversion luminescence materials?including the energy transfer mechanism,chemical composition of such materials?,luminescence mechanism,the most widely used synthetic pathways,strategies for constructing luminescence sensors,biosensing and detection of different analytes,as well as current problems and future trends.Finally,the research significance and prospects of our work are summarized.Chapter 2.Label-free upconversion nanoparticles-based luminescent probes for sequential sensing of Cu²⁺,pyrophosphate and alkaline phosphatase activityIn this work,an efficient NIR luminescence probe has been developed for the sequential detection of Cu²⁺,pyrophosphate(P₂O₇^4-,PPi),and alkaline phosphatase?ALP?,which is based on the"off-on-off"luminescence switch of branched polyethyleneimine?PEI?-capped NaGdF₄:Yb/Tm UCNPs.The luminescence is quenched via energy transfer from UCNPs to Cu²⁺for the coordination of PEI with Cu²⁺.The strong affinity between Cu²⁺and PPi leads to the formation of Cu²⁺-PPi complex and results in the detachment of Cu²⁺from the surface of UCNPs,thus the luminescence is triggered on.ALP-directed hydrolysis of PPi causes the disassembly of Cu²⁺-PPi complex and re-conjugation between Cu²⁺with PEI,which leads to the switch-off luminescence of UCNPs.The system allows sequential analysis of Cu²⁺,PPi,and ALP by modulating the switch of the luminescence of UCNPs with detection limits of 57.8 nM,184 nM,and 0.019 U/mL for Cu²⁺,PPi,and ALP,respectively.By virtue of the NIR feature and excellent biocompatibility,the UCNPs-based probes are suitable for bioimaging.Taking Cu²⁺visualization as a model,the nanoprobes have been successfully applied for intracellular imaging of Cu²⁺in living cells.Chapter 3.Upconversion nanoparticles-MoS₂ nanoassembly as a luminescent turn-on probe for bioimaging of reactive oxygen species in living cells and zebrafishNanoassemblies for bioimaging in living cells have attracted much attention.In this work,an efficient and sensitive turn-on luminescent detection platform for reactive oxygen species?ROS?in living cells has been constructed using the nanoassemblies of UCNPs-MoS₂ nanoflakes.In this nanostructure,the positively charged UCNPs could assemble with negatively charged poly?acrylic acid?modified MoS₂ nanoflakes by electrostatic force,which led to the remarkable luminescence quenching of UCNPs owing to the excellent quenching ability of MoS₂ nanoflakes.In contrast,in the presence of ROS,the luminescence recovery of UCNPs is successfully realized owing to the decomposition of MoS₂ nanoflakes through the chemical reaction with ROS.The ROS-mediated disassembly of the nanoarchitecture display excellent luminescent response toward ROS.Furthermore,the disassembly of UCNPs-MoS₂ nanoflakes has been successfully used for ROS bioimaging in cells and zebrafish.Chapter 4.Cationic cyanine chromophore-assembled upconversion nanoparticles for sensing and imaging H₂S in living cells and zebrafishElevated hydrogen sulfide?H₂S?level is closely associated with various diseases.So the sensing of H₂S is noteworthy for divulging its role in diagnosing these diseases.Herein,we proposed poly?acrylic acid?-modified UCNPs assembled with cationic NIR cyanine chromophores?Cy7-Cl?as the nanoprobe?Cy7-UCNPs?based on thiolation reactions for monitoring H₂S.The presence of H₂S can cause a 4.8-fold enhancement in the luminescence intensity of Cy7-UCNPs and showed a good linear dependence?R²=0.9952?over the range of H₂S?1.0–90?M?.The probe possessed many excellent properties including high sensitivity,good selectivity,and low cytotoxicity.Furthermore,Cy7-UCNPs was successfully employed in sensing and imaging of exogenous and endogenous H₂S in live cells and zebrafish.Chapter 5.A turn-on ratiometric upconversion luminescent probe for detection of ascorbic acid based on inner filter effectIn this study,we developed a nanosensing system based on the inner filter effect?IFE?between UCNPs and squaric acid-iron?III?chelate[SA-Fe?III?]for high sensitivity and selective detection of ascorbic acid?AA?.In this system,Fe?III?can chelate with SA to form SA-Fe?III?quickly?<1 min?.The absorption band of SA-Fe?III??400-750 nm?largely covers the blue emission band at 400-500 nm of UCNPs,resulting in the effective quenching of luminescence in this range.When AA reduced Fe?III?to Fe?II?,the blue light emission of UCNPs at 400-500 nm increased significantly,while the luminescence at 800 nm remains unchanged.Therefore,accurate and sensitive detection of AA can be achieved by constructing a ratiometric probe based on the formation of SA-Fe?III?.Under the optimal conditions,I₄₇₄/I₈₀₀exhibited a good linear response to AA with a concentration range of 3-150?M and a detection limit of 0.71?M.In addition,the system has been successfully used for the detection of AA in real samples.