Controllable Preparation Of New-type Of Highly Hydrophilic Quantum Dots And Its Fluorescent Biological Detection Application

Quantum dots(QDs)are affected by their own quantum effects due to their particle size in the nanometer range[1-3],which will produce excellent properties that many macroscopic materials don't have,such as:wide excitation peak and narrow emission peak,which can realize single-element excitation and multiple-element emission;fluorescence emission wavelength can be changed with the change of its particle size and composition;high fluorescence intensity,strong light drift resistance and so on.These excellent optical properties have promoted quantum dots to show great application value in fields such as energy,electronic display,and biomedicine in just a dozen years.With the continuous improvement and maturity of quantum dots in synthesis,surface modification and biological functionalization,more and more quantum dots with good biocompatibility have taken up a place in the field of fluorescent biological applications.In this paper,we have conducted an in-depth study on the controllable preparation of two new types of highly hydrophilic quantum dots that have developed rapidly in recent years and the corresponding biological detection applications.The main content ideas are as follows:1.As a new type of semiconductor nanomaterials,perovskite quantum dots(CsPbBr3 QDs)have the advantages of excellent photoelectric properties and high fluorescence quantum yield.They have been widely used in the fields of optics and optoelectronics.However,CsPbBr3 QDs are very sensitive to water,oxygen,light and heat,resulting in poor stability,which further limits its application in the biological field.In order to improve the hydrophilicity and water stability of CsPbBr3 QDs,a simple "one-pot method" ligand modification strategy is adopted in this paper.After adding L-type combinatorial ligands(OAM and OPA)to the precursor,its fluorescence performance is comparable to that of water.The stability and hydrophilicity have been significantly improved,and then the reaction conditions such as the proportion of ligand input(the quality of OPA input)and temperature have been optimized to prepare OPA/OAM CsPbBr3 QDs with excellent fluorescence performance and good water stability..In addition,this experiment explored and optimized its fluorescence performance in cell buffer,which laid a good foundation for its application in biological systems.However,the fluorescence emission wavelength of OPA/OAM CsPbBr3QDs is located in the visible light region,and it is difficult to adjust to the near-infrared region.This limits its application to complex sample detection and biological imaging to a certain extent.Therefore,we will focus on the near-infrared fluorescence in the following text.In-depth research on quantum dots.2.Near-infrared(NIR)fluorescent quantum dots have excellent optical properties,high tissue penetration,low autofluorescence background and low tissue scattering.They are very promising in biomedical applications.However,near-infrared quantum dots are currently facing fluorescence The quantum yield is low and the synthesis method is complicated.Ag2S QDs is a new type of quantum dots in the NIR region that has developed rapidly in recent years.It has the characteristics of narrow band gap,low toxicity,and adjustable emission in the NIR window.It has become an excellent candidate material for biological imaging and detection.However,due to the high mobility of Ag+in Ag2S nanocrystals,it is easy to cause lattice defects.In order to improve this shortcoming of Ag2S QDs,this paper adopts a simple"one-pot method" metal ion doping strategy to dope different metal cations in Ag2S QDs.Among them,Ag2S QDs doped with Pb2+ show the best fluorescence performance.The emission wavelength is adjustable in the range of 950-1200 nm,and the reaction time before and after doping is significantly shortened.Then,the influence of doping ratio on the crystal structure and fluorescence properties of the best product Pb2+ doped-Ag2S QDs is explored,and finally through a series of characterizations,It further shows that the "one-pot method"doping strategy realizes the simple,high-quality and low-energy synthesis of Ag2S QDs.The synthesis of high-quality NIR-? Pb2+ doped Ag2S QDs provides important support for biological detection applications.3.Based on the NIR-? Pb2+-doped Ag2S QDs prepared above,which has high hydrophilicity and good fluorescence stability,we constructed a hydrogen peroxide(H2O2)fluorescent biosensor in the NIR-? region.After H2O2 is catalyzed and decomposed by horseradish catalase(HRP),the product can oxidize tetramethylbenzidine(TMB)to produce the product TMB-Ox with maximum absorption at 650 nm,due to the maximum excitation wavelength of thepreparedNIR-? Pb2+ doped-Ag2S QDs is 650 nm,so there will be a fluorescence internal filtering effect between QDs and TMB-Ox,which causes the fluorescence of QDs to be quenched.Then,the analytical performance of the fluorescent biosensor was studied under the optimal reaction conditions.The experimental results show that the sensor has good anti-interference performance and stability,and the H2O2 concentration is in a linear relationship with the fluorescence recovery efficiency in the range of 40?800 ?M.The detection limit is 5 ?M.Further research shows that the H2O2 biosensor has good reliability and accuracy when used in actual sample detection.In addition,we found that the introduction of reduced GSH can restore the fluorescence performance of Pb2+ doped-Ag2S QDs.Based on this,we constructed an off-on GSH sensor.The results show that the off-on GSH sensor we constructed has good anti-interference performance and stability,and the fluorescence recovery efficiency has a linear relationship with the GSH concentration when the GSH concentration is 5-20 ?M.Finally,it was measured in human serum,which showed that the sensor has good accuracy when applied to actual samples.