Construction Of ZnCdS And CdTeS Quantum Dots Based Fluorescent Probe And Their Application In The Detection Of Biological Molecules

As an important part of the organism,active biological molecules participate in a variety of biological metabolism and life processes of the body,and their concentration levels are closely related to human health.Therefore,It has become one of the research hot-spots to realize the effective monitoring of the concentration level of active biological molecules.Based on the excellent optical properties of quantum dots（QDs）,QDs-based fluorescent probes show great application potential in the field of active biological molecules detection.In this dissertation,a series of studies were carried out on synthesis methods and property modulation of ternary QDs,probe construction,and detection of active biological molecules.The main research contents are as follows:（1）The ternary ZnCdS QDs（ZnCdS only means that the ternary quantum dot is composed of Zn,Cdand S elements）were synthesized by the water-phase refluxing method,and and the controlled tuning of their optical properties was achieved by changing the Zn/Cdmolar ratio.Since Cu²⁺can undergo ion-exchange reaction with metal ions on the surface of QDs,the fluorescence emission of ZnCdS QDs was effectively inhibited under the mediation of Cu²⁺.Meanwhile,considering that the active biological molecule glutathione（GSH）can form a 2:1 chelate with Cu²⁺,the fluorescence emission of ZnCdS QDs will be restored when the GSH was added to the mixed system of ZnCdS QDs and Cu²⁺(ZnCdS QDs/Cu²⁺).A Cu²⁺mediated ZnCdS QDs-based"off-on"fluorescent probe was constructed for the quantitative detection of GSH based on the variation of the fluorescence intensity of ZnCdS QDs.The variation of fluorescence intensity at the maximum emission wavelength（F₂/F₁）of the ZnCdS QDs/Cu²⁺system was used as the detection signal,there was a good linear relationship between F₂/F₁and the GSH concentration in the range of 5～1500μM with the linear correlation coefficient R²of 0.991,and the detection limit could reach 3.64μM.The experimental results showed that the constructed ZnCdS QDs-based fluorescent probes have high sensitivity and selectivity for GSH.（2）A two-step aqueous phase method was performed to synthesis ternary CdTeS QDs（CdTeS only means that the ternary quantum dot is composed of Cd,Teand S elements）,and the fluorescence emission of CdTeS QDs could be tuned to the near-infrared region by increasing the molar ratio of Te/S.Under suitable conditions,the fluorescence emission spectra of CdTeS QDs overlap with the absorption spectra of noble metal Ag nanoparticles（Ag NPs）,satisfying the conditions for the occurrence of the internal filtration effect（IFE）.While in the presence of L-cysteine（L-cys）,it is possible for L-cys to combine with Ag NPs in the complex system to disrupt the onset of the IFE,resulting in the changes of the fluorescence properties of CdTeS QDs.Similarly,the change in fluorescence intensity（F/F₀）of the CdTeS QDs/Ag NPs system before and after the action of L-cys was used as the detection signal,and linear fitting was performed with the concentration of L-cys.It showed a good linear relationship in the concentration range of 20～400μM with the linear correlation coefficient R²and detection limit of 0.994 and 0.025μM,respectively,and the constructed Ag NPs and CdTeS QDs-based fluorescent probe exhibited high selective for L-cys.（3）The core-shell type CdTeS QDs@Si O₂nanoparticles were obtained by wrapping silicon dioxide（Si O₂）on the surface of CdTeS QDs as the core material.The results showed that the Si O₂coating not only did not change the optical properties and crystal form of CdTeS QDs,but also increased the specific surface area of the nanoparticles to provide more active sites for the recognition of folic acid（FA）.Therefore,CdTeS QDs@Si O₂was used as a fluorescent probe,and the intrinsic fluorescence emission of the probe was quenched in the presence of FA,while the fluorescence emission center of FA itself appeared at 445 nm.The intensity ratio(F₄₄₅/F₆₈₀)of the CdTeS QDs@Si O₂（680 nm）and FA（445 nm）at the emission centers was used as the detection signal to realize the visual and selective detection of FA.The detection range was 5～80μM,and the detection limit was 0.3μM.（4）As an artificial receptor,molecularly imprinted polymers have specific recognition sites matching the template molecules on their surface.On the basis of this,ZnCdS QDs-based molecularly imprinted polymers（ZnCdS QDs@MIP）were synthesized with active biological molecule ascorbic acid（AA）as the template molecule,and the specific recognition cavity of AA existed on the surface of the synthesized ZnCdS QDs@MIP.In addition,in order to reduce the influence of probe concentration,instrument equipment,test temperature and other factors on the test results,ZnCdS QDs@MIP was combined with a small amount of CdTeS QDs@Si O₂to construct a ratiometric fluorescent probe for detecting AA.Among them,the emission peaks of ZnCdS QDs@MIP and CdTeS QDs@Si O₂were used as the response signal and reference signal,respectively,and the fluorescence intensity ratio(F₅₃₀/F₇₀₅)was used as the detection signal to achieve the quantitative analysis of AA.The fluorescent probe was used to detect the AA content in the commercially available vitamin C tablets and satisfactory results were obtained.The fluorescent probe is expected to be used in medical fields such as drug supervision.