Studies On Preparation Of CdTe Quantum Dots And Their Interaction With Proteins

Quantum dots?QDs?are semiconductor nanocrystal with particle sizes ranging from1.5 to 12 nm,which composed of groups IIB-VIA or IIIA-VA of the Periodic Table of the Elements.By virtue of unique electrical and optical properties and good size-dependence,QDs have shown broad application prospects in the fields of biological imaging,photoelectrochemical sensors,and fluorescent probes.Since size effect,complex surface functional groups and Cd²⁺released,QDs can induce certain toxic effects in the bodies.The safety issues of QDs have limited their promotion and application.After QDs enter the bodies,they can interact with proteins and combine with the protein to form QDs-protein corona,which effects the structure and function of the protein and changes the surface properties of the QDs.And it affects absorption and toxicity of QDs in the cell.Therefore,the preparation of excellent QDs and the study of the interaction mechanism with protein are of great value and guiding significance to the deep understanding of the toxic mechanism of QDs and their application.In this paper,we first synthesized N-acetyl-L-cysteine?NAC?capped CdTe QDs and investigated the NAC-CdTe QDs and plasma protein fibrinogen?FIB?interaction to clarify the reaction mechanism between QDs and FIB.Subsequently,mouse hepatocytes cell were selected to study the toxic effects of QDs-FIB corona formation.Then we modified the NAC-CdTe QDs with Zn²⁺to improve the QDs'fluorescence performance and thermal stability.Furthermore,the interaction between the two prepared QDs and trypsin?TRY?was further studied.And the interaction mechanism between TRY and two QDs was compared and analyzed.The main research contents of this article are as follows:1.I used N-acetyl-L-cysteine?NAC?as a stabilizer to synthesize water-solubility NAC-CdTe QDs via a“one-pot”method.Different size of QDs was synthesized by different reflux reaction times.Finally,NAC-CdTe QDs with reflux time of 2 h were selected and their structures and optical properties were characterized by UV-visible absorbance spectrum,fluorescence spectrum,X-ray diffraction spectrum?XRD?and transmission electron microscope?TEM?.The results have shown that QDs at 2 h reflux time have better fluorescence performance and sphalerite crystal phase structure,exhibiting a uniform spherical shape.Particle size of QDs is about 3 nm.Then,the prepared QDs were used to study the mechanism of its interaction with fibrinogen?FIB?and the formation of QDs-protein coronas.These effect protein structure and the cytotoxicity.Studies have shown that the main binding forces of the interaction of QDs and FIB are van der Waals forces and hydrogen bonds.During the binding process,QDs cause changes in the secondary and tertiary structures of the FIB,and the protein backbone becomes loose and misfolded.QDs can reduce cell viability.After adding FIB to the system,FIB can form protein coronas with QDs reducing the toxicity of QDs.2.NAC-CdTe QDs were modified by doping Zn²⁺with“one-pot”method.NAC-CdTe:Zn²⁺QDs were successfully synthesized during the water phase.QDs are characterized by various spectroscopic methods,XRD,high-resolution transmission electron microscopy?HRTEM?,X-ray photoelectron spectroscopy?XPS?,thermogravimetric analysis?TA?,and so on.I obtained water-soluble QDs with different optical and different sizes by controlling the reflux time and Cd/Zn doping ratio.CdTe:Zn²⁺QDs,which synthesized under the conditions of doping ratio of Cd/Zn=10/1and reflux time of 2 h,had the highest fluorescence intensity and better quantum yield?QY?.Therefore,CdTe:Zn²⁺QDs under these conditions were selected as the following study objects.Comparing NAC-CdTe:Zn²⁺QDs with NAC-CdTe QDs,it is found that the QY and thermal stability of Zn-doped QDs are significantly improved and the original crystal phase of CdTe is not changed.Thereby the application range of semiconductor QDs can be expanded.3.The interactions between TRY with NAC-CdTe QDs and NAC-CdTe:Zn²⁺QDs were studied using ITC method,multiple spectrometry methods,enzyme activity detection methods.And the interaction mechanism were compared and analyzed.The results show that the binding reaction between QDs and TRY is a spontaneous process.The main forces of the CdTe:Zn²⁺QDs-TRY and CdTe QDs-TRY binding processes are Van der Waals forces and hydrogen bonds.There was also electrostatic force during the combination of QDs and TRY.The binding constant K of CdTe:Zn²⁺QDs with TRY is greater and the binding force is stronger.The addition of QDs results in the loosening of polypeptide chains of TRY.And the changes of the secondary and tertiary structure of TRY are not obvious.The interaction between the two kinds of QDs and TRY can make enzyme activity increased,but CdTe:Zn²⁺QDs have less effect on TRY activity.The above research helps to explain the interaction mechanism between QDs and proteins,and provides a new research strategy to study the formation of QDs-protein coronas and the effect of QDs on cytotoxicity.It provides a reference for developing QDs with better biocompatibility and reducing the toxicity of QDs.