The Effects Of Water-soluble CdTe QDs With Different Structures On The Physiological Function Of Mitochondria

Nowadays quantum dots(QDs)have been widely applied in biological and medicine area due to their unique optical properties.Meanwhile,the bio-safety of the QDs has attracted more and more attention.However,previous studies of the toxicity of QDs mostly focused on the level of animals,cells and biomolecules,and the study of the effects of QDs on sub-cellular level has rarely been reported.The cytotoxicity study of QDs have shown QDs can induce oxidative stress and the decrease of mitochondrial membrane potential.Mitochondria may be the targeted organelles for QDs-induced toxicity.Thus,it is of great significance to study the effects of QDs on the physiological function of isolated mitochondria,and it will be helpful for the comprehensive understanding of the toxicity of QDs.In biological systems,the uptake,transportation and clearance mechanism of QDs with different structure by cells may be different.Thus,they may show different biological effects.In this thesis,the impacts of the structure of QDs on their bioeffect were systematically studied at isolated mitochondria level using QDs with different sizes,surface ligands and charges.This thesis consists of six chapters.Chapter 1:This portion introduced a comprehensive overview of bioconjugate,biological application progress and bioeffect of QDs.A simple introduction of the relationship between mitochondria and cell death was also included in this part.Chapter 2:Water-soluble CdTe QDs with different sizes,surface ligands and charges were prepared by an aqueous synthesis method.The QDs were then characterized by UV-vis absorption spectroscopy,photoluminescence spectroscopy,infrared spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy and transmission electron microscope.The hydrodynamic size and ζ potential of QDs were also tested.Chapter 3:The effects of CdTe modified with thioglycollic acid(TGA)and mercaptopropionic acid(MPA)on mitochondrial respiration,membrane lipid peroxidation,swelling,inner membrane permeability to H+ and K+,membrane potential and fluidity were firstly studied.It was found that these two types of QDs could impair the physiological function of mitochondria.The two QDs could induce the inhibition of mitochondrial respiration,the swelling of mitochondria,the reducing of membrane potential,the increase of membrane fluidity and the opening of mitochondrial permeability transition(MPT)pore.Then the effects of the two QDs on mitochondrial functions were compared.The results demonstrated that MPA-CdTe QDs had a stronger effect on mitochondrial MPT than TGA-CdTe QDs,resulting in their higher toxicity to mitochondria.Later,the reason of their different effects on MPT were explored by studying the effects of ligands on mitochondrial swelling,the mitochondrial uptake of QDs,the mechanism of QDs-induced MPT as well as the releasing Cd2+ of QDs.The results showed the stronger effect of MPA-CdTe QDs on MPT was owing to their more remarkable release of Cd2+.The reason why MPA-CdTe released more Cd2+ was also analyzed by the discussion how ligands affected the structure and properties of QDs.Chapter 4:The effects of MPA-CdTe with three different sizes on mitochondrial respiration,membrane lipid peroxidation,swelling,inner membrane permeability to H+and K+,membrane potential and fluidity were firstly studied.It was found that QDs with these three different sizes could induce the inhibition of mitochondrial respiration,the swelling of mitochondria,the reducing of membrane potential,the increase of membrane fluidity and the opening of MPT pore.Then the effects of the three QDs on mitochondrial functions were compared.The results demonstrated QDs with bigger size had a stronger effect on MPT.Later,the reason of their different effects on MPT were explored by studying the mechanism of QDs-induced MPT as well as the releasing Cd2+of QDs.The results showed the stronger effect of QDs with bigger size on MPT was due to their more releasing of Cd2+.Chapter 5:The effects of three different surface charged QDs,mercaptoethylamine-CdTe(MEA-CdTe)QDs,L-Cysteine-CdTe(L-Cys-CdTe)QDs and thioglycolic acid-CdTe(TGA-CdTe)QDs,on mitochondrial respiration,membrane lipid peroxidation,swelling,inner membrane permeability to H+ and K+,membrane potential and fluidity were firstly studied.It was found all the three QDs could induce the inhibition of mitochondrial respiration,the swelling of mitochondria,the reducing of membrane potential,the change of membrane fluidity and the opening of MPT pore.Then the effects of the three QDs on mitochondrial functions were compared.The results showed all the three QDs could induce MPT,while they induce MPT in a quite different way.MEA-CdTe QDs and L-Cys-CdTe QDs showed similar effects on mitochondrial swelling and membrane potential,while TGA-CdTe QDs showed bigger effects.MEA-CdTe QDs could decrease the membrane fluidity,and L-Cys-CdTe QDs showed little effects on membrane fluidity,while TGA-CdTe QDs could increase the membrane fluidity.Later,the reason of their different effects on MPT were explored by studying the mechanism of QDs-induced MPT as well as the releasing Cd2+ of QDs.The results showed the effects of QDs with different surface charges on MPT was not only related to their ability of releasing Cd2+ but also their impacts on membrane proteins.Chapter 6:This portion gave a summary and discussion of the thesis as well as the outlook of the methods for the assessment of biological toxicity of QDs.