Probing The Effects Of Different Charged CdTe Quantum Dots On Simulated Cell Membrane And Cell Internalization

In the past few decades,light-emitting semiconductor nanocrystals,also known as quantum dots(Quantum dots,QDs)have aroused widespread concern.Quantum dots have particle size controllability,high fluorescence quantum yield,superior light stability,long fluorescence lifetime and good biocompatibility.Which makes them widely used in biomedical imaging,drug delivery,solar power and electronics fields.As human have more and more opportunity to be accessible to quantum dots,the potential toxicity of quantum dots to human health and the environment has attracted more and more attention.Cell membrane is the first barrier of a living cell.It controls the material exchange of cells and creates a relatively stable environment for the various physiological activities within the cells.However,direct contact of quantum dots with cell membrane may cause cell damage.Therefore,the study of the interaction between cell membrane and quantum dots is important for understanding the cytotoxicity of quantum dots and subsequent cellular uptake processes.In this paper,we selected water-soluble CdTe quantum dots to discuss its effects on cell membrane and cell internalization process.Firstly,in order to eliminate the interference of a series of physiological activities of living cells,giant unilamellar vesicles(GUVs),small unilamellar vesicles(SUVs),supported phospholipid bilayer(SLB)and plasma membrane vesicles(GPMVs)were prepared as endocytosis-free model cell membrane to study the interaction between amino-/carboxyl-coated CdTe quantum dots and the cell membrane.The morphology of the cell membrane exposed to CdTe quantum dots was observed by a laser scanning confocal microscope.The adsorption of quantum dots on the surface of the cell membrane was monitored by a quartz crystal microbalance(QCM-D)in real time.Secondly,rat basophilic leukemia(RBL-2H3)cells were used to further study the cell internalization process of CdTe quantum dots,and the cell viability was detected by MTT and LDH experiments to evaluate the cytotoxicity of CdTe quantum dots.Our main findings include:(1)The positively charged amino-coated CdTe quantum dots can adhere to the surface of negatively charged phospholipid membranes.Negatively charged carboxyl-coated CdTe quantum dots can adhere to the surface of positively charged phospholipid membranes.However,both quantum dots have no significant effects on the phospholipid membrane with the like charge.In addition,the amino-coated CdTe quantum dots can adhere to the surface of negatively charged GPMVs,and the carboxyl-coated quantum dots cannot,indicating that the adsorption of quantum dots on the model cell membrane is dominated by electrostatic interaction.(2)The amino-coated CdTe quantum dots can penetrate the GPMVs into the interior via the endocytosis-free mechanism,whereas the carboxyl-coated CdTe quantum dots have no such ability,indicating that sufficient CdTe quantum dots adhere on the membrane can trigger their passive membrane penetration.(3)CdTe quantum dots cannot accumulate on living cells after their adhesion,and they will pass through the cell membrane and enter the cytoplasm via endocytosis.Endocytosis is the primary way in which quantum dots are internalized into living cells.The process is fast,so that almost all of the quantum dots are internalized before they accumulate on the cell membrane.Moreover,compared with the adherent RBL-2H3 cells,the suspended cells after trypsin digestion can take more CdTe quantum dots.This demonstrates that the nanoparticles are more accessible to the cells which were digested the interstitial proteins,as well as adhere to the cell membrane and internalization.(4)The results of MTT and LDH experiments show that the cytotoxicity of amino-coated is higher than that of carboxyl-coated quantum dots.There may be two reasons:Firstly,the electrostatic force makes the positively charged quantum dots to be close to the negatively charged cells and bind to a large number of cationic binding sites present on the cell membrane,making it more susceptible to be taken by cells;secondly,when dissolved in water or glucose,the amino-coated quantum dots have less slightly agglomeration than carboxyl-coated quantum dots,and smaller particle size makes it easier to be internalized into cells and cause cell damage.The above results provide a better theoretical basis for the adhesion of the quantum dots to the cell membrane and its internalization process.In addition,the cytotoxicity of the amino-coated CdTe quantum dots is more significant than the carboxyl-coated quantum dots,which is very useful to evaluate the environmental hazard of QDs and their improvements and safe use in the future.