Application And Study On Quantum Dots Composites For Drug Carriers And Metal Ion Detection

In recent years,the unique size-dependent optical properties of semiconductor quantum dots have been extensive used in the field of fluorescent labeling,biosensor,and solar cells.However,the multifunctional drug carriers prepared by complexing quantum dots with magnetic nanoparticles appear some common problems,such as insufficient drug loading,poor stability and fluorescence quenching,so limiting its wide applications.At the same time,based on the fluorescence performance of quantum dots,it has developed a variety of fluorescent probes for metal ions detection,but because of the low selectivity and detection sensitivity,how to achieve the high selectivity analysis of target analyte is still a challenging subject.In this paper,we study the surface modification and functionalization of quantum dots,and further realize the assembling and combination quantum dots with other nano-materials,in order to obtain more practical and valuable of quantum dots.The key technique for preparing composite nano-drug carriers is to select a good medium to simultaneously stabilize magnetic materials and quantum dots.Chitosan and its derivatives have good stability and sustained release properties,as surface modification materials and drug carriers have obvious advantages.Therefore,this paper first selects the polymer(CM-?-CD or CMCS)to modify the surface of the magnetic particles.The modified layer can not only increase the loading of the drug,reduce the effect on the fluorescence performance of the quantum dots,and its functional groups facilitate efficient binding to quantum dots.Secondly,the polymer-modified magnetic nanoparticles and quantum dots were co-embedded in the chitosan matrix by chemical bonding to obtain a stable composite nano-drug carrier.At the same time,based on the fluorescence quenching properties and electrocatalytic properties,and the specific surface ligand molecular modification,three kinds of strategies were used for metal ion detection via electrochemical sensors or fluorescence sensors,including the ZnSe QDs solution,the ZnSe-XG nanocomposites and CS/ZnSe biofilms,in order to achieve the high selectivity determination of metal ions.The main contents are summarized as follows:(1)Chitosan(CS)matrix nano-drug carriers were synthesized for delivering hydrophobic anticancer drugs 5-fluorouracil(CS-CDpoly-MNPs).Carboxymethyl-?-cyclodextrin being grafted on the Fe3O4 nanoparticles(CDpoly-MNPs)contributed to an enhancement of adsorption capacities because of its inclusion abilities of insoluble anticancer drugs through host-guest interactions.Experimental results indicated that the amounts of crosslinking agent and bonding times played a crucial role in determining morphology features of the hybrid nanocarriers.The amount of CM-?-CD grafted on the MNPs is 6.5 wt%.The nanocarriers exhibited a high loading efficiency(44.7±1.8%)with a high saturation magnetization being 43.8 emu/g.(2)A multi-functional magnetic/fluorescent nanocomposites were developed using glutaraldehyde as crosslinking agent to integrate MNPs and QDs into chitosan matrix.Due to the abundance of amino groups in CS,CMCS coated Fe3O4 and GSH capped CdTe@ZnS,glutaraldehyde with carboxyl groups was introduced as a crosslinking agent to form covalent cross-linking reaction between them.The surfaces of MNPs were modified by carboxymethyl chitosan(CMCS)to minimise the possible fluorescence quenching triggered by magnetic cores.The obtained nanocomposites have excellent magnetic and fluorescent properties and good stability while used in vitro for cell culture and imaging.DOX,as an anti-cancer drug could be loaded and released form the composite.The pH-dependant cumulative release of DOX was related to the solubility of chitosan at different pHs and electrostatic interaction between various charged components.In vitro biocompatibility test shows that the nanocomposite without DOX loading has a low cytotoxicity.CLSM images ascertain the cell fluorescent labelling properties and time-dependent cellular uptake.(3)A CMCS-based nanocomposite has been successfully fabricated through incorporating surface modified QDs,MNPs and FA into CMCS matrix.Because of the abundance of-COOH groups and-NH2 groups in CMCS,amide linkage(-CONH-)can develop between the different components.Comparing with physical interactions,such as electrostatic force,strong chemical bonds between each component ensure the stability of obtained nanocomposites in physiological environments.The resulting composite possesses desirable magnetic property and strong fluorescence.In vitro study also suggests low cytotoxicity,sustained and pH-dependent drug release profiles,high cellular uptake efficiency,and receptor-specific endocytosis.Apoptosis data shown that the percentage of early apoptosis and late apoptosis increases with the prolonged incubation time.(4)Water soluble ZnSe QDs functionalized by L-glutathione has been successfully synthesized and used as a fluorescence probe for the determination of trace amount of copper in environmental samples.Compared with the reported methods using QDs as the fluorescent probe for copper determination,it shows superior detection limit and excellent selectivity.Based on the effective electron transfer from GSH to Cu2+ and the surface ligand stripping occurs onto the surface of ZnSe QDs,it results in the reduction of Cu2+ to Cu+ and increment of surface defection on the surface of the QDs.The results show that foreign ions do not significantly interfere with the use of ZnSe QDs as Cu2+ probes,and the detection limit was 2×10-10 mol/L at pH 7.4.Moreover,based on the invariable absorption peak position and curtate luminescence lifetime of ZnSe QDs,the quenching process has also been confirmed to be a dynamic quenching procedure.(5)A ZnSe-XG nanocomposite was developed as an electrode modifier and an electrochemical sensor for Cd(?)selective detection was constructed based on the modified electrode.Due to the hydrogen bonding and complexing association between ZnSe and XG,the stability and affinity to Cd(?)of the cast film ZnSe-XG on the GC electrode exhibited significant advantages over the ZnSe QDs film alone.Due to the electrocatalytic properties of MWCNT and excellent electroanalytical performance of ZnSe-XG complex,the new electrode significantly enhances the sensitivity and selectivity for the detection of Cd(?).The detection concentration of the reported electrode covered two linear ranges from 0.336 to 5.6 mg/L and showed a high sensitivity of 22.257 ?A·mg-1·L-1 and a low detection limit of 6.11 ?g/L.The electrocatalytic oxidation performance of the cast film for removing Cd(?)is demonstrated to be a surface adsorption-controlled process and the saturated absorption capacity is calculated to be 3.45×10-9 mol/cm2.These results suggest that the proposed composite film can be applied as a simple,reliable tool for the rapid detection of cadmium and provide a new powerful platform of QDs in electrochemical analysis of heavy metals.(6)We firstly developed a sensitive fluorescence sensor for detection of Cd2+ and Cu2+ based on the fluorescence quenching of QDs solution and QDs biofilms.In contrast,QDs-based thin films(CS/ZnSe)are promising for the development of portable sensing devices.With the increase of the concentration of metal ions,the PL emission intensity of QDs-based fluorescence sensor proportionably decrease and the quenching results coincide with the modified Stern-Volmer equation.A highly sensitive and selective electrochemical sensor for separately and synchronous detection of metal ions are established based on a nanocomposite of xanthan gum(XG)and ZnSe quantum dots(ZnSe-XG)through hydrogen bonding and complexing association.Under optimum conditions,the peak currents had a good linear relationship with the concentration of metal ions and the detection limits were 6.1 and 0.074 ?g/L for Cd(?)and Cu(?)ions,respectively.The three methods have higher detection sensitivity and lower detection limit for Cu2+ than Cd2+.The results show that QDs-based electrochemical sensor provided several significant advantages over fluorescence sensing in achieving a better LOD,specific recognition and better reproducibility.