“Phosphine-Free” Synthesis Of Multishell Quantum Dots And Their Applications To Biological Detection And Cytotoxicity

Semiconductor quantum dots(QDs)have drawn great attention for the potential applications in solar cells,light-emitting diodes(LEDs)and biomedicine due to their unique optical properties,including tunable emission with narrow full width at half maximum(FWHM),high fluorescence quantum yields(QYs),long PL lifetime and high photostability.The II-VI core/multishell quantum dots were most widely researched among the all kind of quantum dots.However,some problems still exsited in the green and red emitting QDs,which are the most appealing and widely studied QDs:(1)the high Cd ion content.It is well known that the researches about the biotoxicity of QDs are still inadequacy.Moreover,the Cd can pollute the environment.(2)The alkylphosphine(such as trioctylphosphine(TOP)and tributylphosphine(TBP)),as common materials in the synthesis of QDs,are expensive,hazardous and unstable materials and generally need to be operated in glove box.(3)The type-I QDs are widely researched due to their improved PL intensity and photostability,but they can lead to re-absorption and fluorescence loss,which seriously limits the improvement of the efficiency of the light emitting devices and the biological detection sensitivity.We have synthesized green and red emitting core/multishell quantum dots by “phosphine-free method” to overcome all the above mentioned shortages via the adjustment of the thickness and kind of shell.Then we tried to explore the biomedicine application of the QDs.The main results are shown as following:(1)The high-quality green-emitting Cd S0.5Se0.5/Zn Cd S/Zn S core/multishell QDs were first synthesized by “Thermal Cycling Using a Single-source Precursor(TC-SP)mothod” without alkylphosphine.The QYs could reach 70 % by optimizing the composition gradient of the Zn Cd S alloyed shell.The as-prepared core/multishell QDs still kept high PL QYs(60%)and stability after being transferred to water.The Hela cells were incubatd by the hydrophilic quantum dots to text the biocompatibility by MTT.The cell viability reached 90 % under low QDs concentration,and still kept 80 % under high QDs concentration.It was proven that the as-prepared core/multishell QDs had low cytotoxicity.Then the confocal laser scanning microscope(CLSM)measurement showed bright fluorescence and the distortionless cell nucleuses.It proved that the as-prepared Cd S0.5Se0.5/Zn Cd S/Zn S core/multishell QDs had excellent biocompatibility.(2)We first synthesized Zn Se/Cd S/Zn S type-II/type-I red-emitting core/multishell QDs via “one-pot phosphine-free route” by adding the mixture of Cd(OA)2/Zn(OA)2 and Octanethiol without purifying the Zn Se core QDs which were synthesized by “green” precursor such as Se-ODE and Zn(OA)2.The as-prepared core/multishell QDs had lower level of Cd content(~13 %),larger Stocks shift,less re-absorption and longer PL lifetime,compared to traditional Cd Se/Zn S type-I QDs.Moreover,the QDs had high stability after transferred to water.(3)C-reactive protein(CRP)has been regarded as an early indicator of infection and autoimmune disorders.Compared with traditional enzyme-linked immunosorbent assay(ELISA),FLISA is time-saving without the enzymatic reaction process and less sensitive to environmental conditions deriving from the optical quality of fluorescent QDs.The red-emitting Zn Se/Cd S/Zn S type-II/type-I core/multishell QDs have the reabsorption-suppressed property which benefits the fluorescent signal output of quantitative detection.We first demonstrated FLISA quantitative immunoassay using water-soluble Zn Se/Cd S/Zn S type-II/type-I core/shell QDs as fluorescent probe.The limit of detection(LOD)for quantitative detection of CRP protein reached 0.85 ng/m L which was 15% more sensitive than that of the Cd Se/Zn S type-I QDs based FLISA in control experiments.The high QYs,excellent optical stability,and low reabsorption effect may promote the application of Zn Se/Cd S/Zn S type-II/type-I core/multishell QDs in biomedicine and photoelectric field.