高性能CdTe/CdS核壳型量子点的制备及应用于小麦面粉中呕吐毒素的荧光免疫检测研究

量子点荧光免疫法的广泛应用迫切需要提高量子点的发光强度和抗体的稳定性. 分别采用巯基乙酸和谷胱甘肽作稳定剂, 水相合成CdTe量子点, 再包覆CdS制备核壳型CdTe/CdS量子点. 以EDC/NHS作交联剂将CdTe/CdS量子点标记到呕吐毒素抗体上, 然后用牛血清蛋白封闭抗体. 研究发现, 谷胱甘肽稳定剂优于巯基乙酸. 与CdTe量子点相比, 谷胱甘肽修饰的CdTe/CdS量子点其荧光的强度和稳定性分别提高6倍和2倍以上. 谷胱甘肽碳链较长, 减少了量子点对抗体尤其是活性位点处的空间构型影响, 从而大大提高抗体的稳定性. 监测不同储藏时间(4 ℃)的CdTe/CdS量子点-抗体偶联复合物与呕吐毒素免疫反应前后荧光强度变化值, 结果显示抗体至少可以稳定7 d. 基于谷胱甘肽稳定的高性能CdTe/CdS量子点, 我们建立了一种新的呕吐毒素荧光免疫检测方法. 呕吐毒素浓度在0～0.9 ng•mL^－1之间相对荧光强度呈线性关系, 相关系数(R²)为0.9992, 检出限是0.038 ng•mL^－1. 方法的灵敏度高于文献报道的其它方法, 如GC-ECD, HPLC和HPLC-MS, 已成功应用于小麦面粉样品中痕量呕吐毒素的测定.     

CdTe/CdS量子点的Ⅰ-Ⅱ型结构转变与荧光性质

制备了壳层厚度可以精确控制的CdTe/CdS核壳量子点, 利用紫外-可见吸收光谱、光致发光光谱、透射电镜和时间分辨光谱等技术, 分析了CdS壳层厚度对CdTe量子点的荧光量子产率和光谱结构的影响规律. 发现了不同于CdSe/CdS, CdSe/ZnS, CdTe/ZnS等核壳量子点的荧光峰展宽、大幅度红移以及荧光寿命大幅度增加现象. 根据能带的位置关系, 随着CdS厚度的增加, CdTe从Ⅰ型结构逐渐过渡到Ⅱ型核壳结构. 对于Ⅱ型CdTe/CdS核壳量子点, 不仅存在CdTe核区导带电子与价带空穴间的直接复合, 还存在CdS壳层导带电子与CdTe核价带空穴界面处的间接复合, 发光机制的变化导致荧光峰的展宽、明显红移和荧光寿命的增加. 当壳层过厚时, 壳层表面新引入的缺陷会阻碍荧光寿命和量子产率的进一步提高.     

室温水相合成CdTe/CdS核/壳结构量子点

开发了一种以聚乙烯吡咯烷酮为分散剂和稳定剂经条件温和的室温水相合成光谱可调的水溶性CdTe/CdS核/壳结构量子点的方法:向新鲜制备的CdTe量子点溶液中加入硫源,继续反应即可生成CdS壳层,通过控制硫源的浓度即可控制CdS壳层厚度,从而调节光谱性质和增强稳定性.采用XRD、TEM、HRTEM、荧光光谱以及紫外-可见光...     

CdTe量子点与蛋白质相互作用的荧光猝灭效应

本文在水热法合成水溶性CdTe及核壳结构CdTe/CdS量子点的基础上,分别研究了细胞色素c对CdTe量子点及CdTe/CdS核壳量子点荧光的猝灭效应和CdTe量子点对牛血清白蛋白荧光的猝灭效应,并阐述了猝灭机理。结果显示,细胞色素c对CdTe量子点的荧光猝灭效应具有一定的粒径依赖性,粒径越小,猝灭效应越强;细胞色素c对CdTe/CdS核壳量子点的猝灭效应比对CdTe量子点的更强,揭示了受激电子的表面传递机理。CdTe量子点通过松散牛血清白蛋白的螺旋结构而猝灭其荧光。     

CdTe/CdS核壳量子点与蛋白质荧光标记

利用连续离子层吸附技术合成了水溶性的CdTe／CdS核壳量子点．通过CdS壳层的包覆,量子点的量子效率由原来的15％（裸核）提高到38％（核壳）,这种核壳结构量子点的化学和光学性质具有更好的稳定性,可以用于生物标记．本文采取共价连接与静电吸附两种方法,实现了量子点的生物标记,电泳技术已证明,应用这种量子点成功地实现了对蛋白质分子的生物标记．通过对量子点与蛋白质偶联前后的荧光光谱分析,发现量子点与蛋白质作用后荧光增强是由于蛋白质对量子点进行了表面修饰,从而降低了表面缺陷引起的非辐射跃迁几率所致．通过共价连接量子点的荧光峰位红移,主要是由于偶极-偶极相互作用引起的;量子点与蛋白质静电吸附作用引起的荧光峰位蓝移主要起因于量子点表面电荷量的降低．     

CdS/ZnS-CdTe量子点间荧光共振能量转移测定痕量汞

研究了CdS/ZnS核壳型量子点为能量给体,CdTe量子点为能量受体的荧光共振能量转移机理,及其在超痕量汞测定中的应用。实验表明在十二烷基苯磺酸钠存在下,于pH 7.8的硼酸-硼酸钠缓冲液,CdS/ZnS与CdTe量子点之间能发生有效的能量转移。探讨了CdS/ZnS与CdTe量子点间能量转移机理。实验结果表明:Hg2+的加入能使CdS/ZnS-CdTe体系发生荧光猝灭,且Hg2+的浓度与体系荧光猝灭强度在一定范围内有良好的线性,据此建立了CdS/ZnSCdTe-Hg2+体系测定超痕量Hg2+的方法。在优化条件下,Hg2+的线性范围为2.0×10-10~2.0×10-8g/L,检出限为6.67×10-11g/L(n=11)。方法应用于水样中Hg2+的测定,其RSD≤4.1%(n=6),回收率为97.2%~99.8%。     

CdTe/CdS量子点-蛋白质与头孢曲松钠的相互作用

以3-巯基丙酸为稳定剂,采用水热法合成了具有优异光学性质的CdTe/CdS核壳型量子点,量子产率为13.8%。量子点与牛血清白蛋白(BSA)偶联后荧光强度明显增大。通过测定荧光强度确定了偶联的最佳反应条件:pH7.4,反应温度37℃,反应时间40min。研究了溶液pH值和NaCl浓度对量子点及量子点-BSA溶液荧光强度的影响。对牛血清白蛋白测定的线性范围为1.1~19.5mg/L;检出限为0.47mg/L。头孢曲松钠对量子点-BSA的荧光有明显猝灭作用,荧光猝灭程度与其浓度有良好的线性关系。实验结果表明为静态猝灭,头孢曲松钠与BSA按1∶1结合,结合常数为6.31×103L/mol。用圆二色光谱技术探讨了其对BSA构象的影响。     

CdTe/CdS-罗丹明荧光共振能量转移猝灭法测定铅(Ⅱ)及相互作用机制的研究

以巯基乙酸为修饰剂,水相合成量子产率高达75％的CdTe/CdS核壳型量子点,建立了以CdTe/CdS QDs作为能量供体,罗丹明B作为能量受体组成的荧光共振能量转移体系.在此基础上,以CdTe/CdS-罗丹明B为荧光探针,荧光共振能量转移猝灭为理论基础,设计出一种检测pb2+含量的方法.在0～9.62×10-11mo...     

CdTe/ZnSe核壳量子点免疫层析试纸条检测克伦特罗的研究

采用巯基丁二酸作为表面修饰剂,水相法合成水溶性的CdTe/ZnSe核壳量子点,然后在N-羟基琥珀酰亚胺(NHS)的作用下,将CdTe/ZnSe核壳量子点与抗克伦特罗多克隆抗体(Anti-CLE pAb)连接。通过凝胶电泳和斑点杂交实验,验证CdTe/ZnSe核壳量子点与Anti-CLE pAb连接成功,并且CdTe/ZnSe-Anti-CLE pAb偶联物能识别克伦特罗-BSA抗原(CLE-BSA)。光谱分析表明,量子点与抗体连接后荧光增强,荧光峰位从628nm红移至635nm。将合成的CdTe/ZnSe-Anti-CLE pAb偶联物作为指示克伦特罗(CLE)分子的荧光标记物,制备出一种用于检测CLE的免疫层析试纸条,其最低检测量可达1μg/L。与ELISA法的对比实验表明,此试纸条能应用于CLE残留的快速检测。     

谷胱甘肽稳定水溶性CdTe/ZnTe量子点的制备与表征

用还原型谷胱甘肽(GSH)作为稳定剂, 合成了水溶性的CdTe/ZnTe核壳结构的半导体量子点. 考察了Zn/Cd反应物配比及GSH用量对CdTe/ZnTe量子点的性能影响. 用高分辨透射电子显微镜(HRTEM)和X射线粉末衍射(XRD)光谱对CdTe和CdTe/ZnTe的形貌和晶体结构进行了表征. 荧光光谱结果表明, 核壳结构的CdTe/ZnTe量子点比单一的CdTe量子点具有更高的荧光量子产率和更好的光活化性能.     

Effect of CdS Interlayer on Properties of CdTe Based Quantum Dots

Highly luminescent thioglycolic acid-capped CdTe-based core/shell quantum dots (QDs) were synthesized through encapsulating CdTe QDs in various inorganic shells including CdS, ZnS and CdZnS. CdTe/CdS core/shell QDs exhibited a significant redshift of emission peaks (a maximum emission peak of 652 nm for the core/shell QDs and 575 nm for CdTe cores) with increasing shell thickness. In contrast, the redshift of photoluminescence (PL) peak wavelength of CdTe/ZnS QDs was less than 15 nm. The PL peak wavelengths of the core/shell QDs depended strongly on core size and shell thickness. The PL quantum yields (QYs) of the CdTe/CdS core/shell QDs are up to 67 % while that of CdTe/ZnS core/shell QDs is 45 %. A composite CdZnS shell made CdTe cores a high PL QY up to 51 % and broadly adjusted PL spectra (a maximum PL peak wavelength of 664 nm). The epitaxial growth of the shell was confirmed by X-ray powder diffraction analysis and luminescence decay experiments. Because of high PL QYs, tunable PL spectra, and low toxicity from a ZnS surface layer, CdTe/CdZnS core/shell QDs will be great potential for bioapplications.     

Ultrafast synthesis of near-infrared-emitting aqueous CdTe/CdS quantum dots with high fluorescence

The traditional aqueous route to synthesis CdTe/CdS Core/shell (c/s) quantum dots (QDs) via decomposition of Cd-thiol complexes is usually time consuming. Herein, an ultrafast and facile aqueous synthetic approach under atmospheric pressure for CdTe/CdS c/s QDs with emission from the green to the near-infrared window (535–820 nm) is reported. With purified CdTe core QDs diluted in solution of Cd-3-mercaptopropionic acid (MPA) complexes, CdTe/CdS c/s QDs with emission wavelengths at 700 and 800 nm can be obtained within 20- and 45-min refluxing under the optimized experimental conditions, respectively. This is the most rapid way to prepare CdTe/CdS c/s QDs in aqueous phase, and the obtained QDs were highly luminescent without postsynthesis treatment. The influences of various experimental factors, including Cd²⁺ concentration, MPA-to-Cd ratio, pH value, and dilution ratio on the growth rate and luminescent properties of the obtained CdTe/CdS c/s QDs, have been taken into consideration. The three processes “purification-dilution-addition” ensure the synthesis environment with high pH value and low core concentration and have a marked impact on the rapid synthesis rate and the resulting high fluorescence of CdTe/CdS c/s QDs.     

Synthesis of Multifunctional Mn‐Doped CdTe/ZnS Core/Shell Quantum Dots

The synthesis of a novel water‐soluble Mn‐doped CdTe/ZnS core‐shell quantum dots using a proposed ultrasonic assistant method and 3‐mercaptopropionic acid (MPA) as stabilizer is descried. To obtain a high luminescent intensity, post‐preparative treatments, including the pH value, reaction temperature, reflux time and atmosphere, have been investigated. For an excellent fluorescence of Mn‐doped CdTe/ZnS, the optimal conditions were pH 11, reflux temperature 100°C and reflux time 3 h under N₂ atmosphere. While for phosphorescent Mn‐doped CdTe/ZnS QDs, the synthesis at pH 11, reflux temperature 100°C and reflux time 3 h under air atmosphere gave the best strong phosphorescence. The characterizations of Mn‐doped CdTe/ZnS QDs were also identified using AFM, IR, powder XRD and thermogravimetric analysis. The data indicated that the photochemical stability and the photoluminescence of CdTe QDs are greatly enhanced by the outer inorganic ZnS shell, and the doping Mn²⁺ ions in the as‐prepared quantum dots contribute to strong luminescence. The strong luminescence of Mn‐doped CdTe/ZnS QDs reflected that Mn ions act as recombination centers for the excited electron‐hole pairs, attributing to the transition from the triplet state (⁴T₁) to the ground state (⁶A₁) of the Mn²⁺ ions. All the experiments demonstrated that the surface states played important roles in the optical properties of Mn‐doped CdTe/ZnS core‐shell quantum dots.     

Water-soluble silica-overcoated CdS:Mn/ZnS semiconductor quantum dots

Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts.     

Aqueous synthesis of glutathione-capped CdTe/CdS/ZnS and CdTe/CdSe/ZnS core/shell/shell nanocrystal heterostructures

Here we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. The inner CdTe/CdS and CdTe/CdSe heterostructures have type-I, quasi-type-II, or type-II band offsets depending on the core size and shell thickness, and the outer CdS/ZnS and CdSe/ZnS structures have type-I band offsets. The emission maxima of the assembled heterostructures were found to be dependent on the CdTe core size, with a wider range of spectral tunability observed for the smaller cores. Because of encapsulation effects, the formation of successive shells resulted in a considerable increase in the photoluminescence quantum yield; however, identifying optimal shell thicknesses was required to achieve the maximum quantum yield. Photoluminescence lifetime measurements revealed that the decrease in the quantum yield of thick-shell nanocrystals was caused by a substantial decrease in the radiative rate constant. By tuning the diameter of the core and the thickness of each shell, a broad range of high quantum yield (up to 45%) nanocrystal heterostructures with emission ranging from visible to NIR wavelengths (500-730 nm) were obtained. This versatile route to engineering the optical properties of nanocrystal heterostructures will provide new opportunities for applications in bioimaging and biolabeling.     

Optical properties of Ag/CdTe nanocomposite self-organized by electrostatic interaction

Ag/CdTe nanocomposite was prepared via self-organization process by electrostatic interaction between positively charged CdTe quantum dots and negatively charged Ag nanoparticles and examined with respect to their optical properties. The positively charged CdTe quantum dots and negatively charged Ag nanoparticles were synthesized separately by modifying nanoparticles surface with cationic and anionic thiol compounds, respectively. The result showed that the mixing ratio of Ag nanoparticles to CdTe quantum dots is an important parameter for controlling resulting composites. The resulting solution is optically transparent if one component is in excess. Photoluminescence of CdTe quantum dots undergoes considerably quenching if CdTe nanocrystals are in excess and SERS spectra of BVPP absorbed on Ag colloid became stronger if Ag nanoparticles are in excess. Nevertheless, while the ratio is approximately 1, micrometer-sized solid composite is obtained with the elapse of 1h after mixing. SERS spectra for solid composite only exhibit the signals of the CdS nanocrystal which reflected that prolonged refluxing during the synthesis leads to a partial hydrolysis of the thiols and to the incorporation of the sulfur from the thiol molecules into the the growing nanoparticles to form mixed CdTe(S) nanocrystal, similar to CdTe/CdS core/shell structure. From the results, we conclude that optical properties of Ag/CdTe are dependent on the mixing ratio of both nanoparticles.     

CdTe/CdS半导体量子点作为农药百草枯的高灵敏传感器

用硫普罗宁(Tiopronin, TP)作为稳定剂合成了水溶性的高荧光CdTe/CdS量子点. 研究了该量子点与10种农药的相互作用. 实验发现, 当农药浓度为4.76×10^-6 mol/L时, 农药百草枯(Paraquat)能显著猝灭CdTe/CdS量子点的荧光, 使其荧光强度下降87.3%, 而分别加入乙酰甲胺磷及辛硫磷等其它9种农药, 仅能使CdTe/CdS量子点的荧光强度下降0.1%～5.1%, 显示了该CdTe/CdS量子点对百草枯的特异性传感作用. 采用吸收光谱和时间分辨荧光动力学研究了百草枯对CdTe/CdS量子点的荧光猝灭机理. 计算得出荧光强度猝灭的Stern-Volmer常数K为2.03×10⁶, 而寿命猝灭的Stern-Volmer常数K为4.25×10⁵. 结果表明, 百草枯对CdTe/CdS量子点的荧光猝灭主要为静态过程, 而动态过程的贡献较小. 利用二者的猝灭作用建立了对农药百草枯的高灵敏检测新方法, 校正曲线的线性范围为9.90×10^-9～1.50×10^-6 mol/L, 检出限为6.35×10^-9 mol/L, R=0.999. 用该方法对3种食品和3种水样中残留农药进行了检测, 加标回收率均在82.2%～98.5%之间, 其相对标准偏差为2.62%~8.35%.     

Aqueous synthesis of type-II core/shell CdTe/CdSe quantum dots for near-infrared fluorescent sensing of copper(II)

Type-II core/shell CdTe/CdSe quantum dots (QDs) were synthesized in aqueous medium by employing thiol-capped CdTe QDs as core template and CdCl(2) and Na(2)SeSO(3) as shell precursors, respectively. Compared with the original CdTe cores, the core/shell CdTe/CdSe QDs showed an obvious red-shifted emission with the color-tune capability to the near-infrared (NIR) wavelength, because of the formation of an indirect excitation. The prepared QDs exhibited high stability and moderate fluorescence quantum yields (10-20%), and their core/shell heterostructure was characterized by UV-vis absorption, steady-state and time-resolved fluorescence spectra, X-ray powder diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The fluorescence of the core/shell QDs could be markedly quenched by Cu(II), and approximate concentrations of other physiologically important cations, such as Zn(II), Ca(II), Na(I) and K(I) etc., had no effect on the fluorescence. Based on this, a simple and rapid method for Cu(II) determination was proposed using the NIR CdTe/CdSe QDs as fluorescent probes. Under optimal conditions, the response was linearly proportional to the concentration of Cu(II) between 0.05 to 50.0 x 10(-6) mol L(-1), the limit of detection was 2.0 x 10(-8) mol L(-1). The developed method was successfully applied to the detection of trace Cu(II) in real samples.