Cell labeling and cytotoxicity of aqueously synthesized CdTe/CdS/ZnS core–shell–shell quantum dots by a water bath-hydrothermal method

CdTe/CdS/ZnS core–shell–shell quantum dots (QDs) were synthesized in aqueous solution via water-bathing combined hydrothermal method using L-cysteine as a stabilizer. The present method features markedly reduced synthesis time, higher fluorescent intensity and lower cytotoxicity of the QDs. Structural and spectroscopic properties of core–shell–shell QDs are well characterized by absorption and fluorescence spectroscopy, X-ray diffraction, transmission electron microscopy, and fourier transform infrared spectroscopy. Both CdS and ZnS shells were capped on the CdTe core and the fluorescence was greatly enhanced by the ZnS coating. The ternary QDs conjugated with transferrins were successfully employed for the biolabeling and fluorescent imaging of HeLa cells. Cytotoxicity evaluation shows that CdTe/CdS/ZnS was less toxic for cells than CdTe and CdTe/CdS due to the presence of a ZnS coating on surface, which inhibited the release of cadmium ions.     

HgTe/CdS/ZnS多壳层量子点的制备与表征

采用一种简单的方法合成HgTe/CdS/ZnS多壳层量子点。首先,以1-硫代甘油为稳定剂,在水相溶液中制备出HgTe核量子点;然后,采用外延生长法依次在HgTe核量子点表面包覆CdS和ZnS壳层,合成出最终具有稳定近红外发光的HgTe/CdS/ZnS多壳层量子点。该合成方法仅需3个步骤,具有操作简单、成本低廉的优点。实验结果显示,当反应温度为90 ℃、反应溶液pH为11.0、反应加热回流时间为4 min时,HgTe/CdS/ZnS多壳层量子点具有最高荧光量子产率36%。     

ZnO/ZnS核-壳量子点的双光子吸收效应

利用飞秒激光Z-扫描与泵浦-探测技术,研究了室温下ZnO/ZnS与ZnO/ZnS/Ag核-壳胶体量子点的双光子吸收效应.研究发现:ZnO基核-壳量子点的本征双光子吸收系数比ZnO体材料增大了3个数量级;测量得到的660 nm处的ZnO/ZnS核-壳量子点双光子吸收截面约为4.3×10^-44 cm⁴·s·photon^-1,比相应的ZnS、ZnSe及 CdS量子点大2个数量级;当ZnO/ZnS核-壳量子点镶嵌了银纳米点时,非线性吸收有所增强.ZnO基复合纳米结构的双光子吸收增强可归因于量子限域与局域场效应.     

Luminescence of CdS:Ag Quantum Dots in a Polymethacrylate Matrix

Semiconductor quantum dots (QDs) exhibit intense luminescence and reproduce optical characteristics. Doping with metal ions has a positive effect on their properties. Introduction of QDs into polymer matrices leads to the formation of a required morphology of composites. There is a problem in synthesis of optically transparent polymer composites containing QDs of the А²В⁶ group that consists in the extremely low solubility of metal chalcogenides and most of their precursors in monomers. To solve this problem, we used colloidal synthesis. CdS QDs were synthesized by the method of appearing reagents in situ in methylmethacrylate (MMA). Doping with Ag⁺ ions was performed by adding a silver salt into the reaction mixture during the synthesis of CdS QDs. The PMMA/CdS:Ag luminescent polymer glasses were synthesized by radical block polymerization of MMA. The transparency of the composites at wavelengths exceeding 500 nm reaches 92% (5 mm). The luminescence excitation is related to the interband electron transitions in CdS crystals. Luminescence in the range of 500–600 nm is observed due to electron relaxation via a system of levels in the band gap of doped CdS crystals. The positions and intensities of the spectral bands depend on the Ag⁺ concentration, particle size, excitation wavelength, and other factors. The formation of Cd(Ag)S/Ag₂S structures at Ag⁺ concentrations higher than 5.0 × 10^–3 mol/L quenches the luminescence.     

Facile synthesis of mercaptosuccinic acid-capped CdTe/CdS/ZnS core/double shell quantum dots with improved cell viability on different cancer cells and normal cells

Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdS_thin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ～3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications.     

核/壳结构ZnS : Mn/CdS纳米粒子的制备及发光

利用溶剂热法制备了Mn离子掺杂的ZnS纳米粒子(ZnS : Mn),利用沉淀法对ZnS ∶ Mn纳米粒子进行了不同厚度的CdS无机壳层包覆。采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)及光致发光(PL)光谱等手段对样品进行了表征。TEM显示粒子为球形,直径大约在14~18 nm之间。由XRD结果可以看出CdS壳层的形成过程受到了ZnS ∶ Mn核的影响,导致其结晶较差。XRD和XPS测量证明了ZnS : Mn/CdS的核壳结构。随着CdS壳层的增厚,样品的发光强度呈现一直减弱的现象。     

脂溶性CdSe/ZnS量子点脂质体复合物的制备及表征

在油相中成功合成了脂溶性CdSe/ZnS核壳量子点纳米粒,粒径平均为4.5 nm,量子产率达29%,发射波长为540 nm。通过薄膜分散法,以蛋黄卵磷脂、胆固醇为膜材,将脂溶性的CdSe/ZnS核壳量子点包覆于脂质体磷脂双分子层中,由于磷脂分子的两亲性,使得脂溶性的CdSe/ZnS核壳量子点同时又具有亲水性。通过透射电镜对脂质体形态进行了表征,倒置荧光显微镜证实了发光CdSe/ZnS核壳量子点成功包埋于脂质体双分子层中,包裹的发光CdSe/ZnS核壳量子点具有更稳定的发光及抗光漂白性质。     

CdSe/ZnSe/ZnS多壳层结构量子点的制备与表征

展示了一种简捷的多壳层量子点合成路线。在含有过量Se源的CdSe体系中直接注入Zn源,"一步法"合成了CdSe/ZnSe量子点;进一步以CdSe/ZnSe为"核",表面外延生长ZnS壳层制备了核/壳/壳结构CdSe/ZnSe/ZnS量子点。相对于以往报道的多壳层结构量子点的制备方法,该方法通过减少壳层的生长步骤有效地简化了实验操作,缩短了实验周期,同时减少对原料的损耗。对量子点进行高温退火处理,能够大幅提高CdSe/ZnSe/ZnS量子点的发光量子产率。透射电镜、XRD以及光谱研究表明:所制备的量子点接近球形,核与壳层纳米晶均为闪锌矿结构,最终获得的CdSe/ZnSe/ZnS量子点的光致发光量子产率达到53％。为了实现量子点的表面生物功能化,通过巯基酸进行了表面配体交换修饰,使量子点表面具有水溶性的羧基功能团,并且能够维持较高的光致发光量子产率。     

ZnS薄膜参数对有机/无机复合发光器件特性的影响

半导体量子点(QDs)具有发光效率高和发光波长可调等特点。采用胶体CdSe QDs作电致发光器件的有源材料,TPD(N,N′-biphenyl-N,N′-bis-(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine)作空穴传输层,ZnS作电子传输层,研究了有机/无机复合发光器件ITO/TPD/CdSe QDs/ZnS/Ag的电致发光特性。TPD和CdSe QDs薄膜采用旋涂方法、ZnS薄膜采用磁控溅射方法沉积,器件表面平整。CdSe QDs的光致发光和电致发光谱峰位波长均位于～580 nm,属于量子点的带边激子发光。我们与以前的ITO/ZnS/CdSe QDs/ZnS/Ag发光器件结构进行了对比,发现新的器件结构的电致发光谱没有观察到QDs表面态的发光,而且新器件的发光强度是ITO/ZnS/CdSe QDs/ZnS/Ag结构的～10倍。发光效率的提高归因于碰撞激发与载流子注入两种发光机制并存的结果：一方面电子经过ZnS 层加速后,碰撞激发CdSe QDs发光;另一方面,空穴从TPD层注入CdSe QDs 与QDs中激发的电子复合发光。我们进一步研究了ZnS电子加速层厚度对发光特性的影响,选择ZnS薄膜的厚度分别是80,120 和160 nm,发现随着ZnS层厚度增大,器件启亮电压升高,EL强度增大,但是击穿电压降低。EL峰位随着ZnS厚度的减小发生明显蓝移,对上述实验现象进行了机理解释。     

CdTe,核 壳型CdTe/CdS及CdTe/ZnS量子点的合成及表征

在水相中制备了半导体CdTe纳米晶,核 壳型CdTe/CdS和CdTe/ZnS纳米晶（即量子点;QDs）.利用扫描隧道显微镜（STM）和荧光光谱(FS)对合成的纳米晶量子点进行了研究,并且根据FS的数据进行了量子效率的计算.STM的结果表明合成的量子点直径约为3 nm并且分布良好.为了提高量子效率,对Cd2+浓度和Cd2+∶S2－比例等反应条件进行了研究,结果表明随着回流时间的增加,核 壳型量子点CdTe/CdS的量子效率总体上呈下降趋势.CdTe/CdS在pH8.5,Cd2+∶S2－=10∶1（摩尔比）时可获得80.0%的最大量子效率.同时制备了核 壳型量子点CdTe/ZnS,其最大发射波长由551 nm（CdTe）红移到635 nm（CdTe/ZnS）表明量子点的尺寸在增长,但是量子效率下降到14.4%. 当前研究的量子点可适用于生物标记,生物成像,以及基于共振能量转移的生物传感研究.     

Microwave-Assisted Aqueous Synthesis of Highly Luminescent Carboxymethyl Chitosan-Coated CdTe/CdS Quantum Dots as Fluorescent Probe for Live Cell Imaging

This paper describes the development of a simplified and rapid method for the aqueous synthesis of quantum dots (QDs) with CdTe cores and gradient CdS external shells (CdTe/CdS QDs) aided by microwave irradiation. Several synthesis parameters, such as molar ratio of reagents, pH, reaction temperature, and reaction time, were studied in details. Under the optimized conditions, highly effective CdTe/CdS QDs could be synthesized in aqueous phase in only 15 min. In order to improve the biocompatibility of the CdTe/CdS QDs, these QDs were then interacted with carboxymethyl chitosan (CMC) so as they could be used as fluorescent probes in the aqueous phase. With the incorporation of CMC, the stability of modified QDs was found to have improved significantly (from 4 months to more than 10 months at room temperature). The photoluminescence quantum yield (PLQY) of the modified QDs could reach 75%, other parameters include a full width at half maximum of the emission (FWHM) spectrum as 40 ~ 60 nm, and an average size, estimated from electron microscopic images, as 3.5 nm. As fluorescent probes, these modified QDs were successfully used for imaging live Madin–Darby canine kidney (MDCK) cells, in which the preliminary results indicated that these modified QDs demonstrated good biocompatibility and showed promising applications for bio-labeling and imaging.     

Luminescence Quantum Yield and Recombination Constants in Colloidal Core/Shell Ag2S/ZnS and Ag2S/SiO2 Quantum Dots

Optics and Spectroscopy - The luminescence properties of colloidal Ag2S quantum dots (QDs) with ZnS or SiO2 shells coated with thioglycolic or 2-mercaptopropionic acids are comparatively analyzed....     

RGDS-conjugated CdSeTe/CdS quantum dots as near-infrared fluorescent probe: preparation,characterization and bioapplication

In the experiments, high-quality, water-soluble and near-infrared (NIR)-emitting CdSeTe and CdSeTe/CdS quantum dots (QDs) were successfully prepared. The average size of CdSeTe?CdS QDs was 7.68 nm and CdSeTe QDs was 4.33 nm. Arginine-glycine-aspartic-serine acid (RGDS) peptides were linked to CdSeTe/CdS QDs by N-(3-(dimethylamino)propyl)-N′-ehtylcarbodiimide hydrochloride (EDC) and N′-hydroxysuccinimide (NHS). The prepared RGDS-tagged NIR CdSeTe/CdS QDs (denoted as RGDS-CdSeTe/CdS) had an average diameter of 24.83 nm and were used for cancer cell immunofluorescence imaging. The characteristics of RGDS-conjugated CdSeTe/CdS such as morphology, structure, spectra, stability, cytotoxicity, and near-infrared microscopic imaging were investigated in detail. HepG2 cells were incubated with the novel fluorescent probe (RGDS-CdSeTe/CdS), which realized immunofluorescence targeting and imaging. The results reported here open up new perspectives for integrin-targeted near-infrared imaging and may aid in tumor detection including imaging-guided surgery.     

CdS量子点的酿酒酵母仿生合成及光谱表征

以酿酒酵母为载体,常温下利用仿生法成功合成了CdS量子点。荧光发射光谱、紫外吸收光谱以及荧光显微镜照片证明,该方法合成的CdS量子点的荧光发射峰位置在443nm,在紫外灯下能发蓝绿色荧光。透射电子显微镜(TEM)表征结果表明,该仿生法合成的CdS量子点为六方纤锌矿结构。以荧光发射和紫外吸收光谱为性能指标,考察了酿酒酵母生长时期、Cd2+的反应浓度以及反应时间等条件对合成CdS量子点的影响。当酿酒酵母处于生长稳定期初期时,与浓度为0.5mmol.L-1的Cd2+共培养24h后所合成的CdS量子点荧光最强。实验中观察到,换液培养可有效提高酿酒酵母合成CdS量子点的产量。     

ZnS overlayer on in situ chemical bath deposited CdS quantum dot-assembled TiO2 films for quantum dot-sensitized solar cells

ZnS overlayers were deposited on the CdS quantum dot (QD)-assembled TiO₂ films, where the CdS QDs were grown on the TiO₂ by repeated cycles of the in situ chemical bath deposition (CBD). With increasing the CdS CBD cycles, the CdS QD-assembled TiO₂ films were transformed from the TiO₂ film partially covered by small CdS QDs (Type I) to that fully covered by large CdS QDs (Type II). The ZnS overlayers significantly improved the overall energy conversion efficiency of both Types I and II. The ZnS overlayers can act as the intermediate layer and energy barrier at the interfaces. However, the dominant effects of the ZnS overlayers were different for the Types I and II. For Type I, ZnS overlayer dominantly acted as the intermediate layer between the exposed TiO₂ surface and the electrolyte, leading to the suppressed recombination rate for the TiO₂/electrolyte and the significantly enhanced charge-collection efficiency. On the contrary, for Type II, it dominantly acted as the efficient energy barrier at the interface between the CdS QDs and the electrolyte, leading to the hindered recombination rate from the large CdS QDs to the electrolyte and thus enhanced electron injection efficiency.     

Luminescent Properties of Hybrid Nanostructures Based on Quantum Dots of CdS,Europium 1,3-Diketonate,and Methylene Blue Molecules

The luminescent properties of hybrid nanostructures constructed from colloidal quantum dots (QDs) of CdS passivated with thioglycolic acid, europium(III) tris(tenoyltrifluoroacetonate), and methylene blue dye molecules are studied. Spectral features typical for the formation of core/shell QDs of the CdS/CdS:Eu³⁺ type are found. It is noted that the adsorption of the europium complex at the QD interfaces and the formation of QDs of the CdS/TGA/Eu³⁺ are probable. Spectral patterns that reveal nonradiative energy transfer from the recombination luminescence centers of CdS QDs to the Eu³⁺ ions in the CdS/CdS:Eu³⁺ and CdS/TGA/Eu³⁺ structures are obtained. This is manifested in quenching the recombination luminescence of QDs and in the ignition of the intracentric luminescence of Eu³⁺, which enhance with an increase in the concentration of the europium complex. When such structures are combined with methylene blue molecules, the half-width of the absorption spectra is found to increase by 10–15% with an unchanged position of the absorption band maximum. With an increase in the concentration of methylene blue molecules, decreases in the intensity of the recombination luminescence band of CdS QDs at a wavelength of 530 nm and in the luminescence intensity of Eu³⁺ ions and simultaneously the rise up of the fluorescence of methylene blue at a wavelength of about 675 nm are observed. At the same time, a decrease in the luminescence lifetime of the bands of QDs and europium ions are observed. It is concluded that the nonradiative excitation energy transfer from both the recombination luminescence centers and Eu³⁺ ions to methylene blue molecules takes place.     

Effect of ZnS layers on optical properties of prepared CdS/TiO<Subscript>2</Subscript> nanotube arrays for photocatalyst

The TiO₂ nanotube arrays (TiO₂ NTAs) prepared by re-oxidation were chosen as basement. The NTAs prepared through re-oxidation show smoother surface and more uniform tube mouth on large scale compared with the first as-grown one. We use successive ionic layer adsorption and reaction method to deposit quantum dots (ZnS and CdS) onto the sample successively. The findings reveal that two kinds of quantum dots (～10 nm) distribute regularly and the nanotube mouth is open. From the UV–Vis absorption spectrum of samples, the red shift occurs after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650 nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency of 90.7% compared with bare TiO₂ NTAs (52.9%) and just CdS QDs sensitized sample (65.8%). In the test of photocatalysis durability, the decay percentages of CdS/TiO₂ NTAs and ZnS/CdS/TiO₂ NTAs were 35.8 and 48.4%, respectively, which means that the ZnS passivation layer plays a crucial role in enhancing photocatalytic activities.     

Photostability and Photoinduced Processes in CuInS2/ZnS Quantum Dots and Their Hybrid Structures with Multilayer Graphene Nanoribbons

Optics and Spectroscopy - The photostability of the luminescent properties of CuInS2/ZnS quantum dots (CIS/ZnS QDs) as a monolayer on a dielectric substrate and as part of a hybrid structure with...     

ZnO作为电子传输层的绿光胶体CdSe量子点LED(QD-LED)的制备与表征

通过调节作为发光层的量子点的尺寸,可以制作出覆盖可见光(380～780 nm)以及近红外光谱的量子点LED(QD-LED),其光谱范围很窄且半高宽可达30 nm。然而量子点LED的寿命、亮度以及效率需要进一步提高才能满足商业化的需求。为了研究QD-LED器件的特性,本文采用523 nm波长的CdSe/ZnS核壳型量子点为发光层、poly-TPD为空穴传输层、ZnO为电子传输层,制备了绿光量子点LED,并表征了器件的特性。     

Effect of the Semiconductor Quantum Dot Shell Structure on Fluorescence Quenching by Acridine Ligand

The main line of research in cancer treatment is the development of methods for early diagnosis and targeted drug delivery to cancer cells. Fluorescent semiconductor core/shell nanocrystals of quantum dots (e.g., CdSe/ZnS) conjugated with an anticancer drug, e.g., an acridine derivative, allow real-time tracking and control of the process of the drug delivery to tumors. However, linking of acridine derivatives to a quantum dot can be accompanied by quantum dot fluorescence quenching caused by electron transfer from the quantum dot to the organic molecule. In this work, it has been shown that the structure of the shell of the quantum dot plays the decisive role in the process of photoinduced charge transfer from the quantum dot to the acridine ligand, which is responsible for fluorescence quenching. It has been shown that multicomponent ZnS/CdS/ZnS shells of CdSe cores of quantum dots, which have a relatively small thickness, make it possible to significantly suppress a decrease in the quantum yield of fluorescence of quantum dots as compared to both the classical ZnS thin shell and superthick shells of the same composition. Thus, core/multicomponent shell CdSe/ZnS/CdS/ZnS quantum dots can be used as optimal fluorescent probes for the development of systems for diagnosis and treatment of cancer with the use of anticancer compounds based on acridine derivatives.