CdTe量子点的微波合成及其在双光子显微成像中的应用

采用微波辐射加热的方法,以亚碲酸钠(Na2TeO3)作碲源,以谷胱甘肽(GSH)作稳定剂,在水相中合成出高质量的CdTe量子点。所合成量子点的发射波长从515～630nm可调,荧光量子产率(PLQYs)最高达95%。利用X射线粉末衍射(XRD)、高分辨透射电镜(HRTEM)、紫外-可见吸收光谱(UV-Vis)和荧光发射光谱(PL)等技术表征产物的物相结构和光学性质。用双光子激发荧光法研究CdTe量子点的双光子吸收性质。用双光子激发荧光成像技术,以发红光的CdTe量子点作为双光子荧光探针成功标记了人肺腺癌细胞(A549)。     

Exploring feasibility of multicolored CdTe quantum dots for in vitro and in vivo fluorescent imaging

We report the use of novel multicolored CdTe quantum dots (QDs) as fluorophores for biological fluorescence imaging. The CdTe QDs were prepared to exhibit emission wavelengths in the green, yellow, and red range by using trifluoroacetic acid (TFA), L-cysteine and thioglycolic acid (TGA) as surface stabilizers, respectively. The particles have good water solubility and photostability. Fluorescence imaging potential was evaluated in vitro and in vivo using a multispectral Maestro CRI Fluorescence Imaging system. The results show that different colored CdTe QDs allow sensitive detection simultaneously or separately both in vitro and in vivo against background fluorescence. The studies indicate that CdTe QDs can provide alternative fluorescent probes for biological imaging.     

Evaluation of red CdTe and near infrared CdHgTe quantum dots by fluorescent imaging

Non-invasive fluorescent imaging of preclinical animal models in vivo is a rapidly developing field with new emerging technologies and techniques. Quantum dot (QD) fluorescent probes with longer emission wavelengths in red and near infrared (NIR) emission ranges are more amenable to deep-tissue imaging, because both scattering and autofluorescence are reduced as wavelengths are increased. We have designed and synthesized red CdTe and NIR CdHgTe QDs for fluorescent imaging. We demonstrated fluorescent imaging by using CdTe and CdHgTe QDs as fluorescent probes both in vitro and in vivo. Both CdTe and CdHgTe QDs provided sensitive detection over background autofluorescence in tissue biopsies and live mice, making them attractive probes for in vivo imaging extending into deep tissues or whole animals. The studies suggest a basis of using QD-antibody conjugates to detect membrane antigens.     

Interaction of porphyrins with CdTe quantum dots

Porphyrins may be used as photosensitizers for photodynamic therapy, photocatalysts for organic pollutant dissociation, agents for medical imaging and diagnostics, applications in luminescence and electronics. The detection of porphyrins is significantly important and here the interaction of protoporphyrin-IX (PPIX) with CdTe quantum dots was studied. It was observed that the luminescence of CdTe quantum dots was quenched dramatically in the presence of PPIX. When CdTe quantum dots were embedded into silica layers, almost no quenching by PPIX was observed. This indicates that PPIX may interact and alter CdTe quantum dots and thus quench their luminescence. The oxidation of the stabilizers such as thioglycolic acid (TGA) as well as the nanoparticles by the singlet oxygen generated from PPIX is most likely responsible for the luminescence quenching. The quenching of quantum dot luminescence by porphyrins may provide a new method for photosensitizer detection.     

Hydrothermal synthesis for high-quality CdTe quantum dots capped by cysteamine

We present a facile hydrothermal approach to synthesize high-quality cysteamine (CA)-capped CdTe quantum dots (QDs). Oil bath heating and vigorous stirring were used to obtain better heat transfer and more homogenous solutions during the synthesis process. By this approach, the quantum yield (QY) of the resultant QDs can reach as high as 19.7%, which is the best reported data for CA-stabilized CdTe QDs. The synthesis process is under a high concentration of the precursor (> 10 mM), suggesting the potential of this route to be used in mass production of CA-capped CdTe QDs. Moreover, the pH-dependent optical properties of CA-capped CdTe QDs were also investigated.     

Fluorescent and nonlinear optical features of CdTe quantum dots

The study of photoluminescence and nonlinear optical properties of red (emitted at 650 nm), yellow (emitted at 570 nm) and green (emitted at 530 nm) CdTe quantum dots (QD) spin coated on quartz substrate that had been prepared by changing the ratio between octadecylphosphonic acid and octadecence within 0.1:1–1:1 was carried out. Spectral width of the emission spectra indicates an enhancement with the increasing of QDs sizes, namely ca. 25, 28 and 50 nm for the QD size of 2.5, 3.5 and 5 nm, correspondingly. The entire QDs samples feature a spherical morphology with a relatively narrow size distribution. The optical second harmonic generation (SHG) stimulated by coherent bicolor treatment at 1,540 nm and its second harmonic generation was studied versus the laser light power density and incident angle.     

Monolithic ZnTe-based pillar microcavities containing CdTe quantum dots

Micropillars of different diameters have been prepared by focused ion beam milling out of a planar ZnTe-based cavity. The monolithic epitaxial structure, deposited on a GaAs substrate, contains CdTe quantum dots embedded in a ZnTe λ-cavity delimited by two distributed Bragg reflectors (DBRs). The high refractive index material of the DBR structure is ZnTe, while for the low index material a short-period triple MgTe/ZnTe/MgSe superlattice is used. The CdTe quantum dots are formed by a novel Zn-induced formation process and are investigated by scanning transmission electron microscopy. Micro-photoluminescence measurements show discrete optical modes for the pillars, in good agreement with calculations based on a vectorial transfer matrix method. The measured quality factor reaches a value of 3100.     

Zinc incorporation into CdTe quantum dots in glass

We report zinc incorporation into CdTe nanoparticles grown by two-step solid phase precipitation in commercial borosilicate glass quenched from the melt, based on a co-evaluation of the results of resonant Raman and optical absorption measurements. Resonant Raman spectra display a two-peak structure at wave-number positions corresponding to ternary compound Zn_xCd_1?xTe. We attribute the higher intensity peak between 190 and 195 cm^?1 to the first harmonic of the zone-center longitudinal optical mode (LO₁) and, the lower intensity peak between 157 and 160 cm^?1 to the second harmonic (LO₂) of Zn_xCd_1?xTe crystal. The wave-number of vibrational Raman modes indicates that zinc content varies between 39 and 50% during the growth of quantum dots. The asymptotic absorption edge against heat-treatment time plot extrapolates to a bulk band gap of 1.714 eV which sets a lower limit of 31% for zinc incorporated into quantum dots which is consistent with the results of resonant Raman measurements. The energetic position of asymptotic absorption edge of 1.592 eV and an additional unresolved weak structure in Raman spectrum between 166 and 182 cm^?1 observed for as-received glass might serve as a evidence for the occurrence of a different nanocrystalline phase with 13% zinc content.     

荧光CdTe量子点和CdTe／SiO2纳米粒子的制备与表征

采用巯基乙酸为稳定剂，在水相中直接合成了不同荧光发射波长的CdTe量子点（QDs），在此基础上，采用反相微乳法对所获得的QDs进行硅烷化处理，得到大小均一、水溶性好的CdTe／SiO2纳米粒子，为该材料的进一步生物应用奠定了良好的基础。     

Aqueous CdPbS quantum dots for near-infrared imaging

Quantum dots (QDs) are semiconducting nanocrystals that have photoluminescent (PL) properties brighter than fluorescent molecules and do not photo-bleach, ideal for in vivo imaging of diseased tissues or monitoring of biological processes. Near-infrared (NIR) fluorescent light within the window of 700-1000 nm, which is separated from the major absorption peaks of hemoglobin and water, has the potential to be detected several millimeters under the surface with minimal interference from tissue autofluorescence. Here we report the synthesis and bioimaging demonstration of a new NIR QDs system, namely, CdPbS, made by an aqueous approach with 3-mercaptopropionic acid (MPA) as the capping molecule. The aqueous-synthesized, MPA-capped CdPbS QDs exhibited an NIR emission in the range of 800-950 nm with x(i) ≥ 0.3, where x(i) denotes the initial Pb molar fraction during the synthesis. Optimal PL performance of the CdPbS QDs occurred at x(i) = 0.7, which was about 4 nm in size as determined by transmission electron microscopy, had a rock salt structure and a quantum yield of 12%. Imaging of CdPbS QDs was tested in membrane staining and transfection studies. Cells transfected with CdPbS QDs were shown to be visible underneath a slab of chicken muscle tissue of up to 0.7 mm in thickness without the use of multiple-photon microscopy.     

Semiconductor quantum dots for in vivo imaging

Quantum dots play an important role in the in vitro, ex vivo, and in vivo optical imaging. Dramatic improvements have been achieved in the aspect of surface modification, biocompatibility, and targeting specificity, which had significant impact on the in vivo applications of quantum dots. This review summarizes the recent advances of quantum dots for in vivo imaging using both non-specific and targeted approaches. The toxicity of cadmium chalcogenide materials and alternative approaches such as the use of doped nanocrystal quantum dots were also discussed. The integration of quantum dots with other imaging techniques is also expected to give rise to a new generation of multifunctional probes for biomedical applications.     

高质量水溶性CdTe量子点的合成与表征

以CdCl2和TeO2为原料,硼氢化钠为还原剂,采用水相合成法制备巯基丁二酸稳定CdTe量子点。研究了反应时间、碲和镉的物质的量之比等实验条件对CdTe量子点发光性能的影响,并用X射线粉末衍射、透射电镜、红外光谱、紫外-可见吸收光谱和荧光光谱等分析技术对其进行表征。实验表明,合成的量子点为立方晶型,颗粒大小分布均匀。反应时间及碲和镉的物质的量之比对量子点的发光性能有明显影响,随着反应时间的延长,量子点的吸收与荧光光谱都向长波方向移动,在pH值为10.5的碱性条件下,当n(Cd)∶n(Te)∶n(MSA)=1∶0.05∶1.4时,在5h的时间内可获得发绿色到红色荧光的量子点,最高荧光量子产率为70.3%。     

Highly fluorescent fluoride-responsive hydrogels embedded with CdTe quantum dots

Functionalized CdTe quantum dots (QDs) synthesized via ion exchange demonstrated a selective response toward fluoride in aqueous solutions based on a rapid sol-gel transition that was visible to the naked eye. The fluoride-induced hydrogel exhibited excellent fluorescent performance because of the incorporation of QDs. As a result, this highly fluorescent fluoride-induced hydrogel may pave a new way to sense fluoride using a visible sol-gel transition.     

Recombination dynamics in CdTe/CdSe type-II quantum dots

Recombination dynamics in CdTe/CdSe core-shell type-II quantum dots (QDs) has been investigated by time-resolved photoluminescence (PL) spectroscopy. A very long PL decay time of several hundred nanoseconds has been found at low temperature, which can be rationalized by the spatially separated electrons and holes occurring in a type-II heterostructure. For the temperature dependence of the radiative lifetime, the linewidth and the peak energy of PL spectra show that the recombination of carriers is dominated by delocalized excitons at temperatures below 150?K, while the mixture of delocalized excitons, electrons and holes overwhelms the process at higher temperature. The binding energy of delocalized excitons obtained from the temperature dependence of the non-radiative lifetime is consistent with the theoretical value. The energy dependence of lifetime measurements reveals a third power relationship between the radiative lifetime and the radius of QDs, the light of which can be shed by the quantum confinement effect. In addition, the radiative decay rate is found to be proportional to the square root of excitation power, arising from the change of wavefunction overlap of electrons and holes due to the band bending effect, which is an inherent character of a type-II band alignment.     

Versatile immunosensor using CdTe quantum dots as electrochemical and fluorescent labels

A versatile immunosensor using CdTe quantum dots as electrochemical and fluorescent labels has been developed for sensitive protein detection. This sandwich-type sensor is fabricated on an indium tin oxide chip covered with a well-ordered gold nanoparticle monolayer. Gel imaging systems were successfully introduced to develop a novel high-efficient optical immunoassay, which could perform simultaneous detection for the samples with a series of different concentrations of a target analyte. The linear range of this assay was between 0.1 and 500 ng/mL, and the assay sensitivity could be further increased to 0.005 ng/mL with the linear range from 0.005 to 100 ng/mL by stripping voltammetric analysis. The immunosensor showed good precision, high sensitivity, acceptable stability, and reproducibility and could be used for the detection of real sample with consistent results in comparison with those obtained by the ELISA method.     

Cathodic stripping synthesis and cytotoxity studies of glutathione-capped CdTe quantum dots

A cathodic stripping of Te precursor in the presence of Cd2+ and biocompatible glutathione (GSH) was reported for facile synthesis of lowly cytotoxic and highly luminescent CdTe quantum dots (QDs) in aqueous solution. The photoluminescence, electrogenerated chemiluminescence (ECL), toxicity, and cyto-osmosis of the QDs were evaluated to reveal their potential bio-applications. The morphology and composition of as-prepared QDs were investigated by HRTEM and powder XRD spectroscopy, which indicated that the QDs consisted of a CdTe core coated with a CdS shell. The obtained CdTe/CdS core/shell QDs possessed good crystallinity, narrow monodispersity and long-term stability. These QDs showed high fluorescence quantum yields of 49% to 63% over a broad spectral range of 540-650 nm. Efficient and stable ECL of QDs was observed on the anodic potential region upon the electrode potential cycled between 1.5 and -2.0 V versus Ag/AgCl. Furthermore, human liver cancer HepG2 cells were chosen as model cells for toxicity assay of QDs. Effects of the concentration, size, and incubation time of CdTe QDs capped with GSH or mercaptoacetic acid (MAA) on the cell metabolic viability and cyto-osmosis were evaluated. GSH-capped CdTe QDs could infiltrate cytomembrane and karyothecas, and were less cytotoxic than MAA-capped ones under the same experimental conditions. The reported CdTe QDs could be good candidates of fluorescent and ECL probes for biosensing and cell imaging.