One‐Pot Synthesis of CdSe Quantum Dots in Aqueous Solution for Biological Labeling

The one‐pot synthesis of water‐soluble and biologically compatible yellow CdSe quantum dots (QDs) featuring the use of glutathione (GSH) as the capping and reducing agent was achieved under aqueous conditions at 150 °C. The synthesized yellow CdSe QDs with quantum yield (QY) up to 20% exhibit zinc blende cubic structure particles with an average diameter of 4‐5 nm. It was found that both molar ratio of Se/Cd and reaction time had a significant effect on size distribution of GSH‐CdSe QDs. Meanwhile, the interaction of QDs bioconjugated to bovine hemoglobin (BHb) was studied by absorption and fluorescence(FL) spectra. With addition of BHb, the FL intensity of CdSe QDs largely quenched due to the static mechanism. The linear range is 5.0 × 10^?8 mol/L to 3.0 × 10^?6 mol/L, and the correlation coefficient is 0.9991, suggesting that could be used as a probe to label biological molecules and bacterial cells.     

Long-term exposure to CdTe quantum dots causes functional impairments in live cells

Several studies suggested that the cytotoxic effects of quantum dots (QDs) may be mediated by cadmium ions (Cd2+) released from the QDs cores. The objective of this work was to assess the intracellular Cd2+ concentration in human breast cancer MCF-7 cells treated with cadmium telluride (CdTe) and core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) nanoparticles capped with mercaptopropionic acid (MPA), cysteamine (Cys), or N-acetylcysteine (NAC) conjugated to cysteamine. The Cd2+ concentration determined by a Cd2+-specific cellular assay was below the assay detection limit (<5 nM) in cells treated with CdSe/ZnS QDs, while in cells incubated with CdTe QDs, it ranged from approximately 30 to 150 nM, depending on the capping molecule. A cell viability assay revealed that CdSe/ZnS QDs were nontoxic, whereas the CdTe QDs were cytotoxic. However, for the various CdTe QD samples, there was no dose-dependent correlation between cell viability and intracellular [Cd2+], implying that their cytotoxicity cannot be attributed solely to the toxic effect of free Cd2+. Confocal laser scanning microscopy of CdTe QDs-treated cells imaged with organelle-specific dyes revealed significant lysosomal damage attributable to the presence of Cd2+ and of reactive oxygen species (ROS), which can be formed via Cd2+-specific cellular pathways and/or via CdTe-triggered photoxidative processes involving singlet oxygen or electron transfer from excited QDs to oxygen. In summary, CdTe QDs induce cell death via mechanisms involving both Cd2+ and ROS accompanied by lysosomal enlargement and intracellular redistribution.     

Optical sensing quantum dot-labeled polyacrolein particles prepared by layer-by-layer deposition technique

Optical sensing polymer particles with tailored semiconductor nanocrystal (QD) loading are prepared by layer-by-layer deposition technique (LbL). Polyacrolein particles of 1.2 μm diameter are used as solid support for deposition of hydrophilic CdSe/ZnS nanocrystal/polyelectrolyte multilayers formed by electrostatic interactions. The pH-dependent fluorescence of QDs and pH-dependent conformations of polyelectrolytes, which likely passivate the surface state of nanocrystals, allow a creation of both mono- and multiplex coded polymer particles with pH-dependent fluorescence intensity. Bovine serum albumin (BSA) as outermost layer makes it possible to design the optical sensing polymer particles with reversibly responded fluorescence at pH variations. The fluorescence of such polymer particles with BSA outer layer is sensitive to copper(II) ion while the fluorescence of these particles is practically insensitive to the other divalent cations (Zn(2+), Ca(2+), Ba(2+), Co(2+), Mg(2+)). The detection limit of Cu(2+) is about 15 nM. Adaptation of LbL method to prepare QD-labeled polymer particles with enhanced complexity (e.g. several types of QDs, multiple biofunctionality) is expected to open new opportunities in biotechnological applications.     

Surface-amplified ligand disorder in CdSe quantum dots determined by electron and coherent vibrational spectroscopies

This Article reports measurements of the intra- and intermolecular ordering of tight-binding octylphosphonate ligands on the surface of colloidal CdSe quantum dots (QDs) within solid state films, and the dependence of this order on the size of the QDs. The order of the organic ligands, as probed by vibrational sum frequency generation (SFG) spectroscopy, decreases as the radius of the QDs decreases; this decrease is correlated with a decrease in the order of underlying Cd(2+), as detected by X-ray photoelectron spectroscopy (XPS) line width measurements, for radii of the QDs, R > 2.4 nm, and is independent of the disorder of the Cd(2+) for R < 2.4 nm. We believe that, for R < 2.4, the decreasing order of the ligands with decreasing size is due to an increase in the curvature of the QD surfaces. Disorder in the Cd(2+) results from the presence of a shell of Cd(2+)-surfactant complexes that form during synthesis, so this work demonstrates the possibility for chemical control over molecular order within films of colloidal QDs by changing the surfactant mixture.     

Synthesis of protein‐assisted aqueous Ag2S quantum dots in the bovine serum albumin solution

A one‐step method was developed for preparing Ag₂S quantum dots (QDs) using a common protein [bovine serum albumin (BSA)] to entrap QDs precursors (BSA–Ag⁺). Fluorescence (FL) and ultraviolet spectra showed that the molar ratio of Ag⁺/BSA, temperature, and pH are the crucial factors for the quality of QDs. The QDs absorption wavelength and emission wavelength were about 340 and 450 nm. The average QDs particle size was estimated to be less than 5 nm, determined by transmission electron microscopy. The X‐ray power diffraction and XPS results showed that the synthesized product was indeed monoclinic Ag₂S. With Fourier transform infrared spectra and thermogravimetry analysis, there might be conjugated bonds between Ag₂S QDs and –OH, –NH, and –SH groups in BSA. In addition, FL spectra suggest that the designed QDs can produce static quenching with BSA and the Stern–Volmer quenching constant (K_sv) was calculated as 2.145 × 10⁴. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly luminescent CdSe/Cd(x)Zn(1-x)S quantum dots coated with thickness-controlled SiO2 shell through silanization

A silanization technique of hydrophobic quantum dots (QDs) was applied to SiO(2)-coated CdSe/Cd(x)Zn(1-x)S QDs to precisely control the SiO(2) shell thickness and retain the original high photoluminescence (PL) properties of the QDs. Hydrophobic CdSe/Cd(x)Zn(1-x)S core-shell QDs with PL peak wavelengths of 600 and 652 nm were prepared by a facile organic route by using oleic acid (OA) as a capping agent. The QDs were silanized by using partially hydrolyzed tetraethyl orthosilicate by replacing surface OA. These silanized QDs were subsequently encapsulated in a SiO(2) shell by a reverse micelles synthesis. The silanization plays an important role for the QDs to be coated with a homogeneous SiO(2) shell and retain a high PL efficiency in water. Transmission electron microscopy observation shows that the shells are 1-9 nm with final particle sizes of 10-25 nm, depending on the initial QD size. In the case of short reaction time (6 h), the QDs were coated with a very thin SiO(2) layer because no visible SiO(2) shell was observed but transferred into the water phase. The silica coating does not change the PL peak wavelength of the QDs. The full width at half-maximum of PL was decreased 4 nm after coating for QDs emitting at both 600 and 652 nm. The PL efficiency of the SiO(2)-coated is up to 40%, mainly determined by the initial PL efficiency of the underlying CdSe/Cd(x)Zn(1-x)S QDs.     

硒化镉量子点膜的拉曼光谱及拉曼成像分析

研究了CdSe量子点膜的Raman光谱,发现CdSe量子点的横模(TO)振动活性较强,表面模(SO)、纵模(LO)振动不明显。比较了量子点、氧化三辛基膦及十六胺的Raman光谱,证明量子点表面大部分区域被十六胺及二辛胺修饰。在此基础上,对量子点膜的TO模振动及C-H弯曲振动峰进行了Raman成像分析,并与明场图像进行了对比,表明拉曼成像信号对量子点膜的表面变化非常敏感。     

Stamping transfer of a quantum dot interlayer for organic photovoltaic cells

An organophilic cadmium selenide (CdSe) quantum dot (QD) interlayer was prepared on the active layer in organic solar cells by a stamping transfer method. The mother substrate composed of a UV-cured film on a polycarbonate film with strong solvent resistance makes it possible to spin-coat QDs on it and dry transfer onto an active layer without damaging the active layer. The QD interlayers have been optimized by controlling the concentration of the QD solution. The coverage of QD particles on the active layer was verified by TEM analysis and fluorescence images. After insertion of the QD interlayer between the active layer and metal cathode, the photovoltaic performances of the organic solar cell were clearly enhanced. By ultraviolet photoelectron spectroscopy of CdSe QDs, it can be anticipated that the CdSe QD interlayer reduces charge recombination by blocking the holes moving to the cathode from the active layer and facilitating efficient collection of the electrons from the active layer to the cathode.     

Organic-inorganic nanocomposites via directly grafting conjugated polymers onto quantum dots

Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized by directly grafting vinyl-terminated P3HT onto [(4-bromophenyl)methyl]dioctylphosphine oxide (DOPO-Br)-functionalized CdSe quantum dot (QD) surfaces via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The photophysical properties of nanocomposites were found to differ from the conventional composites in which P3HT and CdSe QDs were physically mixed. Solid-state emission spectra of nanocomposites suggested the charge transfer from P3HT to CdSe QDs, while the energy transfer from 3.5 nm CdSe QD to P3HT was implicated in the P3HT/CdSe composites. A faster decay in lifetime further confirmed the occurrence of charge transfer in P3HT-CdSe nanocomposites.     

Characterization of primary amine capped CdSe, ZnSe, and ZnS quantum dots by FT-IR: determination of surface bonding interaction and identification of selective desorption

Surface ligands of semiconductor quantum dots (QDs) critically influence their properties and functionalities. It is of strong interest to understand the structural characteristics of surface ligands and how they interact with the QDs. Three quantum dot (QD) systems (CdSe, ZnSe, and ZnS) with primary aliphatic amine capping ligands were characterized primarily by FT-IR spectroscopy as well as NMR, UV-vis, and fluorescence spectroscopy, and by transmission electron microscopy (TEM). Representative primary amines ranging from 8 to 16 carbons were examined in the vapor phase, KBr pellet, and neat and were compared to the QD samples. The strongest hydrogen-bonding effects of the adsorbed ligands were observed in CdSe QDs with the weakest observed in ZnS QDs. There was an observed splitting of the N-H scissoring mode from 1610 cm(-1) in the neat sample to 1544 and 1635 cm(-1) when bound to CdSe QDs, which had the largest splitting of this type. The splitting is attributed to amine ligands bound to either Cd or Se surface sites, respectively. The effect of exposure of the QDs dispersed in nonpolar medium to methanol as a crashing agent was also examined. In the CdSe system, the Cd-bound scissoring mode disappeared, possibly due to methanol replacing surface cadmium sites. The opposite was observed for ZnSe QDs, in which the Se-bound scissoring mode disappeared. It was concluded that surface coverage and ligand bonding partners could be characterized by FT-IR and that selective removal of surface ligands could be achieved through introduction of competitive binding interactions at the surface.     

Optimized Synthesis and Fluorescence Spectrum Analysis of CdSe Quantum Dots

An optimized synthesis route was applied for controlling the preparation of CdSe quantum dots (QDs) in an aqueous solution. Some key factors which influencing the properties of CdSe QDs, such as initial pH, stabilizers, ratio of precursor, etc. were investigated. The size, shape, crystal structure, and optical property of CdSe QDs were also characterized by TEM, XRD, UV-Vis, and fluorescence (FL) spectra. The result showed that high-quality cubic CdSe QDs with 3 nm were obtained. The experiments also confirmed that thioglycolic acid (TGA), under the conditions of weak acid, is a better stabilizer than others. The ratio of [Cd²⁺] to [SeSO₃ ^2?] played an important role in the formation of CdSe QDs. The mechanisms about the influence factors were also presented.     

Preparation of multilayered CdSe quantum dot sensitizers by electrostatic layer-by-layer assembly and a series of post-treatments toward efficient quantum dot-sensitized mesoporous TiO2 solar cells

A multilayer of CdSe quantum dots (QDs) was prepared on the mesoporous surface of a nanoparticulate TiO(2) film by a layer-by-layer (LBL) assembly using the electrostatic interaction of the oppositely charged QD surface for application as a sensitizer in QD-sensitized TiO(2) solar cells. To maximize the absorption of incident light and the generation of excitons by CdSe QDs within a fixed thickness of TiO(2) film, the experimental conditions of QD deposition were optimized by controlling the concentration of salt added into the QD-dissolved solutions and repeating the LBL deposition a few times. A proper concentration of salt was found to be critical in providing a deep penetration of QDs into the mesopore, thus leading to a dense and uniform distribution throughout the whole TiO(2) matrix while anchoring the oppositely charged QDs alternately in a controllable way. A series of post-treatments with (1) CdCl(2), (2) thermal annealing, and (3) ZnS-coating was found to be very critical in improving the overall photovoltaic properties, presumably through a better connection between QDs, effective passivation of QD's surface, and a high impedance of recombination, which were proved by transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS) experiments. With a proper post-treatment of multilayered QDs as a sensitizer, the overall power conversion efficiency in the CdSe QD-sensitized TiO(2) solar cells could reach 1.9% under standard illumination condition of simulated AM 1.5G (100 mW/cm(2)).     

CdSe Quantum Dots and N719‐Dye Decorated Hierarchical TiO2 Nanorods for the Construction of Efficient Co‐Sensitized Solar Cells

Three‐dimensional hierarchical TiO₂ nanorods (HTNs) decorated with the N719 dye and 3‐mercaptopropionic or oleic acid capped CdSe quantum dots (QDs) in photoanodes for the construction of TiO₂ nanorod‐based efficient co‐sensitized solar cells are reported. These HTN co‐sensitized solar cells showed a maximum power‐conversion efficiency of 3.93 %, and a higher open‐circuit voltage and fill factor for the photoanode with 3‐mercaptopropionic acid capped CdSe QDs due to the strong electronic interactions between CdSe QDs, N719 dye and HTNs, and the superior light‐harvesting features of the HTNs. An electrochemical impedance analysis indicated that the superior charge‐collection efficiency and electron diffusion length of the CdSe QD‐coated HTNs improved the photovoltaic performance of these HTN co‐sensitized solar cells.     

Interaction of Globular Plasma Proteins with Water‐Soluble CdSe Quantum Dots

The interactions between water‐soluble semiconductor quantum dots [hydrophilic 3‐mercaptopropionic acid (MPA)‐coated CdSe] and three globular plasma proteins, namely, bovine serum albumin (BSA), β‐lactoglobulin (β‐Lg) and human serum albumin (HSA), are investigated. Acidic residues of protein molecules form electrostatic interactions with these quantum dots (QDs). To determine the stoichiometry of proteins bound to QDs, we used dynamic light scattering (DLS) and zeta potential techniques. Fluorescence resonance energy transfer (FRET) experiments revealed energy transfer from tryptophan residues in the proteins to the QD particles. Quenching of the intrinsic fluorescence of protein molecules was noticed during this binding process (hierarchy HSA<β‐Lg <BSA, lower binding affinity for hydrophobic protein molecules). Upon binding with QD particles, the protein molecules underwent substantial conformational changes at the secondary‐structure level (50 % helicity lost), due to loss in hydration.     

Study on the interaction between CdSe quantum dots and hemoglobin

The interaction between CdSe quantum dots (QDs) and hemoglobin (Hb) was investigated by ultraviolet and visible (UV-vis) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and fluorescence (FL) spectroscopy. The intensity of UV-vis absorption spectrum of a mixture of CdSe QDs and Hb was obviously changed at the wavelength of 406nm at pH 7.0, indicating that CdSe QDs could bind with Hb. The influences of some factors on the interactions between CdSe QDs and Hb were studied in detail. The binding molar ratio of CdSe QDs and Hb was 12:1 by a mole-ratio method. The mechanism of the interaction between CdSe QDs and Hb was also discussed.     

Synthesis of Cysteine-Capped Zn(x)Cd(1)(-)(x)Se alloyed quantum dots emitting in the blue-green spectral range

Alloyed ZnxCd1-xSe quantum dots (QDs) have been successfully prepared at low temperatures by reacting a mixture of Cd(ClO4)2 and Zn(ClO4)2 with NaHSe using cysteine as a surface-stabilizing agent. The photoluminescence (PL) spectra of the alloyed QDs are determined on the basis of the Zn2+/Cd2+ molar ratio, reaction pH, intrinsic Zn2+and Cd2+ reactivities toward NaHSe, concentration of NaHSe, and the kind of thiols. A systematic blue shift in emission wavelength of the alloyed QDs was found with the increase in the Zn mole fraction. This result provides clear evidence of the formation of ZnxCd1-xSe QDs by the simultaneous reaction of Zn2+ and Cd2+ with NaHSe, rather than the formation of separate CdSe and ZnSe nanocrystals or core-shell structure CdSe/ZnSe nanocrystals. The size and inner structure of these QDs are also corroborated by using high-resolution transmission electron microscopy and X-ray powder diffraction. To further understand the formation mechanism, the growth kinetics of Zn0.99Cd0.01Se was studied by measuring the PL spectra at different growth intervals. The results demonstrated that, in the initial stage of growth, Zn0.99Cd0.01Se has a structure with a Cd-rich core and a Zn-rich shell. The post-preparative irradiation of these QDs improved their PL properties, resulting in stronger emission.     

CdSe quantum dot-dispersed DOBAMBC: an electro-optical study

Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system.     

Thermodynamic and conformational investigation of the influence of CdTe QDs size on the toxic interaction with BSA

Water-soluble fluorescent colloidal quantum dots (QDs) have been widely used in some biological and biomedical fields, so the interaction of QDs with biomolecules recently attracts increasing attention. In this study, the fluorescence (FL) quenching method, circular dichroism (CD) technique, attenuated total reflection-Fourier transform infrared (ATR-FTIR) and UV-vis absorption spectra were used to investigate systematically the influence of CdTe QDs size on the toxic interaction with bovine serum albumin (BSA). Three size CdTe QDs with maximum emission of 543 nm (green-emitting QDs, GQDs), 579 nm (yellow-emitting QDs, YQDs) and 647 nm (red-emitting QDs, RQDs) were tested. The Stern-Volmer quenching constant (K_sv) at different temperatures, corresponding thermodynamic parameters (ΔH, ΔG and ΔS), and information of the structural features of BSA were gained. The FL results indicated that QDs can effectively quench the FL of BSA in a size-dependent manner, electrostatic interactions play a major role in the binding reaction, and the nature of quenching is static, resulting in forming QDs-BSA complexes. The CD and ATR-FTIR spectra showed that the secondary structure of BSA was changed by QDs, indicating the toxic on protein.     

Characterization of quantum dot bioconjugates by capillary electrophoresis with laser-induced fluorescent detection

In this paper, we present a universal, highly efficient and sensitive method for the characterization of quantum dot (QD) bioconjugates based on capillary electrophoresis with laser-induced fluorescent (LIF) detection. We first prepared CdTe QDs in aqueous phase by a chemical route with mercaptopropionic acid as a ligand, and then were coupled to certain proteins using bifunctional linkage reagent or electrostatic attraction. The QD bioconjugates were characterized by capillary electrophoresis with LIF detection. We found that QD bioconjugates were efficiently separated with free QDs by the optimization of buffer pH. Furthermore, we found that ultrafiltration was an effective and simple approach to purify QD conjugates with bovine serum albumin (BSA). Due to their broad absorption spectra and size dependent emission wavelength tunability, QDs can be excited to emit different colour fluorescence using a single wavelength laser source, and therefore, we believe that CE with LIF detection will become a universal and efficient tool for the characterization of QD bioconjugates.     

高温热解法制备硒化镉纳米晶

以脂肪酸和三辛基氧化膦为表面活性剂,采用高温热解硒与镉的前聚体,制备出分散性好的CdSe纳米晶.吸收光谱和荧光光谱研究表明,控制反应时间可以改变CdSe纳米晶的荧光强度.