Investigation of ultrafast dynamics of CdTe quantum dots by femtosecond fluorescence up-conversion spectroscopy

The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.

Using capillary electrophoresis mobility shift assay to study the interaction of CdTe quantum dots with bovine serum albumin

In this work, the capillary electrophoresis mobility shift assay （CEMSA） was first adopted to study the interaction of protein with quantum dots （QDs）. In this study, bovine serum albumin （BSA） and CdTe QDs were used as model samples. We observed that BSA was facilely adsorbed to CdTe QDs surface, and the QD-BSA complex was formed by a 1：1 stoichiometric ratio. A value of 2.17 4-0.27 × 10^6 mol^-1 L^-1 （at 25 ℃） for the association constant was obtained by CEMSA.

Luminescent properties dependence of water-soluble CdTe quantum dots on stabilizing agents and reaction time

The influence of stabilizing agents and reaction time on the luminescent properties of water-soluble CdTe quantum dots(QDs) was discussed.The thioglycolic acid(TGA)-CdTe ODs were characterized by TEM,XRD and FTIR.It is found that larger-size QDs can be synthesized more easily when L-cysteine(Cys) or golutathione(GSH) is chosen as stabilizing agent and TGA is proper to prepare highly luminescent QDs because of the effect between Cd2+ and sulfhydryl group.Furthermore,the absorption wavelength,full width at half maximum(FWHM),stokes shift,photoluminescence(PL) quantum yield and PL stability of TGA-CdTe are strongly dependent on reaction time,in which the absorption wavelength changes against reaction time with an exponential function.The TGA-CdTe QDs prepared at 2 h possess more excellent luminescent properties.

Exploring Feasibility for Application of Luminescent CdTe Quantum Dots Prepared in Aqueous Phase to Live Cell Imaging

This paper explored the feasibility for the application of luminescent CdTe quantum dots prepared in aqueous phase to live cell imaging. The highly luminescent CdTe quantum dots （QDs） were first prepared in aqueous phase, and then were covalentiy coupled to a plant lectin （UEA-1）, as a fluorescent probe. After incubating with of human umbilical vein endothelial cells （HUVECs）, the QD probe with UEA-1 was able to specifically bind the corresponding cell receptor. The good cell images were obtained in live cells using laser confocal scanning microscopy. We predict that QDs prepared in water phase will probably become an attractive alternative probe in cellular imaging and bio-labeling.

MTT Detection of the Toxicity on CdTe Quantum Dots

Objective: The quantum dots are the useful materials in microelectronics and biomedical research. However its toxicity has to be considered. We studied the effect of cell inhibition with ZnS core quantum dots and CdTe quantum dots modified with Thioglycolic acid or Cysteine functional group (TGA-CdTe, TGA-CdTe/ZnS, Cys-CdTe, Cys-CdTe/ZnS) on Caco-2 cell proliferation. Methods: We studied the effect of cell inhibition with ZnS core QDs and CdTe QDs modified with functional group on Caco-2 cell proliferation by MTT assay at 0, 12.5, 25, 50, 100 μg/ml and 6, 24, 48 h. Result: Our results showed that all QDs have inhibited cell proliferation and reached maximum 79.21%. The inhibition rate of Cys-modified QDs increased with the increase of concentration and reached maximum 66.72%. The inhibition rate of TGA-modified QDs increased with the increase of time. The ratios of Cys-modified to TGA-modified were less than 1 at all concentrations and three exposure times (P ≤ 0.01). The average ratios of Cys-CdTe/ZnS to Cys-CdTe reached 1.11 only for 48 h (P ≤ 0.05). The ratios of TGA-CdTe/ZnS to TGA-CdTe were closed to 1 at all concentrations and exposure times. Conclusion: The regularity of QDs modified with functional group is that inhibition of TGA-modified higher than Cys-modified. Inhibition exhibited dose-dependent for Cys-modified while exhibited time-dependent for TGA-modified. The regularity of CdTe-QDs with ZnS or not is that the inhibition of Cys-CdTe/ZnS was higher than Cys-CdTe while TGA-CdTe/ZnS and TGA-CdTe were consistent.

Cytotoxicity and DNA Damage Effect of TGA-capped CdTe Quantum Dots

The cytotoxicity and DNA damage caused by thioglycolic acid（TGA）-capped cadmium telluride（CdTe） quantum dots（QDs） to hepatocyte line HL-7702 were investigated.Cell viability was measured by 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide（MTT） assay;DNA damage was detected by single cell gel electrophoresis（SCGE）;the change of cell cycle progression was examined by propidium iodide（PI）-flow cytometry（FCM）;apoptosis was measured by acridine orange/ethidium bromide（AO/EB） assay and Annexin V-FITC/PI-FCM（FITC：fluorescein isothiocyanate）.The results show that the cytotoxicity induced by CdTe QDs was increased in a dose-dependent and time-dependent manner;after exposure to QDs for 24 h,as the exposure dose increased,the rate of DNA damage was significantly increased（P0.05）,and the degree of DNA damage was elevated.As the dose of CdTe QDs increased,the percentage of G 0 /G 1 phase cells was significantly decreased（P0.001）,while the percenttages of S and G 2 /M phases cells were significantly increased（P0.001）.In AO/EB assay,apoptotic cells could be observed under a fluorescence microscope,and apoptotic rate was increased as exposure dose increased.In Annexin V-FITC/PI-FCM assay,the apoptotic rates of CdTe QDs treated groups were significantly increased compared with that of control group（P0.05）.Our studies indicate that CdTe QDs could influence cell viability,and induce DNA damage,the S and G2 /M phases arrest and apoptosis of HL-7702.

Luminous composite ultrathin films of CdTe quantum dots/silk fibroin co-assembled with layered doubled hydroxide:Enhanced photoluminescence and biosensor application

Quantum dots(QDs)luminescent films are extensively applied to optoelectronics and optical devices.However,QDs aggregation results in the quenching of their fluorescence property which limits their practical applications to a greater extent.In order to resolve this issue,3-mercaptopropionic acid(3-MPA)functionalized Cadmium Tellurium(CdTe)QDs were stabilized by silk fibroin(SB)and coassembled with layered doubled hydroxide(LDH)to form(QDs@SF/LDH)_(n)ultrathin films(UTFs)via the layer-by-layer(LBL)technique.UV-Vis absorption and fluorescence spectroscopy showed a stepwise and normal growth of the films upon increasing the number of deposition cycles.XRD and AFM studies confirmed the formation of a periodic layered structure and regular surface morphology of the thin films.As compared to(CdTe QDs/LDH)_(n)UTFs,the(CdTe QDs@SF/LDH)_(n)UTFs displayed fluorescence enhancement and longer fluorescent lifetime,both in solid states and aqueous solutions.Furthermore compared with the solution state,the fluorescence enhancement of SF-RC and SF-β are,respectively,7 times and 17 times in the(CdTe QDs@SF/LDH)_(n)UTFs,indicating that the LDH nanosheets favor the fluorescence enhancement effect on the CdTe QDs@SF.The fabricated materials displayed fluorescence response to a biological molecule such as immune globulin,lgG.Thus,the(CdTe QDs@SF/LDH)_(n)UTFs has a potential to be used as biosensor.

Picomolar Level Detection of Copper(II)and Mercury(II)Ions Using Dual‑Stabilizer‑Capped CdTe Quantum Dots

In this paper,dual-stabilizer-capped CdTe quantum dots were used as modulated photoluminescence(PL)sensors for the subpicomolar level detection of copper(II)(Cu^(2+))and mercury(II)(Hg^(2+))ions in aqueous solution for the first time.The dual-stabilizer-capped CdTe quantum dots were synthesized using mercaptopropionic acid(MPA)and sodium hexametaphosphate(SHMP)as surface-modified ligands via a convenient hydrothermal process.The researches showed a low interference response of the MPASHMP-capped CdTe quantum dots towards other metal ions.The highly efficient PL quenching ability in the presence of Hg^(2+)or Cu^(2+)ions due to the formed nonfluorescent metal complexes via robust Hg^(2+)–O interaction with the carboxy oxygen elements of surface ligands of MPA,and on the basis of the competitive binding of the mercapto groups of the MPA between the CdTe quantum dots and the Cu^(2+)ions,respectively,which allowed the analysis of Hg^(2+)or Cu^(2+)ions down to the picomolar levels.Under optimal conditions,the response of the MPA-SHMP-capped CdTe quantum dot PL intensity is linearly proportional to the Cu^(2+)and Hg^(2+)ion concentration ranging from 0.1 to 1000 and 0.3 to 1000 nM with a detection limit of 41.6 and 97.0 pM,respectively.The diagnostic capability and potential in practical applications of this method have been demonstrated by detecting Cu^(2+)and Hg^(2+)ions in environmental water samples.

Boric Acid-Based Dual Modulation Photoluminescent Glucose Sensor Using Thioglycolic Acid-Capped CdTe Quantum Dots

Most luminescent glucose sensors based on the interaction of glucose with organic boric acids or borates.Herein,a new luminescent glucose sensor is designed using thioglycolic acid-capped CdTe quantum dots in the presence of cheap inorganic boric acid.Both peak position and intensities change upon the addition of glucose because of the interaction of boric acid with glucose and thioglycolic acid-capped CdTe quantum dots,which enables glucose detection by either color change or intensity change.The luminescent intensities change linearly with glucose concentrations in the ranges from 0.03 to 1 mM and 1–25 mM with a detection limit of 10μM(S/N=3).Moreover,glucose concentrations can be conveniently detected by color change in the range from 1 mM–25 mM.It displays a highly selective response to glucose over other interfering but biologically important saccharides,amino acids,and common ions.Graphical Abstract A thioglycolic acid-capped CdTe QD-based sensor can detect glucose with wide linear range by change in intensity or color in the presence of cheap inorganic boric acid.

Interaction of CdTe/CdS quantum dots with antibodies

In the study, we observed the strong adsorption of CdTe/CdS QDs to antibodies and the formation of QDs-antibodies conjugates. Capillary electrophoresis with laser-induced fluorescence detection （CE-LIF）, fluorescence spectrometry and fluorescence correlation spectroscopy （FCS） were used to characterize the QDs conjugates with antibody. We found that the QDs-antibody conjugates possessed high fluorescence, small hydrodynamic radii and good stability in aqueous solution. 2009 Ji Cun Ren. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots（QDs） are fabricated on Si nanowires（NWs） substrates with and without Au nanoparticles（NPs）. The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence（PL） intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.

Cytotoxicity and cellular imaging of quantum dots protected by polyelectrolyte

The nanocomposites of poly-diallyldimethylammonium chloride (PDADMAC) and CdTe quantum dots (QDs) (i.e. QDs-PDADMAC nanocomposites) have been prepared based on electrostatic interaction and their fluorescence stability in aqueous solution has been investigated. MTT method (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method) was used to study their cytotoxicity and A549 lung cancer cell as a model cell was also used to evaluate their cellular imaging. It was shown that the fluorescence stability of QDsPDADMAC nanocomposites was much better than that of bare QDs both in aqueous solution and cell. Meanwhile, QDs-PDADMAC nanocomposites display very low cytotoxicity in the low concentrations and better staining ability compared with QDs. QDs-PDADMAC nanocomposites will have great advantage on the cell analysis detection and imaging.

Selective Detection of Mercury（Ⅱ） and Copper（Ⅱ） Based on the Opposite Size-dependent Fluorescence Quenching of CdTe Quantum Dots

Three different size CdTe quantum dots （QDs） capped by 3-mercaptopropionic acid （MPA） have been prepared in aqueous solutions, and their interactions with Cu^2＋ and Hg^2＋ have been investigated. The opposite size-dependent fluorescence quenching of CdTe QDs by Hg^2＋ and Cu^2＋ was observed： Hg^2＋ quenched smaller particles more efficiently than larger ones while larger particles were more markedly quenched by Cu^2＋. Based on the different size responses, Hg^2＋ and Cu^2＋ were respectively detected with high sensitivity and selectivity, for the first time, using the QDs with different sizes but the same components and capping ligands.

Enhanced chemiluminescence from reactions between CdTe/CdS/ZnS quantum dots and periodate

A novel chemiluminescence（CL） performance of CdTe/CdS/ZnS quantum dots（QDs） with periodate（KIO_4） was studied.Effects of concentration and pH on the CL system were investigated.Electron spin resonance（ESR） and the effects of radical scavenger analysis were employed for identification of intermediate species.The CL spectra for this system showed only one maximum emission peak centered around 620 nm,which was similar with photoluminescence（PL） spectra of CdTe/CdS/ZnS QDs.The CL of CdTe/CdS/ZnS QDs was induced by direct chemical oxidation and the possible mechanism could be explained by radiative recombination of injected holes and electrons.This investigation not only provided new sight into the optical characteristics of CdTe/CdS/ZnS QDs,but also broadened their potential optical utilizations.

One-bath synthesis of hydrophilic molecularly imprinted quantum dots for selective recognition of chlorophenol

A simple one-bath strategy has been developed to synthesize a novel CdTe@SiO_2@MIP（molecularly imprinted and silica-functionalized CdTe quantum dots,MISFQDs）,in which a silica shell was coated on the surface of CdTe quantum dots （CdTe@SiO_2 QDs） and then a polymer for selective recognition of 4-chlorophenol（4-CP） was constructed on the surface of CdTe@SiO_2 QDs using mercaptoacetic acid as stabilizer,3-aminopropyl-trimethoxysilane（APTES） as functional monomers and tetraethoxysilane（TEOS） as crosslink agent.The structures of CdTe@SiO_2@MIP were analyzed by ultraviolet-visible absorption. Fluorescence,FT-IR spectrum and powder X-ray diffraction.The application and characterization of the CdTe@SiO_2@MIP were investigated by experiments.All results indicated that the CdTe@SiO_2@MIP can selectively recognize 4-chlorophenol.

Biosynthesis of Biocompatible Cadmium Telluride Quantum Dots Using Yeast Cells

We demonstrate a simple and efficient biosynthesis method to prepare easily harvested biocompatible cadmium telluride(CdTe)quantum dots(QDs)with tunable fluorescence emission using yeast cells.Ultraviolet-visible(UV-vis)spectroscopy,photoluminescence(PL)spectroscopy,X-ray diffraction(XRD),and transmission electron microscopy(TEM)confirm that the CdTe QDs are formed via an extracellular growth and subsequent endocytosis pathway and have size-tunable optical properties with fluorescence emission from 490 to 560 nm and a cubic zinc blende structure with good crystallinity.In particular,the CdTe QDs with uniform size(2-3.6 nm)are protein-capped,which makes them highly soluble in water,and in situ bio-imaging in yeast cells indicates that the biosynthesized QDs have good biocompatibility.This work provides an economic and environmentally friendly approach to synthesize highly fluorescent biocompatible CdTe QDs for bio-imaging and bio-labeling applications.