Synthesis Of CdTe Quantum Dots Research Articles

Synthesis of CdTe quantum dots using Glutathione promoted in Vitro Interaction between Lysozyme and Flavanoids: An investigation through spectroscopic methods

We investigated the interaction of four flavonoids in this study, such as 4′,5,7-trihydroxy-isofavonethe or 5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one (Genistein-GES), 5,7-Dihydroxy-2-phenyl-4H-1-benzopyran-4-one (Chrysin-CRS), 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one (Quercetin-QRS) and 7-Hydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one (Daidzein-DIA), [0–5 × 10−6 M] and lysozyme without and the existence of the GSHCdTe quantum dots. Here, the spectrofluorimetric technique is used to investigate the interaction and quenching observations are rationalized in terms of a static quenching way. The binding constant (K) and the number of binding sites (n) are calculated based on the fluorescence quenching data. The affinities of flavonoids and lysozyme system enhance with smaller size quantum dots. The as-prepared GSH-capped QDs clearly reveal the linkage attractions of lysozyme and flavonoids enhanced with diminishing the quantum dots size and the interaction depends on physicochemical and environmental factors.

Green Synthesis of CdTe Quantum Dots and Their Effect on Human and Animal Cells

Green Synthesis of CdTe Quantum Dots and Their Effect on Human and Animal Cells

Aqueous Synthesis of CdTe Quantum Dots and Optical Characterization Under High Voltage

Aqueous Synthesis of CdTe Quantum Dots and Optical Characterization Under High Voltage

SYNTHESIS OF CdTe QUANTUM DOTS IN AQUEOUS PHASE USING MERCAPTOSUCCINIC ACID

Highly luminescent CdTe quantum dots (QDs) are the most widely used nanoparticles for making fluorescent biosensors and optoelectronic devices. In this paper, we present the successful synthesis of CdTe QDs in the aqueous phase using mercaptosuccinic acid (MSA) as a capping ligand. The CdTe QDs were formed by the reaction of the Te precursor (in TeO2) with Cd2+/MSA in solution at 80 oC for 30 min, then annealing in an autoclave at different temperatures (110 - 150 oC) and time intervals (60 - 180 min). The synthesis of QDs in water has many advantages such as the simplicity, environmental friendliness, and using cheap chemical agents, and particularly make the CdTe QDs suitabble for bioapplications because of the biocompatibility. The high quality of the synthesized CdTe QDs was confirmed by X-ray diffraction (XRD) and their optical properties. The XRD pattern shows the cubic zinc blende structure of the synthesized CdTe QDs. Additionally, the influences of the synthesis parameters, namely the annealed temperature, time to the optical properties of the obtained QDs were systematically investigated with regard to the growth rate and particle size. As a result, CdTe QDs become bigger causing the red-shifted of peaks in their absorption and photoluminescence spectra with increasing annealed temperature and time. This provides evidence for the quantum confinement effect.

Aqueous-phase synthesized CdTe quantum dots: an insight into nanoparticle architecture-quantum yield relationship, characterization, and computational study of small clusters

Aqueous-phase synthesis of highly luminescent CdTe QDs, insight on the influence of core composition, ligand type, molar ratio, reaction time, and shell type over QY, and computational study of small non-stoichiometric clusters.

Selective Hydrothermal Synthesis of Water-Soluble CdTe and CdTe/CdS Colloidal Quantum Dots by Controlling the Te/Cd Molar Ratio of the Precursor Solution

Abstract During the synthesis of CdTe quantum dots (QDs) by the hydrothermal method, a CdS shell layer is naturally formed by the thermal decomposition of thiol ligands, and CdTe/CdS core/shell QDs are produced. Herein, we investigate the selective synthesis of CdTe and CdTe/CdS QDs to control the thermal decomposition of thiol ligands by changing the Te/Cd molar ratio of the precursor solutions. From the experimental results of X-ray photoelectron spectroscopy and optical properties of absorption and photoluminescence (PL) spectra and PL decay profiles of the synthesized colloidal QDs, it was found that the formation of the CdS shell can be controlled by varying the Te/Cd ratio of the precursor solution. Thus, the selective synthesis of CdTe and CdTe/CdS QDs with the same PL energy but different PL decay times is possible.

Biological Synthesis of CdTe Quantum Dots and Their Anti-Proliferative Assessment Against Prostate Cancer Cell Line.

Quantum dots (QDs) are semiconducting materials which have a wide array of applications starting from semiconducting devices, in humidity and pressure sensors and in medical imaging including cancer therapy. In the present study, cadmium telluride (CdTe) QDs were synthesized by a biological method using yeast cells, Saccharomyces cerevisiae in modified Czapek's medium. QDs were characterized by transmission electron microscopy and X-ray diffraction. Cancer cells were treated with 2, 4, 8 and 16 μM concentrations of CdTe QDs for 24 h. The anti-proliferative activity was determined by using MTT assay, by evaluating the production of reactive oxygen species (ROS), and also by nuclear apoptosis and cell cycle analysis using a flow cytometer against human prostate carcinoma cell line PC-3. The size of the CdTe QDs was approximately 2 nm. In vitro anti-proliferative study showed that CdTe QDs induced cell death and nuclear apoptosis in a dosedependent manner. CdTe QDs induced significant increase in ROS level in PC-3 cells which was dose-dependent. Moreover, CdTe also arrested growth of PC-3 cells in the G2/M phase of the cell cycle. This study elucidates the apoptotic activity of CdTe QDs on prostate carcinoma which could provide useful insights to researchers for its clinical application.

Cysteine mediated synthesis of quantum dots: Mechanism and application in visual detection of hydrogen peroxide and glucose

A novel visual detection method was developed for H2O2 and glucose detection via the L-Cysteine (L-Cys) mediated synthesis of quantum dots (QDs). The mechanism of the ligand effect during QDs synthesis was also studied by theoretical calculation. This strategy is based on that L-Cys can be used as both H2O2 substrate and ligand to mediate biomimetic synthesis of luminescent CdTe QDs. Iodide (I−) can catalytic oxidized L-Cys to L-cystine in the presence of H2O2, which inhibits the synthesis of QDs. Hence, the degree of inhibition for the QDs synthesis is proportional to the H2O2 concentration. Additionally, the ligand effect of L-Cys and L-cystine for CdTe QDs synthesis was studied. The density functional theory (DFT) calculations showed that the combination of CdTe QDs with L-Cys had higher energy and more stable configuration than that with L-cystine, indicating that L-Cys is the more stable ligand of QDs. Under the optimized conditions, a low limit of detection (LOD) was obtained for H2O2 (0.3 nM). Then, we used H2O2 as a bridge for glucose detection, with a LOD of 5 nM. The feasibility of this sensor was demonstrated by rapid detection of H2O2 and glucose by naked-eye at a level of 10 nM.

Branched Ligand Ethyl 2‐Mercaptopropionate as a Stabilizer for CdTe Quantum Dots and its use as a Cu2+ Ions Probe in Aqueous Medium

AbstractIn the present work, we explored the possibility of using a novel stabilizing ligand namely ethyl 2‐mercaptopropionate for the synthesis of CdTe quantum dots (QDs). The QDs were synthesized and stabilized by the ligand and it was realized to be emitting at 560 nm. Extensive microscopic and photo physical characterization were carried out in order to unearth the nature of the QDs synthesized. Interestingly, it was observed that, the photoluminescence emission of as synthesized QDs were getting quenched linearly in the presence of Cu2+, which prompt us to make use of these QDs for the detection of Cu2+ ions in aqueous media. A detailed mechanism of quenching was also proposed. The linear range over which the QDs was selective to Cu2+ ions was from 0.5 nM to 129.5 nM with a detection limit (LOD) of 0.5 nM providing a pathway for the QDs based Cu2+ probe.

Application of ratiometric fluorescence sensor-based microwave-assisted synthesized CdTe quantum dots and mesoporous structured epitope-imprinted polymers for highly efficient determination of tyrosine phosphopeptide

Molecularly imprinted polymer coated quantum dot sensor modified with ratiometric fluorescence methods and mesoporous structured epitope imprinted silica materials (QDs@SiO2@EMSiO2) have been fabricated for detection of tyrosine phosphopeptide.

Synthesis of CdTe quantum dots capped with castor oil using a hot injection solution method

Castor oil (CSTO), an extract from castor bean was used as capping material for CdTe quantum dots (QDs), synthesized from cadmium chloride and tellurium powder using a modified hot injection method. The formation of CdTe QDs in the colloidal solution was monitored by UV–Vis spectrophotometry. The average particle sizes were deduced from the absorption data, transmission electron microscopy (TEM) images and powdered-X-ray diffraction (p-XRD). The average particle size of CdTe QDs deduced from the UV–Vis absorption measurements range from 4.94 nm to 10.04 nm for CdTe QDs synthesized at 230 °C, 250 °C and 280 °C. TEM images of the CdTe QDs synthesized at 250 °C and 280 °C, for 2 h showed close to spherical geometry with average diameter of 7.38 ± 0.43 nm and 9.88 ± 0.67 nm, respectively. The p-XRD patterns confirmed the presence of CdTe crystallites with a cubic phase. The average diameter of CdTe QDs as deduced from the p-XRD patterns was 7.54 ± 0.03 nm and 9.69 ± 0.13 nm, respectively, which is in good agreement with the results from TEM and UV–Vis absorption measurements. The photoluminescence spectroscopy showed the formation of nearly monodispersed particles with emission maxima at 673 nm, 714 nm and 743 nm for CdTe QDs prepared at 230 °C for 30 min, 60 min and 120 min, respectively. These results show that green biomasses are valuable eco-friendly materials which can be used to stabilize nanomaterials.

Band edge alignment for tuning interfacial charge transfer: a case study of NaTaO3 as photoelectron platform by anchoring CdTe quantum dots

CdTe quantum dots (QDs) were anchored on NaTaO3 nanocubes with the aim into tuning the charge kinetics for spatial separation of the photogenerated electrons and holes by modifying the relative potential of the conduction band of CdTe QDs. In this work, CdTe QDs (particle size 2–3 nm) and NaTaO3 were synthesized via reflux and hydrothermal reaction. Thioglycolic acid (TGA) acted as both a stabilizer and linker molecules during the synthesis of CdTe QDs and NaTaO3/CdTe heterostructure. On accounts of density functional theory (DFT) predictions, electrons can transfer from NaTaO3 to CdTe due to the difference of the Fermi level between two semiconductors, which will establish a built-in electric field at semiconductor interfaces, accelerating the charge separation kinetics between CdTe and NaTaO3. In response, electronic structure tunable CdTe QDs were surface engineered on NaTaO3 nanocubes to enhance the visible light (VL) harvesting capability. By carefully controlling the fine nature of CdTe QDs, photogenerated electrons in CdTe can be efficiently injected into the conduction band of NaTaO3, leading to spatial charge separation between CdTe and NaTaO3. This could be affirmed by applied bias photo to current efficiency (ABPE), incident photocurrent responses as well as electrochemical impedance curves. With well-defined crystallinity, electronic structure, and interfacial contact between NaTaO3 and CdTe, the optimized photocatalytic activity toward hydrogen production over NaTaO3/CdTe heterostructure achieved an evolution rate of 56 μmol·g−1·h−1, which is far surpassed than that of pristine NaTaO3 and CdTe.

Branched mercapto acid capped CdTe quantum dots as fluorescence probes for Hg2+ detection

Herein, we report the synthesis of CdTe quantum dots prepared by colloidal synthesis route using the branched mercapto acid, 3 Mercaptoisobutyric acid (3-MIBA) as capping agent. The as synthesized 3-MIBA capped CdTe quantum dot (CdTe@3-MIBA) was used as fluorescent probe to detect Hg2+. Further, the performance was linear in the range 1.5–100 nM with a limit of detection of 1.5 ± 0.5 nM. The results demonstrated that fluorescence quenching of CdTe@3-MIBA by mercury follow different routes: (i) strong affinity of Hg towards S causes depassivation of capping agents thus resulting in aggregation of quantum dots (ii) excitonic electron transfer from the lowest unoccupied molecular orbital (LUMO) of CdTe@3-MIBA to the LUMO of Hg2+ thus preventing emission.

Surface engineering of CdTe quantum dots using ethanol as a co-solvent for enhanced current conversion efficiency in QDSSC

Achieving a cost-effective synthesis of QDs with superior surface quality will dictate the feasibility of quantum dots in commercial photovoltaic devices. Here we report a simple aqueous synthesis of CdTe quantum dots coated with thin CdS layer in water-ethanol solvent mixture for better surface eminence. Enhanced solubility of capping agent and slow growth rate of CdS over CdTe taking place in water ethanol solvent mixture leads to strain free interface construction resulting in 51% enhancement of Photo Luminescence Quantum Yield. Controlling the solubility and growth rate of CdS coating over CdTe core QDs via ethanol addition exhibits a 28.4% and 44.6% improvement in short circuit current densities and quantum dot sensitized solar cells with a conversion efficiency of 2.5% is achieved. Our results show that mixed solvents can be utilized for optimizing the aqueous synthesis of CdTe/CdS QDs with enhanced optical properties leading to better performing photovoltaic devices.

Capillary electrophoresis-driven synthesis of water-soluble CdTe quantum dots in nanoliter scale

‘Green nanotechnology’ is a term used for the design of nanomaterials and processes that reduce or eliminate the use and/or generation of hazardous substances. In this paper, a capillary electrophoresis (CE)-driven synthesis of CdTe quantum dots (QDs) and their subsequent conjugation with a metal-binding protein metallothionein (isofom MT1) is reported. Even though the toxic materials (cadmium and potassium borohydride) were used for synthesis, the proposed method can be labeled as ‘environmentally friendly’ because the whole process (synthesis of QDs and MT1 conjugation) was carried out under mild conditions: ultra-low volume (nanoliter scale), relatively low temperature (50 °C), atmospheric pressure, and completed in a short time (under 90 s). Prepared QDs were also characterized by classical fluorescence spectroscopy and transmission electron microscopy. This study opens up new possibilities for the utilization of classical CE in the synthesis of nanoparticles and on-line labeling of biomolecules in the nanoliter scale in short period of time.

Detection of nucleic acids via G-quadruplex-controlled l-cysteine oxidation and catalyzed hairpin assembly-assisted signal amplification.

The development of simple, sensitive and cost-effective methods for specific nucleic acid detection has attracted tremendous attention due to its importance to the early diagnosis of genetic diseases and to biodefense applications. In this work, we demonstrated a fluorescent turn-off mode DNA assay based on l-cysteine-modulated synthesis of CdTe quantum dots (CdTe QDs), horseradish peroxidase-mimicking G-quadruplex–hemin–K+ complex controlled oxidation of l-cysteine to cystine, and catalyzed hairpin assembly (CHA)-assisted signal amplification. After the addition of target DNA, the CHA signal amplification reaction was triggered and numerous H1–H2 double-stranded DNA were formed, initiating the release of G-quadruplex sequences in H2 simultaneously. Thus, the degree of inhibition of the synthesis of CdTe QDs is proportional to the concentration of the G-quadruplex sequence in this method. In contrast, when the target DNA was absent, the CHA could not be triggered, and the fluorescence signal was high due to the remaining intact l-cysteine. Under optimal experimental conditions, the homogeneous fluorescence method achieved the detection of HIV DNA with a linear range from 0.1 pM to 1 nM and a detection limit of 0.12 pM. This novel biosensor exhibits excellent specificity in differentiating DNA sequences with a single-base and two-base mismatch. To the best of our knowledge, this a label-free and highly sensitive bioassay utilizing CHA-assisted signal amplification and G-quadruplex control of in situ synthesis of CdTe QDs strategy was not reported in previous. Thus, this proposed strategy is anticipated to find use in basic biochemical research and clinical diagnosis.

Study about Electrostatic Deposition of CdTe Quantum Dots on Glassy Carbon Electrodes

Quantum Dots (QDs) are semiconductor nanocrystals. These materials are characterized for its continuous absorption spectra at wavelengths ranging from ultraviolet to visible. This feature is directly related to the size of the nanoparticle. Considering their applications, these materials can be employed in solar cells, lasers, light emitting diodes, electronic devices, among others. However, one of the most attractive applications for QDs has been as sensors or biosensor. In this work, the synthesis of CdTe Quantum Dots was carried out in aqueous media using Na2TeO3 and CdCl2 as precursors of Te2- and Cd2+ ions, respectively, mercaptosuccinic acid (MSA) as capping agent and NaBH4 as reducing agent. The QDs obtained as colloids were purified and characterized by transmission electron microscopy (TEM), while their optical properties were characterized by UV-visible spectroscopy. After, an electrostatic deposition of the QDs on a Glassy Carbon (GC) electrode was done. This last was carried out applying a positive potential value regarding to the zero charge potential of the electrode in an aqueous media, and the influence of the potential value, deposition time was determined by means cyclic voltammetry. A study of surface conductivity changes of the glassy carbon electrodes after QDs deposition was performed by means Scanning Electrochemical Microscopy (SECM). With this was possible to observe aggregates of CdTe QDs deposited on GC electrodes indicating a possible irreversible electrostatic deposition

Study about Overall Adhesion-Spreading Process of Liposomes on a Gold Electrode. Influence of the Presence of CdTe Quantum Dots

The utilization of quantum dots (QDs) it has been grown up into the material science area, because these nanoparticles have particular optical and electronic properties. These properties are dependent on the particle size, which can be controlled by the modification of some experimental conditions: temperature, reaction time, pH and molar ratio of precursors. QDs present a wide absorption spectrum, narrow emission fluorescence spectrum, high photo-stability, tunable band gap, high quantum yield, among others. These properties have allowed its application in different areas such as photovoltaic cells, biomedicine, chemical analysis, biosensors and biomarkers. However, particularly in the medicine field is very important to know what is the effect of QDs in contact with cell membranes. An approximation to this process could be the utilization of structures like lipid vesicles or liposomes, which also can be used as drug and biomarkers carriers. Some authors [1], [2] have used electrochemical methods in the study of liposomes, because the vesicles deposition process (adhesion and spreading processes) on metallic electrodes are similar to the lipid membranes fusion, providing information about e.g. exo- and endocytosis processes. In this context, this work is related with the influence of the interaction between CdTe QDs and 1,2-dimyristoyl-sn-phosphatidylcholine (DMPC) liposomes on the overall adhesion-spreading processes of liposomes modified by QDs. Synthesis of CdTe QDs was carried out in aqueous media, by using CdCl2 and Na2TeO3 as precursors, mercaptosuccinic acid (MSA) as capping agent and NaBH4 as reducing agent. Using a Doehlert’s experimental design was possible the optimization of the QDs sizes controlling the synthesis variables, i.e. temperature, reaction time, pH and molar ratio of precursors. After QDs were purified through ultracentrifugation with 1:1 water:isopropanol mixture and re-suspended in a buffer solution (borate buffer; pH 9.20). Finally, these were characterized by UV-Vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). On the other hand, DMPC liposomes were prepared by dissolving DMPC in chloroform, then evaporating solvent with Argon and suspending the lipids in borate buffer. Lipid suspension was cooled with liquid nitrogen and then heated below the phase transition temperature. Finally, lipids were extruded to obtain large unilamellar vesicles. After, the DMPC liposomes were deposited on gold electrode and characterized by CV observing the coverage degree by charge analysis. Additionally, the overall adhesion-spreading process of liposomes on gold electrode was characterized by means of chronoamperometry technique analyzing the corresponding current-time transients. Both analysis were performed after the mixing with CdTe QDs. The results show a decrease in the constant rate values of the adhesion-spreading processes of DMPC liposomes on gold electrode suggesting that the interaction CdTe(QD)-DMPC produces an increase in the activation energy of the lipid membranes fusion

Easy, one-step synthesis of CdTe quantum dots via microwave irradiation for fingerprinting application

A novel one-step microwave irradiation method has been introduced to synthesize 3-mercaptopropionic acid capped CdTe QDs (Quantum dots). The synthesis process required no special conditions such as an inert nitrogen atmosphere but was carried out using TeO2 (Tellurium oxide) as opposed to the Te powder, Na2TeO3 or Al2TeO3 usually used for the tellurium source. The characterization of the QDs revealed that they were 2–3nm in size. The application of aqueous synthesis of capped CdTe QDs for latent fingerprinting was explored and fast turnaround times were achieved.

Phosphine-free synthesis of high-quality CdTe quantum dots: The combination of TeO2-dodecanethiol and oleylamine as Te precursor

Currently, the synthesis of CdTe quantum dots (QDs) in organic phase has basically involved costly and air-sensitive reagents such as alkylphosphines, making a more economical approach desirable. Here, a phosphine-free approach has been developed to prepare CdTe QDs, in which TeO2 dissolved in 1-dodecanethiol (DT) was employed as the Te source. The obtained QDs were highly luminescent and exhibited desirable size-tunability and narrow size distribution. More importantly, oleylamine (OLA), the specific solvent in this method, has been found to be crucial for TeO2-DT to provide reactive Te species for the formation of CdTe. These results suggest that the combination of TeO2-DT and OLA should be an efficient Te precursor for the preparation of colloidal tellurides.