CdTe Semiconductor Quantum Dots Research Articles

Exploring the probing capacities of MSA capped CdTe semiconductor quantum dots as optical chemsensors via analytical and isotherms modeling for selective Hg2+ detection

Heavy metal ions bioaccumulation can cause severe damage to environment and human health. Hence, the development of an effective detection assay of trace amounts of these ions is of great importance. Here, CdTe quantum dots (QDs) capped with mercaptosuccinic acid (MSA) ligands have been synthesized in aqueous solution with significant stability and good fluorescence properties. Photophysical characterization was performed using FTIR, XRD, HRTEM and UV–Vis. Absorption, PL and PLRT techniques, seeking their subsequent application as fluorescent probes for metal cations. CdTe-MSA QDs showed selective sensitivity toward Hg2+ ions by monitoring quantitative fluorescence quenching with increasing analyte content. Under optimal conditions, the linear range for the detection was 0.2–6 μM with a detection limit of 0.05 μM. According to the Stern–Volmer model, it can be inferred that a static quenching mechanism via Hg2+ selective binding to MSA carboxylate groups is operating with electron transfer process. Excess of mercuric ions further decreased and red shifted the fluorescence possibly due to competitive cation exchanges. To further explain the corresponding ligation mechanisms, adsorption behavior study was conducted via several isotherms as well as statistical physics models. The pseudo-first-order model can describe the adsorption kinetics of Hg2+ on CdTe-MSA QDs more accurately and the experimental data fitted well the Langmuir isotherm model of monolayer adsorption on homogeneous surface. Furthermore, this spontaneous process conforms to the Hill model as a physisorption with an adsorption energy of 32 kJ.mol−1 associated with the electrostatic interactions and hydrogen bonding. The developed system was assayed in the Hg2+ trace amount detection in real tap water and showed satisfactory accuracy performance meeting analytical requirements. The relevant results demonstrated that CdTe-MSA QDs could be deployed as promising Hg2+ fluorescent chemosensing system with high sensitivity and selectivity over wide linear detection range that have great potential for real water samples analysis.

Preparation of CdTe quantum dots for detecting Cu(II) ions

Although copper is needed by the human body, excessive copper can cause diarrhea, vomiting, and neurological disorders. In this study, CdTe semiconductor quantum dots (QDs) with different emission wavelengths were fabricated and used for detection of copper ions. By controlling the temperature, nucleation and growth of the crystals in the aqueous phase were separated, which improved the optical properties of QDs. They were characterized with Fourier-transform infrared (FT-IR), Transmission electron microscope (TEM) and X-ray diffraction (XRD). After being coated by the sol-gel method, the QDs were used to detect Cu(II) ions. There was a good linear relationship between the concentration of Cu(II) ions and the quenching efficiency of fluorescent probes over the range 0–1 mg L−1, and the detection limit was 1.18 μg L−1 (n = 10). Ratiometric fluorescent probes were also fabricated, which exhibited better Cu(II) ion detection, with a detection limit as 0.13 μg L−1 (0.002 μmol/L) that was far lower than the detection standard of copper ions in water.

Preparation and Fluorescence Characterization of CdTe Semiconductor Quantum Dots

Preparation and Fluorescence Characterization of CdTe Semiconductor Quantum Dots

Dual-emission ratiometric probe combining carbon dots and CdTe quantum dots for fluorometric and visual determination of H2O2

In this work, blue-emitting carbon quantum dots and distinctly sized CdTe semiconductor quantum dots were combined to implement a ratiometric probe for the monitoring of H2O2. By implementing a sensing scheme that combines multiple nanoprobes, excited at the same wavelength and emitting at different ones, which exhibit also dissimilar reactivity, it was possible to minimize detrimental factors associated with the use of a single photoluminescence wavelength such as fluctuations in excitation source or measured signal, fluorophore concentration, matrix effects and background fluorescence. The developed ratiometric probe was applied on the implementation of a conventional fluorometric assay and on a visual assay relying on the red, green and blue (RGB)-based colour changes promoted by increasing H2O2 concentrations.For the fluorometric determination assay, a good linear relationship between the fluorescence intensity ratio (FICD434/FIMPA587) and H2O2 concentration within the range of 0.0100–0.2125% (w/w) was obtained (R = 0.9994, n = 7). The detection limit was about 0.00793% (w/w). The obtained results in the determination of H2O2 in contact lens solutions were in agreement with those provided by the reference procedure, with relative deviations between −4.71 and 1.89%. Regarding the RGB-visual assay, a linear working range for hydrogen peroxide concentrations up to 0.150% (w/w) was verified (n = 9) with a correlation coefficient of 0.9966, which confirms its potential as valuable analytical tool for on-the-spot semi-quantitative detection of H2O2.

Breaking of the phosphodiester bond: a key factor that induces hemolysis.

In-depth understanding the toxicity of nanomaterials in red blood cells (RBCs) is of great interest, because of the importance of RBCs in transporting oxygen in blood circulation. Although the toxic effects of nanoparticles in RBCs have been revealed, the conclusions from the literature are conflicting, and in particular, the toxic mechanism is still at the infant stage. Herein, we investigated the size-dependent toxicity of well-known CdTe semiconductor quantum dots (QDs) and revealed the exact toxic mechanism at the molecular level by confocal microscopy and Fourier transform infrared (FT-IR) spectroscopy techniques. We found that smaller mercaptosuccinic acid-capped CdTe QDs (MSA-QDs) with the green-emitting color could cause hemagglutination whereas the middle-size yellow-emitting MSA-QDs induced the formation of stomatocytes and echinocytes and the bigger size red-emitting MSA-QDs induced heavy hemolysis and the formation of lots of ghost cells. The FT-IR data proved that all the MSA-QDs were likely to bond to the RBCs membranes and caused the structural changes of lipid and protein in RBCs. But only the red-emitting MSA-QDs caused the breakage of the phosphodiester bond, which might cause the heavy hemolysis. To some extent, this is the first example that reveals the hemolysis mechanism at the molecular level.

Synthesis and enhanced fluorescence of Ag doped CdTe semiconductor quantum dots.

Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs.

Ab initio study of ZnSe and CdTe semiconductor quantum dots

We apply first principles density functional and time dependent density functional computational methods to study the structures, densities of states, absorption spectra, and optical gaps of spherical ZnSe and CdTe semiconductor quantum dots in the size range 0.3–2.2nm. Our calculations are performed in real space without an explicit basis. The surfaces of the quantum dots are passivated with partially charged hydrogen atoms. We find that this passivation technique effectively removes the electronic states associated with the surface atoms from the gaps of ZnSe and CdTe nanocrystals, but does not affect the energies of the quantum-confined electronic states. Our study shows that the absorption gaps of ZnSe and CdTe quantum dots decrease with increasing dot diameter. The size-dependent variations of the computed optical gaps in surface-passivated ZnSe and CdTe quantum dots are found to be consistent with the effects of quantum confinement observed in group IV and group III–V semiconductor nanocrystals.

Facile, sensitive, and ratiometric detection of mercuric ions using GSH-capped semiconductor quantum dots

Glutathione (GSH) capped CdTe semiconductor quantum dots (QDs) are applied for detecting mercuric ions (Hg(2+)) of trace quantity. The synthesis of GSH-capped CdTe (CdTe@GSH) QDs is cost-efficient and straightforward. We observed that Hg(2+) can quantitatively quench the fluorescence of CdTe@GSH QDs and further induce the slight redshift of emission peaks due to the quantum confinement effect. Detailed studies by spectroscopy, dynamic light scattering (DLS), and electrospray ionization mass spectrometry (ESI-MS) demonstrated that the competitive Hg(2+) binding with GSH makes the surface of CdTe QDs exposed, results in gradual aggregation, and quantitatively changes the photophysical properties of QDs. The whole procedure for detecting Hg(2+) by this protocol took less than 10 min. The experimental limit of detection (LOD) of Hg(2+) can be as low as 5 nM using CdTe@GSH with a low concentration (0.5 nM) because of the excellent fluorescent properties of QDs. This strategy may become a promising means to simply detect Hg(2+) in water with high sensitivity.

Aqueous Synthesis of Highly Monodispersed Thiol-Capped CdTe Quantum Dots Through Electrochemical Approach

A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdTe semiconductor Quantum dots (QDs) via the electrochemistry method. The Low growth temperature and slow injection of Te precursors are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during nanocrystal growth. The experimental results showed that a low concentration of Te precursor would definitely influence the growth procedure. The narrow absorption peaks in the UV-visible absorption spectra, as well as transmission electron microscopy images indicated that the as-prepared CdTe QDs had a good monodispersity. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The QDs exhibited high fluorescence QYs about 50% and the best of QY 67% without any postpreparative treatment over a broad spectral range of 516-609 nm, which could be further broadened by long-term refluxing. The current work suggested that electrochemical method was an attractive approach to the synthesis of high-quality II-VI semiconductor QDs at a large scale.

Novel Fluorescence Method for Detection of α-l-Fucosidase Based on CdTe Quantum Dots

The enzyme α-L-fucosidase (AFu) plays an important role in the diagnosis of hepatocellular carcinoma (HCC) and fucosidosis. In this paper, a simple, sensitive and precise method based upon measuring the fluorescence quenching of CdTe semiconductor quantum dots (QDs) was developed for detecting the enzymatic activity of AFu. The detection limit of AFu was 0.01 U/L (n = 3) and the linear relationship was 0.01-4 U/L. The selectivity experiment indicated excellent selectivity for AFu over a number of interfering species. We have also studied the detection mechanism of AFu by X-ray photoelectron spectroscopy (XPS) and found that the quenching effect was caused by the oxidation of tellurium by 2-chloro-4-nitrophenol (2-CNP) which produced in AFu catalytic reaction. Moreover, the AFu sensor based on QDs was used satisfactorily for the assessment of AFu activity in serum samples. It will most probably be applicable in assembling diagnostic microdevice to realize the rapid clinic analysis of AFu.

Deep tissue bio-imaging using two-photon excited CdTe fluorescent quantum dots working within the biological window

A new approach to deep tissue imaging is presented based on 8 nm CdTe semiconductor quantum dots (QDs). The characteristic 800 nm emission was found to be efficiently excited via two-photon absorption of 900 nm photons. The fact that both excitation and emission wavelengths lie within the "biological window" allows for high resolution fluorescence imaging at depths close to 2 mm. These penetration depths have been used to obtain the first deep tissue multiphoton excited fluorescence image based on CdTe-QDs. Due to the large thermal sensitivity of CdTe-QDs, one may envisage, in the near future, their use in high resolution deep-tissue thermal imaging.

Highly-sensitive organophosphorous pesticide biosensors based on nanostructured films of acetylcholinesterase and CdTe quantum dots

The optical transducer of CdTe semiconductor quantum dots (QDs) has been integrated with acetylcholinesterase enzyme (AChE) by the layer-by-layer (LbL) assembly technique, resulting in a highly sensitive biosensor for detection of organophosphorus pesticides (OPs) in vegetables and fruits based on enzyme inhibition mechanism. The detection limits of the proposed biosensors are as low as 1.05×10−11 M for paraoxon and 4.47×10−12 M for parathion, which are significantly better than those of the conventional GC/MS methods or amperometric biosensors (0.5nM). These biosensors are used for quick determination of low concentrations of OPs in real vegetable and fruit samples and exhibit satisfactory reproducibility and accuracy. Moreover, the stock stability of the biosensors are very good due to the stabilizing environment for the enzyme in the nanostructures made by LbL technique. Many advantages provided by these biosensors, like fluorescent change recognized by naked eyes and mass production with low cost, will facilitate future development of rapid and high-throughput screening of OPs.

Enhancement effect of CdTe quantum dots–IgG bioconjugates on chemiluminescence of luminol–H 2O 2 system

In this paper we developed an entirely new and highly sensitive luminol–H 2O 2 flow injection chemiluminescence system using the enhancement effect of CdTe quantum dots–IgG bioconjugates. Immunoglobulin G (IgG) as a kind of bio-molecule was conjugated to different sized CdTe semiconductor quantum dots (QDs). Using PL spectra and CL intensity profiles, it was found that chemiluminescence resonance energy transfer (CRET) was possibly occurring between CdTe–IgG bioconjugate and luminol. Under optimum conditions, increase of IgG concentration in CdTe–IgG bioconjugate resulted enhancing effect on CL intensity of luminol–H 2O 2 system. Moreover quenching effects on CL intensity by addition of different proteases can construct turn off biosensor for these proteases with low detection limits and wide linear range. Furthermore, the effects of various organic and inorganic species on CdTe–IgG bioconjugates enhanced luminol–H 2O 2 CL system were also studied in this paper.

Glucose Biosensor Based on Nanocomposite Films of CdTe Quantum Dots and Glucose Oxidase

A blood glucose sensor has been developed based on the multilayer films of CdTe semiconductor quantum dots (QDs) and glucose oxidase (GOD) by using the layer-by-layer assembly technique. When the composite films were contacted with glucose solution, the photoluminescence of QDs in the films was quickly quenched because the enzyme-catalyzed reaction product (H2O2) of GOD and glucose gave rise to the formation of surface defects on QDs. The quenching rate was a function of the concentration of glucose. The linear range and sensitivity for glucose determination could be adjusted by controlling the layers of QDs and GOD. The biosensor was used to successfully determine the concentration of blood glucose in real serum samples without sample pretreatment and exhibited satisfactory reproducibility and accuracy.

Synthesis of CdTe colloidal quantum dots (QDs) in water

The comparison of growth processes and fluorescent properties of CdTe semiconductor quantum dots (QDs) that are synthesized in water with different modifiers are discussed in this paper. The samples are characterized through ultraviolet-visible spectra (UV-Vis), photoluminescence spectra (PL) and zeta potential. The results show that when the reaction time is prolonged for the same modifier, the ultraviolet absorption peak and fluorescent emission peak present obvious red shifts and the diameters of the QDs continuously increase. With the same reaction time but different modifiers, QDs with different diameters can be gained. The average full width at half maximum of the photoluminescence spectra is about 50 nm which shows that the monodispersity is quite good. Under the best reaction conditions, the highest quantum yield (QY) can be attained by using thioglycollic acid (TGA) as modifier when the reaction time is 240 min. The zeta potential is influenced by the modifier and pH.

Radiation-pressure-induced mode splitting in a spherical microcavity with an elastic shell

In this work, we present a novel method to reveal azimuthal whispering gallery modes (WGMs) in a spherical microcavity coated with a nano-meter thick polyelectrolyte shell and one monolayer of CdTe semiconductor quantum dots. The new approach in this experiment is based on the deformation of the spherical shape in a non-contact way using the radiation pressure from a laser beam, which causes the lifting of the degeneracy of the WGMs. The resonance peak linewidth and splitting parameters can be efficiently controlled by the strength of the radiation pressure and the elastic properties of the surface shell.

Zeeman effect and magnetic field induced spin-hybridization in semiconductor quantumdots

We present a systematic theoretical study of the effective Zeeman spin- and non-linear-splittingof a single spherical quantum dot based on the Hamiltonian model. The effect of spin-hybridization on conduction band states is pointedout as the main source of the strong dependence of Landè factors and effective masses onexternal fields. The topology of the electronic orbitals is highly sensitive to themagnetic field tuning and to the spin polarization. The electron, hole and excitonicg-factors, as well as the diamagnetic coefficient are calculated for CdTe semiconductorquantum dots. Different systematic experimental methods are proposed in order todetermine the behaviour of the electronic properties under analysis as a function ofmagnetic field and confinement geometry. Complementary optical transitions, in Faradayand Voigt configurations, can be used in the determination of electron, hole andexciton Landè factors, effective magnetic masses and diamagnetic coefficients.