TGA-capped CdTe Research Articles

Controlling Fluorescence Wavelength in the Synthesis of TGA-Capped CdTe Quantum Dots

Quantum dots (QDs) are semiconductor materials, with a size range between 1–10 nm, showcasing unique size-dependent physical and chemical properties. Such properties have potentiated their use in areas like medical imaging and biosensing. Herein, we present an open-air approach for synthesis of QDs, reducing the need for controllable atmospheric conditions. Furthermore, we present a predictive mathematical model for maximum emission wavelength (λmax) control. Through a straightforward microwave-based aqueous synthesis of TGA-CdTe QDs, we investigated the influence of time, temperature, and Te:Cd and TGA:Cd molar ratios on λmax, using a chemometric experimental design approach. CdTe-QDs were characterized by UV-Vis and fluorescence spectroscopies. Additionally, Fourier-Transform Infrared spectroscopy, X-ray photoelectron spectroscopy, Transmission Electron Microscopy, and Energy Dispersive X-ray were conducted. Stable QDs with fluorescence ranging from green to red (527.6 nm to 629.2 nm) were obtained. A statistical analysis of the results revealed that time and temperature were the most significant factors influencing λmax. After fine-tuning the variables, a mathematical model with 97.7% of prediction accurately forecasted experimental conditions for synthesizing TGA-CdTe QDs at predefined λmax. Stability tests demonstrated that the QDs retained their optical characteristics for over a month at 4 °C, facilitating diverse applications.

Investigations on TGA-Capped CdTe Quantum-Dots for Detection and Quantitative Assessment of Chikungunya Infection through Lateral Flow Immunoassay

In this paper, we report improved sensitivity of the lateral flow immunoassay (LFI) for diagnosis of chikungunya using highly luminescent Thioglycolic acid (TGA) capped CdTe quantum dots (QDs). The size of the CdTe QDs was controlled by varying the refluxing time during the chemical route synthesis. The systematically optimized TGA capped CdTe QDs were conjugated with the anti-chikungunya virus (CHIKV) antibodies and were utilized to fabricate the LFIs. These LFIs were tested using different concentrations of the recombinant protein of CHIKV, and the quantified results were compared with those obtained by colloidal gold-based LFIs. It has been shown that the LFIs based on TGA capped CdTe QDs show significantly higher sensitivity to chikungunya detection due to enhanced luminescence of the QDs at C and T lines of the LFI under UV illumination as compared to state of the art colloidal gold-based LFIs under normal light.

A smart-phone based ratiometric nanoprobe for label-free detection of methyl parathion

The widespread use of pesticides in pest management has boosted the demands for developing highly sensitive probes for on-site monitoring. Herein we presented a sensitive enzyme-free ratiometric probe for determination of methyl parathion (MP), as an organophosphate pesticide using TGA-capped CdTe QDs and carbon dots (CDs). Unlike previous methods in which hydrolysis product of MP is instrumental in the response of the sensors, here, self-assembly of cetyltrimethylammonium bromide (CTAB) on the surface of non-modified yellow-emissive CdTe QDs facilitates the quenching of CTAB-QDs upon addition of MP while the fluorescence intensity of CDs remains constant. Using a smartphone, the ratiometric probe shows visual emission color changes from orange-peach into pink, purple, weak blue, and dark blue, which is highly appropriate for quantitative detection of MP based on the hue-saturation-lightness color model. A wide linear range from 0.001 μg.mL−1 to 10 μg. mL−1 MP with a low limit of detection of 1.2 ng. mL−1 (S/N = 3) were obtained under optimized condition. Furthermore, with high sensitivity and selectivity, this platform has the capability to detect MP in rice and tap water samples with desired results.

Fluorescent biosensor for the selective determination of dopamine by TGA-capped CdTe quantum dots in human plasma samples

As a vital catecholamine neurotransmitter released by the brain in human central nervous system, dopamine (DA) plays an important role in a wide range of physiological functions and the mechanism of actions in human body, and its accurate detection is required in medicine. The present study reports a novel, simple and cost-effective nano-biosensor based on a thioglycolic acid (TGA)-capped cadmium telluride (CdTe) quantum dots (QDs) for the sensitive detection of DA in alkaline media. The assembled QDs-based biosensor showed a linear working range of 0.5–10 μM and a detection limit of 0.35 μM. The highest recovery of 97% was obtained by using the prepared biosensor for the detection of DA in human blood plasma samples. Additionally, the biosensor exhibited high selectivity toward DA without the interfering effects of biomolecules including some amino acids and chlorides. The concept of TGA-capped CdTe QDs will open up a new insight into the determination of DA in biological fluids where DA is at low levels.

Femtosecond laser induced photoluminescence enhancement of TGA-capped CdTe quantum dots

In this paper, we demonstrate a technique of femtosecond laser induced enhancement in the photoluminescence efficiency of TGA-capped CdTe quantum dot/water colloid. The average laser power required is of the order of few W/cm2 and the time required is few tens of minutes. This process results in stable quantum dots with negligible shift in the PL peak wavelength.

Flow-based determination of methionine in pharmaceutical formulations exploiting TGA-capped CdTe quantum dots for enhancing the luminol-KIO4 chemiluminescence

A novel flow-injection chemiluminescence method (FI-CL) was established for the determination of methionine in this paper, based on its strong enhancement on CL intensity of the luminol-KIO4 system catalyzed by thioglycolic acid-capped CdTe quantum dots in alkaline media. Under the optimized conditions, the relative CL intensity was in proportion to methionine concentration in the range from 1.0×10−8 to 1.0×10−5gmL−1 with a detection limit of 6.6×10−9gmL−1 (3σ). The relative standard deviation (RSD) of the CL intensity for 1.0×10−6gmL−1 standard methionine solution was 0.97% (n=11). The proposed method was successfully applied to determine methionine in commercial pharmaceutical formulations with recoveries between 98.0% and 101.9%. The possible CL mechanism was discussed as well.

Fluorescence Determination of Warfarin Using TGA-capped CdTe Quantum Dots in Human Plasma Samples.

In this study, some effort has been performed to provide low temperature, less time consuming and facile routes for the synthesis of CdTe quantum dots using ultrasound and water soluble capping agent thioglycolic acid. TGA-capped CdTe quantum dots were characterized through x-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible and fluorescence spectroscopy. The prepared quantum dots were used for warfarin determination based on the quenching of the fluorescence intensity in aqueous solution. Under the optimized conditions, the linear range of quantum dots fluorescence intensity versus the concentration of warfarin was 0.1-160.0μM, with the correlation coefficient of 0.9996 and a limit of detection of 77.5nM. There was no interference to coexisting foreign substances. The selectivity of the sensor was also tested and the results show that the developed method possesses a high selectivity for warfarin.

A selective determination of copper ions in water samples based on the fluorescence quenching of thiol‐capped CdTe quantum dots

CdTe quantum dots (QDs) capped with different stabilizers, i.e. thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA) and glutathione (GSH) were investigated as fluorescent probes for the determination of Cu(2+). The stabilizer was shown to play an important role in both the sensitivity and selectivity for the determination of Cu(2+). TGA-capped CdTe QDs showed the highest sensitivity, followed by the MPA and GSH-capped CdTe QDs, respectively. The TGA- and MPA-capped CdTe QDs were not selective for Cu(2+) that was affected by Ag(+). The GSH-capped CdTe QDs were insensitive to Ag(+) and were used to determine Cu(2+) in water samples. Under optimal conditions, quenching of the fluorescence intensity (F0/F) increased linearly with the concentration of Cu(2+) over a range of 0.10-4.0 µg/mL and the detection limit was 0.06 µg/mL. The developed method was successfully applied to the determination of Cu(2+) in water samples. Good recoveries of 93-104%, with a relative standard deviation of < 6% demonstrated that the developed simple method was accurate and reliable. The quenching mechanisms were also described.

Photodegradation of Mercaptopropionic Acid- and Thioglycollic Acid-Capped CdTe Quantum Dots in Buffer Solutions.

CdTe quantum dots (QDs) were synthesized by 3-mercaptopropionic acid (MPA) and thioglycollic acid (TGA) as capping agents. It is confirmed that TGA and MPA molecules were attached on the surface of the QDs using Fourier transform infrared (FT-IR) spectra. The movement of the QDs in agarose gel electrophoresis indicated that MPA-capped CdTe QDs had small hydrodynamic diameter. The photoluminescence (PL) intensity of TGA-capped QDs is higher than that of MPA-capped QDs at same QD concentration because of the surface passivation of TGA. To systemically investigate the photodegradation, CdTe QDs with various PL peak wavelengths were dispersed in phosphate buffered saline (PBS) and Tris-borate-ethylenediaminetetraacetic acid (TBE) buffer solutions. It was found that the PL intensity of the QDs in PBS decreased with time. The PL peak wavelengths of the QDs in PBS solutions remained unchanged. As for TGA-capped CdTe QDs, the results of PL peak wavelengths in TBE buffer solutions indicated that S(2-) released by TGA attached to Cd(2+) and formed CdS-like clusters layer on the surface of aqueous CdTe QDs. In addition, the number of TGA on the CdTe QDs surface was more than that of MPA. When the QDs were added to buffer solutions, agents were removed from the surface of CdTe QDs, which decreased the passivation of agents thus resulted in photodegradation of CdTe QDs in buffer solutions.

Synthesis and characterization of TGA-capped CdTe nanoparticles embedded in PVA matrix

This paper reports the synthesis and characterization of TGA-capped CdTe nanoparticles and its nanocomposite in a PVA matrix prepared by ex situ technique. The crystallite sizes of the CdTe nanoparticles and nanocomposite calculated from X-ray diffraction patterns are 6.07 and 7.75 nm with hexagonal structure, respectively. The spherical nature of the CdTe nanoparticles is confirmed from transmission electron microscopy measurements. Fourier transform infrared spectroscopy shows good interaction between the CdTe nanoparticles and PVA matrix. The absorption and emission spectra have also been studied. The stability of the TGA-capped CdTe nanoparticles increases after dispersion in a PVA matrix. In electrical measurements, the dark conductivity and the steady-state photoconductivity of CdTe nanocomposite thin films have been studied. The effect of temperature and intensity on the transient photoconductivity of CdTe nanocomposite is also studied. The values of differential life time have been calculated from the decay of photocurrent with time. The non-exponential decay of photoconductivity is observed indicating that the traps exist at all the energies in the band gap, making these materials suitable for various optoelectronic devices.

Electrochemical synthesis of TGA-capped CdTe and CdSe quantum dots

The electrochemical preparation of Te2− and Se2− ions was carried out in NaOH aqueous solution, with high yield and good stability, and applied in the preparation of negatively charged CdTe and CdSe quantum dots (QDs). A CdCl2 aqueous solution containing thioglycolic acid (TGA) stabilizer was mixed with the electrochemically generated Te2− or Se2− ions in a quite reproducible and clean one pot process, without the use of chemical reducing agents. The CdTe and CdSe QDs had good stability and high luminescence with an average size of d = 3.9 nm and 2.6 nm, respectively, the quantum yields and lifetimes were also determined. Hg2+ was efficiently quantified in the presence of the synthesized TGA-capped CdTe and CdSe, making possible the application of these QDs as chemical sensors.

Ligand exchange on the surface of cadmium telluride quantum dots with fluorosurfactant-capped gold nanoparticles: Synthesis, characterization and toxicity evaluation

CdTe quantum dots (QDs) can provide high-intensity and photostable luminescent signals when they are used as labeling materials for sensing trace amounts of bioanalytes. However, a major concern is whether the capping ligands of CdTe QDs cause toxic effects in living systems. In the current study, we address this problem through the complete ligand transformation of CdTe QDs from toxic thiolglycolic acid (TGA) to green citrate, which is attributed to the CdS bond breaking and the AuS bond formation. The highly efficient depletion of S atom from the surface of the CdTe QDs occurs after the addition of fluorosurfactant (FSN)-capped gold nanoparticles into TGA-capped CdTe QDs, accompanying with the rapid aggregation of FSN-capped gold nanoparticles via noncrosslinking mechanism in the presence of high salt. After the ligand transformation, negligible differences are observed on both photoluminescence spectra and luminescent quantum yield. In addition, the cytotoxicity of the original and new-born CdTe QDs is detected by measuring cell viability after the nanoparticle treatment. In comparison with the original TGA-capped QDs, the new-born CdTe QDs can induce minimal cytotoxicity against human hepatocellular liver carcinoma (HepG2) cells even at high dosages. Our study indicates that the extremely simple method herein opens up novel pathways for the synthesis of green CdTe QDs, and the as-prepared citrate-capped CdTe QDs might have great potential for biological labeling and imaging applications.

A new fluorimetric method for determination of valproic acid using TGA-capped CdTe quantum dots as proton sensor

Valproic acid (VA) is an acidic anticonvulsant and mood stabilizing drug with very weak fluorescence and absorption properties. A simple, inexpensive and sensitive method was established for determination of VA using thiogycolic acid (TGA)-capped CdTe quantum dots (QDs) based on pH-dependent fluorescence of the prepared QDs. The TGA-capped CdTe QDs of various sizes were successfully synthesized in aqueous medium and characterized by fluorescence spectroscopy, UV–vis absorption spectra, infrared spectroscopy and transmission electron microscopy (TEM). Under the optimal conditions, plotting ln(F0/F) versus concentration of VA showed a linear relationship in the range of 0.3–7.5mg/L with correlation coefficient of 0.998. The limit of detection (LOD) was 0.24µgmL−1. The proposed method was successfully applied for determination of VA in commercial tablets, human serum, and urine samples satisfactorily.

Electron irradiation effects on TGA-capped CdTe quantum dots

8 MeV electron irradiation effects on thioglycolic acid (TGA)-capped CdTe quantum dots (QD) are discussed in this study. CdTe QDs were characterized using x-ray diffraction (XRD), transmission electron microscope (TEM) and x-ray photoelectron spectroscopy (XPS). Steady-state and time-resolved emission spectroscopy and UV–visible absorption spectroscopy were performed before and after irradiation with 8 MeV electrons. XRD and TEM confirm the growth of TGA-capped CdTe QDs. The photoemission wavelength, intensity and lifetimes were found to vary with electron dose. At lower doses, they were found to be increasing (red-shift of photoluminescence (PL) peak and intensity) while the intensity decreased at higher electron doses. The observed changes in PL property, XPS and XRD analysis suggest possible epitaxial growth of the CdS shell on the CdTe core. This work demonstrates electron beam induced formation of the CdS layer on the CdTe core, which is a key step towards growth of the water soluble CdTe/CdS core–shell structure for biomedical labelling applications.

Efficient Quenching of TGA-Capped CdTe Quantum Dot Emission by a Surface-Coordinated Europium(III) Cyclen Complex

Extremely efficient quenching of the excited state of aqueous CdTe quantum dots (QDs) by photoinduced electron transfer to a europium cyclen complex is facilitated by surface coordination to the thioglycolic acid capping ligand. The quenching dynamics are elucidated using steady-state emission and picosecond transient absorption.

H2O2‐ and pH‐sensitive CdTe quantum dots as fluorescence probes for the detection of glucose

A novel fluorescence assay system for glucose was developed with thioglycollic acid (TGA)-capped CdTe quantum dots (QDs) as probes. The luminescence quantum yield of the TGA-capped CdTe QDs was highly sensitive to H2 O2 and pH. In the presence of glucose oxidase, glucose is oxidized to yield, gluconic acid and H2 O2 . H2 O2 and H(+) (dissociated from gluconic acid) intensively quenched the fluorescence of QDs. The experimental results showed that the quenched fluorescence was proportional to the glucose concentration within the range of 0.01-5.0 mm under optimized experimental conditions. Compared with most of the existing methods, this newly developed system possesses many advantages, including simplicity, low cost, high flexibility, and good sensitivity. Furthermore, no complicated chemical modification of QDs and enzyme immobilization was needed in this system.

The Effect of Photo-Irradiation on the Optical Properties of Thiol-Capped CdTe Quantum Dots

In this report, the effect of photo-irradiation on the optical properties of thioglycolic acid (TGA) capped CdTe QDs was investigated. The photo-irradiation led to an increase in the photoluminescence (PL) efficiency of TGA-capped CdTe QDs with a low quantum yield under both the open air and nitrogen atmosphere. The photo-irradiation caused a blue-shift of PL peak under the open air and almost no change of PL peak position under the nitrogen atmosphere. The XPS study revealed the oxidation of the unpassivated surface of the Te atoms which mainly contributed to the observed optical property changes for CdTe QDs photo-irradiated under the open air. While for the CdTe QDs photo-irradiated under the nitrogen atmosphere, the decomposition of TGA led to the release of sulphur which formed a CdS shell on the CdTe core, resulting in an enhanced PL efficiency.

Facile aqueous synthesis of functionalized CdTe nanoparticles and their application as fluorescence probes for determination of adenine and guanine

Thioglycolic acid (TGA)-capped CdTe nanoparticles (NPs) were synthesized in aqueous medium, and their application as fluorescence probes in the detection of adenine and guanine was studied. The TGA-capped CdTe NPs were characterized by transmission electron microscopy, X–ray diffraction spectrometry, spectrofluorometry, Fourier transform infrared, and ultraviolet-visible spectrometry. Based on the significant enhancement of fluorescence emission of these CdTe fluorescence probes in the presence of adenine or guanine, a quantitative analysis method for these purines was proposed. Experimental conditions that govern the extent of fluorescence enhancement were optimized. Under the optimal conditions, the relative fluorescence intensity versus adenine or guanine concentrations gave a linear response, permitting the dynamic range of 7.0 × 10−7–1.0 × 10−4 mol/L and 6.0 × 10−7–9.0 × 10−5 mol/L for adenine and guanine, respectively. The method has also been applied successfully to the detection of adenine and guanine in synthetic samples with satisfactory results.

Effects of long-term exposure of gelatinated and non-gelatinated cadmium telluride quantum dots on differentiated PC12 cells

BackgroundThe inherent toxicity of unmodified Quantum Dots (QDs) is a major hindrance to their use in biological applications. To make them more potent as neuroprosthetic and neurotherapeutic agents, thioglycolic acid (TGA) capped CdTe QDs, were coated with a gelatine layer and investigated in this study with differentiated pheochromocytoma 12 (PC12) cells. The QD - cell interactions were investigated after incubation periods of up to 17 days by MTT and APOTOX-Glo Triplex assays along with using confocal microscopy.ResultsLong term exposure (up to 17 days) to gelatinated TGA-capped CdTe QDs of PC12 cells in the course of differentiation and after neurites were grown resulted in dramatically reduced cytotoxicity compared to non-gelatinated TGA-capped CdTe QDs.ConclusionThe toxicity mechanism of QDs was identified as caspase-mediated apoptosis as a result of cadmium leaking from the core of QDs. It was therefore concluded that the gelatine capping on the surface of QDs acts as a barrier towards the leaking of toxic ions from the core QDs in the long term (up to 17 days).

Study on the interaction between CdTe quantum dots and folic acid by two-photon excited fluorescence spectroscopic techniques

Water-soluble CdTe QDs modified by thioglycolic acid were synthesized with a facile one-pot method. Two-photon excited fluorescence spectroscopic technique was used to study the interaction between TGA-capped CdTe quantum dots and folic acid. Experiments results showed that the two-photon fluorescence of TGA-capped CdTe QDs in PBS buffer solution was quenched in the presence of folic acid. A good linear relationship was observed between the two-photon fluorescence intensity of TGA-capped CdTe QDs and the concentration of folic acid. The two-photon excited fluorescence quenching mechanism was also presented.