Capped Cadmium Telluride Research Articles

Mercaptosuccinic acid capped cadmium telluride quantum dots as luminescent thermometer over a wide temperature range of −100 to 60℃

Thermal-sensitive photoluminescence (PL) properties of cadmium telluride quantum dots capped with mercaptosuccinic acid (MSA-CdTe QDs) were investigated by collecting QDs’ PL steady-state spectra and decay curves from a cryogenic temperature of −100℃ to 60℃. These QDs display peak wavelength redshift and shorten fluorescence lifetime with the increase of temperature. In situ XRD patterns showed that the QDs’ grain size increases due to thermal expansion induced by the increasement of temperature, which further leads to the redshift of luminescence peak wavelength position. The results prove MSA-CdTe QDs are excellent candidates for luminescence thermometry over a broad temperature range of −100 to 60℃.

An investigation on the structural and optical properties of mercaptosuccinic acid capped cadmium telluride quantum dots

In this work, a sonication induced modified wet chemical approach is adopted to synthesize highly luminescent and water soluble cadmium telluride (CdTe) quantum dots (QDs). The morphology, size, crystal structural, and optical properties of CdTe QDs are investigated for different refluxing time (1–4 h). The refluxing time-dependent optical constants viz. band gap energy and Urbach energy of the QDs are estimated from UV–Visible absorption spectra. The optical band gap energy decreased from ~ 2.12 to 1.92 eV and the Urbach energy increased from ~ 361 to 487 meV, with the increase in refluxing time. CdTe QDs are found to be uniform in size. The average size of the QDs estimated from the High Resolution Transmission Electron Microscope image analysis is about 5.8 and 8.2 nm for refluxing times 1 and 4 h, respectively. The growth mechanism of the QDs as a function of refluxing time has also been discussed. The fluorescence spectra of the QDs, revealed emission peaks having wavelength from ~ 534 to 585 nm, under the excitation wavelength of 320 nm. The fluorescence emission peaks showed a bathochromic shift with increasing refluxing time. CdTe QDs also exhibit excitation-dependent fluorescence behaviour. Two crystalline phases of the CdTe QDs, namely hexagonal and cubic are confirmed from the High Resolution Transmission Electron Microscope images and Selected Area Electron Diffraction patterns analysis. The phase transformation from hexagonal to cubic is successfully achieved by tuning the refluxing time from 1 to 4 h.

Construction of ratio fluorescence sensor based on CdTe quantum dots and benzocoumarin-3-carboxylic acid for Hg2+ detection

A new ratio fluorescence sensor based on mercaptamine capped cadmium telluride quantum dots (Mea-CdTe) and benzocoumarin-3-carboxylic acid (BTA) were constructed. The ratio fluorescence sensor ([email protected]) was synthesized by amidation reaction between the amino groups on the surface of Mea-CdTe quantum dots and the carboxyl groups of BTA. It is found that Hg2+ ions react with the amino groups on the surface of the quantum dots in the [email protected] sensor to quench the fluorescence, but it has no effect on the fluorescence of grafted BTA. The sensor has good selectivity and high sensitivity for Hg2+ ions detection. The detection linear range is 0.4–1.2 µM, and the detection limit is 0.03 µM. This ratio fluorescence sensor can be used for Hg2+ visual recognition in water sample detection with obvious color change.

Capped cadmium telluride quantum dots fluorescence enhancement by Se(IV) and its application to dietary supplements analysis

A thioglycolic capped CdTe probe for Se(IV) detection was optimised by nanocrystal size, pH, buffer composition and concentration, and the order of reagent addition. A large increase in fluorescence (>90%) was observed upon sequential addition of Se(IV), buffer, and CdTe probe, caused by surface passivation due to the presence of singly charged Se(IV) in ammoniacal buffer (0.01 mol L–1) at pH 8.4. This result indicated the possibility of inorganic Se speciation. The method presented a detection limit of 60.5 μg L–1 with RSD ≤ 3.5% (n = 8) and was successfully applied to dietary supplements analysis.

Tuning the optical properties of colloidal Quantum Dots using thiol group capping agents and its comparison

Mercapto Succinic Acid (MSA), Mercapto Propionic Acid (MPA) and Thio Glycolic Acid (TGA) capped Cadmium Telluride Quantum Dots (CdTe QDs) were synthesized by aqueous phase method. The growth mechanisms of the prepared CdTe QDs were observed to be dependent on the molecular structure of the surfactants used, which in turn had impact on the CdTe QDs growth kinetics, size and shape. The functional groups attached to the surfactant were found to get influenced by the diffusion length, electron confinement and charge transfer. Henceforth, the photo physical and electronic properties of these CdTe QDs were also determined by its molecular structure. In addition, the refluxing time during the synthesis played a significant role in defining the CdTe QDs size and its luminescence effect. Based on the selection of surfactants, the luminescence property of CdTe QDs can be altered, which will make these materials a suitable candidate for extensive variety of applications. Using UV–Visible and Photo Luminescence spectrum the growth kinetics of the CdTe QDs with three different capping agents has been explored first time and this can be utilized for different applications.

Fast fluorometric enumeration of E. coli using passive chip

In this report, a passive microfluidic chip design was developed for fast and sensitive fluorometric determination of Escherichia coli (E. coli) based on sandwich immunoassay. Initially, magnetic nanoparticles (MNPs) and chitosan modified mercaptopropionic acid capped cadmium telluride (CdTe) quantum dots (QDs) were functionalized with E.coli specific antibody to form a sandwich immunoassay with the E. coli. The magnetic separation and preconcentration of the E.coli from the sample solution was performed in the vial. Conjugation of QDs to the magnetically captured E. coli and washing were performed using a passive type of microchip. The microfluidic chip consists of four microchambers connected to each other by microchannels which act as capillary valves. Signal measurement was performed at the last chamber by using a hand-held spectrofluorometer equipped with a fiber optic reflection probe. The selectivity of the method was tested with Enterobacter aerogenes (E. aerogenes) and Salmonella enteritidis (S. enteritidis), it was observed that these bacteria have no interference effect on E.coli determination. The calibration curve was found to be linear in the range of 101–105 cfu/mL with a correlation coefficient higher than 0.99. The limit of detection was calculated as 5 cfu/mL. The method was successfully applied to spiked tap and lake water samples. The results suggest that the developed method is applicable for on-site E. coli detection and offers several advantages such as large dynamic range, high sensitivity, high selectivity and short analysis time.

Ultrasensitive detection of glibenclamide based on its enhancing effect on the fluorescence emission of CdTe quantum dots.

Glibenclamide (GB), as a sulfonylurea-based medication is commonly prescribed for the treatment of type 2 diabetes. Due to its increasing consumption, there is a need to develop a simple, fast, and reliable detection method to follow its concentration in pharmaceutical and biological samples. Herein, a novel fluorometric method is developed for the sensitive measurement of GB. The method is based on the enhancing effect of GB on the fluorescence emission of mercaptopropionic acid (MPA) capped cadmium telluride quantum dots (CdTe QDs). QDs were synthesized in aqueous solution and were characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Fluorescence intensity of QDs was enhanced by adding GB in a very low concentration. The effect of operative factors such as pH, buffer, contact time and concentration of CdTe QDs were investigated and in the optimized condition, a linear increase was achieved for the emission intensity of QDs by increasing GB concentration in the range 49-345ng mL-1 , with a detection limit of 17.84ng mL-1 . The offered method has an acceptable precision (relative standard deviations were<2.8%) and was satisfactorily applied for the determination of GB in pharmaceutical products and human urine samples.

One pot synthesis of stable water soluble thiol capped CdTe nanoparticles: Effect of precursor ratio, refluxing time and capping group on the optical property

Highly crystalline, monodispersed and stable water soluble thiol capped cadmium telluride nanoparticles (CdTe NPs) were synthesized via an environmental friendly, simple one-pot method in the absence of an inert atmosphere at constant pH. The effect of varying the precursor ratio and capping agent while keeping all other parameters constant, on the optical and structural properties of the as-synthesized nanocrystals was investigated. The optical and structural properties of the as-synthesized CdTe NPs was explored by using UV–visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy, Fourier transform infra-red spectroscopy (FTIR) and transmission electron microscopy (TEM). Optical analysis shows that all the as-synthesized CdTe NPs possesses good optical properties with 1:0.8 ratio showing the highest absorbance and emission wavelength at different reaction time. The thiol capped water soluble CdTe NPs were optically stable at ambient conditions for several months.

Determination of ethanol in biodiesel samples using mercaptopropionic acid-capped cadmium telluride quantum dots as photoluminescence probes

A method for determining ethanol in biodiesel samples was developed using quantum dots (QDs) as fluorescent probes. The photoluminescence intensity of the mercaptopropionic acid capped cadmium telluride quantum dots (MPA-CdTe QDs) increased linearly in the presence of ethanol as a result of the interaction between the analyte and QDs. MPA-CdTe QDs were synthesized via the colloidal route in aqueous medium. Among the synthesized QDs, a nanoparticle size of 3.44 nm, corresponding to fluorescence emission at 599 nm, was chosen because it presented the most pronounced increase in the analytical response. Experiments were performed at different pH levels and QD concentrations. The system showed the best analytical performance with citrate buffer at pH 4.0 using a 0.5 mM QD solution in the presence of sodium chloride. The system exhibited stability for a period of at least 150 min. The proposed method allowed for the determination of ethanol in the range of 0.003–5.0% (m m−1) with a limit of detection of 0.001% (m m−1). The precision, measured as the relative standard deviation (RSD%, n = 10), was 1.8% for the sample with an ethanol content of 2.0% (m m−1). The proposed method was applied for the determination of ethanol in biodiesel samples after extraction of the analyte with a 1.0% (m v-1) NaCl solution. Recovery tests provided results in the range of 90–114%, and the results of the application showed good agreement with those obtained via the comparative method using gas chromatography.

Successive detection of benzoic acid and total parabens in foodstuffs using mercaptosuccinic acid capped cadmium telluride quantum dots

An approach for the determination of benzoic acid (BA) and total paraben content using mercaptosuccinic acid capped CdTe quantum dots (MSA-CdTe QDs) as an optical probe is presented. The levels of these preservatives in the samples of liquid foodstuff could be determined by both visible and fluorescent detection methods. For the analysis of paraben content, sample hydrolysis under alkaline conditions was required in order to obtain p-hydroxybenzoic acid (PHBA) prior to the addition of MSA-CdTe QDs. Both BA and PHBA could be quantified by their quenching of QD fluorescence, owing to the formation of hydrogen bonds between the carboxylic acid groups of the MSA-CdTe QDs and the analytes. Reverse-phase C18 solid phase extraction cartridge was exploited to reduce sample loss and organic solvent consumption in the sample preparation steps. The developed approach was successfully applied for the determination of the BA and total paraben content found in orange juice, soft drink, energy drink, beer, coconut milk, and fish sauce, giving a limit of detection of 0.3 mg/L for BA analysis, and 0.1 mg/L for PHBA (hydrolyzed form of parabens) analysis, with a linearity range from 1.0 mg/L to 500.0 mg/L. Since the concentrations of most preservatives added to products are controlled and regulated by raw, therefore, quality control is necessary to monitor the levels of these agents in products to better ensure the safety of customers.

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.

Fluorescence Stability of Mercaptopropionic Acid Capped Cadmium Telluride Quantum Dots in Various Biochemical Buffers

Quantum dots are the semiconductor nanocrystals having unique optical and electronic properties. Quantum dots are category of fluorescent labels utilized for biological tagging, biosensing, bioassays, bioimaging and in vivo imaging as they exhibit very small size, signal brightness, photostability, tuning of light emission range, longer photoluminescence decay time as compared to organic dyes. In this work, we have synthesized and characterized mercaptopropionic acid capped cadmium telluride quantum dots (MPA-CdTe QDs) using hydrothermal method. The study further reports fluorescence intensity stability of quantum dots suspended in different buffers of varying concentration (1-100 mM), stored at various photophysical conditions. Fluorescence intensity values were reduced with increase in buffer concentration. When the samples were stored at room temperature in ambient light condition the quantum dots suspended in different buffers lost the fluorescence intensity after day 15 (except TRIS II). Fluorescence intensity values were found stable for more than 30 days when the samples were stored in dark condition. Samples stored in refrigerator displayed modest fluorescence intensity even after 300 days of storage. Thus, storage of MPA-CdTe QDs in refrigerator may be the suitable choice to maintain its fluorescence stability for longer time for further application.

One-pot single step to label microtubule with MPA-capped CdTe quantum dots

The kinesin-microtubule pair has attracted much attention in recent years due to their promising use in the development of synthetic nanotransport machines. One of the challenges to study such system is how to observe the motility of either kinesin or microtubule. The usual technique for observation of the molecular machinery pair is by fluorescence microscopy, where fluorescent probes are bound to one, or both species, through a biotin-avidin linker. Here, the use of mercaptopropionic acid (MPA)–capped cadmium telluride (CdTe) quantum dots (QDs) as a direct fluorescent labeling agent to microtubule biomolecules is reported. QDs are able to not only bind to microtubules in vitro, but also to fluorescently label them in the red spectral region. Surface plasmon resonance (SPR) studies showed the binding of synthesized QDs to microtubules, while quantum dots-labeled microtubules were successfully visualized with fluorescence microscopy. It is believed QDs adsorbs to the microtubule surface mainly through the coordination of Cd with histidine, cysteine and methionine residues, as well as through interactions of the nanocrystal’s carboxylated surface with free amino groups on microtubules.

Evaluation of Reaction Parameters Dependent Optical Properties and Its Photovoltaics Performances of CdTe QDs

High quality thiol capped cadmium telluride quantum dots were prepared in aqueous phase by the optimization of reaction parameters and their photovoltaics performances were studied through the fabrication of quantum dots sensitized solar cells. Mercaptosuccinic acid capped cadmium telluride quantum dots were prepared under different rection conditions (at acidic and basic solutions, different precursors ratios, under different reaction temperatures and are various refluxing times) and their optical absorptionand emission properties were studied. Based on these observations, the reaction parameters were optimized and high quality mercaptosuccinic acid capped cadmium telluride quantum dots were prepared at the optimized reaction conditions. Crystalline structure of the prepared cadmium telluride quantum dots was studied by X-ray diffraction analysis, which confirms the cubic zinc blende structure. Size dependent optical properties of mercaptosuccinic acid capped cadmium telluride quantum dots were revealed by UV–Vis absorption and fluorescence emission studies. The formation of cadmium telluride quantum dots with the thiol capping layer over the quantum dots was studied by the X-ray photoelectron spectroscopy and Fourier Transform Infra Red spectroscopy analysis. Cadmium telluride quantum dots sensitized solar cells were fabricated by using polysulfide electrolytes with TiO2 as the photoanode. The photovoltaic performance of cadmium telluride quantum dots sensitized photoelectrodes was studied by the J–V characteristic curves under the illumination of light with 1 Sun intensity. Mercaptosuccinic acid capped cadmium telluride quantum dots prepared at optimized reaction conditions showed an enhanced solar cell efficiency of 0.87% at 3 h of absorption time.

Quenching-recovery fluorescent biosensor for DNA detection based on mercaptopropionic acid-capped cadmium telluride quantum dots aggregation

A new, label-free, highly sensitive, and selective fluorescent “quenching-recovery” model for the detection of DNA was developed through mercaptopropionic acid (MPA)- capped cadmium telluride (CT) quantum dots (QDs) aggregation. At first, imipramine hydrochloride (IMP) effectively quenched the fluorescence of MPA-CT QDs due to their aggregation, in the “quenching” mode. Then, with the addition of DNA, the binding reaction of IMP to DNA was happened and the fluorescence intensity of MPA-CT QDs was raised, in the following “recovery” mode. Several parameters affect the sensitivity of the method were optimized. Under the optimal conditions, the linear dependence of the fluorescence signal and the concentration of DNA was in the range of 23.0pmolL−1–10.8nmolL−1, with a detection limit of 7.0pmolL−1. This analytical fluorescent reversible “quenching-recovery” sensor offered a method for the detection of DNA with excellent sensitivity and selectivity.

CdTe quantum dot dispersed ferroelectric liquid crystal: Transient memory with faster optical response and quenching of photoluminescence

In the present study, the effect of dispersing Octadecylamine capped Cadmium Telluride quantum dots (CdTe QDs) on the memory behaviour, physical parameters and dielectric relaxations of ferroelectric liquid crystal (FLC) W-327 with the variation of dopant concentration and applied voltage has been examined. Significant changes have been observed in visible light absorbance, photoluminescence (PL), spontaneous polarization, optical response and relative permittivity of the FLC material with the addition of QDs. An average of 19% (Mix.1) and 28% (Mix.2) fastening of optical response in QDs dispersed FLC mixtures was one of the remarkable findings. Enhancement in visible absorbance along with the quenching in PL intensity has also been noticed in FLC/QD mixtures in comparison to pure FLC. The study of tan δ curves confirms the reduction of ionic impurities in the presence of QDs. Pure FLC as well as FLC/QD mixtures show time dependent memory effects. The memory behaviour of mixtures significantly depends upon the concentration of dopant CdTe. The memory effect was confirmed with the help of dielectric spectroscopy, polarizing optical micrographs and electro-optical study. The observed memory effect has been attributed to minimization of the depolarization field and ionic charges. The QDs dispersed FLC plays a major role to enhance memory effects by trapping the impurity ions under the application of bias voltage. These studies would be helpful to provide an idea for ionic impurity free memory devices having micro-second optical response and in security coded transmission.

Quantum Dot Nanotoxicity Investigations Using Human Lung Cells and TOXOR Electrochemical Enzyme Assay Methodology.

Recent studies have suggested that certain nanomaterials can interfere with optically based cytotoxicity assays resulting in underestimations of nanomaterial toxicity. As a result there has been growing interest in the use of whole cell electrochemical biosensors for nanotoxicity applications. Herein we report application of an electrochemical cytotoxicity assay developed in house (TOXOR) in the evaluation of toxic effects of mercaptosuccinic acid capped cadmium telluride quantum dots (MSA capped CdTe QDs), toward mammalian cells. MSA capped CdTe QDs were synthesized, characterized, and their cytotoxicity toward A549 human lung epithelial cells investigated. The internalization of QDs within cells was scrutinized via confocal microscopy. The cytotoxicity assay is based on the measurement of changes in cellular enzyme acid phosphatase upon 24 h exposure to QDs. Acid phosphatase catalyzes dephosphorylation of 2-naphthyl phosphate to 2-naphthol (determined by chronocoulometry) and is indicative of metabolic activity in cells. The 24 h IC50 (concentration resulting in 50% reduction in acid phosphatase activity) value for MSA capped CdTe QDs was found to be 118 ± 49 μg/mL using the TOXOR assay and was in agreement with the MTT assay (157 ± 31 μg/mL). Potential uses of this electrochemical assay include the screening of nanomaterials, environmental toxins, in addition to applications in the pharmaceutical, food, and health sectors.

FRET-based nanobiosensor for detection of scopolamine in hairy root extraction of Atropa belladonna

A simple, sensitive, selective, and rapid optical nanobiosensor based on FRET was designed to detect tropane alkaloids as anti-cholinergic agents in natural and transgenic hairy roots extracts of Atropa belladonna. To achieve that, conjugation of tioglycolyic acid capped cadmium telluride quantum Dots, M2 muscarinic receptor (Cd/Te QDs-M2R) and conjugation of scopolamine-rhodamine123 (Sc-Rho123) were performed. More specifically, proportional amounts of M2 muscarinic receptor and quantum dots (QDs) were conjugated while scopolamine (as a tropane alkaloid) and rhodamine123 were also combined and these moieties functioned as donor and acceptor pairs, respectively. The system response was linear over the range of 0.01–4µmolL−1 of scopolamine hydrochloride concentration with a detection limit of 0.001µmolL−1. The developed nanobiosensor was successfully used for in vitro recognition of scopolamine as an anti-cholinergic agent in the investigated plant extracts. In addition, Agrobacterium rhizogenesis mediated gene transfer technique was employed to generate hairy roots and to enhance the production of tropane alkaloids in the studied medicinal plant.

Chemiluminescence studies between aqueous phase synthesized mercaptosuccinic acid capped cadmium telluride quantum dots and luminol-H2O2

Mercaptosuccinic acid capped Cadmium telluride quantum dots have been successfully synthesized via aqueous phase method. The products were well characterized by a number of analytical techniques, including FT-IR, XRD, HRTEM, and a corrected particle size analysis by the statistical treatment of several AFM measurements. Chemiluminescence experiments were performed to explore the resonance energy transfer between chemiluminescence donor (luminol-H2O2 system) and acceptor CdTe QDs. The combination of such donor and acceptor dramatically reduce the fluorescence while compared to pristine CdTe QDs without any exciting light source, which is due to the occurrence of chemiluminescence resonance energy transfer (CRET) processes.

‘Turn-on’ fluorescence assay for inorganic phosphate sensing

Phosphorus (in the form of phosphate) is the second most abundant mineral in the human body and is essential for normal body activities. Abnormal concentrations of phosphate can cause serious disorders and may be fatal if not treated. One of the drawback of current phosphate sensing method is its lack of sensitivity and specificity. This issue can be overcome by using photoinduced electron transfer (PET) based fluorescent on/off sensors. Semiconductor quantum dots (QDs) are used for the purpose of phosphate sensing because of their excellent size tunable optical properties (fluorescence and absorbance). Here we report the synthesis and characterization of thiol capped cadmium telluride (CdTe) QDs and their use in ‘turn on’ assay for inorganic phosphate sensing. The assay utilizes europium nitrate which forms complex with CdTe QDs (QD-Eu complex) and quenches fluorescence of QDs through photoinduced electron transfer (PET) process. Addition of phosphate solution results in recovery of fluorescence intensity of TGA capped CdTe QDs. Fluorescence recovery was quantified in terms of the concentration of inorganic phosphate. The fluorescence intensity versus Pi concentration curve fits to the sigmoid shape after optimization for the desired range of phosphate concentration. This ‘turn on’ sensing assay method is reliable, repeatable and might be useful for determination of physiological inorganic phosphate level.