Acid Capped Cadmium Telluride Quantum Research Articles

Synthesis of a dual-emission fluorescent probe using graphitic carbon nitride as a carrier for the rapid detection of mesosulfuron-methyl

Pesticides play an irreplaceable role in ensuring increased food production and income, but the overuse of pesticides can also pose a threat to food and environmental safety. A novel dual-emission fluorescent probe was developed for the facile and accurate detection of sulfonylurea herbicides. A Förster resonance energy transfer system, based on N-doped carbon dots (N-CDs) and thioglycolic acid-capped cadmium telluride quantum dots (TGA-CdTe QDs) as energy donor–acceptor pairs, was established using graphitic carbon nitride (g-C3N4) as a substrate and successfully applied for the micro-detection of mesosulfuron-methyl (Mes). The CDs-CdTe/C3N4 probe exhibits emission peaks at 445 and 593 nm with strong fluorescence intensity under single-wavelength excitation. Mes was shown to significantly decrease the fluorescence intensity of each emission peak via different quenching mechanisms, and the degree of quenching was proportional to Mes concentration. The linear range of fluorescence measurement was 0–90 µM, with limits of detection at 1.3 µM (445 nm) and 0.8 µM (593 nm). The dual-emission fluorescent probe exhibited excellent selectivity for Mes compared with the other eleven herbicides. The fluorescent probe has a satisfying detection performance in environmental water samples and wheat samples, and has potential application in the portable detection of pesticide residues.

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.

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.

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.

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.

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.

A rapid and sensitive assay for determination of doxycycline using thioglycolic acid-capped cadmium telluride quantum dots

A rapid, simple and inexpensive spectrofluorimetric sensor for determination of doxycycline based on its interaction with thioglycolic acid-capped cadmium telluride quantum dots (TGA/CdTe QDs) has been developed. Under the optimum experimental conditions, the sensor exhibited a fast response time of <10s. The results revealed that doxycycline could quench the fluorescence of TGA/CdTe QDs via electron transfer from the QDs to doxycycline through a dynamic quenching mechanism. The sensor permitted determination of doxycycline in a concentration range of 1.9×10−6–6.1×10−5molL−1 with a detection limit of 1.1×10−7molL−1. The sensor was applied for determination of doxycycline in honey and human serum samples.

Antibacterial potential of rutin conjugated with thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs)

Quantum dots not only act as nanocarrier but also act as stable and resistant natural fluorescent bio markers used in various in vitro and in vivo photolabelling and biological applications. In this study, the antimicrobial potential of TGA-CdTe QDs and commercial phenolics (rutin and caffeine) were investigated against Escherichiacoli. UV absorbance and fluorescence quenching study of TGA-CdTe QDs with rutin and caffeine complex was measured by spectroscopic technique. QDs–rutin conjugate exhibited excellent quenching property due to the –OH groups present in the rutin structure. But the same time caffeine has not conjugated with QDs because of lacking of –OH group in its structure. Photolabelling of E. coli with QDs–rutin and QDs–caffeine complex was analyzed by fluorescent microscopic method. Microbe E. coli cell membrane damage was assessed by atomic force (AFM) and confocal microscopy. Based on the results obtained, it is suggested that QDs–rutin conjugate enhance the antimicrobial activity more than the treatment with QDs, rutin and caffeine alone.

Hybrid Cadmium Tellurium Quantum Dots for Rapid Visualization of Trace-Level Nitroaromatic Explosives

Instant detection of trace-level nitroaromatic explosives is highly desirable for national security and environmental protection. In this paper, a new strategy for the construction of nitroaromatic-indicator paper was proposed based on a mixture of red emitting cysteamine modified cadmium telluride quantum dots and green emitting thioglycollic acid capped cadmium telluride quantum dots which served as the nitroaromatic sensor and reference probes, respectively. Nitroaromatic-indicator paper showed excellent response to trinitrotoluene and picric acid with visual detection limits of 1.59 and 1.16 ng mm−2. The screening process was accomplished within half a minute. The visualization of the nitroaromatic-indicating paper was significantly enhanced when the green reference probe was used as the background. Therefore, a rapid, simple, convenient, and high selectivity paper sensor was developed for nitroaromatics.

Enhancement of anti arthritic effect of quercetin using thioglycolic acid-capped cadmium telluride quantum dots as nanocarrier in adjuvant induced arthritic Wistar rats

In this present study, we investigated thio glycolic acid-capped cadmium telluride quantum dots (TGA-CdTe QDs) as nano carrier to study the antiarthritic activity of quercetin on adjuvant induced arthritic Wistar rats. The free radical scavenging activity of QDs-QE complex was evaluated by 2,2′-azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO) and superoxide anion scavenging assays. Fifteen days after adjuvant induction, arthritic rats received QDs-QE complex orally at the dose of 0.2 and 0.4mg/kg daily for 3 weeks. Diclofenac sodium (DF) was used as a reference drug. Administration of QDs-QE complex showed a significant reduction in inflammation and improvement in cartilage regeneration. Treatment with QDs-QE complex significantly (P<0.05) reduced the expressions lipid peroxidation and showed significant (P<0.05) increase in activities of antioxidant enzymes such as superoxide dismutase (SOD), reduced glutathione (GSH), glutathione peroxidase (GPx) catalase (CAT) levels in paw tissue. C-reactive protein (CRP), rheumatoid factor (RF), red blood cells (RBC) and white blood cells (WBC) count and erythrocyte sedimentation rate (ESR) of experimental animals were also estimated. Histology of hind limb tissue in experimental groups confirmed the complete cartilage regeneration in arthritis induced rats treated with QDs-QE complex. Based on our findings, we suggest that the QDs act as nano carrier for the drugs used in the treatment of various degenerative diseases.

In vitro antioxidant and antimicrobial activities of Merremia emarginata using thio glycolic acid-capped cadmium telluride quantum dots

This study was undertaken to evaluate the antioxidant potential of an aqueous extract from Merremia emarginata leaves because this plant has a very high flavonoid and phenol content. The in vitro antioxidant activity was measured by diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid (ABTS), superoxide anion scavenging assay and lipid peroxidation activity; the total reducing capability of the plant extract indicates that this plant is a source for natural antioxidants. Furthermore, we investigated thio glycolic acid-capped cadmium telluride quantum dots (TGA-CdTe QDs) as fluorescent probes to study the antioxidant activity of the M. emarginata extract through fluorescence quenching. The antimicrobial activity was also investigated using a disc diffusion method and fluorescence microscopy. The TGA-CdTe QDs and M. emarginata complex could provide antimicrobial activity through a reactive oxygen species pathway and/or microbial endocytosis through an electrostatic attraction. Based on our findings, we suggest that the QDs act as potential probes for the in vitro antioxidant and antimicrobial activities. In addition, their cooperative effect with the plant extract indicates that QDs could be used as nanocarriers to enhance the antimicrobial capability. Further in vivo studies on the photolabelling of antioxidants with QDs will provide insights into the mechanistic pathways of secondary metabolites against various degenerative diseases.