Glutathione-capped CdTe Quantum Dots Research Articles

Glutathione-Capped CdTe Quantum Dots Based Sensors for Detection of H2O2 and Enrofloxacin in Foods Samples.

Additives and antibiotic abuse during food production and processing are among the key factors affecting food safety. The efficient and rapid detection of hazardous substances in food is of crucial relevance to ensure food safety. In this study, a water-soluble quantum dot with glutathione as a ligand was synthesized as a fluorescent probe by hydrothermal method to achieve the detection and analysis of H2O2. The detection limits were 0.61 μM in water and 68 μM in milk. Meanwhile, it was used as a fluorescent donor probe and manganese dioxide nanosheets were used as a fluorescent acceptor probe in combination with an immunoassay platform to achieve the rapid detection and analysis of enrofloxacin (ENR) in a variety of foods with detection limits of 0.05-0.25 ng/mL in foods. The proposed systems provided new ideas for the construction of fluorescence sensors with high sensitivity.

Immobilization of Glucose Oxidase on Glutathione Capped CdTe Quantum Dots for Bioenergy Generation

An efficient immobilization of Glucose oxidase (GOx) on an appropriate substrate is one of the main challenges of developing fuel cells that allow energy to be obtained from renewable substrates such as carbohydrates in physiological environments. The research importance of biofuel cells relies on their experimental robustness and high compatibility with biological organisms such as tissues or the bloodstream with the aim of obtaining electrical energy even from living systems. In this work, we report the use of 5,10,15,20 tetrakis (1-methyl-4-pyridinium) porphyrin and glutathione capped CdTe Quantum dots (GSH-CdTeQD) as a support matrix for the immobilization of GOx on carbon surfaces. Fluorescent GSH-CdTeQD particles were synthesized and their characterization by UV-Vis spectrophotometry showed a particle size between 5–7 nm, which was confirmed by DLS and TEM measurements. Graphite and Toray paper electrodes were modified by a drop coating of porphyrin, GSH-CdTeQD and GOx, and their electrochemical activity toward glucose oxidation was evaluated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Additionally, GOx modified electrode activity was explored by scanning electrochemical microscopy, finding that near to 70% of the surface was covered with active enzyme. The modified electrodes showed a glucose sensitivity of 0.58 ± 0.01 μA/mM and an apparent Michaelis constant of 7.8 mM. The addition of BSA blocking protein maintained the current response of common interferent molecules such as ascorbic acid (AA) with less than a 5% of interference percentage. Finally, the complex electrodes were employed as anodes in a microfluidic biofuel cell (μBFC) in order to evaluate the performance in energy production. The enzymatic anodes used in the μBFC allowed us to obtain a current density of 7.53 mAcm−2 at the maximum power density of 2.30 mWcm−2; an open circuit potential of 0.57 V was observed in the biofuel cell. The results obtained suggest that the support matrix porphyrin and GSH-CdTeQD is appropriate to immobilize GOx while preserving the enzyme’s catalytic activity. The reported electrode arrangement is a viable option for bioenergy production and/or glucose quantification.

Charge transfer dynamics of the CdTe quantum dots fluorescence quenching induced by ferrous (II) ions

Size dependence of glutathione capped CdTe quantum dots (GSH-CdTe QDs) on the sensitivity and selectivity in the fluorometric detection of ferrous (II) ions (Fe2+) has been systematically investigated. Smaller-size QDs show higher sensitivity in the detection of Fe2+, resulting in higher quenching efficiency and red shift of the fluorescence peak of QDs. Stern–Volmer plots indicate that the charge transfer model can be employed to account for the observed fluorescence quenching effect. Fe2+ is bound to the surface of QDs by GSH and excited electrons are transferred from QDs to Fe2+, which facilitates a nonradiative recombination process and a decrease in the PL efficiency. In addition, the results from time resolved photoluminescence and a confocal scanning fluorescence microscope have shown that smaller-size QDs have a faster decrease in the fluorescence lifetime compared with that of larger-size QDs with Fe2+ addition, suggesting that the fast charge transfer in smaller-size QDs should be responsible for the observed fluorescence quenching effect. This Letter provides a comprehensive understanding of the mechanism of the fluorescence for the CdTe QDs quenched by Fe2+.

Förster Resonance Energy Transfer from Quantum Dots to Rhodamine B As Mediated by a Cationic Surfactant: A Thermodynamic Perspective

Forster resonance energy transfer (FRET) has attracted much attention for its wide applications in the fields of bioimaging, bioanalysis, etc. One of the critical problems in FRET is the construction of suitable donor–acceptor pair. The fluorescent quantum dots (QDs) can well meet the requirements both for a donor and an acceptor, owing to their tunable emission and broad absorption. Besides, the QDs possess high quantum yield, which highly benefits the FRET efficiency. In this work, glutathione-capped CdTe QDs (GSH-CdTe QDs) was chosen as the energy donor (D) and Rhodamine B (RhB) as the energy acceptor (A). However, no FRET occurred when there were only QDs and RhB, even though there was much overlap between the absorption spectrum of RhB and the emission spectrum of QDs. Interestingly, after the addition of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), FRET was induced favorably. Further understanding of this phenomenon was studied by fluorescence spectroscopy, dynamic light scattering,...

Observation of Distinct Two-Photon Transition Channels in CdTe Quantum Dots in a Regime of Very Strong Confinement.

We report here on the direct observation of distinct two-photon transition channels in glutathione-capped (GSH) CdTe quantum dots (QDs) in a very strong confinement regime. CdTe-GSH QDs with different average diameters (2.5, 3.0, and 3.3 nm) were synthesized through the one-pot method and their two-photon absorption (2PA) spectrum determined by a femtosecond wavelength-tunable Z-scan. Our results show that the two lower-energy one-photon-allowed excitonic transitions, 1S3/2(h) → 1S(e) and 2S3/2(h) → 1S(e), are also accessed via 2PA. These results were ascribed to the relaxation of the parity selection rules due to the noncentrosymmetric structure of the CdTe QDs (zinc-blended structure), whose magnitude are determined by surface defects and structural irregularities present in CdTe-GSH QDs, in the strong confinement regime.

New Perspectives of Quantum Dots in the Food Field: Determination of β-Carotene in Tropical Fruit Juices and Food Supplements

A novel and simple method for the determination of β-carotene, a carotenoid abundant in plants and fruits, is proposed. Multicommutated flow injection analysis (MCFIA) has been applied as automated flow methodology to the analysis of β-carotene in tropical fruit juices and food supplements, making use of the quenching effect caused by this analyte over glutathione-capped CdTe quantum dots (QDs) fluorescence signal. Under optimized conditions, the method was linear in the range of 0.3–15 μg mL−1, with a detection limit of 0.09 μg mL−1 and relative standard deviations lower than 3%. The determination rate was of about 80 h−1, and results were in good agreement with those provided by both the manufacturer and a chromatographic reference method.

A simple and sensitive label-free fluorescence sensing of heparin based on Cdte quantum dots.

A rapid, simple and sensitive label-free fluorescence method was developed for the determination of trace amounts of an important drug, heparin. This new method was based on water-soluble glutathione-capped CdTe quantum dots (CdTe QDs) as the luminescent probe. CdTe QDs were prepared according to the published protocol and the sizes of these nanoparticles were verified through transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS) with an average particle size of about 7 nm. The fluorescence intensity of glutathione-capped CdTe QDs increased with increasing heparin concentration. These changes were followed as the analytical signal. Effective variables such as pH, QD concentration and incubation time were optimized. At the optimum conditions, with this optical method, heparin could be measured within the range 10.0-200.0 ng mL(-1) with a low limit of detection, 2.0 ng mL(-1) . The constructed fluorescence sensor was also applied successfully for the determination of heparin in human serum. Copyright © 2015 John Wiley & Sons, Ltd.

Sensitive determination of enoxacin in pharmaceutical formulations by its quench effect on the fluorescence of glutathione-capped CdTe quantum dots.

A sensitive and simple method for the determination of enoxacin (ENX) was developed based on the fluorescence quenching effect of ENX for glutathione (GSH)-capped CdTe quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 4.333 × 10(-9) mol⋅L(-1) to 1.4 × 10(-5) mol⋅L(-1) with a correlation coefficient (R) of 0.9987, and the detection limit (3σ/K) was 1.313 × 10(-9) mol⋅L(-1). The corresponding mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV) light absorption, fluorescence spectroscopy, and the measurement of fluorescence lifetime. The method has been applied to the determination of ENX in pharmaceutical formulations (enoxacin gluconate injections and commercial tablets) with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

A regenerable fluorescent quantum dot based nanoprobe for zinc(II), and the design of a molecular logic gate

We report on a simple, sensitive and regenerable fluorescent nanoprobe for Zn(II) ion. It is based on the use of glutathione capped CdTe quantum dots (GSH-CdTe Q-dots). The bright fluorescence of these Q-dots is quenched on addition of diethylenetriaminepentaacetic acid (DTPA) due to the binding of DTPA to GSH. If, however, Zn(II) is added, it will bind DTPA and detach it from the surface of the Q-dots, this resulting in the fluorescence recovery. Under optimum conditions, the intensity of the restored fluorescence is proportional to the concentration of Zn(II) in the 0.48 to 90 μmol · L−1 range, with a limit of detection of 0.14 μmol · L−1. The nanoprobe was applied to the determination of Zn(II) in spiked tap water and river water and gave satisfactory results. The findings were also applied to design a molecular logic gate where DTPA acts as the first input to the system by quenching the fluorescence of the GSH-CdTe Q-dots. Zn(II) acts as the second input and causes the detachment of DTPA from the Q-dots and a restoration of fluorescence. This system therefore represents a new IMP (IMPLICATION) logic gate.

Sensitive detection of sodium cromoglycate with glutathione-capped CdTe quantum dots as a novel fluorescence probe.

A sensitive and simple analytical strategy for the detection of sodium cromoglycate (SCG) has been established based on a readily detectable fluorescence quenching effect of SCG for glutathione-capped (GSH-capped) CdTe quantum dots (QDs). The fluorescence of GSH-capped CdTe QDs could be efficiently quenched by SCG through electron transfer from GSH-capped CdTe QDs to SCG. Under optimum conditions, the response was linearly proportional to the concentration of SCG between 0.6419 and 100 µg/mL, with a correlation coefficient (R) of 0.9964; the detection limit (3δ/K) was 0.1926 µg/mL. The optimum conditions and the influence of coexisting foreign substances on the reaction were also investigated. The very effective and simple method reported here has been successfully applied to the determination of SCG in synthetic and real samples. It is believed that the established approach could have good prospects for application in the fields of clinical diseases diagnosis and treatment.

Label-free and turn-on fluorescent cyanide sensor based on CdTe quantum dots using silver nanoparticles

A turn-on fluorescence sensor is introduced for determination of trace amount of cyanide, based on glutathione-capped Cd–Te quantum dots.

Water Soluble CdTe Quantum Dots for Mercury Detection

Nanomaterials are becoming one of the most important classes of material research [1]. For example, quantum dots (QDs), especially water soluble QDs, have been used in many areas of research [2-3]. QDs are nanosize crystals of inorganic semiconductors with diameter in the range of 1-10 nm [4]. At such small sizes (close to or smaller than the dimensions of the exciton Bohr radius within the corresponding bulk material), these nanostructured materials behave differently from bulk solids, because of quantum-confinement effects [4]. As a result of quantum-confinement, they have unique optical and electronic properties such as broad excitation spectra and narrow, symmetric and tunable emission spectra [4]. Therefore, QDs have been used as novel luminescent sensors for chemical and biological species [5-8].This study fabricated cadmium telluride (CdTe) QDs from aqueous solution containing CdCl2 and Te precursor in presence of thioglycolic acid. The resulted QDs were characterized by using Uv-Vis. spectroscopy, photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). The results demonstrated that low concentration, in nano-molar range, of Hg(II) ions could effectively quench the CdTe QDs fluorescence because Hg(II) ions form a stable complex with QDs coating (thioglycolic acid) which allow for an effective electron transfer from the QDs to the Hg(II). A linear response to Hg(II) ions in the concentration range from 0.625 to 8.0 n M was observed and the detection limit of this sensor was 0.625 nM and sensitivity was equal to 53.4 /nM. References Rosi NL, Mirkin CA Nanostructures in biodiagnostics. Chem Rev 105:1547–1562 (2005)Goldman ER, Balighian ED, Mattoussi H, Kuno MK, Mauro JM, Tran PT, Anderson GP (2002) Avidin: a natural bridge for quantum dot-antibody conjugates. J Am Chem Soc 124:6378–6382Chen Y, Rosenzweig Z (2002) Luminescent CdS quantum dots as selective ion probes. Anal Chem 74:5132–5138Alivisatos AP (1996) Perspectives on the physical chemistry of semiconductor nanocrystals. J Phys Chem 100:13226–13239Chan WCW, Maxwel DJ, Gao X, Bailey RE, Han M, Nie S (2002) Luminescent quantum dots for multiplexed biological detection and imaging. Curr Opin Biotechnol 13:40–46Zhang L, Ci Xu, Li B (2009) Simple and sensitive detection method for chromium(VI) in water using glutathione—capped CdTe quantum dots as fluorescent probes. Microchim Acta 166: 61–68Landes C, Burda C, Braun M, El-Sayed MA (2001) Photoluminescence of CdSe nanoparticles in the presence of a hole acceptor: n-Butylamine. J Phys Chem B 105:2981–2986Dong F, Hu K, Han H, Liang J (2009) A novel method for methimazole determination using CdSe quantum dots as fluorescence probes. Microchim Acta 165:195–201

Determination of copper in biodiesel samples using CdTe-GSH quantum dots as photoluminescence probes

The use of glutathione-capped CdTe quantum dots is proposed for the determination of copper in biodiesel samples. The developed method was based on proportional quenching of photoluminescence intensity of the nanocrystals with the copper concentration. Three different sizes of CdTe quantum dots (QDs) were prepared and modified in aqueous dispersion by glutathione (GSH), and their interactions with copper were investigated. As a result of the interaction, the CdTe-GSH QDS photoluminescence intensity decreased linearly in the presence of Cu(II) in the range of concentration from 2.2 to 30.0μgL−1. The maximum photoluminescence intensity was obtained at pH6.5, with excitation and emission wavelengths at 400 and 532nm, respectively. The detection limit was 0.67μgL−1, and the precision expressed as relative standard deviation (RSD%, n=10) was 1.0% for a sample with a copper concentration of 5.0μgL−1. Accuracy was assessed by means of addition and recovery experiments carried out in biodiesel samples, with results ranging from 98.4% to 102.5%. The proposed method can be regarded as an efficient and expeditious alternative for copper determination in biodiesel, after extraction employing ultrasound-assisted sample treatment, as confirmed by the good correlation between the obtained results and those provided by graphite furnace atomic absorption spectrometry, after acid digestion.

A novel and sensitive turn-on fluorescent biosensor for the DNA detection using Sm3+-modulated glutathione-capped CdTe quantum dots

A novel and sensitive turn-on fluorescent biosensor for herring sperm DNA (hsDNA) detecting was designed based on hsDNA-induced fluorescence enhancement of Sm3+-modulated glutathione (GSH)-capped CdTe quantum dots (QDs). The fluorescent biosensor was based on the following two properties. First, the high fluorescence of GSH-capped CdTe QDs could be effectively quenched by Sm3+ due to the binding of Sm3+ to the GSH on the surface of the QDs and the electron transfer from the photoexcited GSH-capped CdTe QDs to Sm3+. Second, the high affinity of hsDNA to Sm3+ enabled Sm3+ to be dissociated from the surface of GSH-capped CdTe QDs to form more stable complex with hsDNA in aqueous solution, thereby enhancing the fluorescence of Sm3+-modulated GSH-capped CdTe QDs. Experimental results showed that the enhanced fluorescence intensity of Sm3+-modulated GSH-capped CdTe QDs was directly proportional to the concentration of hsDNA in the range from 0.012 to 14.0μgmL−1 with a good correlation coefficient of 0.9977, and the detection limit (3σ/S) was 3.61ngmL−1. To further investigate perfect analysis performance, the developed biosensor was applied to the determination of hsDNA in synthetic samples and human fresh serum samples with satisfactory results.

Quantum dot-based assay for Cu2+ quantification in bacterial cell culture

A simple and sensitive method for quantification of nanomolar copper with a detection limit of 1.2×10−10M and a linear range from 10−9 to 10−8M is reported. For the most useful analytical concentration of quantum dots, 1160μg/ml, a 1/Ksv value of 11μM Cu2+ was determined. The method is based on the interaction of Cu2+ with glutathione-capped CdTe quantum dots (CdTe–GSH QDs) synthesized by a simple and economic biomimetic method. Green CdTe–GSH QDs displayed the best performance in copper quantification when QDs of different sizes/colors were tested. Cu2+ quantification is highly selective given that no significant interference of QDs with 19 ions was observed. No significant effects on Cu2+ quantification were determined when different reaction matrices such as distilled water, tap water, and different bacterial growth media were tested. The method was used to determine copper uptake kinetics on Escherichia coli cultures. QD-based quantification of copper on bacterial supernatants was compared with atomic absorption spectroscopy as a means of confirming the accuracy of the reported method. The mechanism of Cu2+-mediated QD fluorescence quenching was associated with nanoparticle decomposition.

Detection of DNA using an "off-on" switch of a regenerating biosensor based on an electron transfer mechanism from glutathione-capped CdTe quantum dots to nile blue.

Although various strategies have been reported for double-stranded DNA (DNA) detection, development of a time-saving, specific, and regeneratable fluorescence sensing platform still remains a desired goal. In this study, we proposed a new DNA detection method that relies on an "off-on" switch of a regenerated fluorescence biosensor based on an electron transfer mechanism from glutathione (GSH)-capped CdTe quantum dots (QDs) to nile blue (NB). Initially, the high fluorescence of GSH-capped CdTe QDs could be effectively quenched by NB due to the binding of NB to the GSH on the surface of the QDs and the electron transfer from the photoexcited GSH-capped CdTe QDs to NB. Then, the high affinity of DNA to NB enabled the NB to be dissociated from the surface of GSH-capped CdTe QDs to form a more stable complex with DNA and suppress the electron transfer process between GSH-capped CdTe QDs and NB, thereby restoring the fluorescence of NB surface modified GSH-capped CdTe QDs (QDs-NB). In addition, we have testified the regenerability of the proposed DNA senor. The corresponding result shows that this DNA sensor is stable for two reuses. This fluorescence "off-on" signal was sensitive to the concentration of DNA in the range from 0.0092 to 25.0 μg mL(-1) with a good correlation coefficient of 0.9989, and the detection limit (3σ/S) was 2.78 ng mL(-1). To further investigate for perfect analysis performance, the developed biosensor was applied for the determination of DNA in human fresh serum samples with satisfactory results.

Glutathione-capped CdTe quantum dots for the determination of fleroxacin with dual-wavelength fluorescence signals

A sensitive and simple method for the determination of fleroxacin (FLO) was developed based on the changes of dual-wavelength fluorescence signals of glutathione (GSH)-capped CdTe quantum dots (QDs). Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 555 nm against the concentration of FLO was observed in the range of 0.0262–35.0 μg mL−1 with a correlation coefficient (R) of 0.9992. Meanwhile, a linear calibration plot of the enhanced fluorescence intensity at 429 nm against the concentration of FLO was observed in the range of 0.1966–35.0 μg mL−1 with a correlation coefficient (R) of 0.9986. The corresponding detection limits (3σ/K) are 17.93 ng mL−1 at 555 nm and 59.58 ng mL−1 at 429 nm. In addition, a detailed reaction mechanism has also been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-vis) absorption, fluorescence (FL) spectroscopy and the measurement of fluorescence lifetime. The method has been applied for the determination of FLO in pharmaceutical preparations with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

Simple and sensitive detection method for diprophylline using glutathione-capped CdTe quantum dots as fluorescence probes

A simple and sensitive method for detecting diprophylline (DPP) was developed based on the fluorescence quenching of glutathione-capped CdTe quantum dots (GSH–CdTe QDs) by using diprophylline in a KH2PO4–Na2HPO4 medium. Parameters affecting the quenching efficiency, including types and pH of buffer solutions as well as temperature, reaction time, adding sequence, and interfering substances, were investigated and optimized. In optimum conditions, the calibration plot of the quenched fluorescence intensity F0/F with a DPP concentration range of 1.67×10–6molL−1 to 1.33×10–5molL−1 was linear. The detection limit (with signal to noise ratio of 3) for DPP was 2.24×10–7molL−1. The proposed method was successfully applied for detecting DPP in human serum. The recovery of the method was in the range of 87.41% to 117.94%. Finally, the possible quenching mechanism of GSH–CdTe QDs and DPP was also discussed.

Effect of CdTe Quantum Dots Size on the Conformational Changes of Human Serum Albumin: Results of Spectroscopy and Isothermal Titration Calorimetry

Quantum dots (QDs) are recognized as some of the most promising candidates for future applications in biomedicine. However, concerns about their safety have delayed their widespread application. Human serum albumin (HSA) is the main protein component of the circulatory system. It is important to explore the interaction of QDs with HSA for the potential in vivo application of QDs. Herein, using spectroscopy and isothermal titration calorimetry (ITC), the effect of glutathione-capped CdTe quantum dots of different sizes on the HSA was investigated. After correction for the inner filter effect, the fluorescence emission spectra and synchronous fluorescence spectra showed that the microenvironment of aromatic acid residues in the protein was slightly changed when the glutathione (GSH)-cadmium telluride (CdTe) QDs was added, and GSH-CdTe QDs with larger particle size exhibited a much higher effect on HSA than the small particles. Although a ground-state complex between HSA and GSH-CdTe QDs was formed, the UV-vis absorption and circular dichroism spectroscopic results did not find appreciable conformational changes of HSA. ITC has been used for the first time to characterize the binding of QDs with HSA. The ITC results revealed that the binding was a thermodynamically spontaneous process mainly driven by hydrophobic interactions, and the binding constant tended to increase as the GSH-CdTe QDs size increased. These findings are helpful in understanding the bioactivities of QDs in vivo and can be used to assist in the design of biocompatible and stable QDs.

Quantum dot coating of baculoviral vectors enables visualization of transduced cells and tissues

Imaging of transduced cells and tissues is valuable in developing gene transfer vectors and evaluating gene therapy efficacy. We report here a simple method to use bright and photostable quantum dots to label baculovirus, an emerging gene therapy vector. The labeling was achieved through the non-covalent interaction of glutathione-capped CdTe quantum dots with the virus envelope, without the use of chemical conjugation. The quantum dot labeling was nondestructive to viral transduction function and enabled the identification of baculoviral vector-transduced, living cells based on red fluorescence. When the labeled baculoviral vectors were injected intravenously or intraventricularly for in vivo delivery of a transgene into mice, quantum dot fluorescence signals allow us monitor whether or not the injected tissues were transduced. More importantly, using a dual-color whole-body imaging technology, we demonstrated that in vivo viral transduction could be evaluated in a real-time manner in living mice. Thus, our method of labeling a read-to-use gene delivery vector with quantum dots could be useful towards the improvement of vector design and will have the potential to assess baculovirus-based gene therapy protocols in future.