Fluorescence Of CdTe Quantum Dots Research Articles

Extracellular biosynthesis of CdTe quantum dots by the fungus Fusarium oxysporum and their anti-bacterial activity

The growing demand for semiconductor [quantum dots (Q-dots)] nanoparticles has fuelled significant research in developing strategies for their synthesis and characterization. They are extensively investigated by the chemical route; on the other hand, use of microbial sources for biosynthesis witnessed the highly stable, water dispersible nanoparticles formation. Here we report, for the first time, an efficient fungal-mediated synthesis of highly fluorescent CdTe quantum dots at ambient conditions by the fungus Fusarium oxysporum when reacted with a mixture of CdCl2 and TeCl4. Characterization of these biosynthesized nanoparticles was carried out by different techniques such as Ultraviolet–visible (UV–Vis) spectroscopy, Photoluminescence (PL), X-ray Diffraction (XRD), X-ray Photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and Fourier Transformed Infrared Spectroscopy (FTIR) analysis. CdTe nanoparticles shows antibacterial activity against Gram positive and Gram negative bacteria. The fungal based fabrication provides an economical, green chemistry approach for production of highly fluorescent CdTe quantum dots.

Sensitive fluorescent detection of carbamate pesticides represented by methomyl based on the inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

Based on the inner filter effect (IFE) of Au nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs), a novel fluorescence method for the rapid assay of carbamate pesticides has been developed. The fluorescence of CdTe QDs was remarkably quenched in the presence of AuNPs via IFE. Acetylcholinesterase (AChE) catalyzed the hydrolysis of acetylthiocholine into thiocholine, which could induce the aggregation of AuNPs and decrease their characteristic absorption, thereby recovering the IFE-decreased fluorescence of the CdTe QDs. Carbamate pesticides can inhibit the activity of AChE, thus preventing the aggregation of AuNPs and the fluorescence recovery of CdTe QDs. Therefore, the IFE of the fluorescence between AuNPs and CdTe QDs could convert the absorption signal to a fluorescence signal, which improved the detection sensitivity of carbamate pesticides in vegetables. The calibration curve for methomyl was established in the range of 0.017–0.5 μg mL−1 with a detection limit of 0.011 μg mL−1 (S/N = 3) which is superior to the HPLC coupled with UV detection method. This method was successfully carried out for the assessment of methomyl in vegetables, and has many advantages such as high sensitivity, low cost and rapidity in comparison with traditional methods.

Luminescence switching of CdTe quantum dots in presence of water-soluble spironaphthoxazine

The typical reaction of spironaphthoxazine is the conversion between the non-polar spiro form and polar merocyanine form. Quantum dots (QDs) have unique optical properties and several advantages over conventional organic dyes. In this work, the CdTe QDs containing a water-soluble spironaphthoxazine was used as the optical probe photoisomerization between spiro and merocyanine. The initial bright fluorescence of CdTe QDs was effectively quenched by water-soluble spironaphthoxazine using UV irradiation. Reversible modulation of fluorescence intensity of CdTe QDs was achieved using alternating irradiation with UV and visible light. The possible mechanism is discussed.

A sensitive enzyme biosensor for catecholics detection via the inner filter effect on fluorescence of CdTe quantum dots

In this paper, a new type of fluorescent biosensing system for catechol and 2,3-dihydroxybiphenyl (DHB) was described based on the inner filter effect (IFE), with the combination of CdTe quantum dots (QDs) and an extradiol dioxygenase, 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC). In the presence of BphC and its substrates, catechol and DHB, the excitation of QDs was partially weakened by the competitive absorption of the enzymatic reaction products, resulting in the quenching of QDs. The dependence of the emission intensity quenching on “quencher” concentration obeyed the quadratic equation, and the detection limits for catechol and DHB were 0.02 and 2 μM, respectively. The present QD–BphC system also exhibited good selectivity to either catechol or DHB in the mixtures of other phenolic compounds. However, when catechol and DHB coexisted, the QD–BphC system could not separate the signals of these two compounds from each other due to the inherent substrate range of BphC. Nevertheless, the developed BphC-based fluorescent biosensor via the IFE on fluorescence of QDs could be employed as a robust support for the construction of other enzyme-based biosensors.

Sensitive fluorescent detection of melamine in raw milk based on the inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

A simple, rapid and sensitive fluorescent assay for determination of melamine has been developed based on inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs). When thioglycolic acid-capped CdTe QDs was mixed with citrate-stabilized AuNPs, the fluorescence of CdTe QDs was significantly quenched via the IFE of AuNPs. With the presence of melamine, melamine could induce the aggregation and corresponding absorbance change of AuNPs, which then resulted in the recovery of IFE-decreased emission of CdTe QDs. Under the optimum conditions, the detection limit for melamine in raw milk was 0.02mgL−1. The application of this method in samples of melamine-spiked raw milk suggested a recovery between 103% and 104%. Therefore, the obvious merits provided by the present assay, such as simplicity, rapidity, low cost, and high sensitivity, would make it promising for on-site screening of melamine adulterant in raw milk.

基于水溶性CdTe量子点-绿原酸-血管紧张素I相互作用的荧光可逆调控

Using mercaptopropinic acid (MPA) as the stabilizer, CdTe quantum dots (QDs) were synthesized in aqueous solution. Their particle sizes and morphology were characterized by transmission electron microscope (TEM) and atomic force microscope (AFM). Chlorogenic acid (CHA) can quench the fluorescence of CdTe QDs effectively, and the quenching values of fluorescence were proportional to the concentration of CHA in a certain concentration range. The interaction between CdTe QDs and CHA was investigated via fluorescence spectrometry, UV-Vis absorption spectrometry and Fourier transform infrared spectrometry. The preliminary judgement of the quenching mechanism is dynamic quenching, and a theoretical basis of fluorescent spectrometry methods for the determination of trace amounts of CHA was provided. When angiotensinⅠhuman acetate salt hydrate (AngⅠ) was added into the CdTe QDs-CHA system, the fluorescence of CdTe QDs was recovered in a certain concentration range, thus reversible control of fluorescence of the QDs was realized. The process of fluorescent quenching and recovering of CdTe QDs has a guiding significance for the design of fluorescence sensor and the study of mechanism of reversible control of fluorescence.

The double-effect mechanism between Fe3O4 nanoparticles and MSA-capped CdTe QDs

Water-soluble mercaptosuccinic acid (MSA)-capped CdTe quantum dots (QDs) of two sizes and superparamagnetic Fe3O4 nanoparticles have been synthesized and used to investigate the effect of the mechanism of Fe3O4 nanoparticles on the fluorescence intensity of QDs. In the presence of a low concentration of Fe3O4 nanoparticles, the CdTe QDs with smaller particle size exhibit fluorescence quenching while fluorescence enhancement of CdTe QDs with larger particle size was observed, and the fluorescence intensity changes with the excitation wavelength and the concentration of Fe3O4 nanoparticles. The mechanism study shows that there is a double-effect between the Fe3O4 and CdTe QDs: one is the fluorescence quenching effect due to Fe3O4 strong absorption of excitation and emission light, the other is the fluorescence enhancement effect resulting from a localized electromagnetic field caused by the absorption of exciting light. The fluorescence of CdTe QDs with lower concentration of Fe3O4 nanoparticles was determined via the synergy of the double-effect. To our best knowledge, this is the first systematic study on the interaction between Fe3O4 nanoparticles and CdTe QDs, which finds the fluorescence enhancement effect in the presence of low concentration of Fe3O4.

Photochemical synthesis of highly fluorescent CdTe quantum dots for “on–off–on” detection of Cu(II) ions

A novel environment-friendly photoillumination procedure was developed to produce highly fluorescent thiol-capped CdTe quantum dots (QDs). Based on it, the hydrophilic QDs were incorporated into multilayer films by layer-by-layer self-assembly. It was found that the as-prepared nanocomposite presented high photostability and allowed highly sensitive and selective determination of copper(II) ions. Under optimum conditions, the FL quenching effect of low concentrations of copper(II) ions could be well described by Langmuir-type binding isotherm in the range from 0.02 to 1.0μM, with a detection limit of 8.0nM. Furthermore, at low concentration levels, it was observed that the FL intensity of nanocomposite could recover to optimal level with the attenuation rate less than 5.8% for five “on–off–on” times. At high concentrations, the FL responses fitted fairly well to the typical Stern–Volmer equation range from 1.0 to 30μM, while the quenching process turned out to be irreversible.

Homogeneous fluorescence-based immunoassay via inner filter effect of gold nanoparticles on fluorescence of CdTe quantum dots

Homogeneous immunoassays are becoming more and more attractive for modern medical diagnosis because they are superior to heterogeneous immunoassays in sample and reagent consumption, analysis time, portability and disposability. Herein, a universal platform for homogeneous immunoassay, using human immunoglobulin (IgG) as a model analyte, has been developed. This assay relies upon the inner filter effect (IFE) of gold nanoparticles (AuNPs) on CdTe QDs fluorescence. The immunoreaction of antigen and antibody can induce the aggregation of antibody-functionalized AuNPs, and after aggregation the IFE of AuNPs on CdTe QDs fluorescence is greatly enhanced, resulting in a decrease of fluorescence intensity in the system. Based on this phenomenon, a wide dynamic range of 1-100 pg mL(-1) for determination of IgG can be obtained. The proposed method shows a detection limit of 0.3 pg mL(-1) for human IgG, which is much lower than the corresponding absorbance-based approach and compares favorably with other reported fluorescent methods. This immunoassay method is simple, rapid, cheap, and sensitive. The proposed method has been successfully applied to measuring IgG in serum samples, and the obtained results agreed well with those of the enzyme-linked immunosorbent assay (ELISA).

Layer-by-Layer Assembled Fe3O4@C@CdTe Core/Shell Microspheres as Separable Luminescent Probe for Sensitive Sensing of Cu2+ Ions

A novel multifunctional microsphere with a fluorescent CdTe quantum dots (QDs) shell and a magnetic core (Fe(3)O(4)) has been successfully developed and prepared by a combination of the hydrothermal method and layer-by-layer (LBL) self-assembly technique. The resulting fluorescent Fe(3)O(4)@C@CdTe core/shell microspheres are utilized as a chemosensor for ultrasensitive Cu(2+) ion detection. The fluorescence of the obtained chemosensor could be quenched effectively by Cu(2+) ions. The quenching mechanism was studied and the results showed the existence of both static and dynamic quenching processes. However, static quenching is the more prominent of the two. The modified Stern-Volmer equation showed a good linear response (R(2) = 0.9957) in the range 1-10 μM with a quenching constant (K(sv)) of 4.9 × 10(4) M(-1). Most importantly, magnetic measurements showed that the Fe(3)O(4)@C@CdTe core/shell microspheres were superparamagnetic and they could be separated and collected easily using a commercial magnet in 10 s. These results obtained not only provide a way to solve the embarrassments in practical sensing applications of QDs, but also enable the fabrication of other multifunctional nanostructure-based hybrid nanomaterials.

Application of CdTe Quantum Dots to Development Fingerprints on Adhesive Surfaces

Water-soluble fluorescent CdTe quantum dots were synthesized using TGA (Thiolglycolic acid) as the stabilizer and characterized by fluorescence spectroscopy. This fluorescent material was applied to development fingerprints deposited on the sticky side of adhesives. The development conditions such as development time, temperature and pH value of QDs solution were investigated. The comparison experimental with traditional methods and development rate were also studied. The results show that this material exhibited strong visible fluorescence under excitation at 365 nm. CdTe QDs can detect fingerprints on different adhesive surfaces. In addition, the development rate of fingerprints on the adhesive side of cellulose tape was discussed and the effective development rate for 30-days-aged fingerprints can reach to 72%. Furthermore, the developed fingerprints have higher and stable fluorescence intensity, weaker background interference and better contrast between fingerprints and the substrate. CdTe QDs is a promising reagent for fingerprints development on adhesive surfaces.

Substance P conjugated to CdTe quantum dots triggers cytosolic calcium concentration oscillations and induces quantum dots internalization in the pancreatic carcinoma cell line AR4-2J

Highly fluorescent CdTe quantum dots (QDs) stabilized by 3-mercaptopropionic acid were prepared by an aqueous solution approach and used as a fluorescent label to link substance P (SP) in studying the interaction of SP with NK-1 receptor, which was expressed on the AR4-2J cell line. Nonspecific adsorptions of CdTe QDs on the AR4-2J cell membrane were observed, whereas the QD-SP conjugates successfully crossed the cell membrane and entered the cytosol. SP is a neurotransmitter, and neurotransmitter-induced calcium concentration oscillation is a common phenomenon in diverse cells especially of secretory type. Cytosolic calcium concentration responses were studied in the AR4-2J cell line during stimulation with SP and QD-SP conjugates. The oscillations triggered by SP and QD-SP conjugates were dose-dependent and very similar. Such QD-SP conjugates readily internalized into the cytosol as would be expected of an active NK-1 ligand. Therefore QD-SP conjugates could be used successfully to study ligand and NK-1 receptor interactions in live cells. Our research may provide a meaningful reference for congener research.

A simple fluorescence quenching method for roxithromycin determination using CdTe quantum dots as probes

A new method for the determination of roxithromycin based on the fluorescence quenching of 3-mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) was developed. In ethanol medium, the fluorescence of CdTe quantum dots at 552nm was quenched in the presence of roxithromycin. Based on this a simple, sensitive, and selective method for rapid determination of roxithromycin was described. Reaction time, interfering substances on the fluorescence quenching, and mechanism of the interaction of CdTe QDs with roxithromycin were investigated. After optimization, the proposed method allows the determination of roxithromycin over the range 25.0–350.0μgml−1. The detection limit is 4.6μgml−1. The proposed method was successfully applied to commercial capsules and tablets with satisfactory results. The recovery of the method was in the range of 96.8–102.5%.

CdTe quantum dots for an application in the life sciences

This report highlights the results of the preparation of semiconductor CdTe quantum dots (QDs) in the aqueous phase. The small size of a few nm and a very high luminescence quantum yield exceeding 60% of these materials make them promisingly applicable to bio-medicine labeling. Their strong, two-photon excitation luminescence is also a good characteristic for biolabeling without interference with the cell fluorescence. The primary results for the pH-sensitive CdTe QDs are presented in that fluorescence of CdTe QDs was used as a proton sensor to detect proton flux driven by adenosine triphosphate (ATP) synthesis in chromatophores. In other words, these QDs could work as pH-sensitive detectors. Therefore, the system of CdTe QDs on chromatophores prepared from the cells of Rhodospirillum rubrum and the antibodies against the beta-subunit of F0F1–ATPase could be a sensitive detector for the avian influenza virus subtype A/H5N1.

Interfacial Charge Transfer between CdTe Quantum Dots and Gram Negative Vs Gram Positive Bacteria

Oxidative toxicity of semiconductor and metal nanomaterials to cells has been well established. However, it may result from many different mechanisms, some requiring direct cell contact and others resulting from the diffusion of reactive species in solution. Published results are contradictory due to differences in particle preparation, bacterial strain, and experimental conditions. It has been recently found that C(60) nanoparticles can cause direct oxidative damage to bacterial proteins and membranes, including causing a loss of cell membrane potential (depolarization). However, this did not correlate with toxicity. In this study we perform a similar analysis using fluorescent CdTe quantum dots, adapting our tools to make use of the particles' fluorescence. We find that two Gram positive strains show direct electron transfer to CdTe, resulting in changes in CdTe fluorescence lifetimes. These two strains also show changes in membrane potential upon nanoparticle binding. Two Gram negative strains do not show these effects-nevertheless, they are over 10-fold more sensitive to CdTe than the Gram positives. We find subtoxic levels of Cd(2+) release from the particles upon irradiation of the particles, but significant production of hydroxyl radicals, suggesting that the latter is a major source of toxicity. These results help establish mechanisms of toxicity and also provide caveats for use of certain reporter dyes with fluorescent nanoparticles which will be of use to anyone performing these assays. The findings also suggest future avenues of inquiry into electron transfer processes between nanomaterials and bacteria.

Glycosylated Quantum Dots for the Selective Labelling of Kluyveromyces bulgaricus and Saccharomyces cerevisiae Yeast Strains

Highly fluorescent CdTe quantum dots (QDs) stabilized by thioglycolic acid (TGA) were prepared by an aqueous solution approach and used as fluorescent labels in detecting yeast cells. Sugars (mannose, galactose or glucose) were adsorbed on CdTe@TGA QDs and the interaction of these nanoparticles with yeast cells was studied by fluorescence microscopy. Results obtained demonstrate that galactose and mannose functionalized QDs associate respectively with Kluyveromyces bulgaricus and Saccharomyces cerevisiae yeast strains due to saccharide/lectin specific recognition. Glucose-functionalized CdTe QDs, which are not recognized by cell lectins, preferentially localize in the bud scars of S. cerevisiae.

Carbon nanotube-based magnetic-fluorescent nanohybrids as highly efficient contrast agents for multimodal cellular imaging

We developed a simple and novel layer-by-layer (LBL) assembly in combination with covalent connection strategy for the synthesis of multifunctional carbon nanotubes (CNTs)-based magnetic-fluorescent nanohybrids as multimodal cellular imaging agents for detecting human embryonic kidney (HEK) 293T cells via magnetic resonance (MRI) and confocal fluorescence imaging. Superparamagnetic iron oxide nanoparticles (SPIO) and near-infrared fluorescent CdTe quantum dots (QDs) were covalently coupled on the surface of CNTs in sequence via LBL assembly. It was indicated that the SPIO layer acted not only as a contrast agent for MRI, but also as a spacer between CdTe QDs and CNTs for prohibiting fluorescence quenching of QDs on the surface of the CNTs. The multifunctional CNT-based magnetic-fluorescent nanohybrids showed an enhanced MRI signal as contrast agent for detecting 293T cells in comparison with the pure SPIO. This is due to the magnetic coupling between the orderly arrayed SPIO, the function of CNTs for lowering the transverse relaxation and the ability of CNTs for penetrating into cells. Moreover, the multifunctional CNT-based magnetic-fluorescent nanohybrids exhibited the higher intracellular labeling efficiency due to the ability of CNTs for penetrating into cells in comparison with pure SPIO-CdTe nanoparticles.

Water-soluble multicolored fluorescent CdTe quantum dots: Synthesis and application for fingerprint developing

Multicolored water-soluble fluorescent CdTe quantum dots (QDs) have been synthesized by using Te, NaBH 4, and CdCl 2 as precursors and several mercapto-based compounds as modifiers. The effects of ratio of the precursor, type of modifier, refluxing time and initial pH value of the reaction on fluorescence intensity of CdTe QDs have been studied. XRD, HRTEM and fluorescence spectra were employed to characterize these samples. It is found that CdTe QDs with a crystalline size of 3–4 nm are homogeneously embedded in the organic matrix. The maximum fluorescence emission peaks of CdTe QDs solutions shifted from 525 nm to 591 nm according to the refluxing time. The fingerprint details on the surface of smooth objects were clearly developed with CdTe QDs solution under irradiation of UV lights.

Preparation and characterization of Fe3O4/CdTe magnetic/fluorescent nanocomposites and their applications in immuno-labeling and fluorescent imaging of cancer cells.

The synthesis of a new kind of magnetic, fluorescent multifunctional nanoparticles (approximately 30 nm in diameter) was demonstrated, where multiple fluorescent CdTe quantum dots (QDs) are covalently linked to and assembled around individual silica-coated superparamagnetic Fe(3)O(4) nanoparticles and active carboxylic groups are presented on the surface for easy bioconjugation with biomolecules. The Fe(3)O(4) nanoparticles were first functionalized with thiol groups, followed by chemical conjugation with multiple thioglycolic acid modified CdTe QDs to form water-soluble Fe(3)O(4)/CdTe magnetic/fluorescent nanocomposites. X-ray diffraction, infrared spectroscopy, transmission electron microscopy, absorption and fluorescence spectroscopy, and magnetometry were applied to fully characterize the multifunctional nanocomposites. The nanocomposites were found to exhibit magnetic and fluorescent properties favorable for their applications in magnetic separation and guiding as well as fluorescent imaging. The carboxyl groups on the nanocomposite surface were proved to be chemically active and readily available for further bioconjugation with biomolecules such as bovine serum albumin and antibodies, enabling the applications of the nanocomposites for specific recognition of biological targets. The Fe(3)O(4)/CdTe magnetic/fluorescent nanocomposites conjugated with anti-CEACAM8 antibody were successfully employed for immuno-labeling and fluorescent imaging of HeLa cells.

Chemical Redox Modulation of the Surface Chemistry of CdTe Quantum Dots for Probing Ascorbic Acid in Biological Fluids

Most of the fluorescence resonance energy transfer (FRET)-based sensors employing quantum dots (QDs) usually use organic fluorophores and gold nanoparticles as the quenchers. However, complex processes for the modification/immobilization of the QDs are always necessary, as the generation of FRET requires strict distance between the donor and acceptor. Herein, a simple chemical redox strategy for modulating the surface chemistry of the QDs to develop a QD-based turn-on fluorescent probe is reported. The principle of the strategy is demonstrated by employing CdTe QDs with KMnO(4) as the quencher and ascorbic acid as the target analyte. The fluorescence of CdTe QDs is quenched with a blue-shift upon addition of KMnO(4) due to the oxidation of the Te atoms on the surface of the QDs. The quenched fluorescence of the QDs is then recovered upon addition of ascorbic acid due to the reduction of CdTeO(3)/TeO(2) on the surface of the QDs to CdTe. The recovered fluorescence of the QDs increases linearly with the concentration of ascorbic acid from 0.3 to 10 microM. Thus, a novel QD-based turn-on fluorescent probe with a detection limit as low as 74 nM is developed for the sensitive and selective detection of ascorbic acid in biological fluids. The present approach avoids the complex modification/immobilization of the QDs involved in FRET-based sensors, and opens a simple pathway to developing cost-effective, sensitive, and selective QD-based fluorescence turn-on sensors/probes for biologically significant antioxidants.