Water-soluble CdTe Quantum Dots Research Articles

Copper ion ratio chemiluminescence probe based on chemiluminescence resonance energy transfer

We synthesized the water-soluble CdTe quantum dots (CdTe QDs) with longer emission wavelength, constructed the luminol-CdTe QDs chemiluminescence resonance energy transfer (CRET) system, and realized the high selectivity ratio detection for Cu2+. Herein, based on the Irving-William sequence, it was found that the paramagnetic ion Cu2+ generally binds more strongly than the diamagnetic ion Cd2+. When Cu2+ is added to the system, Cu2+ tends to bind to the sulfhydryl group (SH) of stabilizer on CdTe QDs, leading to surface defects of CdTe QDs, which quenches the chemiluminescence (CL) signal remarkably. Meanwhile, due to the superior coordination ability of Cu2+ and ratio detection, the system has better selectivity and anti-interference performance. The method achieved a highly sensitive, selective, yet reliable measurement of Cu2+ in the concentration range of 0.5 × 10-7-20 × 10-7 M, with a low detection limit of 8.4 nM. Importantly, the sensor has been successfully exploited to detect Cu2+ in tap water and lake water.

Effects of Zn (II) on the Optical Properties of CdTe Quantum Dots and Their Photoluminescence Response to Lead Ion

Water-soluble CdTe quantum dots (QDs) have been utilized as photoluminescence probes for the detection of metal ions such as Pb2+, Hg2+, Cd2+, etc. We initially developed highly photoluminescence (PL) Zn-doped CdTe for toxic ions detection. A study on the changes of optical properties of Zn-doped CdTe and CdTe QDs when exposed to Pb2+ suggested that Pb2+ could act as a surface passivating agent to reduce Te2- dangling bonds while Zn2+ dopant stabilizes the QDs surface against ambient oxidation. The results demonstrated herein provide useful understandings of the interactions between water-soluble QDs and metal ions. These results suggest further applications of QDs in sensing metal ions.

Fabrication of cell penetrating peptide labelled biodegradable poly(methacrylamide) nanoparticles for delivery of doxorubicin in HeLa cells

Advancements in cancer nano-therapeutics have led to the development of new and improved drug delivery systems but challenges still persist in the form of several limitations such as ineffective drug distribution, poor water solubility, and drug degradation. In lieu of this, the aim of this work is the development of a highly efficient nanomaterial based drug delivery system to overcome these limitations. In this work, we have successfully developed a theranostic platform where biodegradable polymeric nanoparticles have been used to reduce drug toxicity, control drug release, and provide biocompatibility with enhanced bioimaging. Anticancer drug, doxorubicin (DOX) was encapsulated in polymeric nanoparticles composed of P(N-(3-aminopropyl) methacrylamide) homopolymer, P(APMA), bearing primary amines for further modification. Water soluble CdTe quantum dots (QDs) were used as the fluorescent tag. The encapsulation efficiency of QDs-DOX conjugates into polymeric nanoparticles was found to be very high. To enhance the cellular internalization, a cell penetrating peptide BP100 (KKLFKKILKYL-Amide) was also attached on the surface of these polymeric nanoparticles and characterized using confocal microscopy. The drug release from the nanoconjugates at acidic pH showed enhanced internalization and growth inhibition in HeLa cells. Therefore, the synthesized conjugates can act as promising candidate for the successful treatment of cancer.

Synthesis and characterization of CdTe QDs capped with a branched 3MB3MP ligand and fluorescent switching detection of H2O2

Label free turn-on detection of H2O2 using water-soluble CdTe quantum dots modified with a novel multifunctional branched ligand.

A highly sensitive dual-readout assay for perfluorinated compounds based CdTe quantum dots

Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS) are two typical perfluorinated compounds (PFCs) that poss potential ecological toxicity. In this work, a fluorescence and resonance light scattering (RLS) dual-readout strategy for the detection of PFCs at picomole level based on the water-soluble CdTe quantum dots (CdTe QDs) has been proposed. It is found that the CdTe QDs exhibit a quenching in the presence of PFCs and thus serve as useful probes for PFCs. The linear ranges are 0.032–10.0 nM with a limit of detection(LOD) of 32.02 pM for PFOA and 0.044–15.0 nM with a LOD of 43.96 pM for PFOS, respectively. Meanwhile, PFCs can form complexes with CdTe QDs in acid medium, resulting in remarkable RLS signals. The enhanced RLS intensities are in proportion to the concentrations of PFOA and PFOS, respectively. And the linear ranges are 0.048–5.0 nM with a LOD of 47.78 pM for PFOA, and 0.057–5.0 nM with a LOD of 56.72 pM for PFOS, respectively. This dual-mode detection increases the reliability of the measurement. The proposed method is simple, sensitive and cost-effective, with potential applications in environmental monitoring and assessment.

Fluorescence Characteristics of CdTe Quantum Dot Colloids below the Freezing Point

In this paper, water-soluble CdTe quantum dots (QDs) with different sizes from 3 to 3.9 nm are synthesized by the aqueous phase method using glutathione as the stabilizer, and their fluorescence properties below the freezing point are studied. The results show that the QD dispersion system still maintains the liquid state at −30 °C when the volume fraction of ethanol is 30%, and its fluorescence has a strong temperature dependence below the freezing point; as the temperature decreases from 0 to −30 °C, the fluorescence intensity increases about 62–82%, and the fluorescence emission peak also blue-shifts (5–10 nm). After cycles of heating (0 °C)–cooling (−30 °C), the fluorescence intensity can still be recovered, indicating a strong fluorescence reversibility. This work provides help for expanding the application of QDs in the fields of biomedicine.

Quenched or alive quantum dots: The leading roles of ligand adsorption and photoinduced protonation

The fluorescence emission of water-soluble CdTe quantum dots (QDs) capped with mercaptocarboxylic acids (MCAs) is known to be pH-dependent. However, this behaviour is quite different from a study to another, so that literature suffers from a lack of coherence. Here we assume that the QD fluorescence efficiency is actually driven by the acid-base equilibrium of MCA thiol groups, and that light-excited QDs open a non-radiative relaxation path through photoinduced protonation. We address this issue by examining colloidal CdTe QDs with (time-resolved) fluorescence spectroscopy under various conditions of acidity and light excitation. It appears that the emission of QDs is quenched below a critical pH value of 6.87, and that light excitation power strengthens this quenching. We thus demonstrate the existence of an additional photochemical process and developed a mathematical modeling accounting for all our experimental results. With only three parameters, it is possible to accurately predict the fluorescence decay of QDs over time, at any pH. Further, we also related the critical pH value of 6.87 to QD surface properties, explaining why observations may differ from a study to another and making the literature much more coherent.

Enhanced Stokes-shift and dispersibility in non-polar PMMA solvent of CdTe quantum dots by silica coating

Silica-coated cadmium telluride quantum dots (CdTe@SiO 2 ) exhibit increased sensitivity to UV illumination within the 300–400 nm range, allowing long and efficient Stokes-shifted emissions with more than 300 nm of separation from the excitation source. In addition, the surface modification of water-soluble CdTe quantum dots promotes a better dispersibility in a non-polar solvent (chloroform), allowing the facile fabrication of a highly luminescent PMMA/CdTe@SiO 2 composite with uniformly distributed CdTe@SiO 2 clusters suitable for photonic applications.

A highly selective and simple fluorescent probe for salbutamol detection based on thioglycolic acid-capped CdTe quantum dots.

In this paper, a highly fluorescent water-soluble CdTe quantum dots (CdTe QDs) stabilized with thioglycolic acid (TGA) were synthesized for the quantitative and selective determination of salbutamol (SAL). When ten different of 2.09×10-6 mol L-1 alpha-2 adrenoceptor agonist were added to 4.38×10-4 mol L-1CdTe QDs solution, the fluorescence signal of the CdTe QDs quenched obviously by SAL with 57.32% and 0.815% - 7.00% for other nine kinds of veterinary medicine, such as tulobuterol, fenoterol, phenylethanamine A, simatero, penbutolol, clenbuterol, ractopamine, terbutaline and clorprenaline. The result shows that the CdTe QDs is highly sensitive sensor for SAL. The quenching mechanism has been investigated by absorption spectroscopy and KSV at different temperatures, and shew a static quenching process than dynamic quenching. Under the optimal conditions, respectively the straight line equation (F0/F=0.1491×106 C+1.3078) was found between the relative fluorescence intensity and the concentration of SAL was in the range of 6.27×10-8 to 2.09×10-7 mol L-1, and the limit of detection was 4.2×10-8 mol L-1. The proposed method has been applied to the determination of SAL in pig urine samples.

Anodic Electrochemiluminescence of CdTe Quantum Dots Using Tripropylamine as Coreactant: Size-dependent Effect

The quantum size effect of CdTe quantum dots (QDs) has been one of the targets of extensive research concerning the optical spectroscopy of semiconductors, but little is known about their effects on electrochemiluminescence (ECL) behavior, especially in the anodic potential range. In this present study, water-soluble CdTe QDs with different sizes were synthesized with a microwave-assisted hydrothermal method. Upon electrochemical oxidation of the CdTe QD in the presence of tri-n-propylamine (TPrA) as a coreactant, two ECL signals, called ECL1 and ECL2, were observed at potentials corresponding to the oxidation of TPrA (at +0.8 V) and CdTe QDs (at +1.2 V), respectively. The relative intensity of ECL1 significantly increased with increasing the particle size of CdTe QDs, and disappeared when the particle size was less than 2.4 nm. Upon an anodic potential of +0.8 V, TPrA is oxidized at the electrode surface, where the intermediate radical species like TPrA•+ radical cation and CdTe QDs•- radical anion are supposed to be formed to give the excited chemical species of CdTe QDs*. Possible ECL mechanisms are proposed from a view point of thermodynamics.

CdTe Quantum Dots Modified with Cysteamine: A New Efficient Nanosensor for the Determination of Folic Acid.

In this paper, we report the synthesis, characterization, and application of a new fluorescent nanosensor based on water-soluble CdTe quantum dots (QDs) coated with cysteamine (CA) for the determination of folic acid (FA). CdTe/CA QDs were characterized by high-resolution transmission electron microscopy, the zeta potential, and Fourier-transform infrared (FT-IR), UV-visible, and fluorescence spectroscopy. CdTe QDs coated with mercaptopropionic acid (MPA) and glutathione (GSH) were prepared for comparison purposes. The effect of FA on the photoluminescence intensity of the three thiol-capped QDs at pH 8 was studied. Only CdTe/CA QDs showed a notable fluorescence quenching in the presence of FA. Then, a nanosensor based on the fluorescence quenching of the CdTe QDs at pH 8 was explored. Under optimum conditions, the calibration curve showed a linear fluorescence quenching response in a concentration range of FA from 0.16 to 16.4 μM (R2 = 0.9944), with a detection limit of 0.048 μM. A probable mechanism of fluorescence quenching was proposed. The nanosensor showed good selectivity over other possible interferences. This method has been applied for FA quantification in orange beverage samples with excellent results (recoveries from 98.3 to 103.9%). The good selectivity, sensitivity, low cost, and rapidity make CdTe /CA QDs a suitable nanosensor for FA determination.

The size dependent thermal diffusivity of water soluble CdTe quantum dots using dual beam thermal lens spectroscopy

Abstract Size dependent thermal diffusivity of CdTe colloidal quantum dots samples has been studied using dual beam thermal lens spectroscopy. The thermal diffusivity values of the colloidal solution of CdTe quantum dots synthesized in water were found to be less than that of pure water (1.4 × 10−7 m2/s) varying from 0.63 × 10−7 m2/s to 0.15 × 10−7 m2/s. The samples with this kind of very low value of thermal diffusivity can be good thermal insulators. To the best of our knowledge there are no reports on the study of thermal diffusivity of water soluble CdTe quantum dots. The non-radiative relaxation mechanism due to defect states, Brownian motion, capping agent etc. play major roles in controlling the thermal diffusivity of the nano-colloidal sample. The thermal diffusivity is found to be in inverse correlation with the emission intensity.

Preparation of Fluorescent Molecularly Imprinted Polymers via Pickering Emulsion Interfaces and the Application for Visual Sensing Analysis of Listeria Monocytogenes.

In this work, a novel molecularly imprinted polymer (MIP) with water-soluble CdTe quantum dots (QDs) was synthesized by oil-in-water Pickering emulsion polymerization using whole Listeria monocytogenes as the template. Listeria monocytogenes was first treated by acryloyl-functionalized chitosan with QDs to form a bacteria–chitosan network as the water phase. This was then stabilized in an oil-in-water emulsion comprising a cross-linker, monomer, and initiator, causing recognition sites on the surface of microspheres embedded with CdTe QDs. The resulting MIP microspheres enabled selective capture of the target bacteria via recognition cavities. The target bacteria Listeria monocytogenes was detected. Scanning electron microscopy (SEM) characterization showed that the MIPs had a rough spherical shape. There was visual fluorescence detection via quenching in the presence of the target molecule, which offered qualitative detection of Listeria monocytogenes in milk and pork samples. The developed method simplified the analysis process and did not require any sample pretreatment. In addition, the fluorescence sensor provided an effective, fast, and convenient method for Listeria monocytogenes detection in food samples.

Facile aqueous synthesis of Ni-doped CdTe quantum dots as fluorescent probes for detecting pyrazinamide in plasma

Doping with transition-metal ions is an intriguing way to tune the properties of quantum dots. In this study, water-soluble and stable Ni-doped CdTe quantum dots have been successfully synthesized via a facile, novel and green method. Compared with undoped CdTe quantum dots, the Ni-doped CdTe quantum dots exhibited improved photostability, and lower cytotoxicity and enhanced biocompatibility. A simple, affordable, selective, and sensitive method based on the fluorescence quenching of Ni-doped CdTe quantum dots for rapid determination of pyrazinamide (PZA) in plasma samples was developed. Fluorescence of Ni-doped CdTe quantum dots can be effectively quenched by PZA drug due to the binding of PZA drug on the surface of Ni-doped CdTe quantum. Under the optimized conditions, the response was directly proportional to the concentration of PZA in the range of 2 to 100 μM, with a detection limit of 0. 5 μM. The proposed method was applied to the determination of PZA in plasma samples with satisfactory results.

Nanoporphyrin/CdTe quantum dots: A robust tool for effective differentiation among DNA structures

In this study, a novel “off–on” sensor based on water-soluble fluorescent CdTe quantum dots (QDs) was established for the analysis of interactions between nano-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrins (TPP–OCH3 NPs) and various DNA structures, including single-stranded DNA, double-stranded DNA, and G-quadruplexes. QD fluorescence can be quenched by TPP–OCH3 NPs via photo-induced electron transfer, and the interaction between TPP–OCH3 NPs and different DNA structures releases QDs from their quenchers and emits fluorescence with different intensities. The proposed “off–on” method was employed to investigate the parameters, such as base composition, strand length, and spatial configurations, that may affect the interactions between TPP–OCH3 NPs and different DNA structures. Furthermore, the dynamic conversion of G-quadruplex configurations was observed using the proposed sensors. All studied G-quadruplex configurations could be qualitatively and quantitatively identified through chemometric methods with a detection limit of 5 × 10−10 mol·L−1 and a recognition rate of 95.08%. The established detection method provides a new perspective of, as well as guidance for, the water-soluble application of oil-soluble drugs and the rapid analysis of different DNA structures in vitro.

Optical limiting and optical properties of water soluble CdTe quantum dots prepared through a colloidal chemical route

Luminescent, water soluble, CdTe colloidal QDs were synthesized by simple wet chemical method. The prepared CdTe QD samples were showing wide range of color tunability from green to red when irradiated with UV light. The quantum confinement effect of the synthesized QDs was confirmed using UV–vis absorption and fluorescence spectroscopy. The spherical morphology of the synthesized QDs was confirmed using transmission electron microscopy (TEM). The X-ray diffraction (XRD) analysis indicates that the QDs were having cubic structure. Analysis of the third order nonlinear property using Z-scan technique indicates that the QDs were having two photon absorption properties. Unlike the previous reported results, the variations in the third order nonlinear susceptibility (χ3) was found to be in correlation with emission intensity. The value of imaginary part of nonlinear χ3 and refractive index was found to be of the order of 10−11 and 10-7esu respectively. Imaginary part of χ3 is found to be Gaussian dependent function of reaction time, which provides a possible way of tuning of imaginary part of third order susceptibility. The figure of merit (n2/β) of the synthesized QDs was found to be greater than that for the bulk material. Thus these QDs possess good nonlinear optical characteristics which enable them as a potential candidate for the optical limiting application.

Fluorescent CdTe-QD-encoded nanocellulose microspheres by green spraying method

With water-soluble CdTe quantum Dots (QDs) as fluorescent labels and TEMPO-oxidized cellulose nanofibrils (CNF) as matrix, dual-color QD-encoded microspheres were prepared by mechanical spraying, freeze-molding and subsequent electrostatic cross-linking by calcium ion. The entire preparation process was accomplished in aqueous phase without any chemical treatment. The nanocellulose microspheres possessed porous structure and were able to be dispersed stably in water in the form of hydrogels. CdTe QDs were efficiently fixed in the network of intertwined nanofibrils via hydrogen bonding with CNF, making the microspheres to obtain high photoluminescence (PL) intensity and identifiable encoding signals consisting of seven kinds of microsphere arrays. The crystalline structure and chemical composition of both CdTe QDs and CNF were not affected during the preparation process. The comparision of PL behaviors of CdTe QDs and QD-encoded microspheres in different media indicate that CNF matrix provided good protection of QDs and improved the PL intensity and photostability. Dual-color CdTe-encoded nanocellulose microspheres were prepared via pure physical process in aqueous phase. The fluorescent microspheres possessed high photoluminescence intensity and identifiable seven kinds of encoding signals. The nanocellulose matrix provided good protection of CdTe QDs and improved the photoluminescence intensity and photostability.

Synthesis and Properties of Water-Soluble Blue-Emitting Mn-Alloyed CdTe Quantum Dots

In this work, we prepared CdTe quantum dots, and series of Cd1-xMnxTe-alloyed quantum dots with narrow size distribution by an ion-exchange reaction in water solution. We found that the photoluminescence peaks are shifted to higher energies with the increasing Mn2+ content. So far, this is the first report of blue-emitting CdTe-based quantum dots. By means of cyclic voltammetry, we detected features of electrochemical activity of manganese energy levels formed inside the Cd1-xMnxTe-alloyed quantum dot band gap. This allowed us to estimate their energy position. We also demonstrate paramagnetic behavior for Cd1-xMnxTe-alloyed quantum dots which confirmed the successful ion-exchange reaction.

Capillary electrophoresis-driven synthesis of water-soluble CdTe quantum dots in nanoliter scale

‘Green nanotechnology’ is a term used for the design of nanomaterials and processes that reduce or eliminate the use and/or generation of hazardous substances. In this paper, a capillary electrophoresis (CE)-driven synthesis of CdTe quantum dots (QDs) and their subsequent conjugation with a metal-binding protein metallothionein (isofom MT1) is reported. Even though the toxic materials (cadmium and potassium borohydride) were used for synthesis, the proposed method can be labeled as ‘environmentally friendly’ because the whole process (synthesis of QDs and MT1 conjugation) was carried out under mild conditions: ultra-low volume (nanoliter scale), relatively low temperature (50 °C), atmospheric pressure, and completed in a short time (under 90 s). Prepared QDs were also characterized by classical fluorescence spectroscopy and transmission electron microscopy. This study opens up new possibilities for the utilization of classical CE in the synthesis of nanoparticles and on-line labeling of biomolecules in the nanoliter scale in short period of time.

A quantum dot-based lateral flow immunoassay for the sensitive detection of human heart fatty acid binding protein (hFABP) in human serum

We describe the preparation and validation of a novel lateral flow immunoassay test for the detection of human heart fatty acid binding protein (hFABP). Water-soluble CdTe quantum dots (QDs) were selected as the fluorescent label and were linked covalently to anti-hFABP antibodies. Upon conjugation, the secondary structure of the anti-hFABP was preserved and the fluorescence quantum yield of the CdTe QDs increased. The labelled antibodies were transferred to the immunoassay test strip and the antigen–antibody reaction was successfully performed. This evidenced the preserved antibody activity of QD-labelled anti-hFABP towards hFABP, and provided a rapid means for the quantitation of hFABP in human serum within the range of 0–160ng ∙ ml−1, with a much lower detection limit of 221pg.∙ ml−1 compared with other rapid tests based on lateral flow immunoassays. This new immunoassay test has been successfully used for the early detection of acute myocardial infarction.