Water-soluble CdS Quantum Dots Research Articles

Synthesis of water-soluble CdS quantum dots for the fluorescence detection of tetracycline

An effective strategy for combating antibiotic-resistant bacteria (ARB) entails the early detection of antibiotics during the initial stages of water treatment facilities. In this context, cadmium sulfide quantum dots (CdS QDs) were employed for the precise detection of tetracycline (TET), an emerging contaminant, in water. CdS QDs with fluorescence properties were synthesized by culturing Citrobacter freundii bacteria. The CdS QDs were characterized by spectroscopy techniques, and the quantum efficiency was estimated to be 55.8% which is ∼2-fold high compared to the standard rhodamine-B solution. The fluorescence of CdS QDs was quenched at 440 nm in the presence of TET. The linear range of TET was varied from 10 to 100 μM with a lower limit of detection of ∼23 nM. The CdS QDs were used to detect TET in river water, tap water, and milk which showed an excellent recovery rate. Therefore, the novel biosynthesis CdS QDs can be a significant fluorescence probe for the detection of TET that shows exceptional sensitivity and selectivity.

In situ growth of water soluble CdS quantum dots by electron beam radiation and its cytotoxicity on mouse embryonic osteoblast precursor MC3T3-E1 cells in vitro

In situ growth of water soluble CdS quantum dots by electron beam radiation and its cytotoxicity on mouse embryonic osteoblast precursor MC3T3-E1 cells in vitro

Bacterial Synthesis of Ternary CdSAg Quantum Dots through Cation Exchange: Tuning the Composition and Properties of Biological Nanoparticles for Bioimaging and Photovoltaic Applications.

In this study, we introduce a biological method for the production of ternary Quantum Dots (QDs): complex nanostructures with tunable optical and structural properties that utilizes post-synthesis modifications through cation exchange. This versatile in-situ cation exchange method being reported for the first time shows great potential for extending the scope of microbial synthesis. By using this bacterial-based method, we easily synthesize and purify CdS, CdSAg, and Ag2S nanocrystals of a size below 15 nm and with variable morphologies that exhibit fluorescence emissions covering a broad spectral range (from 400 to 800 nm). Energy-dispersive X-ray spectroscopy (EDS) results indicate the partial replacement of Cd2+ by Ag+ when AgNO3 concentration is increased. This replacement produces CdSAg ternary QDs hetero-structures with high stability, fluorescence in the NIR-I (700 - 800 nm), and 36.13% quantum yield. Furthermore, this reaction can be extended for the production of soluble Ag2S nanoparticles (NPs) without any traces of Cd. QDs biosynthesized through this cation exchange process display very low toxicity when tested in bacterial or human cell lines. Biosynthesized ternary hetero-structures were used as red fluorescent dyes to label HeLa cells in confocal microscopy studies, which validates its use in bioimaging applications in the near infrared region. In addition, the application of biologically-produced cadmium NPs in solar cells is reported for the first time. The three biosynthesized QDs were successfully used as photosensitizers, where the CdSAg QDs show the best photovoltaic parameters. Altogether, obtained results validate the use of bacterial cells for the controlled production of nanomaterials with properties that allow their application in diverse technologies. We developed a simple biological process for obtaining tunable Quantum Dots (QDs) with different metal compositions through a cation exchange process. Nanoparticles (NPs) are produced in the extracellular space of bacterial cells exposed to cysteine and CdCl2 in a reaction that depends on S2− generation mediated by cysteine desulfhydrase enzymes and uses cellular biomolecules to stabilize the nanoparticle. Using this extracellular approach, water-soluble fluorescent CdS, CdSAg, and Ag2S Quantum Dots with a tunable emission ranging from 400 to 800 nm were generated. This is the first study reporting the use of microorganisms to produce tunable ternary QDs and the first time that a cation exchange process mediated by cells is described. Obtained results validate the use of biological synthesis to produce NPs with new characteristics and opens a completely new research field related to the use of microorganisms to synthesize complex NPs that are difficult to obtain with regular chemical methods.

Cell Imaging Using Two-Photon Excited CdS Fluorescent Quantum Dots Working within the Biological Window.

In recent years, two-photon excited semiconductor quantum dots (QDs) have been the subject of intense investigation due to their long excitation wavelength which helps to achieve deeper penetration and higher image resolution in optical bioimaging. In this paper, water-soluble CdS QDs were synthesized using a hydrothermal method and applied to human liver hepatocellular carcinoma (HepG2) cells. The first-principles calculation suggested that the S-rich defected structure contributes to a narrower band gap compared to the pristine structure. The resulting fluorescence wavelength was significantly red shifted, which was attributed to the deep defect states emission. The large Stokes shifts (> 200 nm) of the QDs can eliminate the possible cross-talk between the excitation light and the emission light. Two-photon induced red fluorescence emission can avoid overlapping with the autofluorescence emission of biological samples. The uptake and cell viability measurements of the HepG2 cells showed a good biocompatibility and a low toxicity of CdS QDs. Two-photon excited scanning microscopy images revealed that the HepG2 cells incubated with CdS QDs emitted bright red upconversion fluorescence and the fluorescence brightness was 38.2 times of that of the control group. These results support CdS QDs as a good candidate for application in cellular imaging.

Use of MPA-capped CdS quantum dots for sensitive detection and quantification of Co2+ ions in aqueous solution

Water soluble CdS quantum dots (QDs) were synthesized by a simple aqueous chemical route using mercaptopropionic acid (MPA) as a stabilizer. These QDs had a fluorescence emission band maximum at 540 nm with a FWHM ∼130 nm and a quantum yield of ∼12%. Transmission electronic microscopy images were used to determine the QD diameter of 8.9 ± 0.4 nm. From this value we calculated the molecular mass M(QD) = 1.17 × 106 g mol−1 and the extinction coefficient at the band edge (450 nm) ε450 = 4.7 × 106 cm−1 M−1, which allowed to determine the true molar concentration of 17 nM for spectroscopic measurements in solution. The fluorescence intensity of MPA-CdS QDs was quenched only in the presence of Co2+ ions, but not in the presence of thirteen other metal cations. The fluorescence quenching of MPA-CdS QDs appeared proportional to the Co2+ concentration in the range 0.04–2 μM. Based on a fluorescence peak position and a lifetime both independent from Co2+ concentration, the quenching mechanism of MPA-CdS QDs appeared static. Because the strong electronic absorption of Co2+ overlaps the emission of QDs, our results can be explained by Förster energy transfer from QD to the bound Co2+ cations.

Photoluminescence Quenching Based Visual and Spectroscopic Method for Mercury Sensing by Surface-Modified Cadmium Sulphide Quantum Dots.

Here we present a simple yet efficient analytical method for sensing ultratrace levels of Hg2+ ions by highly water soluble CdS quantum dots functionalized with thiourea as a probe. The bluish photoluminescence emission of the probe responded to a systematic linear photoluminescence quenching in the presence of increasing concentration of Hg2+ ions. The photoluminescence quenching by Hg2+ ions was attributed to agglomeration of the quantum dots, which has been confirmed by zeta potential measurements. The sensitivity (31.38 L/mg) and LoD (0.11 μg/L) of Hg2+ ion detection by our method are two folds improved with respect to the existing data of CdS as sensor. The improved detection is attributable to synthesis of less than 3 nm diameter CdS quantum dots which rendered very high water solubility and hence facilitated better interaction with Hg2+ ions. The detection of Hg2+ ion was free from most interfering cations and anions, except for minor interference from Cu2+ and Pb2+ corresponding their concentrations expected in ground water. Further, the scope for visual detection of Hg2+ was explored, which revealed naked eye recognizable photoluminescence quenching of the probe treated 0.3 mg/L of Hg2+ ion when excited by a light source of 365 nm. The suitability of our probe to analyze Hg2+ in real samples has been demonstrated by Hg2+ spike analysis in groundwater and river water samples.

Size dependent ratiometric detection of Pb (II) ions in aqueous solution by light emitting biogenic CdS NPs

We have synthesized water soluble CdS quantum dots (QDs) in different sizes (~ 3, 10 and 25nm) via a green rout using pomegranate peel extract as a reducing and stabilizing agent. The particles with the size of ~ 3, 10 and 25nm respectively exhibit blue, green and yellowish red emission under UV light. We have utilized the NPs for the discrimination of metal ions in aqueous solution. Interestingly, the fluorescence from the NPs undergoes a ratiometric variation only in presence of Pb2+ ions, indicating that the system can act as a potential Pb2+ ion sensor. There was a remarkable size dependent stock shift (~ 270nm) upon the addition of Pb2+ ions, which enables the detection by naked eye. DLS study indicates that Pb2+ ions induce aggregation in the system owing to the complex formation between the capping agent and the metal ion. The aggregation, in turn, generates inter plasmon coupling and results in emission color variation. The naked eye detection limit of Pb2+ ions in solution was found to be 10−9M. This is the first study of Pb2+ ion sensing using CdS quantum systems and the detection procedure is easy-to-make, less time consuming and highly re-producible. The present method enables direct application of the system for detecting Pb2+ ions due to the presence of ratiometric fluorescence, leading to a large Stokes shift and associated color change in the visible region.

Filter paper with chitosan membrane as platform for fast and simple blood glucose assay using phone camera detection

We have synthesized water soluble CdS quantum dots (QDs) in different sizes (~ 3, 10 and 25 nm) via a green rout using pomegranate peel extract as a reducing and stabilizing agent. The particles with the size of ~ 3, 10 and 25 nm respectively exhibit blue, green and yellowish red emission under UV light. We have utilized the NPs for the discrimination of metal ions in aqueous solution. Interestingly, the fluorescence from the NPs undergoes a ratiometric variation only in presence of Pb2+ ions, indicating that the system can act as a potential Pb2+ ion sensor. There was a remarkable size dependent stock shift (~ 270 nm) upon the addition of Pb2+ ions, which enables the detection by naked eye. DLS study indicates that Pb2+ ions induce aggregation in the system owing to the complex formation between the capping agent and the metal ion. The aggregation, in turn, generates inter plasmon coupling and results in emission color variation. The naked eye detection limit of Pb2+ ions in solution was found to be 10−9 M. This is the first study of Pb2+ ion sensing using CdS quantum systems and the detection procedure is easy-to-make, less time consuming and highly re-producible. The present method enables direct application of the system for detecting Pb2+ ions due to the presence of ratiometric fluorescence, leading to a large Stokes shift and associated color change in the visible region.

Highly Sensitive and Selective Method for Detecting Ultratrace Levels of Aqueous Uranyl Ions by Strongly Photoluminescent-Responsive Amine-Modified Cadmium Sulfide Quantum Dots.

Detection of ultratrace levels of aqueous uranyl ions without using sophisticated analytical instrumentation and a tedious sample preparation method is a challenge for environmental monitoring and mitigation. Here we present a novel yet simple analytical method for highly sensitive and specific detection of uranyl ions via photoluminescence quenching of CdS quantum dots. We have demonstrated a new approach for synthesizing highly water-soluble and strong photoluminescence-emitting CdS quantum dots (i.e., CdS-MAA and CdS-MAA-TU) of sizes less than 3 nm. The structural, morphological, and optical properties of both the batches of CdS quantum dots were thoroughly characterized by XRD, high-resolution transmission electron microscopy (HRTEM), zeta potential, UV-visible absorption, and photoluminescence spectroscopy. Compared to the batch of CdS quantum dots prepared by capping with only mercaptoacetic acid (CdS-MAA), the batch prepared by capping with mercaptoacetic acid and thiourea in tandem (CdS-MAA-TU) exhibited higher quantum yield= 16.64 ± 1.02%, and more importantly, CdS-MAA-TU exhibited significantly a higher order of photoluminescence quenching responses when treated with ultratrace concentrations of uranyl ions. Under the optimized conditions, the sensitivity of detecting uranyl ion by CdS-MAA-TU was several folds better (0.316 L/ μg) than that of CdS-MAA (0.0053 (L/μg/), as determined from their respective Stern-Volmer plots. Qualitatively, CdS-MAA-TU probe can be used for visual detection of uranyl ions of concentration greater than 5 μg/L. However, the instrumental method of analysis based on photoluminescence spectroscopy confirmed the feasibility for quantitative analysis of ultratrace concentrations of uranyl ions as implied from a very low limit of detection (LoD = 0.07 μg/L) and limit of quantification (LoQ = and 0.231 μg/L). Systematic studies revealed very high selectivity for uranyl ion detection, though minor interference from Cu(2+), Pb(2+), Hg(2+), CO3(2-), and SO4(2-) was found. The recovery analysis performed by spiking uranyl ions (0.5 μg/L to 10.0 μg/L) in groundwater and river water samples, confirmed the robustness of the as-developed CdS-MAA-TU QDs for detecting ultratrace levels of uranyl ions in real water sample matrix. The very simple and effective strategy reported here should facilitate developing reliable sensors for detecting uranyl ion contamination in drinking water.

Thioglycolic Acid-Capped CdS Quantum Dots Conjugated to α-Amylase as a Fluorescence Probe for Determination of Starch at Low Concentration.

In the present research, water soluble thioglycolic acid-capped CdS quantum dots (QDs) were synthesized by chemical precipitation method. The characteristics of prepared quantum dots were determined using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The obtained results revealed that CdS QDs have 5.60nm crystallite size, hexagonal wurtzite structure and spherical morphology with less than 10nm diameter. The photoluminescence (PL) spectroscopy was performed in order to study the effect of the presence of starch solutions. Blue emission peaks were positioned at 488nm and its intensity quenched by increasing the concentration of starch solutions. The result of PL quenches in range of studied concentrations (0-100ppm) was best described by Michaelis-Menten model. The amount of Michaelis constant (Km) for immobilized α-amylase in this system was about 68.08ppm which showed a great tendency of enzyme to hydrolyze the starch as substrate. Finally, the limit of detection (LOD) was found to be about 2.24ppm.

Determination of total aflatoxin using cysteamine-capped CdS quantum dots as a fluorescence probe

Aflatoxins form a class of potent carcinogens that contaminate a wide range of food products and can be fatal to humans and livestock. We have designed cysteamine-capped CdS quantum dots (QDs) to serve as aflatoxin photodetectors for use in agricultural industries. Water-soluble CdS QDs are synthesized through growth in a poly(vinyl alcohol) matrix using a chemical precipitation method. The prepared QDs are then characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) analyses. The obtained results revealed that these CdS QDs have a 1- to 2-nm crystalline size, hexagonal wurtzite structure, and spherical morphology with a diameter less than 10 nm. Photoluminescence spectroscopy (PL) is performed to study the CdS QDs interactions with a standard solution of aflatoxins (B1, B2, G1, and G2 in a ratio of 5:1:5:1) in order to determine their effectiveness as aflatoxin detectors. A green emission peak is observed at 508 nm, with an intensity enhancement positively correlated with total aflatoxin concentration. The lower limit of detection for total aflatoxin concentration is found to be 0.05 ppb, well below international contamination allowances for food products. PL variations with aflatoxin concentration are best described by a Langmuir-type equation in the concentration range of this study (2.4–48 ppb).

Cadmium Sulfide Quantum Dots as a Fluorescent Probe for Quantitative Determination of Cefixime

Water-soluble fluorescent CdS quantum dots (QDs) capped with thioglycolic acid (TGA) were prepared. The resulting QDs have characteristic emission maximum at 514 nm after excitation at 370 nm. Fluorescent QDs were used for the quantification of cefixime based on its quenching effect on the fluorescence intensity of the QDs. Maximum fluorescence quenching was observed when 0.3 mM of QDs were mixed with cefixime and allowed to stand for 5 min. At optimum experimental conditions, the Stern–Volmer calibration plot of Fo/F against concentration of cefixime was linear in the range of 2–40 μg/mL. The limit of detection (3.3SD/b) and limit of quantification (10SD/b) were found to be 1.3 and 3.9 μg/mL respectively with RSD ≤ 1.56%. The proposed method was successfully applied to commercial formulations with % recovery in the range of 97.17 ± 1.16–100.15 ± 0.61.The results were compared with reference methods and evaluated statistically using student t-test and variance ratio F-test.

Hexametaphosphate-capped quantum dots as fluorescent probes for detection of calcium ion and fluoride

In this paper, we prepared fluorescence-tunable water-soluble CdS quantum dots (QDs) with hexametaphosphate as stabilizers by a simple route. The prepared CdS QDs were utilized to detect calcium ion (Ca2+) based on an obvious fluorescence enhancement of CdS QDs induced by Ca2+. The results demonstrated there was an excellent linear relationship between the fluorescence intensity of hexametaphosphate-capped CdS QDs and Ca2+ concentration in the range from 10μmol/L to 400μmol/L and the detection limit for Ca2+ was 4μmol/L. Furthermore, fluoride ions (F−) can react with Ca2+ to generate the insoluble calcium fluoride that would inhibit the Ca2+-induced fluorescence enhancement of CdS QDs. Therefore, the designed Ca2+-induced fluorescence enhancement system was also able to effectively detect fluoride.

Extracellular Synthesis of Luminescent CdS Quantum Dots Using Plant Cell Culture

The present study describes a novel method for preparation of water-soluble CdS quantum dots, using bright yellow-2 (BY-2) cell suspension culture. Acting as a stabilizing and capping agent, the suspension cell culture mediates the formation of CdS nanoparticles. These semiconductor nanoparticles were determined by means of an UV-visible spectrophotometer, photoluminescence, high-resolution transmission electron microscopy (HRTEM), and XRD. Followed by the electron diffraction analysis of a selected area, transmission electron microscopy indicated the formation of spherical, crystalline CdS ranging in diameter from 3 to 7 nm and showed wurtzite CdS quantum dots. In the present work, the toxic effect of synthesized CdS quantum dots on Nicotiana tabacum protoplasts as a very sensitive model was under study. The results of this research revealed that biologically synthesized CdS nanoparticles in low concentrations did not induce any toxic effects.

CdS quantum dots and tungsten carbide supported on anatase–rutile composite TiO2 for highly efficient visible-light-driven photocatalytic H2 evolution from water

A noble-metal-free CdS/WC/TiO2 photocatalyst with water-soluble CdS quantum dots (<5 nm) and anatase–rutile composite TiO2 is highly efficient for H2 evolution from visible-light-driven photocatalytic water reduction.

Rapid fluorometric determination of perfluorooctanoic acid by its quenching effect on the fluorescence of quantum dots

Analysis of perfluorooctanoic acid (PFOA) usually requires a combination of high-performance liquid chromatography and mass spectrometry, which is expensive and time-consuming. In the present work, water-soluble CdS quantum dots (QDs) were employed to develop a simple and rapid fluorometric method for the determination of PFOA. Strongly fluorescent CdS QDs were prepared by using 3-mercaptopropionic acid (MPA) as a stabilizer. It was observed that PFOA strongly quenched the fluorescence emission of the MPA-CdS QDs because PFOA promotes the aggregation of MPA-CdS QDs through a fluorine–fluorine affinity interaction. Under optimum conditions, the fluorescence intensity of MPA-CdS QDs was observed to decrease linearly with an increase in the concentration of PFOA from 0.5 to 40μmolL−1, with a limit of detection of 0.3μmolL−1. This new method was successfully implemented for the analysis of PFOA-spiked textile samples, with recoveries ranging from 95% to 113%.

Biomanufacturing of CdS quantum dots

A strain ofStenotrophomonas maltophiliais engineered to achieve size controlled synthesis of water soluble CdS quantum dots.

Study on the fluorescence resonance energy transfer between CdS quantum dots and Eosin Y.

Water-soluble CdS quantum dots (QDs) were prepared using mercaptoacetic acid (TGA) as the stabilizer in an aqueous system. A fluorescence resonance energy transfer (FRET) system was constructed between water-soluble CdS QDs (donor) and Eosin Y (acceptor). Several factors that impacted the fluorescence spectra of the FRET system, such as pH (3.05-10.10), concentration of Eosin Y (2-80 mg/L) and concentration of CdS QDs (2-80 mg/L), were investigated and refined. Donor-to-acceptor ratios, the energy transfer efficiency (E) and the distance (r) between CdS QDs and Eosin Y were obtained. The results showed that a FRET system could be established between water-soluble CdS QDs and Eosin Y at pH 5.0; donor-to-acceptor ratios demonstrated a 1: 8 proportion of complexes; the energy transfer efficiency (E) and the distance (r) between the QDs and Eosin Y were 20.07% and 4.36 nm,respectively.

Uniform deposition of water-soluble CdS quantum dots on TiO2 nanotube arrays by cyclic voltammetric electrodeposition: Effectively prevent aggregation and enhance visible-light photocatalytic activity

Water-soluble CdS quantum dots (QDs) covered with cationic surfactant-cetyltrimethylammonium bromide (CTAB) were deposited on the highly ordered TiO2 nanotube arrays (TNTAs) by various methods, such as direct current (DC) electrodeposition, cyclic voltammetric (CV) electrodeposition, and successive ionic layer adsorption reaction (SILAR). The morphology measurements show that CTAB capping could well control the QD size and the CV method could effectively prevent the nanoparticle aggregation and uniformly deposit QDs onto TNTAs. Among all the deposition methods studied, the sample prepared by the CV method possesses superior photoelectrical properties and photocatalytic activity. A maximum photoconversion efficiency of 2.81% is achieved for the CdS/TNTAs prepared by CV electrodeposition, which exhibits about 17 times enhancement over the efficiency of the sample prepared by DC electrodeposition. And the photocatalytic degradation of methyl orange under visible-light irradiation demonstrates that the rate constant of the sample prepared by the CV method is almost seven times of that of the untreated TNTAs. Moreover, the underlying mechanism for the improving properties has been discussed.

Alkaline Post-Treatment of Cd(II)–Glutathione Coordination Polymers: Toward Green Synthesis of Water-Soluble and Cytocompatible CdS Quantum Dots with Tunable Optical Properties

In this study, we demonstrate a facile and environmentally friendly method for the synthesis of glutathione (GSH)-capped water-soluble CdS quantum dots (QDs) with a high cytocompatibility and a tunable optical property based on alkaline post-treatment of Cd-GSH coordination polymers (CPs). Cd-GSH CPs are synthesized with the coordination reaction of Cd(2+) with GSH at different pH values, and the CdS QDs are then formed by adding NaOH to the aqueous dispersion of the Cd-GSH CPs to break the coordination interaction between Cd(2+) and GSH with the release of sulfur. The particle size and optical property of the as-formed CdS QDs are found to be easily tailored by simply adjusting the starting pH values of GSH solutions used for the formation of Cd-GSH CPs, in which the wavelengths of trap-state emission of the QDs red-shift with an increase in the sizes of the QDs that is caused by an increase in the starting pH values of GSH solutions. In addition, the use of GSH as the capping reagent eventually endows the as-formed CdS QDs with enhanced water solubility and good cytocompatibility, as demonstrated with HeLa cells. The method demonstrated here is advantageous in that the cadmium precursor and the sulfur source are nontoxic and easily available, and the size, optical properties, water solubility, and cytocompatibilty of the as-formed CdS QDs are simply achieved and experimentally regulated. This study offers a new and green synthetic route to water-soluble and cytocompatible CdS QDs with tunable optical properties.