Water-soluble Cadmium Research Articles

Preparation of water-soluble cadmium sulfide quantum dots with narrow small-size distribution by controlling hydrodynamic cavitation device parameters

With the increasingly broad application of quantum dots in many fields, how to further improve the performance of quantum dots in various aspects has become an urgent problem to be solved. In this study, hydrodynamic cavitation (HC) technology was applied for the first time in the preparation of quantum dots. Specifically, cadmium sulfide quantum dots (CdS QDs) with small particle size, narrow distribution, high concentration and large Stokes shift are prepared. Firstly, CdS precipitation was obtained in an aqueous solvent, using cadmium nitrate tetrahydrate (Cd(NO3)2·4H2O) and sodium sulfide nonahydrate (Na2S·9H2O) as Cd and S sources, respectively. Subsequently, CdS QDs were formed from top to bottom through hydrodynamic cavitation reactor, which generates high temperature, high pressure, high-speed jets, shear forces, and shock waves. In summary, the intrinsic advantages of HC technology offer a new opportunity for manufacturing large-scale quantum dots with superb performance.

A protonated imine-based water-soluble cadmium complex with N, O donor chelating agent: Synthesis, structure, fluorescence efficiency and catecholase activity

A mononuclear air-stable and water soluble six coordinated cadmium (II) complex [Cd(HL)6](ClO4)2 (1) with bi-dentate phenol based ligand [HL = 2-(benzylimino)methyl)phenol] have been synthesized. The complex has been characterized by various spectroscopic techniques. The solid-state structure, by single crystal X-ray diffraction, revealed that Cd(II) complex crystallizes in trigonal space group R-3. Interestingly, single crystal X-ray structure data show that the Schiff base in the complex is present in a zwitterionic form and coordinated through the phenolic oxygen atom only, providing the first example of more than four monodendate Schiff base in zwitterionic form to be coordinated with the central metal ion. Cyclic voltamogram of the cadmium (II) complex (1) exhibits a quasi-reversible oxidation peak in the positive potential region. The redox process occurs due to the generation of phenoxyl radical from the pheolate group of the attached ligand with the central metal ion. Luminescence spectra show a strong emission band around 500 nm. Additionally, the mononuclear cadmium complex (1) shows catechol oxidase activity in methanol under aerobic conditions. The turnover number of the process is 2.766 × 103 h–1. The oxidation process occurs via formation of ligand oriented phenoxyl radical species.

Ultralong Nanowires of Cadmium Phosphate Hydroxide Synthesized Using a Cadmium Oleate Precursor Hydrothermal Method and Sulfidation Conversion to Ultralong CdS Nanowires.

Ultralong nanowires with ultrahigh aspect ratios exhibit high flexibility, and they are promising for applications in various fields. Herein, a cadmium oleate precursor hydrothermal method is developed for the synthesis of ultralong nanowires of cadmium phosphate hydroxide. In this method, water-soluble cadmium salt is used as the cadmium source, water-soluble phosphate is used as the phosphorus source, and sodium oleate is adopted as a reactant to form cadmium oleate precursor and as a structure-directing agent. By using this method, ultralong nanowires of cadmium phosphate hydroxide are successfully synthesized using CdCl2, sodium oleate, and NaH2PO4 as reactants in an aqueous solution by hydrothermal treatment at 180 °C for 24 h. In addition, a new type of flexible fire-resistant inorganic paper with good electrical insulation performance is fabricated using ultralong nanowires of cadmium phosphate hydroxide. As an example of the extended application of this synthetic method, ultralong nanowires of cadmium phosphate hydroxide can be converted to ultralong CdS nanowires through a convenient sulfidation reaction. In this way, ultralong CdS nanowires are successfully synthesized by simple sulfidation of ultralong nanowires of cadmium phosphate hydroxide under mild conditions. The as-prepared ultralong nanowires of cadmium phosphate hydroxide are promising for applications as the precursors and templates for synthesizing other inorganic ultralong nanowires and have wide applications in various fields.

An investigation on the structural and optical properties of mercaptosuccinic acid capped cadmium telluride quantum dots

In this work, a sonication induced modified wet chemical approach is adopted to synthesize highly luminescent and water soluble cadmium telluride (CdTe) quantum dots (QDs). The morphology, size, crystal structural, and optical properties of CdTe QDs are investigated for different refluxing time (1–4 h). The refluxing time-dependent optical constants viz. band gap energy and Urbach energy of the QDs are estimated from UV–Visible absorption spectra. The optical band gap energy decreased from ~ 2.12 to 1.92 eV and the Urbach energy increased from ~ 361 to 487 meV, with the increase in refluxing time. CdTe QDs are found to be uniform in size. The average size of the QDs estimated from the High Resolution Transmission Electron Microscope image analysis is about 5.8 and 8.2 nm for refluxing times 1 and 4 h, respectively. The growth mechanism of the QDs as a function of refluxing time has also been discussed. The fluorescence spectra of the QDs, revealed emission peaks having wavelength from ~ 534 to 585 nm, under the excitation wavelength of 320 nm. The fluorescence emission peaks showed a bathochromic shift with increasing refluxing time. CdTe QDs also exhibit excitation-dependent fluorescence behaviour. Two crystalline phases of the CdTe QDs, namely hexagonal and cubic are confirmed from the High Resolution Transmission Electron Microscope images and Selected Area Electron Diffraction patterns analysis. The phase transformation from hexagonal to cubic is successfully achieved by tuning the refluxing time from 1 to 4 h.

Preparation of magnetic fluorescent nanoparticles with quaternary ammonium chitosan derivatives and its properties

To explore a novel solution to the challenges in constructing polymer coated magnetic fluorescent nanoparticles, HTCC/Fe3O4/CdTe magnetic fluorescent nanoparticles (MFCNPs) that can be well dispersed in water were prepared via the electrostatic interaction of the cationic N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) and the anion precoated water-soluble cadmium telluride (CdTe) quantum dots (QDs) and the sodium citrate-coated Fe3O4 (SC-Fe3O4) magnetic nanoparticles (MNPs), which overcame the performance defects of hydrophobic polymer for surface coating and the possible toxicity of cross-linking agent induced by the hydrophilic polymer coating materials. The structural characterizations by FTIR, XRD and XPS reveal that the surfaces of SC-Fe3O4 MNPs and CdTe QDs are coated with HTCC. TEM imaging suggests that the MFCNPs are spherical particles with the diameters of ∼15–20 nm. The MFCNPs exhibit good biocompatibility. Further investigation suggests that the UV-Vis and fluorescence spectral properties and surface electrical properties of HTCC/Fe3O4/CdTe MFCNPs are mainly affected by the relative ratios of SC-Fe3O4 MNPs, CdTe QDs and HTCC. The adsorption and release properties of the MFCNPs were studied using bovine serum albumin (BSA) as the model. The results indicate that the chitosan-based magnetic fluorescent composite is a promising delivery carrier candidate with excellent comprehensive properties for both magnetic response and fluorescence imaging.

Synthesis of Water-Soluble Cadmium Selenide/Zinc Sulfide Quantum Dots on Functionalized Multiwalled Carbon Nanotubes for Efficient Covalent Synergism in Determining Environmental Hazardous Phenolic Compounds

Increasing pollution and ecological imbalance have accentuated the need to develop sensors through an efficient technique. Typically, the core–shell nanocrystals of cadmium selenide/zinc sulfide (CdSe/ZnS) with functionalized multiwalled carbon nanotubes (f-MWCNTs) are used for developing an efficient electrochemical sensor that simultaneously detects 4-aminophenol (4-AP) and 4-nitrophenol (4-NP). The composite network formed by CdSe/ZnS quantum dots with the f-MWCNTs (CdSe/ZnS QDs @ f-MWCNT) behaves as an excellent electrocatalyst and provides a transportation pathway by engendering the electron–hole pair. The sensor exhibits low detection limit values of 34.8 and 17.7 nM for detection of 4-AP and 4-NP, respectively. The sensor also showed excellent sensitivity at a linear working range of 0.149–510 μM concentration for both the analytes. Additionally, the study also shows the potential for commercial feasibility of the as-prepared sensor by acquiring a satisfactory recovery percentage of the analytes in real-time biological and environmental sample analyses.

Binding of Water‐Soluble CdSe Quantum Dots with Human Serum Albumin: Further Studies into their Effects on Dietary Polyphenol Binding and Sensing of Antibiotic Lomefloxacin

AbstractSynthesis of surface modified quantum dots (QDs) having potential biological activities are great important in biomedicinal chemistry. Here, we have synthesized mercapto propanoic acid (MPA) and thiolactic acid (TLA) coated water soluble cadmium selenide (CdSe) QDs having biological activity. Dispersion of QDs into a biological fluid can form protein corona. Hence, the binding of CdSe QDs with the carrier protein, human serum albumin (HSA) have been executed using spectroscopic methods. The binding affinity order of CdSe QDs‐HSA complexes were found in the order of 105 M−1 at 298 K. CdSe QDs are also affects the binding affinities of dietary polyphenols (naringin: NG and naringenin: NRG) towards HSA. The synthesized CdSe QDs was employed to sensing of antibiotic lomefloxacin by fluorescence quenching mechanism. The detection limit was found 0.70‐1.83 μg mL−1. The CdSe QDs also demonstrate the detection of lomefloxacin under uv light based on color change of the solutions.

Synthesis and cytotoxic evaluation of gum arabic surface modified cadmium telluride quantum dots

Water-soluble cadmium telluride (CdTe) quantum dots (QDs) were capped with gum Arabic (GA) is a non-toxic, water-soluble glycoprotein polymer commonly used in the food and pharmaceutical industries. The GA was used to stabilise cadmium telluride quantum dots (GA-QDs) and provides functional groups for other molecules such as nucleic acids, peptides and antibodies to be attached to the QDs for biological and biomedical appli- cations. In this study, the GA was used to cap and stabilise QDs using two different methods. These QDs were characterised using Ultraviolet-visible (UV-vis) and Photoluminescence (PL) spectroscopy, X-powder ray diffraction (XRD), High-resolution transmission electron microscopy, zeta potential and particle size distribu- tions. Cytotoxicity of these QDs was also investigated using four different human cell lines; HeLa, MCF-7, PC-3 and U87 cancer cells. The QDs-MPA was capped with 3-mercaptopropionic acid, QDs-GA2 was stabilized and capped with GA at 60 °C for two hours, and QDs-GA12 was stabilized and capped with GA for twelve hours at room temperature (25 °C) with continuous stirring; These QDs were found to be highly luminescent with PL values of 675 nm, 678 nm and 677 nm respectively. The average polydispersity index (PDI) were 0.36 ± 0.02, 0.27 ± 0.02, 0.35 ± 0.01 for QDs-MPA, QDs-GA2 and QDs-GA12, respectively. The average particles size from HRTEM, XRD and hydrodynamic size showed that the QDs-GA have bigger particles sizes; (56.12 nm ± 1.14), (68.69 nm ± 2.08) and (77.85 nm ± 1.69) for QDs-MPA, QD-GA2 and QD-GA12 respectively. Cytotoxicity studies of these QDs were carried out using WST-1 cell proliferation assay on four different tumour cell line. The results showed that these cells were over 50 per cent viable and the QDs-GA capped had higher cell percentage viability.

A luminous off-on probe for the determination of 2,6-pyridinedicarboxylic acid as an anthrax biomarker based on water-soluble cadmium sulfide quantum dots.

A fluorescence off-on sensing platform was developedbased on thioglycolic acid-stabilized cadmium sulfide quantum dots (CdS QDs) as fluorescence probe for the sensitive and selective detection of 2,6-pyridinedicarboxylic acid (DPA) in spores. The fluorescence emission intensity of the quantum dots at 650nm when excited at 460nm was first quenched by mixing with europium ions (Eu3+) and then recovered after the addition of DPA. The interaction of DPA with Eu3+ relieved the quenching effect of Eu3+ toward CdS QDs. As the DPA concentration increases, the color of the probe changes from colorless to red. The method exhibits a wide linear range from 1 to 120μM for DPA determination, with a detection limit of 0.2μM. The CdS QDs based nanoprobe was successfully applied for sensitive determination of DPA released from bacteria spores. In this case, the detection limit is 3.5 × 104CFU·mL-1. Graphical abstract An off-on fluorescence sensor for detecting anthrax markers -2,6-pyridinedicarboxylic acid though restoring the fluorescence of cadmium sulfide quantum dots quenching by europium ions.

Water-Soluble Cadmium Selenide Quantum Dots with Controlled Surface Charge

By chemical modification of poly(maleic anhydride-alt-1-tetradecene) with different negatively and positively charged groups, we demonstrate how magnitude of zeta potential of encapsulated CdSe quantum dots and their sensitivity to pH can be tuned by varying type and proportion of the negatively and positively charged groups on the surface of quantum dots.

Fluorometric determination of copper(II) by using 3-aminophenylboronic acid-functionalized CdTe quantum dot probes.

Water-soluble cadmium telluride quantum dots capped with 3-mercaptopropionic acid were synthesized and further modified with 3-aminophenylboronic acid to form boronic acid-functionalized quantum dots (QDs). Under excitation at 350nm, the modified QDs display yellow fluorescence with a peak at 566nm. On exposure to copper(II), the fluorescence of the QDs is quenched. Under optimal conditions, fluorescence drops linearly in the 0.01 to 20μM Cu(II) concentration range, and the detection limit is 7.6nM. This fluorescent probe was applied to the determination of Cu(II) in spiked human serum and water samples and gave satisfactory results. Graphical abstract Schematic presentation of the principle for fluorometrice detection of copper(II) based on the use of boronic acid-functionalized cadmium telluride quantum dots (CdTe QDs).

Relevance of dissolved organic matter generated from green manuring of Chinese milk vetch in relation to water-soluble cadmium.

Dissolved organic matter (DOM) can become a carrier of soil contaminants. Therefore, an understanding of the evolution and characteristics of DOM produced by Chinese milk vetch during green manuring is crucial. In this study, DOM solutions from 28days' manuring with three different organic materials were characterized using three-dimensional fluorescence excitation-emission matrix (3D-EEM) with parallel factor (PARAFAC) analysis, and ultraviolet-visible spectroscopy. With the green manuring milk vetch at flowering period (MVFP), the DOC and water-soluble cadmium (WS-Cd) in soil solution reached 1875mg/l and 2.64μg/l, respectively, on day 6 after manuring. The PARAFAC analysis modeled three components: protein-like (tryptophan) and two humic-like components (humic acid and fulvic acid); DOM produced by MVFP was primarily protein-like during the early stage of decomposition. The aromaticity and molecular weight of DOM in the MVFP treatment was lower than in the other treatments, which could promote the release of soil particle-adsorbed Cd to soil solution. Principal components analysis showed that aromaticity was the main factor affecting Cd solubility, and the negative linear correlation of aromaticity with WS-Cd reached 0.4827. The results of this study supported the idea that manuring with MVFP might accelerate Cd infiltration to deep soil with water under gravity.

Water soluble cadmium selenide quantum dots for ultrasensitive detection of organic, inorganic and elemental mercury in biological fluids and live cells.

Mercury exists in organic, inorganic, and elemental forms; all of them are highly toxic. A sensor which could detect all forms of mercury below the permissible level in environmental and biological samples would be advantageous. A facile method to synthesize N-acetyl cysteine capped cadmium selenide quantum dots (CdSe QDs) with an emission at 554 nm was reported. CdSe QDs showed high sensitivity and selectivity toward Hg in aqueous media as well as biological fluids like simulated cerebrospinal fluid, saliva, and urine, and also in natural fluids like juices of tomato, sugarcane, and lime. The sensing mechanism is attributed to the interactions between Hg and CdSe QDs inducing fluorescence quenching. The limit of detection is 1.62, 0.75, and 1.27 ppb for organic, inorganic and elemental mercury, respectively, which is below WHO guidelines. The suitability of the sensor for estimating Hg in biological fluids was demonstrated by recovery experiments. Besides sensing, a two color cell imaging method was developed employing CdSe QDs and acridine orange. Using this method, the uptake of Hg in living cells was demonstrated.

Effect of Tellurium Concentration of the Solution on the Structural, Optical and Luminescence Properties of Cadmium Telluride Nanoparticles

Water-soluble cadmium telluride (CdTe) nanoparticles (NPs) were prepared using L-cystine as a capping agent. The reaction was carried out under basic conditions (at pH=11) and refluxed at 100oC for 1 h. In this work, different tellurium (Te) concentrations in the solution of L-cystine functionalized CdTe NPs were prepared at low temperature of 100oC and discussion of its effect was done in detail. The CdTe NPs were analyzed using X-ray diffraction (XRD), ultraviolet-vis and photoluminescence (PL) spectroscopy. Structural parameters estimated by XRD revealed cubic phase of CdTe at lower Te concentrations and hexagonal phase of Te emerging at higher Te concentration. XRD results showed that the NPs consisted of small CdTe nanocrystallites, 3.1-4.5 nm in size. Scanning electron microscopy was used to analyze the surface morphology of the samples and was found that it varied with different Te concentration in the aqueous solution. They consisted of spherical, rod-like and blade-like type of morphologies. The absorption thresholds of the CdTe NPs were red shifted when Te concentration was increased, due to the quantum confinement effects displayed by nanocrystalline CdTe NPs. Optical band gap energy estimated showed a decrease with an increase in the amounts of Te present while the band emissions observed in the PL spectra of CdTe NPs red shifted from 536-559 nm upon an increase in Te ratio. The PL full width at half maximum increased from 49-60 nm with increase in Cd:Te from 1:0.1 to 1:1 displaying narrow size distribution of the NPs. Highest PL intensity was realized for a 1:0.4 Cd:Te molar ratio which is an indication of improved crystallinity.

Cd元素在土壤–水稻系统中的富集和分布

本文选取四川某地为研究区，配套采集了33套水稻土壤和水稻植株样本，分析测试了水稻籽实、茎、叶三部分以及对应土壤中Cd元素的含量；同时测试了土壤中Cd元素不同赋存形态的分量数据。通过对以上数据的分析处理，得出以下结论：该区域水稻中Cd元素超标率达到84.8%，最高达11.85 mg/kg，已经超过了国家食品卫生标准的59倍；从富集情况看，Cd从土壤迁移到水稻各部分迁移能力为籽实 > 茎 >叶；从土壤中Cd的相态来看，离子交换态和水溶态占全量的30.62%，碳酸盐结合态在弱酸性环境下容易释放出来被吸收，占比也达到了8.45%，对于水稻作物来讲，具有一定的安全威胁；从相态的变异系数来看，只有水溶态以及残渣态均超过了50%，尤其是水溶态，达到了152.5%，显示出这两种相态在土壤中分布不均匀；理论上，当样本数量增加到45个，籽实中Cd与土壤中水溶态相关性达到显著正相关；土壤中pH值与水稻茎、叶、籽实以及地上部分均呈负相关，与土壤中Cd含量显著正相关，结合土壤中Cd形态与pH和有机质的相关性分析，pH升高，碳酸盐结合态、腐殖酸结合态、铁锰结合态、强有机结合态均有较大程度的提高，水溶态降低；提高有机质含量有助于降低土壤中Cd活跃形态，同时降低地上部分中Cd含量。 33 sets of paddy soil and rice plants were sampled from a certain place of Sichuan province. Cadmium contents in these rice plant samples, including their rice seeds, stems, leaves, and their corresponding soil system have been analyzed and tested. Component data of cadmium elements in different forms have been screened as well. Based on the data mentioned above, the following conclusions can be drawn: 84.8% of cadmium contents in the rice plants samples were above the regulatory limits, and the maximum cadmium level reached 11.85 mg/kg, 59 times higher than the National Quality Standard for food. In terms of the enrichment, migration abilities of cadmium from soil to 3 parts of rice plants in descending order were: seeds, stem, and leaf. In terms of phase distribution, ion-exchangeable and water-soluble cadmium make up 30.62% of the total cadmium. Carbonate cadmium that was easily released and absorbed in weak acidic environment became security threats to the rice crops, accounting for 8.45%. The coefficient of variation of phase state showed that only the water-soluble and residua were more than 50% and cadmium in water soluble state was most impressive, up to 152.5%. It showed the two phases were not distributed uniformly in the soil. When the amount of samples increases to a certain extent, cadmium element in the rice seeds was directly proportional to the water-soluble. pH of soil was negatively correlated to rice stems, leaves, seeds and the aboveground and was positively correlated with cadmium content. A correlation analysis of cadmium phases, pH and organism showed that the carbonate, humate, iron-manganese and organic increased a lot as pH increased, while the water-soluble decreased as pH increased. The increase of organic matter content contributed to decrease active phases of cadmium in soil, and decreased cadmium content in the aboveground parts as well.

Emergence of the selective ultra-sensing of Ag(I): Thiolactic acid as efficient capping agent for cadmium chalcogenide quantum dots in modulating photoluminescence and metal reception

Stable and water-soluble cadmium telluride quantum dots (CdTe QDs) have been employed for ultra-sensing exclusive to water soluble Ag(I). For this purpose we have designed and synthesized thiolactic acid (TLA) capped exquisite CdTe QDs having exclusive selectivity for silver. The limit of detection (LOD) of Ag(I) is 50nM. The pendant methyl group of TLA effectively impedes the precursor aggregation by inhibiting the secondary coordination of carboxyl oxygen of mercapto acid with the surrounding Cd(II), and this results in highly luminescent TLA-CdTe QDs. This pendant methyl group of TLA also facilitates exclusive surface adsorption of QDs by incoming metal and renders sensing selectivity. Selective adsorption of silver on TLA-CdTe QD surface provides a turn-off photoluminescence-based assay for sensitive detection of Ag(I) without any interference of other commonly coexisting metal ions. Furthermore, analyses of environmental water samples spiked with Ag(I), demonstrate immense practical potential of our TLA-CdTe QD sensor for the detection of silver in real samples. The results also unveiled the possible origin of the sensing selectivity for metal ion by TLA-capped QDs which can serve in the design and selection of appropriate capping in achieving the desired sensing selectivity.

아카시아 수피를 이용한 카드뮴 이온의 제거

Because several wood barks are massively produced in the forest area of Chungbuk province, it is required to develop technologies for their effective utilization. In this study, three kinds of barks from Robina pseudoacacie, Pinus densiflora, and Castanea crenata were used to remove water-soluble cadmium ions having 10, 20, 50, and 100 mg/L concentrations in each batch experiments, and R. pseudoacacie bark was selected as the most excellent biosorbent. Also, treatments with various acids and bases were performed to increase the removal efficiency of 100 mg/L cadmium ions using R. pseudoacacie bark as a biosorbent. When R. pseudoacacie bark was modified with 0.5 M KOH, the relatively high removal efficiency and adsorption amount of cadmium ions were obtained. In addition, when 9 M KOH-treated R. pseudoacacie bark was used for 30 min, the highest removal efficiency of 100 mg/L cadmium ions was 84.3%. Therefore, this experimental result can be effectively used as an environmental-friendly bioremediation technology to remove cadmium ions existed with various concentrations in water bodies and soils.

An impedimetric aptasensor based on water soluble cadmium telluride (CdTe) quantum dots (QDs) for detection of ibuprofen

An impedimetric aptasensor is reported here for the ultrasensitive detection of ibuprofen (IBP) using water soluble cadmium telluride (CdTe) quantum dots (QDs) as the efficient electrochemical platform. The CdTe QD layer was used as a quite suitable interface for the subsequent conjugation of the aptamer (Apt). CdTe QDs owing to their large surface area, caused the increase in the amount of Apt absorbed on the modified electrode which resulted in enhanced signal response. Also, their ion centers may have had a major role on amplifying the signal. In this method, the IBP specific Apt is immobilized onto the glassy carbon electrode (GCE) and through the specific binding of the IBP and its Apt, the IBP/Apt complex is formed. More importantly, the developed strategy shows highly sensitive responses to IBP, responses more sensitive than those of previously reported methods. Under optimal conditions, IBP was detected by electrochemical impedance spectroscopy (EIS) quantitatively. Calibration curve for IBP concentration was linear up to 20μM and the detection limit was as low as 16pM. The developed aptasensor was successfully used to detect IBP in real samples such as spiked human serum and pharmaceutical formulations. The use of CdTe QDs as a unique platform and the elimination of antibodies or enzymes for the amplified detection of the IBP, are the advantages of the developed aptasensor. Our work will shed light on new diagnostic applications of aptasensors and is quite promising as an alternative approach for various target assays.

Cadmium sulfide quantum dots modified with the human transferrin protein siderophiline for targeted imaging of breast cancer cells

We describe the fairly easy preparation of thiol stabilized water soluble cadmium sulfide quantum dots and the modification of their surface with the human transferrin protein siderophiline. The particles are shown to enable targeted imaging of human breast adenocarcinoma cell (type MCF7). The fluorescence quantum yield of the modified QDs is ~0.74. The particles have an average diameter of 8.1 ± 0.1 nm as determined in solution by dynamic light scattering. The cancer cells were imaged by fluorescence microscopy of the QDs which display strong green fluorescenece under 350 nm excitation. A cytotoxicity assay showed 66 and 78 % cell viabilities, respectively, after 24 h of incubation with the QDs and modified QDs.

Low driving voltage in polymer light-emitting diodes with CdS nanoparticles as an electron transport layer

Water-soluble cadmium sulfide (CdS) nanoparticles were synthesized through aqueous thermochemical method using thioglycolic acid as a capping agent. The resulting CdS nanoparticles were characterized using x-ray diffraction, field-emission scanning electron microscopy, ultraviolet–visible, and photoluminescence spectroscopy. The CdS prepared has been used as an electron transport layer (ETL) in a polymer light-emitting diode (PLED) with the structure of poly(ethylene terephthalate)/indium tin oxide/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene/CdS/aluminium (PET/ITO/PEDOT:PSS/MEH-PPV/CdS/Al). The performance of the fabricated device containing CdS nanoparticles as an ETL was compared with the device with the structure of PET/ITO/PEDOT:PSS/MEH-PPV/Al. According to the obtained results, it was shown that the ETL yields a higher current and lower turn-on voltage. The improvement was ascribed to the step barrier theory and hole blocking effect of the CdS layer. These results show that the CdS layer could be very useful in the fabrication of efficient PLEDs.