CdSe quantum dots as luminescent probes for spironolactone determination

Based on the quenching of the fluorescence of CdSe quantum dots (QDs) by spironolactone, a simple, rapid and specific method for spironolactone determination was proposed. In the optimum conditions, spironolactone concentration versus quantum dot fluorescence gave a linear response with an excellent 0.997 correlation coefficient, between 2.5 and 700 mg/mL (6.0-1680 μmol/L) and the limit of detection (S/N = 3) was 0.2 μg/mL (0.48 μmol/L). The contents of spironolactone in pharmaceutical tablets were determined by the proposed method and the results agreed with the claimed values. The possible mechanism for the reaction was also discussed.     

Probing cytotoxicity of CdSe and CdSe/CdS quantum dots

Toxicities of CdSe and CdSe/CdS quantum dots(QDs) synthesized by ultrasound-assisted methods were investigated in vitro and in vivo.Five human cell lines were used to assess the cytotoxicity of as-prepared CdSe and CdSe/CdS by assays of MTT viability,red blood cell hemolysis,flow cytometry,and fluorescence imaging.The results show that these QDs may be cytotoxic by their influence in S and G2 phases in cell cycles.The cytotoxicity of QDs depends on both the physicochemical properties and related to target cells.     

Highly conjugated water soluble CdSe quantum dots to multiwalled carbonnanotubes

Highly conjugated multiwalled carbon nanotube-quantum dot heterojunctions were synthesized by ethylene carbodiimide coupling procedure. The functional multiwalled carbon nanotube with carboxylic groups on sidewall could react with the amino group of L-cysteine capped CdSe quantum dots and then resulted in nanotube-quantum dot heterojunctions. Scanning electron microscopy was used to characterize the heterojunctions.     

Aqueous synthesis of CdSe and CdSe/CdS quantum dots with controllable introduction of Se and S sources

A new and convenient route is developed to synthesize CdSe and core-shell CdSe/CdS quantum dots(QDs) in aqueous solution.The gaseous precursors,H2Se and H2S,generated on-line by reducing SeO 3 2à with NaBH 4 and the reaction between Na 2 S and diluted H2SO 4,are used to form high-quality CdSe and CdSe/CdS QDs,respectively.The synthesized water-soluble CdSe and CdSe/CdS QDs possess high quantum yield(3% and 20%) and narrow full-width-at-half-maximum(43 nm and 38 nm).The synthesis process is easily reproducible with simple apparatus and low-toxic chemicals,and can be readily extended to the large-scale aqueous synthesis of QDs.     

Surface-modified CdSe quantum dots as luminescent probes for cyanide determination

Luminescent surface-modified CdSe semiconductor quantum dots (QDs), with nanoparticle (NP) size distribution in the order of 2-7 nm, have been synthesized for optical determination of cyanide ions. The nanoparticles have been functionalised with tert-butyl-N-(2-mercaptoethyl)-carbamate (BMC) groups and exhibit a strong fluorescent emission at about 580 nm with rather long fluorescence lifetimes (several hundred nanoseconds) in aerated methanolic solution. The observed luminescence emitted by the synthesized nanocrystals was tremendously increased by photo-activation under sunlight exposure. The functionalised QDs turned out to exhibit excellent long-term stability when stored in the dark (no significant changes in QDs luminescence emission intensity was observed even after two months from synthesis). The functionalisation of the NPs with carbamate ligand allowed a highly sensitive determination of free cyanide via analyte-induced changes in the photoluminescence (fluorescence quenching of intensity at 580 nm and lifetime changes) of the modified quantum dots (excited at 400 nm). A detection limit of 1.1 × 10⁻⁷ M (2.9 μg l⁻¹) of cyanide ions was obtained, while the interfering effect of other inorganic anions (including NO₃⁻, Cl⁻ or SCN⁻) was negligible even at 200-fold level concentrations in excess of cyanide.     

Field and photo-field electron emission from self-assembled Ge–Si nanostructures with quantum dots

Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was 10 nm and cluster density was 10¹⁰ cm⁻². A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm.     

CdSe/CdS量子点荧光猝灭法测定芹黄素的研究

以巯基乙酸为稳定剂,在水溶液中合成了具有特殊光学性质的水溶性CdSe/CdS量子点。以该量子点为荧光探针,基于荧光猝灭法对芹黄素进行了定量检测。考察了缓冲体系、反应时间、量子点浓度等多种因素的影响。实验结果表明,在0.001 mol/L、pH为6.80的KH2PO4-Na2HPO4缓冲液中,当量子点浓度为1.2×10^-4mol/L、反应时间为20 min时,该方法的线性范围为0.16-27.02μg/mL,其线性回归方程为F0/F=0.99665＋0.11067ρ（μg/mL）,相关系数r=0.998,检出限为0.13μg/mL,并用于合成样品的分析。     

A luminescent nanosensor for Hg(II) based on functionalized CdSe/ZnS quantum dots

Luminescent and stable CdSe/ZnS core/shell quantum dots (QDs) capped with L-carnitine are firstly prepared for optical determination of mercury ions in ethanol. LC capped QDs have desirable dispersibility, uniformity and good fluorescence properties and were characterized by fluorescence spectroscopy, transmission electron microscopy and infrared spectra. The functionalized QDs turned out to exhibit excellent long-term stability. The modified QDs allowed a highly sensitive determination of mercury ions via analyte-induced changes in the photoluminescence of them. A detection limit of 1.8 × 10⁻⁷ M (36.1 μg · L⁻¹) of mercury ions was obtained, while the interfering effect of other ions (including alkali metal ions, alkali earth metal ions, Ni²⁺, Zn²⁺, Fe²⁺, Ag⁺ and anions such as NO₃ ⁻, SO₄ ²⁻, CO₃ ²⁻ and halogen ions) was negligible even at a very high concentration. The possible mechanism is discussed. Correspondence: Haibing Li, Key Laboratory of Pesticide and Chemical Biology (CCNU), Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P.R. China; Zhinong Gao, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P.R. China     

Use of CdSe/ZnS core-shell quantum dots as energy transfer donors in sensing glucose

In the present work, CdSe/ZnS core-shell quantum dots were synthesized and conjugated with enzymes, glucose oxidase (GOD) and horseradish peroxidase (HRP). The complex of enzyme-conjugated QDs was used as QD-FRET-based probes to sense glucose. The QDs were used as an electron donor, whereas GOD and HRP were used as acceptors for the oxidation/reduction reactions involved in oxidizing glucose to gluconic acid. Electron transfer between the redox enzymes and the electrochemical reduction of H₂O₂ (or O₂) occurred rapidly, resulting in an increase of the turnover rate of the electron exchange between the substrates (e.g. glucose, H₂O₂ and O₂) and the enzymes (GOD, HRP), as well as between the QDs and the enzymes. The transfer of non-radiative energy from the QDs to the enzymes resulted in the fluorescence quenching of the QDs, corresponding to the increase in the concentration of glucose. The linear detection ranges of glucose concentrations were 0–5.0 g/l (R = 0.992) for the volume ratios of 10/5/5, 0.2–5.0 g/l (R = 0.985) for the volume ratios of 10/5/3 and 1.0–5.0 g/l (R = 0.982) for the volume ratios of 10/5/0. Temperature (29–37 °C), pH (6–10) and some ions (NH₄⁺, NO₃⁻, Na⁺, Cl⁻) had no interference effect on the glucose measurement.     

Determination of nitrite based on its quenching effect on anodic electrochemiluminescence of CdSe quantum dots

A novel method for electrochemiluminescent (ECL) detection of nitrite was proposed based on its quenching effect on anodic ECL emission of CdSe quantum dots (QDs). The ECL emission could be greatly enhanced by sulfite and dissolved oxygen in a neutral system and occurred at a relatively low potential in comparison with traditional anodic ECL emitter, leading to high sensitivity and good selectivity. The quenching mechanism followed an “electrochemical oxidation inhibition” process, which was completely different from those of some analytes on the ECL emission of QDs. The coincidence of photoluminescence and ECL spectra of the QDs indicated that the ECL emission resulted from the redox process of QDs core and the sulfite acted as a coreactant. The nitrite quenched ECL emission could be analyzed according to the treatment of Stern-Volmer equation with a linear range from 1 μM to 0.5 mM for detection of nitrite. This work presented a new efficient ECL methodology for quencher-related detection.     

柠檬酸盐稳定的水溶性CdSe量子点的合成及表征

以柠檬酸三钠为稳定剂在水溶液中合成了水溶性CdSe量子点,用X射线粉末衍射、透射电镜、紫外-可见吸收光谱和荧光发射光谱对CdSe量子点的结构、形貌及其荧光性质进行了表征.结果表明合成的CdSe量子点为立方闪锌矿结构,呈球形,分散性良好,平均尺寸约为2.6nm,具有窄且对称的荧光发射光谱,半峰宽为45nm.     

CdS and CdSe quantum dots subsectionally sensitized solar cells using a novel double-layer ZnO nanorod arrays

We report a novel approach for synthesizing CdS and CdSe quantum dots subsectionally sensitized double-layer ZnO nanorods for solar cells, which are comprised of CdS QDs-sensitized bottom-layer ZnO NRs and CdSe QDs-sensitized top-layer ZnO NRs. X-ray diffraction study and scanning electron microscopy analysis indicate that the solar cells of subsectionally sensitized double-layer ZnO NRs, which are the hexagonal wurtzite crystal structure, have been successfully achieved. The novel structure enlarged the range of absorbed light and enhanced the absorption intensity of light. The I-V characteristics show that the double-layer structure improved both the current density (J_sc) and fill factor (FF) by 50%, respectively, and power conversion efficiency (η) was increased to twice in comparison with the CdS QDs-sensitized structure.     

水溶性CdSe量子点的合成及其作为荧光探针对大肠杆菌的快速检测

采用水相法以谷胱甘肽为稳定剂合成高稳定性的CdSe量子点,利用化学偶联剂的作用使得量子点表面基团与菌体之间的成功结合,对偶联的条件进行了优化.基于荧光分析法建立了一种快速简便的大肠杆菌检测定量分析方法.研究结果表明:合成的量子点具有稳定、荧光性能良好等突出优点.通过偶联剂量子点能与大肠杆菌结合,其荧光强度与大肠杆菌浓度...     

Determination of silver ion based on the redshift of emission wavelength of quantum dots functionalized with rhodanine

A simple and selective method for the determination of silver ions was developed by utilizing the red- shift in emission wavelength of the core-shell CdSe/Cd5 quantum dots （QDs） functionalized with rhodanine upon the addition of Ag＋. A linear relationship was observed between the shift and the increase in concentration of Ag＋ in the range of 0.0125-12.5 μmol/L. The mechanism of the red-shift was investigated and suggested that the coordination between Ag＋ and rhodanine on the QDs surface caused an increase of particle size, which resulted in the red-shift of the QDs＇ emission wavelength. A detection limit of 2 nmol/L was achieved. The developed method showed superior selectivity and was successfully applied to the determination of silver in environmental samples.     

Use of CdSe/ZnS luminescent quantum dots incorporated within sol-gel matrix for urea detection

In this work, urea detection techniques based on the pH sensitivity of CdSe/ZnS QDs were developed using three types of sol-gel membranes: a QD-entrapped membrane, urease-immobilized membrane and double layer consisting of a QD-entrapped membrane and urease-immobilized membrane. The surface morphology of the sol-gel membranes deposited on the wells in a 24-well microtiter plate was investigated. The linear detection range of urea was in the range of 0-10 mM with the three types of sol-gel membranes. The urea detection technique based on the double layer consisting of the QD-entrapped membrane and urease-immobilized membrane resulted in the highest sensitivity to urea due to the Michaelis-Menten kinetic parameters. That is, the Michaelis-Menten constant (K_m =2.0745 mM) of the free urease in the QD-entrapped membrane was about 4-fold higher than that (K_m =0.549 mM) of the immobilized urease in the urease-immobilized membrane and about 12-fold higher than that (K_m =0.1698 mM) of the immobilized urease in the double layer. The good stability of the three sol-gel membranes for urea sensing over 2 months showed that the use of sol-gel membranes immobilized with QDs or an enzyme is suitable for biomedical and environmental applications.     

Thiourea functionalized CdSe/CdS quantum dots as a fluorescent sensor for mercury ion detection

CdSe/CdS quantum dots(QDs) functionalized by thiourea(TU) were synthesized and used as a fluorescent sensor for mercury ion detection.The TU-functionalized QDs were prepared by bonding TU via electrostatic interaction to the core/shell CdSe/CdS QDs after capping with thioglycolic acid(TGA).It was observed that the fluorescence of the functionalized QDs was quenched upon the addition of Hg~(2+).The quantitative detection of Hg~(2+) with this fluorescent sensor could be conducted based on the linear relationship between the extent of quenching and the concentration of Hg~(2+) added in the range of1-300 μg L~(-1).A detection limit of 0.56 μg L~(-1) was achieved.The sensor showed superior selectivity for Hg~(2+) and was successfully applied to the determination of mercury in environmental samples with satisfactory results.     

Optical and electrical control of circularly polarised fluorescence in CdSe quantum dots dispersed polymer stabilised cholesteric liquid crystal shutter

In the present communication, we report on the synthesis and electro-optic investigation of photosensitive CdSe quantum dots (QDs) dispersed polymer stabilised liquid crystal (PSCLC) luminescent gel. The assembly of the fluorescence properties of CdSe QDs facilitate the anisotropy of PSCLC gel and hence manipulates the optical and electro-optic switching properties, which was further investigated using polarised fluorescence spectrophotometer. The circularly polarised fluorescence intensity was tuned electrically so as to affect the orientations of liquid crystal in the helix. It was found that the electro-optic switching behaviour of QDs-doped sample predicts the improvement in threshold voltage and hence makes them applicable for the switchable liquid crystal contrivances with low power consumption.     

Capillary electrophoresis of quantum dots: Minireview

It has been already three decades, since the fluorescent nanocrystals called quantum dots (QDs) appeared and attracted attention of a broad scientific community. Their excellent not only optical but also electronic properties predetermined QDs for utilization in a variety of areas. Besides lasers, solar cells, and/or computers, QDs have established themselves in the field of (bio)chemical labeling as well as medical imaging. However, due to the numerous application possibilities of QDs, there are high demands on their properties that need to be precisely controlled and characterized. CE with its versatile modes and possibilities of detection was found to be an effective tool not only for characterization of QDs size and/or surface properties but also for monitoring of their interactions with other molecules of interest. In this minireview, we are giving short insight in analysis of QDs by CE, and summarizing the advantages of this method for QDs characterization.     

A simple selenium source to synthesize CdSe via the two-phase thermal approach

A novel selenium source was developed to synthesize the size-controlled CdSe nanocrystals with relatively narrow size distribution successfully in a two-phase thermal approach. A highly reactive and aqueous soluble selenium source was provided by the reduction of selenite, and in this route the size of the nanocrystals can be adjusted by the reaction temperature and time. The size, crystalline structure and optical characteristics of these nanocrystals were investigated by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, UV–vis spectroscopy, and photoluminescence spectroscopy. The influence factors for this approach were also discussed.