Quantum dots co-sensitized solar cells: a new assembly process of CdS/CdSe linked to mesoscopic TiO2-nano-SiO2 hybrid film

A green and simple method was found to prepare CdS/CdSe co-sensitized photoelectrodes for the quantum dots sensitized solar cells application. All the assembly processes of CdS and CdSe quantum dots (QDs) were carried out in aqueous solution. CdS and CdSe QDs were sequentially assembled onto TiO₂-nano-SiO₂ hybrid film by two steps. Firstly, CdS QDs were deposited in situ over TiO₂-nano-SiO₂ hybrid film by the successive ionic layer adsorption and reaction (SILAR) process in water. Secondly, using 3-mercaptopropionic acid (3-MPA) as a linker molecule, the pre-prepared colloidal CdSe QDs (~3.0 nm) dissolved in water was linked onto the TiO₂-nano-SiO₂ hybrid film by the self-assembled monolayer technique with the mode of dropwise. The mode is simple and advantageous to saving materials and time. The results show that the photovoltaic performance of the cells is enhanced with the increase of SILAR cycles for TiO₂-nano-SiO₂/CdS photoelectrode. The power conversion efficiency of 2.15 % was achieved using the co-sensitization photoelectrode prepared by using 6 SILAR cycles of CdS plus CdSe (TiO₂-nano-SiO₂/CdS(6)/CdSe) under the illumination of one sun (AM1.5, 100 mW/cm²).     

基于血红蛋白/硒化镉量子点多层膜的H2O2生物传感器

合成了水溶性硒化镉(CdSe)量子点,利用组装技术和静电吸附作用,将带正电荷的血红蛋白(Hb)和带负电荷的CdSe量子点层层组装到壳聚糖(chit)修饰的玻碳电极(GCE)表面,构建基于{Hb/CdSe}n多层膜的无电子媒介体的电流型生物传感器({Hb/CdSe}3/chit/GCE).运用紫外-可见吸收光谱、电致化学发光、交流阻抗和循环伏安技术来表征修饰膜,并研究传感器的作用机理、性能及分析应用.结果表明:与量子点薄膜法及量子点/血红蛋白复合物法等固载血红蛋白的其他方法相比,层层组装法能显著提高血红蛋白的固定量,保持血红蛋白的生物活性,增强传感器的灵敏度和稳定性.传感器检测H2O2的线性范围为4.0×10-8～4.8×10-6 mol·L-1(r=0.999 1),检测限为2.0×10-8mol·L-l.多层膜的电致化学发光研究,表明修饰电极有望用于电致化学发光传感器的制备.     

Effects of nanoscale quantum dots in male Chinese loaches (<Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>): Estrogenic interference action,toxicokinetics and oxidative stress

Quantum dots (QDs) have more and more attention as a novel example of nanocrystals due to their unique fluorescent characteristics. Recently, the toxicity and the potential environmental effects of QDs have become a research hotspot. In this work, in vivo endocrine disrupting effect, toxicokinetics and oxidative stress of QDs were characterized following the intraperitoneal dosing in Chinese loaches. Vitellogenin (Vtg) levels induced by E2 decreased significantly when administrated with the mixture of QDs and E2, which was consistent with the observations of histopathology in testes. The release of free Cd²⁺ from QDs and the non-specific adsorption of E2 by QDs might be the joint factors contributing to the inhibition of Vtg expression induced by E2 in the male Chinese loaches. In the muscle, bone, intestines, blood and testis, CdSe QDs reached the maximal concentration (C _max) in approximately 1-h postinjection and subsequently presented downtrend with the prolonged time. Whereas, there were even increasing tendencies of CdSe QDs’ concentrations in the liver and kidney. It is educible that CdSe QDs can be persistent at least for 7 days, indicating the overall half-life of CdSe QDs in the fish body is very long. The measurement of hepatic superoxide dismutase (SOD) activity and reduced glutathione (GSH) content indicate that QDs have smaller effects on the antioxidative system of the organisms compared with free Cd²⁺ due to the effective prevention of the release of Cd by PEG coating of QDs. The comprehensive evaluation of QDs’ toxicity in the present study provides an essential and general framework towards more focused research on the elucidation of the biological effects of QDs in vivo.     

Study on the interaction between CdSe quantum dots and chitosan by scattering spectra

Two different stabilizing agents thioglycolic acid (TGA) and l-cysteine (l-Cys) capped CdSe QDs with the diameter of 2 nm were synthesized, large amounts of stabilizing agents connected to CdSe QDs surface through Cd–S bond. The interaction between chitosan and QDs had been investigated, respectively. The interaction lead to the remarkable enhancement of RRS, RNLS and the enchantments were in proportional to the concentration of chitosan in a certain range. Under the optimal conditions, compared with TGA–CdSe QDs, the interaction between l-Cys–CdSe QDs with chitosan owned more broad linear range 0.042–3.0 μg mL⁻¹ and lower detect limits 1.2 ng mL⁻¹. The influences of factors on the interaction between chitosan with QDs and some foreign substances were all examined, which showed that the methods had a good sensitivity and selectivity. Based on this, it is hoped to build a method for the determination of chitosan using CdSe QDs as probes. Through Fourier transform infrared spectroscopy (FTIR) transmission electron microscopy (TEM), it was speculated that CdSe QDs interacted with chitosan to form a network structure aggregates through electrostatic attraction and hydrophobic forces. The reasons for the enhancement of RRS intensity were assumed as follows: resonance enhanced Rayleigh scattering effect, increase of the molecular volume, and hydrophobic effect.     

Study on DNA damage induced by CdSe quantum dots using nucleic acid molecular “light switches” as probe

The calf thymus DNA (ctDNA) damage induced by water-soluble CdSe quantum dots (QDs) was investigated using nucleic acid molecular “light switches” as probe. It was found that little ctDNA was damaged by CdSe QDs without UV irradiation. However, under UV irradiation, ctDNA was nicked by CdSe QDs very clearly. The mechanism of ctDNA damage was also discussed. The results strongly suggested that the ctDNA damage caused by CdSe QDs was not due to photo-induced liberation of Cd²⁺, but due to the production of free radicals and reactive oxygen species.     

Surface‐State‐Mediated Charge‐Transfer Dynamics in CdTe/CdSe Core–Shell Quantum Dots

Herein, we report the synthesis of aqueous CdTe/CdSe type‐II core–shell quantum dots (QDs) in which 3‐mercaptopropionic acid is used as the capping agent. The CdTe QDs and CdTe/CdSe core–shell QDs are characterized by X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HR‐TEM), steady‐state absorption, and emission spectroscopy. A red shift in the steady‐state absorption and emission bands is observed with increasing CdSe shell thickness over CdTe QDs. The XRD pattern indicates that the peaks are shifted to higher angles after growth of the CdSe shell on the CdTe QDs. HR‐TEM images of both CdTe and CdTe/CdSe QDs indicate that the particles are spherical, with a good shape homogeneity, and that the particle size increases by about 2 nm after shell formation. In the time‐resolved emission studies, we observe that the average emission lifetime (τ_av) increases to 23.5 ns for CdTe/CdSe (for the thickest shell) as compared to CdTe QDs (τ_av=12 ns). The twofold increment in the average emission lifetime indicates an efficient charge separation in type‐II CdTe/CdSe core–shell QDs. Transient absorption studies suggest that both the carrier cooling and the charge‐transfer dynamics are affected by the presence of traps in the CdTe QDs and CdTe/CdSe core–shell QDs. Carrier quenching experiments indicate that hole traps strongly affect the carrier cooling dynamics in CdTe/CdSe core–shell QDs.     

CdSe Quantum Dots and N719‐Dye Decorated Hierarchical TiO2 Nanorods for the Construction of Efficient Co‐Sensitized Solar Cells

Three‐dimensional hierarchical TiO₂ nanorods (HTNs) decorated with the N719 dye and 3‐mercaptopropionic or oleic acid capped CdSe quantum dots (QDs) in photoanodes for the construction of TiO₂ nanorod‐based efficient co‐sensitized solar cells are reported. These HTN co‐sensitized solar cells showed a maximum power‐conversion efficiency of 3.93 %, and a higher open‐circuit voltage and fill factor for the photoanode with 3‐mercaptopropionic acid capped CdSe QDs due to the strong electronic interactions between CdSe QDs, N719 dye and HTNs, and the superior light‐harvesting features of the HTNs. An electrochemical impedance analysis indicated that the superior charge‐collection efficiency and electron diffusion length of the CdSe QD‐coated HTNs improved the photovoltaic performance of these HTN co‐sensitized solar cells.     

Ultrathin zinc selenide nanosheet-based intercalation hybrid coupled with CdSe quantum dots showing enhanced photocatalytic CO_2 reduction

Fabrication of well-designed heterojunctions is an extraordinarily attractive pathway for boosting the photocatalytic activity toward CO_2 photoreduction.Herein,a novel kind of na nosheet-based intercalation hybrid coupled with CdSe quantum dots(QDs) was successfully fabricated by a facile solvothermal method and served as photocatalyst for full-spectrum-light-driven CO_2 reduction.Ultra-small CdSe QDs were rationally in-situ introduced and coupled with lamellar ZnSe-intercalation hybrid nanosheet,resulting in the formation of CdSe Q.Ds/ZnSe hybrid heterojunction.Significantly,the concentration of Cd~(2+) could change directly the crystallinity and micromorphology of ZnSe intercalation hybrid,which in turn would impact on the photocatalysis activity.The optimized CdSe QDs/ZnSe hybrid-5 composite demonstrated a considerable CO yield rate of the 25.6 μmol g~(-1) h~(-1) without any additional cocatalysts or sacrificial agents assisting,making it one of the best reported performance toward CO_2 photoreduction under full-spectrum light.The elevated CO_2 photoreduction activity could be attributed to the special surface heterojunction,leading to improving the ability of light absorption and promoting the separation/transfer of photogenerated carriers.This present study developed a new strategy for designing inorganic-organic heterojunctions with enhanced photocatalyst for CO_2 photoreduction and provided an available way to simultaneously mitigate the greenhouse effect and alleviate energy shortage pressure.     

CdSe/ZnS量子点敏化太阳能电池电子注入与光伏性能表征

合成了CdSe/ZnS核壳结构量子点(QDs), 将其作为光敏剂吸附在TiO2纳米晶薄膜上, 组装成量子点敏化太阳能电池(QDSSCs), 从电子注入速率和电池性能两方面对QDSSCs进行了表征. 为了定量研究ZnS层包覆对电子注入的影响, 运用飞秒瞬态光谱技术, 测试了包覆ZnS前后, CdSe-TiO₂体系的电子注入速率. 实验测得ZnS包覆前后电子注入速率分别为7.14×10¹¹s^-1和2.38×10^-11s^-1, 可以看出包覆后电子注入速率明显降低, 仅为包覆前的1/3. 电池器件J-V性能测试表明, ZnS作为绝缘层包覆在CdSe的表面有效提高了QDSSCs的填充因子和稳定性, 但同时也导致了效率的降低. 上述结果说明了电子注入速率的降低是导致电池电流和效率下降的重要原因, 为今后优化核壳结构QDSSCs的电流和效率提供了依据.     

Synthesis of Mn-doped zinc blende CdSe nanocrystals for quantum dot-sensitized solar cells

Mn-doped CdSe quantum dots (QDs) with a zinc blende structure were synthesized via a phosphine-free method in octadecene (ODE) and oleic acid. The structure, size, morphology, and optical property of the QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible absorption spectra (UV–Vis), respectively. The QDs were assembled onto a microporous TiO₂ photoanode by an ex situ ligand exchange route. Quantum dot-sensitized solar cells (QDSCs) based on the above-synthesized QDs and polysulfide electrolytes were fabricated. The photovoltaic performance and impedance of the CdSe and Mn-doped CdSe QDSCs were further investigated. An improvement in efficiency to 1.84 % was achieved as compared with 0.94 % for the QDSCs based on the pure CdSe QDs. The improvement was ascribed to the existence of long-lived high-energy doping levels on the large-sized Mn-doped CdSe QDs, which provides a significant driving force for faster charge separation and electron transfer.     

The Application of CdSe Quantum Dots with Multicolor Emission as Fluorescent Probes for Cell Labeling

Herein, highly luminescent CdSe quantum dots (QDs) with emissions from the blue to the red region of visible light were synthesized by using a simple method. The emission range of the CdSe QDs could be tuned from λ=503 to 606 nm by controlling the size of the CdSe QDs. Two amino acids, L ‐tryptophan (L ‐Trp) and L ‐arginine (L ‐Arg), were used as coating agents. The quantum yield (QY) of CdSe QDs (green color) with an optimized thickness could reach up to 52 %. The structures and compositions of QDs were examined by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Optical properties were studied by using UV/Vis and photoluminescence (PL) spectroscopy and a comparison was made between uncoated and coated CdSe QDs. The amino acid‐modified β‐cyclodextrin (CD)‐coated CdSe QDs presented lower cytotoxicity to cells for 48 h. Furthermore, amino acid‐modified β‐CD‐coated green CdSe QDs in HepG2 cells were assessed by using confocal laser scanning fluorescence microscopy. The results showed that amino acid‐modified β‐CD‐coated green CdSe QDs could enter tumor cells efficiently and indicated that biomolecule‐coated QDs could be used as a potential fluorescent probe.     

One‐Pot Synthesis of CdSe Quantum Dots in Aqueous Solution for Biological Labeling

The one‐pot synthesis of water‐soluble and biologically compatible yellow CdSe quantum dots (QDs) featuring the use of glutathione (GSH) as the capping and reducing agent was achieved under aqueous conditions at 150 °C. The synthesized yellow CdSe QDs with quantum yield (QY) up to 20% exhibit zinc blende cubic structure particles with an average diameter of 4‐5 nm. It was found that both molar ratio of Se/Cd and reaction time had a significant effect on size distribution of GSH‐CdSe QDs. Meanwhile, the interaction of QDs bioconjugated to bovine hemoglobin (BHb) was studied by absorption and fluorescence(FL) spectra. With addition of BHb, the FL intensity of CdSe QDs largely quenched due to the static mechanism. The linear range is 5.0 × 10^?8 mol/L to 3.0 × 10^?6 mol/L, and the correlation coefficient is 0.9991, suggesting that could be used as a probe to label biological molecules and bacterial cells.     

Directly assembled CdSe quantum dots on TiO2 in aqueous solution by adjusting pH value for quantum dot sensitized solar cells

We report an improved quantum dot sensitized solar cell (QDSSC) by loading mercaptopropionic acid (MPA)-capped CdSe QDs on TiO₂ film in aqueous solution. Under suitable pH value, a power conversion efficiency of 1.19% and an incident photon to current conversion efficiency of 26% for the QDSSC were obtained at AM1.5G irradiation. The improved performance of QDSSC is attributed to the large loading and good coverage of QDs on TiO₂ film with optimal pH value.     

Synthesis of protein‐assisted aqueous Ag2S quantum dots in the bovine serum albumin solution

A one‐step method was developed for preparing Ag₂S quantum dots (QDs) using a common protein [bovine serum albumin (BSA)] to entrap QDs precursors (BSA–Ag⁺). Fluorescence (FL) and ultraviolet spectra showed that the molar ratio of Ag⁺/BSA, temperature, and pH are the crucial factors for the quality of QDs. The QDs absorption wavelength and emission wavelength were about 340 and 450 nm. The average QDs particle size was estimated to be less than 5 nm, determined by transmission electron microscopy. The X‐ray power diffraction and XPS results showed that the synthesized product was indeed monoclinic Ag₂S. With Fourier transform infrared spectra and thermogravimetry analysis, there might be conjugated bonds between Ag₂S QDs and –OH, –NH, and –SH groups in BSA. In addition, FL spectra suggest that the designed QDs can produce static quenching with BSA and the Stern–Volmer quenching constant (K_sv) was calculated as 2.145 × 10⁴. Copyright © 2014 John Wiley & Sons, Ltd.     

L-Cysteine-coated CdSe/CdS core-shell quantum dots as selective fluorescence probe for copper(II) determination

Quantum dots (QDs) or semiconductor nanocrystals have been receiving great interest in the last few years. In this paper, L-cysteine-coated CdSe/CdS core-shell QDs (λ_em = 585 nm) have been prepared, which have excellent water-solubility. The full width at half maximum (FWHM) of the photoluminescence of these nanocrystals is very narrow (about 30 nm), and the quantum yield (QY) is 15% relative to Rhodamine 6G in ethanol (QY = 95%). With excess free L-cysteine in the solution, the fluorescence intensity of L-cysteine-coated CdSe/CdS QDs showed improved stability. It was found that the fluorescence of L-cysteine-capped CdSe/CdS QDs could be quenched only by copper (II) ions and was insensitive to other physiologically important cations, such as Ca²⁺, Mg²⁺, Zn²⁺, Al³⁺, Fe³⁺, Mn²⁺ and Ni²⁺ etc. Based on this finding, the quantitative analysis of Cu²⁺ with L-cysteine-capped CdSe/CdS QDs has been established. The linear range was from 1.0 × 10^− 8 to 2.0 × 10^− 7 mol L^− 1 and the limit of detection (LOD) was 3.0 × 10^− 9 mol L^− 1 (S/N = 3). The proposed method has first been applied to the determination of Cu²⁺ in vegetable samples with recoveries of 99.6–105.8%.     

CdSe Quantum Dots Based Electrochemiluminescence Immunosensor with Simple Structure for Ultrasensitive Detection of Salbutamol

A rapid and ultrasensitive electrochemiluminescence (ECL) competitive immunoassay based on CdSe quantum dots (QDs) and the shorter chain as possible (cysteamine and glutaraldehyde) has been designed for the detection of salbutamol (SAL). Cysteamine and glutaraldehyde made coating antigen immobilize well on the gold electrode surface through the reaction between functional groups, which brought about the simplicity of the immunosensor to some extent. Transmission electron microscopy image, dynamic light scattering, photoluminescence, ultraviolet‐visible absorption and electrochemical impedance spectra were used to characterize the prepared CdSe QDs and the cysteamine/glutaraldehyde/Ovalbumin‐SAL/anti‐SAL‐QDs immunosensor. In the air‐saturated PBS buffer containing 0.1 M K₂S₂O₈ and 0.1 M KCl (pH 9.0), a strong ECL emission of QDs can be observed which depended linearly on the logarithm of the salbutamol concentration with a wide range from 0.05 ng mL^?1 to 100 ng mL^?1, and a detection limit of 0.0056 ng mL^?1. The sensitivity, repeatability, and specificity of the ECL immunosensor have been evaluated. The sensor has been applied to real samples with satisfactory results. This work will open new ways of detecting food additive residue based on QDs ECL in immunoassays.     

Adjusting the Reduction Potential of Electrons by Quantum Confinement for Selective Photoreduction of CO2 to Methanol

The production of CH₃OH from the photocatalytic CO₂ reduction reaction (PCRR) presents a promising route for the clean utilization of renewable resources, but charge recombination, an unsatisfying stability and a poor selectivity limit its practical application. In this paper, we present the design and fabrication of 0D/2D materials with polymeric C₃N₄ nanosheets and CdSe quantum dots (QDs) to enhance the separation and reduce the diffusion length of charge carriers. The rapid outflow of carriers also restrains self‐corrosion and consequently enhances the stability. Furthermore, based on quantum confinement effects of the QDs, the energy of the electrons could be adjusted to a level that inhibits the hydrogen evolution reaction (HER, the main competitive reaction to PCRR) and improves the selectivity and activity for CH₃OH production from the PCRR. The band structures of photocatalysts with various CdSe particle sizes were also investigated quantitatively to establish the relationship between the band energy and the photocatalytic performance.     

Electrochemiluminescence Sensor for Phosphate Ions Based on Europium(III)‐Modulated CdSe Quantum Dots

Phosphate anions are determined based on the electrochemiluminescence (ECL) of CdSe quantum dots (CdSe QDs) capped with 3‐mercaptopropionic acid. The ECL gets quenched with the introduction of Eu³⁺ ions, but it is restored on the further addition of phosphate anions. The sensing mechanism might be due to the strong and specific interaction between phosphate anions and the Eu³⁺ ions, leading to the releasing of CdSe QDs from aggregates. On the basis of the quenching/recovery ECL behaviors, the ECL sensor offer acceptable sensitivity, high selectivity, and a linear response from 0.1 to 120 µM with a detection limit of 0.03 µM (3δ) for phosphate anions.     

Determination of Hydrocortisone in Cosmetics by CdSe/CdS Quantum Dots-Based Fluoroimmunoassay Using Magnetic Fe3O4/Au Nanoparticles as Solid Carriers

This work demonstrated the feasibility of detecting hydrocortisone in cosmetics using a novel CdSe/CdS quantum dots‐based competitive fluoroimmunoassay with magnetic core/shell Fe₃O₄/Au nanoparticles (MCFN) as solid carriers. Hydrocortisone antigen was labeled with the synthesized core/shell CdSe/CdS quantum dots (QDs) to form the antigen‐QDs conjugate. Meanwhile, hydrocortisone antibody was incubated with MCFN and the immobilized antibody was obtained. The immobilized antibody was then mixed sequentially with hydrocortisone and a slightly excess amount of the QDs‐labeled hydrocortisone antigen, allowing their competition for binding with the antibody immobilized on MCFN. The bound hydrocortisone and the antigen‐QDs conjugates on MCFN were removed subsequently after the mixture was applied to a magnetic force. The analyte concentration was obtained by measuring the fluorescence intensity of the unbound hydrocortisone antigen‐QDs conjugates. The proposed method was characterized by simplicity, rapidity, and high sensitivity with a wide linear working range of 0.5 to 15000 pg·mL^?1 and a low detection limit of 0.5 pg·mL^?1. The proposed method was successfully applied to the determination of hydrocortisone in cosmetics with satisfactory results.     

Electochemiluminescence of CdTe/CdS Quantum Dots with Triproprylamine as Coreactant in Aqueous Solution at a Lower Potential and Its Application for Highly Sensitive and Selective Detection of Cu2+

Anodic electrochemiluminescence (ECL) of 3‐mercaptopropionic acid (MPA)‐ capped CdTe/CdS core‐shell quantum dots (QDs) with tripropylamine (TPrA) as the co‐reactant were studied in aqueous (Tris buffer) solution for the first time. The results suggest that the oxidation of TPrA at a glassy carbon electrode (GCE) surface participated in the ECL of QDs, and the onset potential and the intensity of ECL of CdTe/CdS QDs were affected seriously by TPrA, as the co‐reactant, in Tris buffer solution. The onset potential of ECL in this new system was about +0.5 V (vs. Ag/AgCl) and the ECL intensity greatly enhanced when TPrA was present. Various influencing factors, such as the electrolyte, pH, QDs concentration, potential range and scan rates on the ECL were studied. Based on the selective quenching by Cu²⁺ to the light emission from CdTe/CdS QDs/TPrA system, a highly sensitive and selective method for the determination of Cu²⁺ was developed. At the optimal conditions, the relative ECL intensity, I₀/I, was proportional to the concentration of Cu²⁺ from 14 nM to 0.21 μM with the detection limit of 6.1 nM based on the signal‐to‐noise ratio of 3. The possible ECL mechanism of QDs and the quenching mechanism of ECL were proposed.