Citrate-stabilized CdSe/CdS quantum dots as fluorescence probe for protein determination

A rapid, ultrasensitive and convenient fluorescence measurement technology based on the enhancement of the fluorescence intensity resulting from the interaction of functionalized CdSe/CdS quantum dots （QDs） with bov/ne serum albumin （BSA） was proposed. The citrate-stabilized CdSe/CdS （QDs） were synthesized by using Se powder and Na2S as precursors instead of any pyrophoric organometallic precursors. The modified CdSe/CdS QDs are brighter and more stable against photobleaching in comparison with organic fluorophores. At pH 7.0, the fluorescence signal of CdSe/CdS is enhanced by increasing the concentration of BSA in the range of 0.1-10 μg/mL, and the low detection limit is 0.06 μg/mL. A linear relationship between the enhanced fluorescence peak intensity （△F） and BSA concentration （c） is established using equation △F=50.7c＋16.4 （R=0.996 36）. Results of determination for BSA in three synthetic samples are identical with the true values, and the recovery （98.9%-102.4%） and relative standard deviation （RSD, 1.8%-2.5%） are satisfactory.

CdS Quantum Dots as Fluorescence Probes for Detection of Adriamycin Hydrochloride

Water-soluble CdS quantum dots（CdS-QDs） capped with thioglycohc acid were easily prepared, and a detection method of adriamycin was presented based on the fluorescence quenching of CdS-QDs. It was found that a complex could be formed between cetyhrimethyl ammonium bromide（CTAB） and CdS-QDs by using electrostatic interaction in Britton-Robinson（BR） buffer at pH = 7.00, and the strong fluorescence emission of the complex was observed at 500 nm when the complex was excited at 378 run. The presence of adriamycin, however, could strongly quench the fluorescence through hydrophobic interaction. The overall quenching percentage as a function of adriamycin concentration matches the Stern-Volmer equation very well. These properties make CdS-QDs a potential fluorescence probe for the detection of adriamycin. The detection hmit（3σ） of adriamycin is approximately 10^-9 mol/L.

Interaction of CdTe/CdS quantum dots with antibodies

In the study, we observed the strong adsorption of CdTe/CdS QDs to antibodies and the formation of QDs-antibodies conjugates. Capillary electrophoresis with laser-induced fluorescence detection （CE-LIF）, fluorescence spectrometry and fluorescence correlation spectroscopy （FCS） were used to characterize the QDs conjugates with antibody. We found that the QDs-antibody conjugates possessed high fluorescence, small hydrodynamic radii and good stability in aqueous solution. 2009 Ji Cun Ren. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Quantitative Model for the Surface-related Electron Transfer in CdS Quantum Dots

The influence of surface S^2- dangling bonds and surface doped ions（Se^2-, Cu^2＋, and Hg^2＋） on the photoluminescence of Cd^2＋-rich CdS QDs was investigated. A quantitative model was proposed to understand the complex transfer processes of excited electrons in CdS QDs. The transfer of excited electrons from either the conduction band or the Cd^2＋-related trap-state to the surface S^2-related shallow hole trap-state is effective. However, the trap of excited electrons by surface doped ion trap-states from the Cd^2＋-related trap-state is more effective than that from the conduction band. The efficiency of trapping electrons from both the conduction band and the Cd^2＋-related trap-state can be quantitatively understood with the help of the proposed model. The results show that the transfer efficiency of excited electrons is dependent on the location of the energy-level of the relevant surface-related trap-state. The trap of excited electrons by the surface trap-state with energy-level closer to that of the conduction band is more effective, especially for the trap of excited electrons from Cd^2＋-related trap-state.

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots（QDs） are fabricated on Si nanowires（NWs） substrates with and without Au nanoparticles（NPs）. The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence（PL） intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.

High-quality CdS quantum dots sensitized ZnO nanotube array films for superior photoelectrochemical performance

The surface characteristics of ZnO were synthetically optimized by a self-designed simultaneous etching and W-doping hydrothermal method utilizing as-prepared ZnO nanorod(NR)array films as the template.Benefiting from the etching and regrowth process and the different structural stabilities of the various faces of ZnO NRs,the uniquely etched and W-doped ZnO(EWZ)nanotube(NT)array films with larger surface area,more active sites and better energy band structure were used to improve the photoelectrochemical(PEC)performance and the loading quality of CdS quantum dots(QDs).On the basis of their better surface characteristics,the CdS QDs were uniformly loaded on EWZ NT array film with a good coverage ratio and interface connection;this effectively improved the light-harvesting ability,charge transportation and separation as well as charge injection efficiency during the PEC reaction.Therefore,all the CdS QD-sensitized EWZ NT array films exhibited significantly enhanced PEC performance.The CdS/EWZ-7 composite films exhibited the optimal photocurrent density with a value of 12 mA·cm^(-2),2.5 times higher than that of conventional CdS/ZnO-7 composite films under the same sensitization times with CdS QDs.The corresponding etching and optimizing mechanisms were also discussed.

Dual-functional photocatalysis boosted by electrostatic assembly of porphyrinic metal-organic framework heterojunction composites with CdS quantum dots

Photocatalytic dual-functional reaction under visible light irradiation represents a sustainable development strategy.In detail,H2production coupled with benzylamine oxidation can remarkably lower the cost by replacing sacrificial agents.In this work,Cd S quantum dots(Cd S QDs)were successfully loaded onto the surface of a porphyrinic metal-organic framework(Pd-PCN-222)by the electrostatic selfassembly at room temperature.The consequent Pd-PCN-222/CdS heterojunction composites displayed superb photocatalytic activity under visible light irradiation,achieving a H2production and benzylamine oxidation rate of 5069 and 3717μmol g^(-1)h^(-1)with>99%selectivity in 3 h.There is no noticeable loss of catalytic capability during three successive runs.Mechanistic studies by in situ electron spin resonance and X-ray photoelectron spectroscopy disclosed that CdS QDs injected photoexcited electrons to Pd-PCN-222 and then Zr6clusters under visible-light irradiation,and thus Cd S QDs and Zr6clusters behave as the photocatalytic oxidation and reduction centers,respectively.

Ultrafast Carrier Dynamics in CdSe/CdS/ZnS Quantum Dots

The intra- and inter-band relaxation dynamics of CdSe/CdS/ZnS core/shell/shell quantum dots are investigated with the aid of time-resolved nonlinear transmission spectra which are obtained using femtosecond pump-probe technique. By selectively exciting the core and shell carrier, the dynamics are studied in detail. Carrier relaxation is found faster in the conduction band of the CdS shell （about 130 fs） than that in the conduction band of the CdSe core （about 400 fs）. From the experiments it is distinctly demonstrated the existence of the defect states in the interface between the CdSe core and the CdS shell, indicating that ultrafast spectroscopy might be a suitable tool in studying interface and surface morphology properties in nanosystems.

Photoelectrochemical Immunosensor Array Based on Thioglycolic Acid Capped CdS Quantum Dots for Multiplexed Detection of Veterinary Drug Residues

A photoelectrochemical immunosensor based on multi-electrode array was developed for simultaneous and sen- sitive determination of veterinary drug residues. In this system, poly（dimethyldiallylammonium chloride） （PDDA）, Au nanoparticles （Au NPs） and thioglycolic acid （TGA）-capped CdS quantum dots （QDs） were layer-by-layer as- sembled onto the home-made Au electrode array. The assembling process of the （CdS/PDDA/Au NPs/PDDA）, mul- tilayer was characterized by electrochemical impedance spectroscopy. And then the antibodies for clenbuterol （CB）, ractopamine （RAC） and chloramphenicol （CAP） were covalently immobilized onto the Au electrode array by 1-ethyl-3-（3-dimethylaminopropyl） carbodiimide （EDC） coupling reaction, respectively. The concentrations of CB, RAC and CAP were measured based on the photoelectrochemical effects of CdS QDs. Under the optimal conditions the limits of detection （LOD） for CB, RAC and CAP were 25, 50 and 2.2 pg/mL （3a）, respectively, with acceptable recovery over the range of 95.40%--105.5% in pig liver samples. All results indicate that the immunosensor array system has potential application for practical, effective and high throughput analysis of veterinary drugs residues.

Determination of Hydrocortisone in Cosmetics by CdSe/CdS Quantum Dots-Based Fluoroimmunoassay Using Magnetic Fe304/Au Nanoparticles as Solid Carriers

This work demonstrated the feasibility of detecting hydrocortisone in cosmetics using a novel CdSe/CdS quan- tum dots-based competitive fluoroimmunoassay with magnetic core/shell Fe3Oa/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.

g-C_(3)N_(4) encapsulated ZrO_(2) nanofibrous membrane decorated with CdS quantum dots: A hierarchically structured, self-supported electrocatalyst toward synergistic NH3 synthesis

The advancement of electrocatalytic N2 reduction reaction (NRR) toward ambient NH3 synthesis lies in the development of more affordable electrocatalysts than noble metals. Recently, various nanostructures of transition metal compounds have been proposed as effective electrocatalysts;however, they exist in the form of loose powders, which have to be immobilized on a matrix before serving as the electrode for electrolysis. The matrix, being it carbon paper, carbon cloth or metal foam, is electrocatalytically inactive, whose introduction inevitably raises the invalid weight while sacrificing the active sites of the electrode. Herein, we report on the fabrication of a flexible ZrO2 nanofibrous membrane as a novel, self-supported electrocatalyst. The heteroatom doping can not only endow the nanofibrous membrane with excellent flexibility, but also induce oxygen vacancies which are responsible for easier adsorption of N2 on the ZrO2 surface. To improve the electrocatalytic activity, a facile SILAR approach is employed to decorate it with CdS quantum dots (QDs), thereby tuning its Fermi level. To improve the conductivity, a g-C3N4 nanolayer is further deposited which is both conductive and active. The resulting hierarchically structured, self-supported electrocatalyst, consisting of g-C3N4 encapsulated ZrO2 nanofibrous membrane decorated with CdS QDs, integrates the merits of the three components, and exhibits a remarkable synergy toward NRR. Excellent NH3 yield of 6.32 × 10−10 mol·s−1cm−2 (−0.6 V vs. RHE) and Faradaic efficiency of 12.9% (−0.4 V vs. RHE) are attained in 0.1 M Na2SO4.

A Simple and Rapid Label-free Fluorimetric ＂Turn Off-on＂ Sensor for Cadmium Detection Using Glutathione-capped CdS Quantum Dots

A convenient label-free fluorescence（FL） nanoprobe for rapid detection of cadmium（Cd） was established using glutathione-capped CdS quantum dots（QDs） and 1,10-phenanthroline（phen）. The prepared CdS QDs exhibited a strong FL emission at 536 nm, which could be quenched by phen due to the photoinduced hole transfer（PHT） mechanism. The existence of Cd effectively recovered the FL intensity of CdS QDs, which was due to the easy detachment of phen from the surface of QDs to form [Cd（phen）2（H2O）2]2＋ in solution. Cd concentrations were linearly correlated with the FL intensity in the range of 0.0625-1.25 μmol/L under the optimized conditions and the detection limit was 0.01μmol/L. Finally, the Cd concentration was accurately quantified in real water sample using the proposed sensor.

Amperometric Hydrogen Peroxide Biosensor Based on Multiwall Carbon Nanotubes and Cadmium Sulfide Quantum Dots

A novel third-generation hydrogen peroxide（H2O2） biosensor（Hb/CdS/MWNTs/GCE） was fabricated through hemoglobin（Hb） adsorbed onto the mercaptoacetic acid modified CdS QDs/carboxyl multiwall carbon nanotubes＇（MWNTs） films. Cyclic voltammogram of Hb/CdS/MWNTs/GCE showed a pair of well-defined and quasi-reversible redox peaks with a formal potential（E^0） of-0.230 V（vs. Ag/AgCl） in 0.1 mol/L pH=8.0 phosphate buffer solution（PBS）, which was the characteristic of the Hb heme Fe（Ⅲ）/Fe（Ⅱ） redox couple. The biosensor shows an excellent electrocatalytic activity to the reduction of H2O2. The response time of the designed biosensor to H202 at a potential of-0.30 V was less than 2 s and linear relationships were obtained in the concentration ranges of 2.0×10^-6-2.7×10^-3 mol/L and 2.7×10^-3-7.7×10^-3 mol/L with a detection limit of 3.0×10^-7 mol/L（S/N=3）. The apparent Michaelis-Menten constant Km was estimated to be 1.324 mmol/L that illustrated the excellent biological activity of the fixed Hb.

Microwave Synthesis of CdTe/TGA Quantum Dots and Their Thermodynamic Interaction with Bovine Serum Albumin

The thioglycollic acid（TGA） as a capping agent, CdTe/TGA quantum dots（QDs） with excellent properties were synthesized under microwave irradiation. The TGA/Cd/Te molar ratios, reaction time, temperature and p H are the crucial factors for properties of QDs. The QDs were characterized by UVvis absorption and fluorescence spectra, transmission electron microscopy and Fourier transform infrared spectroscopy. The experimental results show that when the p H value is 11.5 and molar ratio of TGA：Cd：Te is 1.2：1：0.4 at 100 ℃ heating for 15 min, the resulted QDs exhibit a high fluorescence quantum yield of 78%. The fluorescence full width at half maximum（FHMW） of QDs is around 23 nm. The products are spherical with average size of 3-5 nm. There is a strong coordination effect between TGA and Cd2＋. Moreover, the results of interaction between as-made QDs and bovine serum albumin（BSA） suggest that the QDs-BSA binding reaction is a static quenching. The negative values of free energy（△G〈0） suggest that the binding process is spontaneous, △H〈0 and △S〈0 show that hydrogen bonds and van der Waals interactions play a major role in the binding reaction between QDs and BSA.

Synthesis and characteristics of multifunctional Fe_3O_4-SiO_2-CdS magnetic-fluorescent nanocomposites

A luminescent superparamagnetic nanocomposite with an Fe3O4 SiO2-CdS structure is synthesised. Coated with a silica shell, Fe3O4 nanoparticles and CdS quantum dots （QDs） are successfully assembled together. Analysed from the test results of X-ray diffraction （XRD）, transmission electron microscopy （TEM）, high resolution transimission electron microscopy （HRTEM）, hysteresis loop, and photoluminescence （PL） spectrum, these nanocomposites exhibit superparamagnetic and photoluminescent properties.

Enhanced chemiluminescence from reactions between CdTe/CdS/ZnS quantum dots and periodate

A novel chemiluminescence（CL） performance of CdTe/CdS/ZnS quantum dots（QDs） with periodate（KIO_4） was studied.Effects of concentration and pH on the CL system were investigated.Electron spin resonance（ESR） and the effects of radical scavenger analysis were employed for identification of intermediate species.The CL spectra for this system showed only one maximum emission peak centered around 620 nm,which was similar with photoluminescence（PL） spectra of CdTe/CdS/ZnS QDs.The CL of CdTe/CdS/ZnS QDs was induced by direct chemical oxidation and the possible mechanism could be explained by radiative recombination of injected holes and electrons.This investigation not only provided new sight into the optical characteristics of CdTe/CdS/ZnS QDs,but also broadened their potential optical utilizations.

Size focusing of colloidal quantum dots under high monomer concentration

The diffusion-controlled growth mode is widely used to narrow the size distribution of colloidal quantum dots.However,this growth mode always suffers from size broadening at the later growth stage.By monitoring the growth process of CdS colloidal quantum dots,we show the size broadening is a result of different growth rates of CdS colloidal quantum dots(CQDs)with different morphologies.Monomer concentration-dependent growth experiments demonstrate the different growth rates are caused by the different ligand permeabilities of CdS CQDs.The cubic ones have lower ligand permeability but higher saturated surface reaction rate than the noncubic ones,leading to unexpected narrower size distribution under higher monomer concentration.More efficient narrowing can be obtained by the addition of chloride ions,which can increase the ligand permeability of all CdS CQDs,as well as the opposite discrepancies in ligand permeability and surface reaction between cubic and noncubic CdS CQDs.The photoluminescence(PL)full width at half maximum(FWHM)of CdS CQDs can be narrowed down to below 80 meV for PL peaks from 430 to 500 nm.Given the inevitable usage of the ligands in the solution synthesis of colloidal nanocrystals,the influence of morphology difference on growth rate should be common.Our results can provide an alternative solution to realize size focusing for the synthesis of colloidal nanocrystals.

Influence of the Cd/S Molar Ratio on the Optical and Structural Properties of Nanocrystalline CdS Thin Films

Nanocrystalline CdS thin films have been deposited using precursors with different thiourea concentrationonto glass substrates by sol-gel spin coating method.The crystalline nature of the films has been observedto be strongly dependent on thiourea concentration and annealing temperature.The CdS films are found tobe nanocrystalline in nature with hexagonal structure.The grain size is found to be in the range of 7.6 to11.5 nm depending on the thiourea concentration and annealing temperature.The high resolution transmissionelectron microscopy （HRTEM） results of the CdS films prepared using cadmium to thiourea molar ratio of0.3：0.3 indicate the formation of nanocrystalline CdS with grain size of 5 nm.Fourier transform infrared （FTIR）analysis shows the absorption bands corresponding to Cd and S.The optical study carried out to determinethe band gap of the nanostructured CdS thin films shows a strong blue shift.The band gap energy has beenobserved to lie in the range of 3.97 to 3.62 eV following closely the quantum confinement dependence ofenergy on crystallite radius.The dependence of band gap of the CdS films on the annealing temperature andthiourea concentration has also been studied.The photoluminescence （PL） spectra display two main emissionpeaks corresponding to the blue and green emissions of CdS.

Multiplexed Detection of Fe^(3+), Cobalamin and Folate Using Fluorescent Nanoprobe-Based Microarrays and a Smartphone

This work reports on a smartphone-based quantitative POCT system which consists of a paper-based microarray chip,a homemade LEGO dark-box,and a smartphone installed with custom-designed FChip-APP,for on-site quantitation of Fe^(3+),Vitamin 12(VB12),and folic acid(FA).Collection and automatic analysis of fluorescence turn-off response of three kinds of fluorescent nanoprobes which are coated onto filter papers by a smartphone-based device is the principle behind this study.The POCT system exhibits good analytical performance for multiplexed analysis of Fe^(3+),VB_(12)and FA with a wide linear range(Fe^(3+),1.0–14.0μg mL^(-1)(R^(2)=0.983);VB_(12),1.35–40.0μg mL^(-1)(R^(2)=0.991);FA,2.0–26.0μg mL^(-1)(R^(2)=0.994))and low detection limit(Fe^(3+),0.35μg mL^(-1);VB12,0.47μg mL^(-1);FA,0.56μg mL^(-1)).The cost and weight of the whole system are~$220 and~600 g per set,highlighting its cost-eff ectiveness and portability.The simple operation procedures and user-friendly interface of the FChip-APP validate the ease-of-use feature of the reported system.This versatile smartphonebased quantitative POCT system provides a cost-eff ective and easy-of-use method for screening the context-specific causes of anemia and thus its eff ective interventions in the future,especially in resource-limited areas.