Acid Capped CdSe Quantum Dots Research Articles

A novel nanocomposite platform of mercaptopropionic acid stabilized CdSe quantum dots-graphene for impedimetric detection of low density lipoprotein

Electrophoretically deposited, 3-mercaptopropionic acid capped CdSe quantum dots (QDs)-grapehene nanpcomposite (rGO-CdSe QDs/ITO) platform have been used for the fabrication of an electrochemical biosensor for detection of low-density lipoprotein (LDL) by immobilizing anti-apolipoprotein B (AAB) via N-ethyl-N’-(3-dimethylaminopropyl carbodiimide N-hydroxysuccinimide) coupling. The modifiedelectrodeswere characterized by various techniques. AAB/rGO-CdSe-QDs/ITO immunoelectrodes studied by EIS revealed detection of LDL in the wide range of 2 mgdL−1–125 mgdL−1.

Paper-based electrochemiluminescence device for the rapid estimation of trimethylamine in fish via the quenching effect of thioglycolic acid-capped cadmium selenide quantum dots

A paper-based electrochemiluminescence device (µPAD-ECL) for the estimation of trimethylamine (TMA) concentration in fish was developed using tris(2,2ʹ-bipyridyl)ruthenium(II) complex coupled with water soluble thioglycolic acid–capped CdSe quantum dots on the inkjet-printed paper-based device. The quenching effect of tertiary amines on the ECL intensity was found to be sensitive and concentration dependent. This effect allows the measurement of TMA at low concentrations. Under the optimal conditions, the linear concentration range was exhibited from 1 × 10−12 to 1 × 10−7 M and a detection limit of 2.09 × 10−13 M, with relative standard deviation of 1.97 %. The applicability of µPAD-ECL is demonstrated by the rapid estimation of trimethylamine concentration in fish tissue, and could be used as a method for screening the total amount of tertiary amines in fishery products in remote communities. The results obtained using the paper-based devices agreed well with those obtained applying high performance liquid chromatography with benzoyl derivatization, at a confidence level of 95%.

One‐Pot, Rapid and Facile Synthesis of Thioglycolic Acid capped CdSe quantum dots: Tuning of Properties, Mechanistic Investigations by Cyclic Voltammetry and Cytotoxicity Studies

AbstractThioglycolic acid (TGA) capped CdSe quantum dots (QD) have been synthesized in aqueous solution using facile, one‐pot and soft chemical route at ambient condition. The excitonic absorption peak and band gap of the QD could be tuned from 435 nm to 472 nm and from 2.37 eV to 2.60 eV respectively. The morphology of these QD were dependent on the precursor's concentration during synthesis. These QD exhibited broad photoluminescence (PL) spectra with large Stokes shift. It was observed that in the synthesis of CdSe QD TGA played twin role of catalyzing and capping agent. Detailed reaction mechanism of synthesis studied using cyclic voltammetry confirms the role of thioglycolate anion in the synthesis of CdSe QD. Cytotoxicity effects of these QD were studied in both the normal and cancer cell, indicted that TGA capped CdSe QD are cytotoxic beyond 10 μg/ml concentration and leads to cell proliferation of cancer cells.

Fluorescent determination of trinitrotoluene with bovine serum albumin mediated enhancement of thioglycolic acid capped cadmium selenium quantum dots

Here, a spectroscopic investigation of the interaction between bovine serum albumin protein and thioglycolic acid capped cadmium selenide (CdSe) quantum dots is presented. Luminescent water-soluble CdSe quantum dots were synthesized at room temperature by a one-step proctocol. Selenium powder and thioglycolic acid were used as the precursor and stabilizer, respectively. The synthesized thioglycolic acid capped CdSe quantum dots were activated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide treatment and conjugated with bovine serum albumin protein. The fluorescence signal of CdSe quantum dots was enhanced proportionally with the bovine serum albumin concentration from 0.25 to 5 µg/mL. This nano-bioconjugate was employed for the determination of trinitrotoluene with a detection limit of 5.65 ppm trinitrotoluene across a linear range of 4.4 × 10−6 M to 35.2 × 10−6 M.

Functionalized Vesicles with Co-Embedded CdSe Quantum Dots and [FeFe]-Hydrogenase Mimic for Light-Driven Hydrogen Production

A photocatalytic hybrid system for the production of hydrogen in purely aqueous solution was prepared by the co-embedding of hydrophobic oleic acid capped CdSe quantum dots (QD) for light harvesting and an amphiphilic [FeFe]-hydrogenase subunit mimic for proton reduction into phospholipid vesicle membranes. These bio-inspired functionalized vesicles concentrate the catalytic subunits in close proximity and show light-driven hydrogen generation in the presence of ascorbic acid resulting in 651 and 2.47 x 105 catalytic turnovers for the membrane-incorporated catalyst and the QDs, respectively.

Synthesis of 2-Mercaptonicotinic Acid-Capped CdSe Quantum Dots and its Application to Spectrofluorometric Determination of Cr(VI) in Water Samples.

The CdSe quantum dots (QDs) capped with 2-mercaptonicotinic acid (H2MN) were prepared through a controllable process at 80°C. The prepared QDs were characterized by XRD, TEM, IR, UV-Vis and fluorescence (FL) techniques. It was found that the QDs were nearly mono-disperse with the diameters in the range of 8-10nm. These QDs are capable to exhibit strong FL even in concentrated acidic media. They exhibit an enhanced fluorescence in the presence of Cr(VI), which was used for the determination of Cr(VI) in water samples. The linear range was found to be 1 × 10(-7)-6.0 × 10(-6) M with the RSD and DL of 0.92% and 5 × 10(-8) M, respectively. Except that Ca(2+) and Fe(3+) which can be eliminated through a simple precipitation process, the other co-existent ions present in natural water were not interfered. The recoveries obtained for the added amounts of Cr(VI) were in the range of 96.9-103.2%, which denote on application of the method, satisfactorily.

Fabrication of CdSe quantum dots/permutite luminescent materials

Permutite incorporating CdSe in mesopores has been prepared with a simple route. Firstly, mercaptosuccinic acid-capped CdSe quantum dots (QDs) were prepared in aqueous solution by using SeO2 as selenium source and NaBH as reductant. Secondly, the commercial permutite was treated with acetic acid to induce a partial dealumnization, which can introduce a large number of intracrystal mesopores, and the CdSe QDs were successfully incorporated in the mesopores with the wet impregnation method. Photoluminescence spectra, X-ray diffraction and scanning electron microscopy were used for the characterization of samples. The spectra analyses results showed that the illuminant colour of QDs/permutite powder was similar to the corresponding QDs colloid. X-ray diffraction measurements indicated that the (1 0 1) diffraction peak at 2𝜃 = 27° for QDs/permutite powder was the same as the raw permutite, and the energy-dispersive X-ray spectra demonstrated that Cd and Se elements existed in the CdSe QDs/permutite powder.

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.

CdSe量子点膨润土复合材料的制备与表征

Mercaptosuccinic acid capped CdSe quantum dots were prepared in aqueous solution by using SeO2as selenium source and NaBH4as reductant. Then,the CdSe quantum dots bentonite luminescent material was prepared by mixing the CdSe quantum dots solution and organic bentonite under stirring. The obtained sample was characterized by photoluminescence spectra,scanning electron microscopy and X-ray diffraction. The spectra analysis results disclosed that the illuminant color of quantum dots bentonite composites was similar to the corresponding quantum dots solution. The energy-dispersive X-ray spectra demonstrated that Cd and Se elements presented in the composites. X-ray diffraction measurements indicated that the(111),(220) and(331) diffraction peak of CdSe appeared in quantum dots bentonite composites,and the(001) diffraction peak at 2θ = 4. 3° in the raw bentonite. These results suggest that the preparation of CdSe quantum dots bentonite composites do not change the structures of quantum dots and bentonite.

Multifunctional nanocarrier based on clay nanotubes for efficient intracellular siRNA delivery and gene silencing

RNA interference-mediated gene silencing relating to disease has recently emerged as a powerful method in gene therapy. Despite the promises, effective transport of siRNA with minimal side effects remains a challenge. Halloysites are cheap and naturally available aluminosilicate clay nanotubes with high mechanical strength and biocompatibility. In this study, a novel multifunctional nanocarrier based on functionalized halloysite nanotubes (f-HNTs) has been developed via electrostatic layer-by-layer assembling approach for loading and intracellular delivery of therapeutic antisurvivin siRNA and simultaneously tracking their intracellular transport, in which PEI-modified HNTs are used as gene vector, antisurvivin siRNA as gene therapeutic agent, and mercaptoacetic acid-capped CdSe quantum dots as fluorescent labeling probes. The successful assembly of the f-HNTs-siRNA complexes was systematically characterized by transmission electron microscopy (TEM), UV-visible spectrophotometry, Zeta potential measurement, fluorescence spectrophotometry, and electrochemical impedance spectroscopy. Confocal microscopy, biological TEM, and flow cytometry studies revealed that the complexes enabled the efficient intracellular delivery of siRNA for cell-specific gene silencing. MTT assays exhibited that the complexes can enhance antitumor activity. Furthermore, Western blot analysis showed that f-HNTs-mediated siRNA delivery effectively knocked down gene expression of survivin and thereby decreased the levels of target proteins of PANC-1 cells. Therefore, this study suggested that the synthesized f-HNTs were a new effective drug delivery system for potential application in cancer gene therapy.

Structural characterization and observation of variable range hopping conduction mechanism at high temperature in CdSe quantum dot solids

We have used Rietveld refinement technique to extract the microstructural parameters of thioglycolic acid capped CdSe quantum dots. The quantum dot formation and its efficient capping are further confirmed by HR-TEM, UV-visible and FT-IR spectroscopy. Comparative study of the variation of dc conductivity with temperature (298 K ≤ T ≤ 460 K) is given considering Arrhenius formalism, small polaron hopping and Schnakenberg model. We observe that only Schnakenberg model provides good fit to the non-linear region of the variation of dc conductivity with temperature. Experimental variation of ac conductivity and dielectric parameters with temperature (298 K ≤ T ≤ 460 K) and frequency (80 Hz ≤ f ≤ 2 MHz) are discussed in the light of hopping theory and quantum confinement effect. We have elucidated the observed non-linearity in the I-V curves (measured within ±50 V), at dark and at ambient light, in view of tunneling mechanism. Tunnel exponents and non-linearity weight factors have also been evaluated in this regard.

Simple and sensitive determination of papain by resonance light-scattering with CdSe quantum dots

In this contribution, a simple and sensitive method for papain detection was established based on the increment of the resonance light-scattering (RLS) intensity of mercaptoacetic acid-capped CdSe quantum dots (MAA-QDs) in aqueous solution. Meanwhile, the RLS characteristics and the optimal conditions were investigated in detail. Under the optimized conditions, the linear range of MAA-QDs RLS intensity versus the concentration of papain was 1.0×10−8M to 6.0×10−7M, with a correlation coefficient (R2) of 0.9977 and a limit of detection (3σ black) of 5.1×10−9M. The relative standard deviation (R.S.D.) for 1.6×10−7M papain was 1.0% (n=5). There was almost no interference to coexisting foreign substances including common ions, proteins and 20 amino acids. The proposed method possessed the advantages of simplicity, rapidity and sensitivity. Three synthetic samples were analyzed by the methodology and the results were satisfying. The interaction between MAA-QDs and papain was also investigated systematically by using visual method, transmission electron microscopy and time-resolved fluorescence spectra, and the results indicated that the main force between MAA-QDs and papain was electrostatic interaction.

Investigation on the Photoinduced Interaction of Water Soluble Thio Glycolic Acid Capped CdSe Quantum Dots with Lysozyme

Investigation on the Photoinduced Interaction of Water Soluble Thio Glycolic Acid Capped CdSe Quantum Dots with Lysozyme

Efficiency enhancement for bulk-heterojunction hybrid solar cells based on acid treated CdSe quantum dots and low bandgap polymer PCPDTBT

We report on the efficiency enhancement for bulk-heterojunction hybrid solar cells based on hexanoic acid treated trioctylphosphine/oleic acid-capped CdSe quantum dots (QDs) and low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4 H-cyclopenta[2,1- b;3,4- b′]-dithiophene)- alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) compared to devices based on poly(3-hexylthiophene) (P3HT). Photovoltaic devices with optimized polymer:QD weight ratio, photoactive film thickness, thermal annealing treatment, and cathode materials exhibited a power conversion efficiency of 2.7% after spectral mismatch correction, which is the highest reported value for spherical CdSe QD based photovoltaic devices. The efficiency enhancement is attributed to the surface treatment of the QDs together with the use of the low bandgap polymer PCPDTBT leading to an increased short-circuit current density due to additional light absorption between 650 and 850 nm. Our results suggest that the hexanoic acid treatment is generally applicable to various ligand-capped CdSe and confirm that low bandgap polymers with adequate HOMO and LUMO levels are promising to be incorporated into hybrid solar cells for further device performance improvement.

Effects of Carbon Nanotubes on Photoluminescence Properties of Quantum Dots

The effects of carbon nanotubes (CNT) with different surface groups on the luminescence properties of mercaptoacetic acid-capped CdSe quantum dots (QD) are reported. Carboxyl-, hydroxyl-, and amine-modified CNTs are used to interact with water-soluble luminescent mercaptoacetic acid-capped CdSe QDs. TEM and ζ-potential analysis results show that CNT and QDs can be assembled into complex nanostructure by electrostatic interaction. The photoluminescence (PL) quenching of QDs caused by CNTs can be described by a Stern−Volmer-type equation as well as by a double-logarithmic equation. Significant differences in the values of binding constants KSV and Kb were found in these experiments. The binding constant for amine-terminated CNT is much higher compared to that of carboxyl- and hydroxyl-terminated CNTs. Dynamic quenching and photoluminescence resonance energy transfer between QDs and CNTs should be responsible for the quenching of photoluminescence emissions of QDs caused by CNTs with different groups. The strategy shown in this paper may be useful for creating a novel methodology for investigating intermolecular interaction, and the quenching phenomena may be used as selective molecular probes and developed as fluorescence sensors.

Electrochemiluminescence Sensors for Scavengers of Hydroxyl Radical Based on Its Annihilation in CdSe Quantum Dots Film/Peroxide System

This work elucidated the detailed electrochemiluminescence (ECL) process of the thioglycolic acid-capped CdSe quantum dots (QDs) film/peroxide aqueous system. The QDs were first electrochemically reduced to form electrons-injected QDs approximately -1.1 V, which then reduced hydrogen peroxide to produce OH* radical. The intermediate OH* radical was a key species for producing holes-injected QDs. The ECL emission with a peak at -1.114 V was demonstrated to come from the 1Se-1Sh transition emission. Using thiol compounds as the model molecules to annihilate the OH* radical, their quenching effects on ECL emission were studied. This effect led to a novel strategy for ECL sensing of the scavengers of hydroxyl radical. The detection results of thiol compounds showed high sensitivity, good precision, and acceptable accuracy, suggesting the promising application of the proposed method for quick detection of both scavengers and generators of hydroxyl radical in different fields.

Nanoscale manipulation of CdSe quantum dots in layer-by-layer films: influence of the host polyelectrolyte on the luminescent properties

Thioglycolic acid-capped CdSe quantum dots (QDs) were assembled on glass substrates with two distinct polyelectrolytes, viz poly(allylamine hydrochloride) (PAH) and poly(amidoamine) (PAMAM), generation 4 dendrimer, via the layer-by-layer (LbL) technique. Films containing up to 30 polyelectrolyte/QD bilayers were prepared. The growth of the multilayers was monitored with UV–vis spectroscopy, which showed an almost linear increase in the absorbance of the 2.8 nm QDs at 535 nm with the number of deposited bilayers. AFM measurements estimated a film thickness of 3 nm per bilayer for the PAH/CdSe films. The adsorption process and the optical properties of the PAMAM/CdSe LbL films were further analyzed layer-by-layer using surface plasmon resonance (SPR), from which a thickness of 3.2 nm was found for a PAMAM/CdSe bilayer. Photoluminescence measurements revealed higher photooxidation of the quantum dots in PAH/CdSe than in PAMAM/CdSe films.

Layer-by-Layer Films of Chitosan, Organophosphorus Hydrolase and Thioglycolic Acid-Capped CdSe Quantum Dots for the Detection of Paraoxon

A polyelectrolyte architecture was fabricated that was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. This film was imaged by epifluorescence microscopy. UV−vis and emission spectroscopies were used to monitor the growth of the bilayer film due to the enhanced optical property of QDs. Photoluminescence of the functionalized QDs improved when sandwiched between the polycations layers. The presence of organophosphorus compounds was confirmed through photoluminescence spectroscopy.

Layer-by-Layer Biosensor Assembly Incorporating Functionalized Quantum Dots

Layer-by-layer (LbL) assembly has been utilized to fabricate an ultrathin film of polyelectrolytes. The architecture was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. The topography of the films was studied using epifluorescence microscopy imaging. The photoluminescence property of the functionalized QDs improved when sandwiched between the polycation layers. The enhanced optical property of QDs allowed easy monitoring of LbL growth and detection of paraoxon with high sensitivity. The presence of organophosphorus compounds was confirmed through UV−vis and emission spectroscopies.