Surface Of Quantum Dots Research Articles

Tannin\u2013Mn coordination polymer coated carbon quantum dots nanocomposite for fluorescence and magnetic resonance bimodal imaging

The MR/FI bimodal imaging has attracted widely studied due to combining the advantages of MRI and FI can bridge gaps in sensitivity and depth between these two modalities. Herein, a novel MR/FI bimodal imaging probe is facile fabricated by coating the Mn-phenolic coordination polymer on the surface of the carbon quantum dots. The structure of the as-prepared nanocomposite probe is carefully validated via SEM, TEM, and XPS. The content of Mn2+ is calculated through the EDS and TGA. The quantum yield (QY) and emission wavelength of the probe are about 7.24% and 490 nm, respectively. The longitudinal r1 value (2.43 mM−1 s−1) with low r2/r1 (4.45) of the probe is obtained. Subsequently, fluorescence and MR imaging are performed. The metabolic pathways in vivo are inferred by studying the bio-distribution of the probe in major organs. Thus, these results indicate that probe would be an excellent dual-modal imaging probe for enhanced MR imaging and fluorescence imaging.MR/FI bimodal imaging probe is built via in-situ coated Mn-phenolic coordination polymer on the surface of the carbon quantum dots. The in vitro and vivo image property of the probe is evaluated.

Directed self-assembly of Ag+-deposited MoS2 quantum dots for colorimetric, fluorescent and fluorescence-lifetime sensing of alkaline phosphatase.

We developed a triple-readout probe for colorimetric, fluorescent, and fluorescence-lifetime sensing of alkaline phosphatase (ALP) through the hydrolyzed ascorbic acid phosphate (AAP)-mediated formation of silver nanoparticles (AgNPs) on Ag+-deposited MoS2 quantum dots (QDs). Ag+ ions were self-assembled on a monolayer MoS2 QD surface through the formation of Ag-S bonds. When ALP hydrolyzed AAP in an alkaline buffer, the resultant ascorbic acid (AA) triggered the reduction of the bound Ag+ ions into AgNPs on the MoS2 QD surface. The resultant AgNPs induced an efficient fluorescence quenching of the MoS2 QDs through simultaneous static and dynamic quenching processes, generated an intense surface plasmon resonance peak, and triggered a reduction in the fluorescence lifetime of the MoS2 QDs. Electron microscopy and spectroscopic techniques revealed the successful fabrication of Ag+-deposited MoS2 QDs and the ALP-mediated formation of AgNPs on the MoS2 QD surface. The linear quantification ranges for ALP were 0.05-2.5, 0.1-4, and 1-4 units L-1 in the fluorescent, colorimetric, and fluorescence-lifetime detection modes, respectively. In addition, the proposed probe integrated with an ALP-linked sandwich immunoassay exhibited high sensitivity and selectivity for the fluorescence sensing of rabbit immunoglobulin G with a detection limit of 8pgmL-1 and linear range of 25-1000pgmL-1. The sensitivity of the probe is comparable to those of previously reported immunoassays involving ultrasensitive electrochemical detection, hydrogen evolution reactions, or electron spin resonance. The probe integrated with the sandwich assay serves as a promising platform for the detection of target proteins in clinical samples.

General and Efficient C–P Bond Formation by Quantum Dots and Visible Light

General and Efficient C–P Bond Formation by Quantum Dots and Visible Light

Dual‐Functional Quantum Dot Seeding Growth of High‐Quality Air‐Processed CsPbI2Br Film for Carbon‐Based Perovskite Solar Cells

The high‐quality perovskite film is a prerequisite for high‐performance optoelectronic devices. Herein, CdSe colloidal quantum dots (QDs) serve as crystallization seeds for the first time to modulate the nucleation and crystal growth processes simultaneously of the CsPbI2Br film in the ambient environment. As additives, CdSe QDs help promote the nucleation process in the initial stage of perovskite formation. In addition, it is revealed that the surface ligands of QDs also have an essential influence on the subsequent crystal growth of the perovskite film. The bifunctional ligands on the surface of QDs are beneficial in delaying the growth process of perovskite due to the free functional groups at the ends. The CsPbI2Br film prepared with bifunctional organic ligand‐capped CdSe QD additives shows better crystallinity than that of the inorganic ligand‐based one due to the dual function of these kinds of QDs in not only promoting nucleation but also retarding crystal growth of CsPbI2Br crystals. As a result, the high‐quality CsPbI2Br film with a low defect state density is prepared in the ambient environment. The optimized efficiency of the assembled hole‐conductor‐free carbon‐based perovskite solar cells (C‐PSCs) is increased from 12.73% to 14.49%, which is one of the best results for all‐inorganic C‐PSCs.

Semiconducting Spaghetti-like Organic–Inorganic Nanojunctions via Sequential Self-Assembly of Conjugated Polymers and Quantum Dots

The ability to direct semiconducting polymers and inorganic nanomaterials into complex assemblies renders the creation of organic–inorganic nanocomposites with unique properties and functionalities. Herein, we report the crafting of highly interconnected semiconducting organic–inorganic nanocomposites (referred to as nanojunctions) comprising long poly(3-hexylthiophene) (P3HT) nanowires and lead telluride (PbTe) quantum dots (QDs) via two successive self-assembly processes. First, P3HT chains self-assemble into ultralong one-dimensional (1D) nanowires owing to interchain π–π stacking, followed by self-assembly of PbTe QDs on both sides of the P3HT nanowires driven by attractive van der Waals interactions between the hexyl side chains of P3HT and aliphatic chains capped on the surface of PbTe QDs. Notably, an integrated experimental and Monte Carlo (MC) simulation study reveals that the surface coverage of PbTe QDs within the P3HT/PbTe nanojunctions as well as the distance between adjacent PbTe QDs could be conveniently tailored via tuning the QD concentration. Interestingly, the photoluminescence of P3HT progressively decreases with an increased loading of PbTe QDs because of effective charge transfer from P3HT to PbTe. Conceptually, this two-step self-assembly strategy can be readily extended to other semiconducting polymers and a diversity of nanomaterials for potential applications in optoelectronic materials and devices.

Versatile scaffold applications based on MoS2 quantum dots for imaging mitochondrial pH in living cells

Sensitive and accurate detection and imaging of mitochondrial pH have become significant methods in biological and biomedical research to elucidate the biological functions of mitochondria. Herein, a mitochondria-targeted ratiometric fluorescent nanoprobe was developed to image mitochondrial pH in living cells. This nanoprobe was prepared by covalently linking a mitochondria-targeted ligand (triphenylphosphonium, TPP) and a pH recognition fluorescent indicator (rhodamine, RhB) onto the surface of MoS2 quantum dots (QDs). In this multifunctional fluorescent nanoprobe, MoS2 QDs serve not only as nanocarrier for the targeting ligand and pH fluorescent indicator, but also as a fluorescent reference for the ratiometric signal. Indeed, the fluorescence intensity of the MoS2 QDs is highly resistant to increasing proton concentrations, while that of RhB is sensitive to pH. Ratiometric detection of pH was carried out by comparing the pH-sensitive fluorescence of the RhB-based group with the pH-resistant fluorescence of MoS2 QDs. After uptake in living cells, the nanoprobe could stain mitochondria specifically, and allowed to image and monitor pH in mitochondria in a satisfactory manner.

Photoinduced Hole Hopping across CdS Quantum Dot Surfaces for Photoelectrochemical Water Oxidation

Photoinduced Hole Hopping across CdS Quantum Dot Surfaces for Photoelectrochemical Water Oxidation

The impact of chemical composition of halide surface ligands on the electronic structure and stability of lead sulfide quantum dot materials.

There is a high fundamental interest in the surface and bulk chemistry of quantum dot (QD) solids, as they have proven to be very promising materials in optoelectronic devices. The choice of surface ligands for quantum dots in solid devices determines many of the film properties, as the ligands influence for example the doping density, chemical stability and charge transport. Lead halide ligands have developed as the main ligand of choice for lead sulfide quantum dots, as they have been shown to passivate quantum dot surfaces and enhance the chemical stability. In this study, we successfully varied the ligand composition on the surface of PbS quantum dot films from pure lead iodide to pure lead bromide and investigated its influence on the chemical and electronic structure of the QD solids using hard X-ray photoelectron spectroscopy (HAXPES). Furthermore, we developed a surface treatment to prevent the surface oxidation of a bulk PbS reference sample. Through measurements of this sample and of lead halide reference samples, we were able to assign the contributions of different chemical bonding to the Pb 4f core level and of different atomic orbitals to the valence band spectral shape of the QD materials. Overall, we found that the valence band edge position was very similar for all different iodide:bromide ratios and that all investigated compositions were able to protect the quantum dot surfaces within solid films from oxidation. However, the ligand composition significantly influences the sample stability under X-rays. The iodide rich QD solids showed the highest stability with very little to no chemical changes over several hours of X-ray exposure, while the bromide rich QD solids changed already within the first hour of exposure.

One-pot synthesis of stable and functional hydrophilic CsPbBr3 perovskite quantum dots for "turn-on" fluorescence detection of Mycobacterium tuberculosis.

All-inorganic CsPbBr3 perovskite quantum dots (QDs) are widely studied owing to their excellent optoelectronic properties; however, they are usually hydrophobic and unstable in water and thus their biomedical applications are seriously limited. In this study, stable and hydrophilic CsPbBr3 QDs functionalized with carboxyl groups (CsPbBr3-COOH QDs) were prepared in one-pot with the aid of new ligands amino-poly(ethylene glycol)-carboxyl and perfluorooctyltriethoxylsilane. The aqueous solution of CsPbBr3-COOH QDs maintained the initial fluorescence intensity after 8 days of storage; the free carboxyl groups on the surface of CsPbBr3-COOH QDs were covalently conjugated with amino-terminal DNA to construct CsPbBr3 QDs-DNA probes for subsequent application. Then, a biosensing platform utilizing fluorescence resonance energy transfer between hydrophilic CsPbBr3 QDs-DNA and MoS2 nanosheets was developed for the sensitive and selective detection of the Mycobacterium tuberculosis DNA with a low limit of detection of 51.9 pM and the identification of drug-resistant clinical strains. This study advances the preparation of hydrophilic carboxyl-functionalized CsPbBr3 QDs with enhanced stability and extends their application in biomolecule detection.

Synthesis of surface dual-template molecularly imprinted silica nanoparticles for extraction of ciprofloxacin and norfloxacin

Synthesis of selective dual-template molecularly imprinted silica nanoparticles (MI-SiNPs) on the surface of graphene quantum dots (GQDs) for the simultaneous extraction of ciprofloxacin (CIP) and norfloxacin (NOR) from biological samples.

Atomic Layer Deposition of Diethylzinc/Zinc Oxide on Inas Surface Quantum Dots: Self-Clean-Up and Passivation Processes

Atomic Layer Deposition of Diethylzinc/Zinc Oxide on Inas Surface Quantum Dots: Self-Clean-Up and Passivation Processes

Synthesis and Characterization of Silver Nanoparticle Zingiber Officinale Extract and their Antibacterial Activity

A commercial accessible noble metal such as Silver exhibits essentially distinct chemical, physical and Biological properties. Today Nano size material have more because of more fascination increase its small size particle dimension, high surface area and quantum dot effect so it give it give wide scope of utilization in drug, catalytical Industry. In past decay, focus on their catalytic, optical and electromagnetic and magnetic application of silver Nano size material. We are utilized green route to synthesis silver Nano size material of Zingiber Officinale extract by using sohelate extraction methods and collected sample using vacuum rotavapour method and characterization for their application observe in different distinct field.

CdSe/ZnS quantum dots capped with oleic acid and L-glutathione: Structural properties and application in detection of Hg2+

Two structures of CdSe/ZnS quantum dots (QDs), with different solubility properties, were prepared, characterized, and applied as fluorescent-based probes to detect Hg2+ ions. From oleic acid-capped CdSe/ZnS QDs (CdSe/ZnS/OA), glutathione-capped CdSe/ZnS QDs (CdSe/ZnS/GSH) were obtained by a ligand exchange reaction upon microwave radiation. X-ray diffraction (XRD), Fourier-Transform Infrared (FT-IR), and X-ray Photoelectron Spectroscopy (XPS) were employed to determine crystallinity, structural characteristics, and chemical composition according to the capping agent. Synthesis methodology produced nanocrystals with cubic zinc blende structure. The coordination mode between the carboxylate group of oleic acid (OA) and the thiol group of glutathione (GSH), and the Zn2+ ions of QDs surface was discussed. Ultraviolet-visible (UV–Vis) spectroscopy and photoluminescence (PL) measurements characterized the optical properties of QDs. The replacement of OA by GSH ligands on QDs surface produced a red-shift of the first absorption maximum and the emission band. Photoluminiscence quantum yield (PL QY) improved from 20% (for CdSe/ZnS/OA) to 26% (for CdSe/ZnS/GSH). The fluorescence (FL) quenching of Hg2+ induction was studied considering the solubility properties of the two structures of QDs. Measurements for hydrophobic CdSe/ZnS/OA QDs were realized in a heterogeneous medium composed of toluene and water. While for CdSe/ZnS/GSH, experiments were carried out in an aqueous solution. Hg2+ ions quenched 100% fluorescence of both structures of QDs, displaying high selectivity, rapid response time. The limit of detection (LOD) for CdSe/ZnS/OA was 74.8 nM and for CdSe/ZnS/GSH was 54.8 nM. Results indicate that the two CdSe/ZnS core/shell QDs are candidates for Hg2+ and other metal ions sensing.

Highly Emissive Blue Quantum Dots with Superior Thermal Stability via In Situ Surface Reconstruction of Mixed CsPbBr3 -Cs4 PbBr6 Nanocrystals.

Although metal halide perovskites are candidate high‐performance light‐emitting diode (LED) materials, blue perovskite LEDs are problematic: mixed‐halide materials are susceptible to phase segregation and bromide‐based perovskite quantum dots (QDs) have low stability. Herein, a novel strategy for highly efficient, stable cesium lead bromide (CsPbBr3) QDs via in situ surface reconstruction of CsPbBr3–Cs4PbBr6 nanocrystals (NCs) is reported. By controlling precursor reactivity, the ratio of CsPbBr3 to Cs4PbBr6 NCs is successfully modulated. A high photoluminescence quantum yield (PLQY) of >90% at 470 nm is obtained because octahedron CsPbBr3 QD surface defects are removed by the Cs4PbBr6 NCs. The defect‐engineered QDs exhibit high colloidal stability, retaining >90% of their initial PLQY after >120 days of ambient storage. Furthermore, thermal stability is demonstrated by a lack of heat‐induced aggregation at 120 °C. Blue LEDs fabricated from CsPbBr3 QDs with reconstructed surfaces exhibit a maximum external quantum efficiency of 4.65% at 480 nm and excellent spectral stability.

Improvement of monodispersity and shape symmetry of silica shell for PbS quantum dots by introducing surface silanization and adjusting reverse micelle size

Semiconductor quantum dots (QDs) are one of the promising constituent materials of quantum information processing devices. The technique of silica coating of colloidal QDs using the reverse micelle method has been realized for improving position controllability, but the problem is that monodispersity and shape symmetry deteriorate when increasing the coating thickness. In this paper, we report three effective ways to achieve large silica-coated QDs with solving this problem, i.e. proper silanization on the QD surface, control of reverse micelle size by adjusting the amount of QD solvent, and two-step formation of silica shell. Proper substitution of ligands on the QD surface in the early stages of silica shell formation was important for uniform coating reaction. An amount of toluene as QD solvent determined the size of reverse micelles during the silica shell formation. There was an optimum combination of inverse micelle size and silica shell size to obtain silica-coated QDs with good monodispersity and high shape symmetry. We succeeded in growing the thick silica shell with expanding reverse micelle size by additionally supplying toluene with the raw material using the optimum silica-coated QDs as a growth nucleus.

Energetic Sulfide Vapor‐Processed Colloidal InAs Quantum Dot Solids for Efficient Charge Transport and Photoconduction

The energetic sulfide vapor process on colloidal indium arsenide (InAs) quantum dots (QDs) for integrated optoelectronic devices is demonstrated. X‐ray photoemission spectroscopy supports the presence of sulfur on QD surface, which increases the air stability, and ultraviolet photoemission spectroscopy and field‐effect transistor analysis confirm n‐type charge transport of corresponding QD films with higher electron mobilities. Photoconductivity of the same devices in near‐infrared wavelength shows gate bias‐dependent recombination of photogenerated carriers, coming from charge accumulation and depletion transition of QD channels. The synergetic approach of the vapor process on colloidal QD solids opens a promising opportunity for scalable and complementary metal‐oxide semiconductor‐compatible optoelectronic devices.

Increased selenium concentration in the synthesis of CdSe magic-sized quantum dots affects how the brain responds to oxidative stress.

CdSe magic-sized quantum dots (MSQDs) have been widely used as fluorescent probes in biological systems due to their excellent optical properties with a broader fluorescence spectrum and stable luminescence in biological media. However, they can be cytotoxic and alter the redox balance depending on the amounts of Cd2+ adsorbed on their surface. Thus, the present study aimed to evaluate whether increases in selenium concentration in the synthesis of CdSe-MSQDs decrease the oxidative stress caused by Cd2+ -based quantum dots. CdSe-MSQDs synthesized with different concentrations of selenium were investigated against oxidative stress in the brain of chicken embryos by examining total antioxidant capacity, lipid peroxidation, thiol, and glutathione contents, as well as the activities of glutathione peroxidase, superoxide dismutase (SOD), catalase (CAT), and glutathione reductase. In addition, the vascularization of the chorioallantoic membrane (CAM) analysis was performed. Higher selenium concentrations alter the surface defect levels (decrease free Cd2+ ) and controlled the oxidative effects of CdSe-MSQDs by reducing the lipid peroxidation, restoring the glutathione defense system and the antioxidant enzymes SOD and CAT, and maintaining the vascular density of the CAM. The current findings reinforce the study of the effects of the presence of Cd2+ ions on the surface of quantum dots, changing toxicity, and aiming interesting strategies of nanomaterials in biological systems.

Quantum dot photoluminescence as a versatile probe to visualize the interaction between plasma and nanoparticles on a surface

We experimentally demonstrate that the interaction between plasma and nanometer-sized semiconductor quantum dots (QDs) is directly connected to a change in their photoluminescence (PL) spectrum. This is done by taking in situ, high resolution, and temporally resolved spectra of the light emitted by laser-excited QDs on an electrically floating sample exposed to a low pressure argon plasma. Our results show a fast redshift of the PL emission peak indicating the quantum-confined Stark effect due to plasma-generated excess charges on the substrate and near the QD surface, while other plasma-induced (thermal and ion) effects on longer timescales could clearly be distinguished from these charging effects. The presented results and method open up pathways to direct visualization and understanding of fundamental plasma–particle interactions on nanometer length scales.

Effects of Parity and Symmetry on the Aharonov-Bohm Phase of a Quantum Ring.

We experimentally investigate the properties of one-dimensional quantum rings that form near the surface of nanowire quantum dots. In agreement with theoretical predictions, we observe the appearance of forbidden gaps in the evolution of states in a magnetic field as the symmetry of a quantum ring is reduced. For a twofold symmetry, our experiments confirm that orbital states are grouped pairwise. Here, a π-phase shift can be introduced in the Aharonov–Bohm relation by controlling the relative orbital parity using an electric field. Studying rings with higher symmetry, we note exceptionally large orbital contributions to the effective g-factor (up to 300), which are many times higher than those previously reported. These findings show that the properties of a phase-coherent system can be significantly altered by the nanostructure symmetry and its interplay with wave function parity.

Enhancement of biexciton generation via resonance energy transfer in nanoclusters of colloidal CdTe quantum dots for optical gain applications

Colloidal CdTe quantum dots (QDs) of two different sizes (2.7 nm and 3.7 nm diameter) were self-assembled into mixed quantum dot donor-acceptor nanoclusters (QDANs) in aqueous solution. The ratio of small QDs (SQDs) to large QDs (LQDs) was 10:1, and the assembly was mediated by electrostatic attraction between oppositely-charged ligands (thioglycolic acid, TGA, and mercaptoethylamine, MA) on the QD surfaces. Under low excitation fluence (well below the threshold for biexciton formation), photoluminescence (PL) emission spectra and time-resolved decays in the QDANs revealed quenching in the SQDs and enhanced emission from the LQDs, providing evidence for resonance energy transfer (RET) from the wider band gap SQDs to the narrower band gap LQDs. The observed RET rate constant, determined from comparison of decays of free SQDs and those in the QDANs, was (3.4 ns)−1. Under these low-fluence conditions, the PL emission lifetimes of the LQDs in QDANs were the same as the free LQDs. Under higher excitation intensity, the decay of the LQDs in the QDAN showed a new, fast (sub-nanosecond), fluence-dependent component, suggesting formation of biexcitons and multiexcitons on the LQDs. The free LQDs required significantly (approximately 4-fold) higher excitation intensity than those in the QDANs to show similar evidence of biexciton formation through lifetime shortening. Since the QDANs contained a 10-fold excess of SQDs, the excitation energy that was initially distributed over the full population of QDs was funneled and concentrated into the small number of LQDs. These results support the idea that optical gain through biexciton formation can be enhanced by using RET, even when the rate constant for RET is much lower than that for biexciton decay.