Combination Of Quantum Dots Research Articles

Boosting External Quantum Efficiency of Blue Perovskite QLEDs Exceeding 23% by Trifluoroacetate Passivation and Mixed Hole Transportation Design.

Perovskite quantum dot-based light-emitting diodes (QLEDs) have been considered a promising display technology due to their wide color gamut for authentic color expression. Currently, the external quantum efficiency (EQE) for state-of-the-art blue perovskite QLEDs is about 15%, which still lags behind its green and red counterparts (>25%) and blue film-based LEDs. Here, blue perovskite QLEDs that achieve an EQE of 23.5% at 490nm is presented, to the best knowledge, which is the highest value reported among blue perovskite-based LED fields. This impressive efficiency is achieved through a combination of quantum dot (QD) passivation and optimal device design. First, blue mixed halide perovskite CsPbCl3- xBrx QDs passivated by trifluoroacetate exhibit excellent exciton recombination behavior with a photoluminescence quantum yield of 84% due to reducing uncoordinated Pb surface defects. Furthermore, the device is designed by introducing a mixed hole-transport layer (M-HTL) to increase hole injection and transportation capacity and improve carrier balance. It is further found that M-HTL can decrease carrier leakage and increase radiative recombination in the device, evidenced by the visual electroluminescence spectrum at 2.0V. The work breaks through the EQE gap of 20% for blue perovskite-based QLEDs and significantly promotes their commercialization process.

Unique dynamics and exocytosis properties of GABAergic synaptic vesicles revealed by three-dimensional single vesicle tracking

Maintaining the balance between neuronal excitation and inhibition is essential for proper function of the central nervous system. Inhibitory synaptic transmission plays an important role in maintaining this balance. Although inhibitory transmission has higher kinetic demands compared to excitatory transmission, its properties are poorly understood. In particular, the dynamics and exocytosis of single inhibitory vesicles have not been investigated, due largely to both technical and practical limitations. Using a combination of quantum dots (QDs) conjugated to antibodies against the luminal domain of the vesicular GABA transporter to selectively label GABAergic (i.e., predominantly inhibitory) vesicles together with dual-focus imaging optics, we tracked the real-time three-dimensional position of single GABAergic vesicles up to the moment of exocytosis (i.e., fusion). Using three-dimensional trajectories, we found that GABAergic synaptic vesicles traveled a shorter distance prior to fusion and had a shorter time to fusion compared to synaptotagmin-1 (Syt1)-labeled vesicles, which were mostly from excitatory neurons. Moreover, our analysis revealed that GABAergic synaptic vesicles move more straightly to their release sites than Syt1-labeled vesicles. Finally, we found that GABAergic vesicles have a higher prevalence of kiss-and-run fusion than Syt1-labeled vesicles. These results indicate that inhibitory synaptic vesicles have a unique set of dynamics and exocytosis properties to support rapid synaptic inhibition, thereby maintaining a tightly regulated coordination between excitation and inhibition in the central nervous system.

On the combination of quantum dots with near-infrared reflective base coats to maximize their urban overheating mitigation potential

Application of highly absorptive construction materials is proved to be one of leading causes of urban overheating in big cities. To avoid the excessive heat by the conventional construction materials, several advanced heat-rejecting coating technologies were developed during the last decades. The main idea behind heat-rejecting coatings is to have colder coatings with the same appearance and colour of conventional coatings. One of the existing technologies for heat-rejecting coatings are advanced coatings with high solar reflection in the infrared range or so-called cool coatings. Recently, re-emission of the visible-range light by nano-scale semiconductors, known as Quantum Dots (QDs), were introduced as another effective heat-rejecting technology. In this paper, we showed that QDs also demonstrate a very high solar transmission in the near-infrared range, and therefore, a highly near-infrared reflective base layer can significantly improve their cooling potential. The high transmission value in the near-infrared range is due to the low absorption coefficient in the wavelengths longer than absorption edge wavelength (i.e. the wavelength corresponding to the bandgap energy) in semiconductors. We show that surface temperature reduction potential of CdSe/ZnS QDs film through fluorescent cooling is about 2.5 °C, which could be increased by another 8.1 °C with a highly near-infrared reflective base layer in a typical sunny day.

Flexible Gas Sensing Fibre Based on Bismuthous Sulfide Nanobelts-Sensitized Graphene Nanoplatelets (GNPs) Nanocomposites

Introduction Gas sensors with high flexibility and favorable extensibility have increasingly attractive prospects. Conventional rigid ceramics or semiconductor-based gas sensors have restricted flexibility and ductility, limiting their use in flexible devices and wearable electronics. Flexible gas sensors possess broad application prospects in the fields of wearable electronics, artificial intelligence, medical health, etc. Two-dimensional (2D) layered nanomaterials have attracted attention due to unique properties, which possess tunable band gaps and excellent mobility inherently. For example, graphene is usually utilized as gas sensing material due to high specific surface area and high carrier mobility [1]. However, the properties of pristine graphene nanoplatelets (GNPs) are influenced by significant adsorption of oxygen in an air environment, leading to instability and carrier mobility recession, limiting the practical application of GNPs gas sensors in atmosphere. The combination of quantum dots or nanobelts and 2D materials could build sensitized nanocomposites, which improves sensing performance of gas sensors. Flexible and ultrafast-response nitrogen dioxide (NO2) gas sensors based on cotton fibre that applies the mechanism of coupling and hydrogen bonding interaction were prepared by facile layered dip-coating methods. The gas sensors were fabricated utilizing cotton fibre as flexible substrate and bismuth sulfide (Bi2S3) nanobelts-sensitized GNPs nanocomposites as sensing layer. The flexible gas sensing fibre demonstrated ultrafast and recoverable response (67 s/45 s for 500 ppb gas), good reproducibility and mechanical robustness. The favorable sensing performance and high flexibility of fibre gas sensors will open potential prospects in intelligent sensing system and wearable electronics. Experimental Preparation of coupling reagent modified cotton fibre: The cleansed fibre substrate was first modified by 3-aminopropyl) triethoxysilane (APTES: coupling reagent) via dipping in APTES ethanol solution, and then rinsed with deionized water and dried in drying oven (100 ℃, 15 min). The organic functional group in coupling agent can be combined with the fiber substrate, meanwhile the silanoxy group in coupling agent is reactive with inorganic substances. When coupling agent is positioned between fiber substrate and gas sensing layer, bonding structure of cotton fibre-coupling agent-sensing layer can be formed. Synthesis of Bi2S3 nanobelts-sensitized graphene nanoplatelets nanocomposites: Solvothermal method was used for Bi2S3 nanobelts synthesis reported in literatures [2]. And GNPs/Sodium laurylsulfonate (SDL) ethanol solution (solution A) and Bi2S3/polyethylene glycol (PEG) ethanol solution (solution B) were prepared for next synthesis. Finally, solution A were injected into solution B under magnetic stirring for six hours to prepare Bi2S3/GNPs nanocomposites. Flexible gas sensor fabrication: The modified fibre was dipped in Bi2S3/GNPs solution for 30 min through dip-coating method, then treated with Pb(NO3)2 for surface ligand exchange to remove insulating organic ligands capping on Bi2S3 surface, lastly annealed in drying oven (60 ℃, 30 min). Results and Conclusions The stereoscopic illustration of electronic fibre gas sensor is shown in figure 1 (a). After two steps dip-coating processes, modified layer and outer Bi2S3/GNPs nanocomposites layer were successively coated on the surface of cotton fibre. Figure 1 (b) shows cross-section structure of fiber-based gas sensors, illustrating bonding structure of fibre-coupling agent-sensing layer. As for Bi2S3/GNPs nanocomposites layer, the intermolecular hydrogen bond [3] between sulfonic groups (-SO3H) of SDL and hydroxyl groups (-OH) of PEG could contribute to the interfacial adhesion between substrate and sensing layer (figure 1 (c)). For one thing, cotton fiber has advantages of large specific surface area and rich skeletal structure, which helps the combination of fiber skeleton and sensing materials. For another, Bi2S3-sensitized GNPs nanocomposites constructed an excellent receptor-transducer gas-sensing layer. Considering the dual-mode characteristics of fast carrier transfer on graphene and strong adsorption of gas molecules in Bi2S3 nanobelts, fiber-based gas sensors demonstrated ultrafast and recoverable response (67 s/45 s for 500 ppb gas), good reproducibility and mechanical robustness (figure 1(f-g)). The device showed excellent reversibility and negligible baseline drift following cycling responses (figure 1(g)). Compared with recently reported fibre-based gas sensors (Figure 1(h)), fibre-based gas sensors showed significantly enhanced response and recovery time. This work indicates that the flexible gas sensing fibre could be used to establish wearable electronics and real-time atmosphere information monitoring system.

Passively Q-switched Nd-doped fiber laser based on PbS/CdS core/shell quantum dots as a saturable absorber.

In our work, PbS/CdS core/shell quantum dots with an absorption peak of 1043nm were successfully employed as a modulator for achieving a passively Q-switched Nd-doped fiber laser. The saturation intensity and modulation depth of the film-type modulator were 7.6 MW/cm2 and 4.1%, respectively. Due to the protection of the CdS shell, the PbS core exhibited good photo-chemical stability, which led to the generation of stable passively Q-switched operation. The maximum average output power was 7.88mW with a minimum pulse width of 235.7ns. To our knowledge, this was the first demonstration focusing on the combination of quantum dot and Nd-doped fiber laser; in addition, 235.7ns was the narrowest pulse width of a passively Q-switched Nd-doped fiber laser. Our results highlighted the excellent nonlinear absorption properties of PbS/CdS core/shell quantum dots and give significant guidance for future optical applications of quantum dots and demonstrations of pulsed Nd-doped fiber lasers.

Single quantum dot tracking reveals the impact of nanoparticle surface on intracellular state

Inefficient delivery of macromolecules and nanoparticles to intracellular targets is a major bottleneck in drug delivery, genetic engineering, and molecular imaging. Here we apply live-cell single-quantum-dot imaging and tracking to analyze and classify nanoparticle states after intracellular delivery. By merging trajectory diffusion parameters with brightness measurements, multidimensional analysis reveals distinct and heterogeneous populations that are indistinguishable using single parameters alone. We derive new quantitative metrics of particle loading, cluster distribution, and vesicular release in single cells, and evaluate intracellular nanoparticles with diverse surfaces following osmotic delivery. Surface properties have a major impact on cell uptake, but little impact on the absolute cytoplasmic numbers. A key outcome is that stable zwitterionic surfaces yield uniform cytosolic behavior, ideal for imaging agents. We anticipate that this combination of quantum dots and single-particle tracking can be widely applied to design and optimize next-generation imaging probes, nanoparticle therapeutics, and biologics.

Identification of the caveolae/raft-mediated endocytosis as the primary entry pathway for aquareovirus

Grass carp reovirus (GCRV), a member of the Aquareovirus genus in the Reoviridae family, is considered the most pathogenic aquareovirus. However, its productive viral entry pathways remain largely unclear. Using a combination of quantum dot (QD)-based live-virus tracking and biochemical assays, we found that extraction of cellular membrane cholesterol with methyl-β-cyclodextrin (MβCD) and nystatin strongly inhibited the internalization of GCRVs, and supplementation with cholesterol restored viral infection. In addition, the entry of the virus was restrained by genistein, an inhibitor known to block caveolar endocytosis. Subsequent real-time tracking experiments revealed that the QD-labeled GCRV particles were colocalized with caveolin-1, and transfection of cells with dominant-negative mutant (caveolin-1 Y14F) significantly reduced GCRV infection. In contrast, no effects on virus infection were detected when the clathrin-mediated endocytosis or the macropinocytosis inhibitors were used. Our results collectively suggest that aquareoviruses can use caveolae/raft-mediated endocytosis as the primary entry pathway to initiate productive infection.

A long-wavelength quantum dot-concentric FRET configuration: characterization and application in a multiplexed hybridization assay.

Quantum dot-based concentric Förster resonance energy transfer (cFRET) is a promising modality for the development of multifunctional fluorescent probes for bioanalysis and bioimaging. To date, the scope of cFRET has been largely limited to a prototypical configuration with a particular combination of quantum dot (QD) and fluorescent dyes linked through peptides. Expansion of the scope of cFRET is critical for its further development. Here, we expand the scope of cFRET in two capacities. First, we design and characterize a new long-wavelength cFRET configuration that combines red- and deep-red fluorescent dyes, Alexa Fluor 633 and Alexa Fluor 680, with an orange-emitting QD. Sequential and competitive energy transfer pathways are characterized through a rate analysis, where the balance of these rates more strongly favours competitive energy transfer in the new long-wavelength configuration versus sequential energy transfer in the previous prototypical configuration. Although the new cFRET configuration is more susceptible to photobleaching, its superior brightness and longer-wavelength excitation and emission provide an order of magnitude higher signal-to-background ratios in biological matrices (e.g., serum, blood) than the previous prototypical configuration. Second, we demonstrate that an oligonucleotide-linked, long-wavelength cFRET configuration has energy transfer similar to an analogous peptide-linked configuration, where the oligonucleotide-linked cFRET configuration can be combined with toehold-mediated strand displacement for the multiplexed detection of unlabeled nucleic acid targets as a single vector. Overall, this work establishes the general applicability of cFRET and introduces new strategies for its bioanalytical application.

Photovoltaic light absorber with spatial energy band gradient using PbS quantum dot layers

Using a combination of quantum dots (QDs) of different sizes, and thus different bandgaps, to extend the light-harvesting spectrum of a photovoltaic device in tandem architecture is a promising strategy for increasing the solar cell efficiency. In this study, we propose a new architecture for a solar cell device consisting of a graded-bandgap active layer made of lead sulfide QDs of different sizes and based on the structure of the Schottky junction. Colloidal PbS QDs with bandgaps of 1.55, 1.44, and 1.36eV were synthesized and used to construct a series of Schottky junction solar cells. Cells with a graded-bandgap active layer exhibited an increase in short-circuit current density (Jsc) but yielded lower open-circuit voltage (Voc) compared with cells having a uniform bandgap. We found that adding a thin electron energy-boosting layer (EEB) made from 1.55-eV-bandgap QDs can partially compensate for the thermalization loss, and thus enhance Jsc and recover Voc. Consequently, this study provides a conceptual basis for further improvement in colloidal QD-based solar cells.

Study of growth of dot and column in porous silicon samples of various thicknesses prepared at a constant current density

Porous silicon is considered to be composed either of spherical shaped interconnected silicon quantum dots or combination of quantum dots and columns. This paper presents a study of a series of porous silicon films of various thicknesses, prepared at a 20mA current density by the electrochemical etching technique. The photoluminescence spectra of the series samples were monitored. Further, we used a photoluminescence fitting model by Singh and John (John–Singh) in its extended form by Elhouichet to estimate the percentage of dots and columns; their average diameters and corresponding variances. The shape of experimental photoluminescence spectra fits well with John–Singh model. As a result, the analytical curves drawn using the fitting parameters showed the decrease in mean crystallite diameter of columns and dot while increase in variance of column and decrease in variance of dots. Hence, more homogenous dots are formed. Thus, it results in the formation of a more ordered nanocrystalline structure with more porosity. It verified the quantum assumptions. The discrepancy in the PL behavior of a sample is well explained by the model.

Quantum Dot Based Sensing Platform for Selective Detection of Volatile Organic Compounds and Biomarkers

Diagnosing and monitoring diseases such as lung cancer often involves expensive testing in advanced stages of disease development. If a low cost method to diagnose and monitor diseases such as lung cancer were available, earlier detection and improved prognosis would result. Diseases such as lung cancer and diabetes cause changes in body chemistry that result in the release of volatile organic biomarkers that are often very distinct and different than those of healthy patients. Therefore, appropriate noninvasive and low cost analysis of patients’ breath can lead to early diagnosis and monitoring. The objective of this research is to understand and improve new non-invasive selective sensors to quantify volatile organic biomarkers for improved health monitoring. These specialized sensors consist of quantum dots, dye, and a current collector. The dye becomes colored when exposed to volatile organic biomarkers without a significant difference in color for different biomarkers. However, when the dye is tethered to quantum dots and exposed to light, the color for each biomarker is quantifiably different. The quantum dots are semiconducting and facilitate the charge transfer event, which is directly related to biomarker concentration, that can be collected using nanostructures such as titania nanotubes on titanium metal. Thus, the combination of quantum dots, dye, and a current collector creates a sensitive and selective sensor for volatile organic biomarkers (VOBs), such as those associated with a variety of diseases.

Semiconductor Nanocrystal Quantum Dots as Solar Cell Components and Photosensitizers: Material, Charge Transfer, and Separation Aspects of Some Device Topologies

Nanocrystalline wide band gap semiconductors photosensitized with semiconductor nanocrystal quantum dots have recently attracted increasing attention as promising photovoltaic devices. This Perspective addresses several issues related to the choice of nanocrystal materials for quantum dot sensitized solar cells, the methods of quantum dot deposition on mesoporous wide band gap semiconductor layers, and combinations of quantum dots and classical ruthenium dyes as panchromatic sensitizers. It further discusses charge transfer kinetics and electron recombination in quantum dot sensitized solar cells. An alternate emerging concept, a structure combining the latter with a quantum dot based Schottky junction solar cell, is also briefly reviewed. Together these areas offer ample scope for improvements making use of the specific advantages of semiconductor nanocrystals.

New combination of quantum dots

New combination of quantum dots

Imaging of multiple mRNA targets using quantum dot based in situ hybridization and spectral deconvolution in clinical biopsies

Gene expression mapping using microarray analysis has identified useful gene signatures for predicting outcome. However, little of this has been translated into clinically effective diagnostic tools as microarrays require high quality fresh-frozen tissue samples. We describe a methodology of multiplexed in situ hybridization (ISH) using a novel combination of quantum dot (QD)-labeled oligonucleotide probes and spectral imaging analysis in routinely processed, formalin-fixed paraffin embedded human biopsies. The conditions for QD-ISH were optimized using a poly d(T) oligonucleotide in decalcified bone marrow samples. Single and multiplex QD-ISH was performed in samples with acute leukemia and follicular lymphoma using oligonucleotide probes for myeloperoxidase, bcl-2, survivin, and XIAP. Spectral imaging was used for post hybridization tissue analysis, enabling separation of spatially colocalized signals. The method allows quantitative characterization of multiple gene expression using non-bleaching fluorochromes. This is expected to facilitate multiplex in situ transcript detection in routinely processed human clinical tissue.

NEWS OF THE WEEK

THE SEMICONDUCTOR NANO particles known as quantum dots have moved closer to biological applications, according to two recent reports. In one paper, scientists at Cornell University, collaborating with Quantum Dot Corp. in Hayward, Calif., use quantum dots as a label for multiphoton imaging in live animals. In the other report, Japanese researchers use chaperone proteins to encapsulate and protect quantum dots, preventing them from aggregating and losing their size-dependent properties. Watt W.Webb, professor of applied physics at Cornell University, and his coworkers injected amphiphiliccoated quantum dots made of CdSe-ZnS intravenously into mice {Science, 300,1434 (2003)}. Using multiphoton microscopy, they obtained images of bloodvessels through skin and fat—tissues that are challenging for imaging because they scatter and absorb radiation. They could easily measure blood flow and detect heart rate direcdy through the skin. The combination of quantum dots and multiphoton microscopy(in which multiple low...