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European Microscopy Congress 2016: Proceedings || Studying membrane proteins in intact cells using nanoparticle labels and liquid-phase electron microscopy
摘要： Cells have receptor proteins in their plasma membranes ‘listening’ to chemical signals from the outside world. These signals consist of ligands, small molecules that bind specifically to a receptor. But how those signals are interpreted and lead to decisions is incompletely understood mainly on account of limitations of present analytical methods. It is typically extremely difficult to directly see how endogenously expressed individual proteins respond to ligand binding in the intact cell, which can lead, for example, to the formation of protein complexes triggering signaling processes. Much knowledge about cellular function has been obtained via biochemical methods but these analyze pooled material from many thousands of cells and the knowledge is thus based on population averages. But we need to look at the individual cell in order to understand the fundamentals of how a cell interprets a signal. Studying membrane proteins at the nanoscale in intact eukaryotic cells is now possible using liquid-phase scanning transmission electron microscopy (STEM) [1, 2]. The key step is to specifically label the proteins of interest in a one-to-one ratio with small probes combined with nanoparticles, for example, gold nanoparticles or quantum dots. Cells in liquid are then placed in a microfluidic chamber enclosing the sample in the vacuum of the electron microscope, and are imaged with STEM. It is not always necessary to enclose the cells in the microfluidic chamber. For some studies, it is sufficient to obtain information from the thin outer regions of the cells, and those can be imaged with high resolution using environmental scanning electron microscopy (ESEM) with STEM detector [3]. Liquid-phase STEM was used to explore the formation of the epidermal growth factor HER2 at the single-molecule level in intact SKBR3 breast cancer cells in liquid state [4]. HER2 is a membrane protein and plays an important role in breast cancer aggressiveness and progression. Data analysis based on calculating the pair correlation function from individual HER2 positions revealed remarkable differences in functionality between different cellular regions, and between cells with possible relevance for studying cancer metastasis and drug response.
关键词： quantum dots,STEM,ESEM,whole cells,liquid-phase,EGFR,HER2
更新于2025-09-23 15:21:21
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Polyoxometalate as Control Agent for the Doping in HgSe Self-Doped Nanocrystals
摘要： Intraband and plasmonic transitions have appeared over the last years as an interesting tool to achieve optical absorption in the mid infrared. Tuning the doping magnitude has become a major challenge not only to tune the optical spectrum but also properties such as the dark current or the time response. Here we investigate the case of self-doped HgSe colloidal quantum dots (CQDs). Tuning of the doping was so far relying on band bending induced by a dipole design at the nanoparticle surface. With such a surface gating approach, it is difficult to conciliate both the massive tuning of the Fermi level with the preservation of transport properties of the CQD arrays. Here we propose a strategy to graft functionalized polyoxometalates (POMs) at the CQD surface and obtain simultaneously a massive tuning of the carrier density (≈5 electrons per nanoparticle) and conduction properties. We bring a consistent demonstration of the HgSe CQD doping decrease by a charge transfer to the POM. This method is highly promising for large tuning of carrier density in degenerately doped semiconductor nanoparticles.
关键词： Intraband,mid infrared,charge transfer,polyoxometalates,plasmonic transitions,doping control,HgSe colloidal quantum dots
更新于2025-09-23 15:21:21
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Long Exciton Dephasing Time and Coherent Phonon Coupling in CsPbBr <sub/>2</sub> Cl Perovskite Nanocrystals
摘要： Fully-inorganic cesium lead halide perovskite nanocrystals (NCs) have shown to exhibit outstanding optical properties such as wide spectral tunability, high quantum yield, high oscillator strength as well as blinking-free single photon emission and low spectral diffusion. Here, we report measurements of the coherent and incoherent exciton dynamics on the 100 fs to 10 ns timescale, determining dephasing and density decay rates in these NCs. The experiments are performed on CsPbBr2Cl NCs using transient resonant three-pulse four-wave mixing (FWM) in heterodyne detection at temperatures ranging from 5 K to 50 K. We found a low-temperature exciton dephasing time of 24.5±1.0 ps, inferred from the decay of the photon-echo amplitude at 5 K, corresponding to a homogeneous linewidth (FWHM) of 54±5 μeV. Furthermore, oscillations in the photon-echo signal on a picosecond timescale are observed and attributed to coherent coupling of the exciton to a quantized phonon mode with 3.45 meV energy.
关键词： quantum dots,coherence,four wave mixing,nanocrystals,heterodyne detection,Perovskite,T2,lead halide,photon echo,phonons
更新于2025-09-23 15:21:21
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Electron–hole correlations govern Auger recombination in nanostructures
摘要： The fast nonradiative decay of multiexcitonic states via Auger recombination is a fundamental process affecting a variety of applications based on semiconductor nanostructures. From a theoretical perspective, the description of Auger recombination in confined semiconductor nanostructures is a challenging task due to the large number of valance electrons and exponentially growing number of excited excitonic and biexcitonic states that are coupled by the Coulomb interaction. These challenges have restricted the treatment of Auger recombination to simple, noninteracting electron–hole models. Herein we present a novel approach for calculating Auger recombination lifetimes in confined nanostructures having thousands to tens of thousands of electrons, explicitly including electron–hole interactions. We demonstrate that the inclusion of electron–hole correlations are imperative to capture the correct scaling of the Auger recombination lifetime with the size and shape of the nanostructure. In addition, correlation effects are required to obtain quantitatively accurate lifetimes even for systems smaller than the exciton Bohr radius. Neglecting such correlations can result in lifetimes that are 2 orders of magnitude too long. We establish the utility of the new approach for CdSe quantum dots of varying sizes and for CdSe nanorods of varying diameters and lengths. Our new approach is the first theoretical method to postdict the experimentally known “universal volume scaling law” for quantum dots and makes novel predictions for the scaling of the Auger recombination lifetimes in nanorods.
关键词： semiconductor nanocrystals,quantum dots,excitons,auger recombination,biexcitons,nanorods
更新于2025-09-23 15:21:21
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Modified Nanopillar Arrays for Highly Stable and Efficient Photoelectrochemical Water Splitting
摘要： Atomically modified graphitic carbon nitride quantum dots (QDs), characterized by strongly increased reactivity and stability, are developed. These are deposited on arrays of TiO2 nanopillars used as a photoanode for the photoelectrochemical water splitting. This photoanode shows excellent stability, with 111 h of continuous work without any performance loss, which outperforms the best-reported results by a factor of 10. Remarkably, our photoanode produces hydrogen even at zero bias. The excellent performance is attributed to the enhancement of photoabsorption, as well as to the promotion of charge separation between TiO2 nanopillars and the QDs.
关键词： hydrogen evolution,quantum dots,graphitic carbon nitride,photoelectrochemistry,TiO2 nanopillars
更新于2025-09-23 15:21:21
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The optical response of self-organized Ag-CdTe metal-semiconductor hybrid nanostructures: Change in interaction vs number density variation
摘要： Using experimental results and a theoretical model, we establish a relation for the optical response of a mixed nanocolloid. We show that colloids prepared by mixing metal and semiconductor nanocolloids in various ratios result in a mixture composed of a particular metal-semiconductor hybrid nanostructure and unattached original particles. Thus, the properties of hybrid samples prepared by such self-organized growth are decided by the variation in number density of the hybrid and the unattached particles and not due to a continuous change in the interaction between metal nanoparticles and semiconductor quantum dots as was assumed earlier. Using these results, a method to prepare a single type of hybrid nanostructure by measuring only its optical response is presented.
关键词： nanoparticles,metal-semiconductor hybrid nanostructures,optical response,quantum dots,self-organized growth
更新于2025-09-23 15:21:21
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Estimation of the lateral dimensions of epitaxial submonolayer CdSe/ZnSe quantum dots
摘要： CdSe fractional monolayer quantum dots (FMQDs) embedded in a ZnSe matrix were produced by atomic layer epitaxy with a nominal coverage of 0.5 monolayer. They have a thickness of a/2, where a is the strained perpendicular lattice constant of cubic CdSe. Their photoluminescence spectra at low temperature exhibit narrow and intense excitonic emission around 2.759 eV. Based on the experimental excitonic emission energy and applying the factorized-envelope approximation, we have estimated that the lateral dimensions of these FMQDs are around 4 - 5 nm and their density is ~ 3 × 1012 cm-2.
关键词： quantum dots size,fractional monolayer quantum dots,epitaxial quantum dots,submonolayer quantum dots,ultra-thin quantum dots,CdSe quantum dots
更新于2025-09-23 15:21:01
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Hybrid of quantum dots for interfacial tension reduction and reservoir alteration wettability for enhanced oil recovery (EOR)
摘要： Nanoparticle stabilized emulsions in enhanced oil recovery are more attractive and practical than conventional emulsions which stabilized by colloidal particles and different surfactants due to their advantages and special characteristics such as high stability in harsh condition, move long distance in reservoirs without high retention due to small size of nanoparticles. Only one third of original oil in place (OIP) is usually produced and two third of oil in place will be trapped to reservoir rockthus suitable chemical enhanced oil recovery (C-EOR) methods should be used. In this research, we have suggested a novel, economical and commercial method for synthesis N-doped graphene quantum dots (N-GQDs)/MoS2 quantum dots (MQDs) nanohybrids for preparing different percentage of Nanoemulsions which can reduce alterfacial tension significantly so it can used for Enhanced Oil Recovery (EOR) application. MoO3 material was used as a base of MQDs. MQDs was synthesized via exfoliation of MoS2 nanoparticles by Butyl lithium under N2 atmosphere condition. N-GQDs were synthesized by citric acid and urea materials via hydrothermal method. GQDs/MQDs were prepared via a simple sol-gel method for 5 h string. Synthetic materials were characterized with X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV–visible absorption, Scanning Microscopic Electron (SEM), EDX profile and mapping, Transmission electron microscopy (TEM), High Resolution Transmission electron microscopy (HRTEM) and differential scanning calorimetry (DSC). Then, emulsions were prepared with two different cationic and anionic surfactants and the stability and morphology of emulsion droplets were investigated in condition close to reservoir environment. Our results show that 10% GQDs/MQDs in cationic surfactant and 50% GQDs/MQDs in anionic surfactant have good stability and very small and fine emulsion droplets in simulated reservoir conditions in laboratory. The Interfacial Tension (IFT) measurement shows N70% improvement which indicates the high ability of these nanohybrids in reducing the surface tension than previous nanohybrids. Contact angle values show that these nanohybrids can alter the wettability of reservoir rock from oil-wet to water-wet so the trapped oil in the porous region of rock can be easily extracted in the presence of a layer of these nanohybrids. Furthermore, according to the results of altering the density and viscosity of nanohybrids, these are not as limiting parameters and only about 1% increasing observed for density and viscosity, respectively. Coreflooding test revealed the high oil recovery efficiency (22%) at very low nanofluid concentration (0.01 wt%).
关键词： Molybdenum disulfide quantum dots,Graphene quantum dots,Nanohybrids emulsion,Enhanced oil recovery (EOR),Quantum dot hybrids,Rock reservoir alteration wettability
更新于2025-09-23 15:21:01
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Role of shell composition and morphology in achieving single-emitter photostability for green-emitting a??gianta?? quantum dots
摘要： The use of the varied chemical reactivity of precursors to drive the production of a desired nanocrystal architecture has become a common method to grow thick-shell graded alloy quantum dots (QDs) with robust optical properties. Conclusions on their behavior assume the ideal chemical gradation and uniform particle composition. Here, advanced analytical electron microscopy (high-resolution scanning transmission electron microscopy coupled with energy dispersive spectroscopy) is used to confirm the nature and extent of compositional gradation and these data are compared with performance behavior obtained from single-nanocrystal spectroscopy to elucidate structure, chemical-composition, and optical-property correlations. Specifically, the evolution of the chemical structure and single-nanocrystal luminescence was determined for a time-series of graded-alloy “CdZnSSe/ZnS” core/shell QDs prepared in a single-pot reaction. In a separate step, thick (～6 monolayers) to giant (>14 monolayers) shells of ZnS were added to the alloyed QDs via a successive ionic layer adsorption and reaction (SILAR) process, and the impact of this shell on the optical performance was also assessed. By determining the degree of alloying for each component element on a per-particle basis, we observe that the actual product from the single-pot reaction is less “graded” in Cd and more so in Se than anticipated, with Se extending throughout the structure. The latter suggests much slower Se reaction kinetics than expected or an ability of Se to diffuse away from the initially nucleated core. It was also found that the subsequent growth of thick phase-pure ZnS shells by the SILAR method was required to significantly reduce blinking and photobleaching. However, correlated single-nanocrystal optical characterization and electron microscopy further revealed that these beneficial properties are only achieved if the thick ZnS shell is complete and without large lattice discontinuities. In this way, we identify the necessary structural design features that are required for ideal light emission properties in these green-visible emitting QDs.
关键词： green-emitting,photostability,quantum dots,morphology,giant quantum dots,shell composition
更新于2025-09-23 15:21:01
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A generalised approach to calculate various transport observables for a linear array of series and parallel quantum dots
摘要： A systematic generalised approach to ?nd transport observables for a linear array of different quantum dot (QD) systems has been discussed, using non-equilibrium Green function (NEGF) formalism, in the presence of on-dot Coulomb interaction and inter-dot tunnelling. The equation of motion (EOM) method has been used to derive expressions for Green functions (GFs) within the simplest mean-?eld approximation to tackle the Coulomb correlation term. Starting from the mathematical structures of GFs for single, double and triple quantum dot systems, the expressions for GFs and transport observables have been generalised for the quantum dot systems containing N number of quantum dots in series as well as parallel linear array of dots. Further, the formulae so obtained have been used for numerical calculations of transmission probability and the I –V characteristics of linear arrays of quantum dots in series as well as parallel con?guration containing up to three dots. The results show that, with the increase in number of dots in the scattering region, transmission probability and electron current decrease in series case, while both quantities increase in parallel con?guration of dots. The inter-dot tunnelling leads to the splitting of transmission peaks in double QD system in series case whereas, it induces Fano effect in triple QD system in parallel con?guration.
关键词： quantum dots,Quantum transport,non-equilibrium Green function,Landauer–Buttiker formula,linear array of dots
更新于2025-09-23 15:21:01