Types Of Quantum Dots Research Articles

Adverse Interactions of Luminescent Semiconductor Quantum Dots with Liposomes and Shewanella oneidensis.

Cadmium-containing luminescent quantum dots (QD) are increasingly used in display, bioimaging, and energy technologies; however, significant concerns have been raised about their potentially adverse impact on human health and the environment. This study makes use of a broad toolkit of analytical methods to investigate and increase our understanding of the interactions of luminescent cadmium-containing (CdSe) and cadmium-free (ZnSe) QD, with and without a passivating higher bandgap energy ZnS shell, with phospholipid vesicles (liposomes), which model bacterial membranes, and with Shewanella oneidensis MR-1, an environmentally relevant bacteria. A unique feature of this study is that all QD types have the same surface chemistry, being capped with uncharged poly(ethylene glycol) ligands. This enables focusing the study on the impact of the QD core on liposomes and bacterial cells. The study reveals that QD association with liposome and bacterial cell membranes is imperative for their adverse impact on liposomes and bacterial cells. The QD' concentration-dependent association with liposomes and bacterial cells destabilizes the membranes mechanically, which leads to membrane disruption and lysis in liposomes and to bacterial cell death. The study also shows that cadmium-containing QD exhibit a higher level of membrane disruption in bacterial cells than cadmium-free QD. ZnSe QD have low membrane impact, and coating them with a ZnS shell decreases their membrane disruption activity. In contrast, CdSe QD exhibit a high level of membrane impact, and coating them with a ZnS shell does not decrease, but in fact further increases, their membrane disruption activity. This behavior might be attributed to higher affinity and association of CdSe/ZnS QD with liposomes and bacterial cells and to a contribution of dissolved zinc ions from the ZnS shell to increased membrane disruption activity.

Fluorescent quantum dots for microbial imaging

Quantum dots (QDs), with several unique optical and chemical features, are becoming desirable fluorescent tags for the biological applications that require long-term and highly sensitive imaging. Besides, the conjugation of various functional biomolecules to QDs has enabled wide applications of QDs in biological imaging. This review focuses on the following four types of QDs: semiconductor quantum dots (semiconductor QDs), carbon nanodots (CDs), silicon quantum dots (SiQDs), and polymer dots (Pdots), and summarizes the recent advancements of using these QDs in imaging microorganisms including viruses, bacteria, and fungi. We hope that this review will promote the development of new fluorescent QDs for microbial imaging and extend the applications of QD-based imaging techniques in cell biology and beyond.

Antimicrobial and biocompatibility of highly fluorescent ZnSe core and ZnSe@ZnS core-shell quantum dots

Present study reports synthesis of Cd-free core-only and core-shell quantum dots (ZnSe of size 3.60 ± 0.12 nm and ZnSe@ZnS of size 4.80 ± 0.20 nm) having excellent fluorescent properties, stability, and aqueous solubility. The fluorescence behavior of these quantum dots (QDs) was utilized for cancer cell imaging and their comparative toxicity in cancerous (HeLa) and normal (HEK-293) cell lines was evaluated. The LC50 parameter of ZnSe (1.8 and 2.6 mg/ml) was significantly lower than that of ZnSe@ZnS (3.8 and 4.5 mg/ml) for the aforesaid cell lines which indicated higher toxicity of the core-only QD in comparison to the core-shell structure. Further, the cellular uptake and fluorescence intensity of core-shell QD was significantly higher. Furthermore, the antimicrobial property of both type of QDs was evaluated on microbes (Escherichia coli and Staphylococcus aureus) and core-shell structure was found to possess higher antimicrobial property towards gram-positive bacteria S. aureus, but was non-toxic to E. coli. These results suggested that surface modification of ZnSe with ZnS shell helps to enhance the fluorescence property and make these more biocompatible for biomedical applications. The non-toxicity towards E. coli also makes it suitable for labeling the microbial cell surface and for mapping the cellular metabolism.

Quasi‐White Light‐Emitting Devices Based on SiC Quantum Dots

White electroluminescence based on quantum dots (QDs) is usually realized by incorporating different types of QDs or QDs plus rare earth ion phosphors into a single device. Herein, we report quasi‐white electroluminescence in pure silicon carbide QDs‐based light‐emitting devices (LEDs). The carrier transport and recombination mechanisms are investigated through analyzing the current density versus bias curves and spatial distribution of energy levels. The carrier transport mechanism is dominated by quantum tunneling at low bias and direct injection at high bias, respectively. The quasi‐white electroluminescence arises from recombination of the injected electrons and holes in the SiC QDs in the devices.

Solvent-Controlled Synthesis of Highly Luminescent Carbon Dots with a Wide Color Gamut and Narrowed Emission Peak Widths.

Carbon dots (CDs) have tremendous potential applications in bioimaging, biomedicine, and optoelectronics. By far, it is still difficult to produce photoluminescence (PL) tunable CDs with high quantum yield (QY) across the entire visible spectrum and narrow the emission peak widths of CDs close to those of typical quantum dots. In this work, a series of CDs with tunable emission from 443 to 745 nm, quantum yield within 13-54%, and narrowed full width at half maximum (FWHM) from 108 to 55 nm, are obtained by only adjusting the reaction solvents in a one-pot solvothermal route. The distinct optical features of these CDs are based on their differences in the particle size, and the content of graphitic nitrogen and oxygen-containing functional groups, which can be modulated by controlling the dehydration and carbonization processes during solvothermal reactions. Blue, green, yellow, red, and even pure white light emitting films (Commission Internationale de L'Eclairage (CIE)= 0.33, 0.33, QY = 39%) are prepared by dispersing one or three kinds of CDs into polyvinyl alcohol with appropriate ratios. The near-infrared emissive CDs are excellent fluorescent probes for both in vitro and in vivo bioimaging because of their high QY in water, long-term stability, and low cytotoxicity.

Enhancement Mechanism of the Photoluminescence Quantum Yield in Highly Efficient ZnS–AgIn5S8 Quantum Dots with Core/Shell Structures

The optical properties of ZnS–AgIn5S8 quantum dots (QDs) with core/shell structures are examined to clarify the enhancement mechanism of the photoluminescence (PL) quantum yield (QY). Two types of QDs are synthesized by varying the concentration of zinc precursors, with alloyed-core (ZnS–AgIn5S8, ZAIS), inner-shell (ZnIn2S4, ZIS), and outer-shell (ZnS) structures, such as ZAIS/ZIS/ZnS and ZAIS/ZnS. Upon alloying/shelling processes from the preformed AgIn5S8 QDs, the evolution of the band gap energy indicates the formation of the solid solution of ZAIS. Due to the difference in the degree of alloying between ZAIS/ZIS/ZnS and ZAIS/ZnS QDs, the blue shift of PL, Stokes shift, and QY are different. The alloying/shelling processes improve the QY of the intrinsic defect states more effectively than the QY of the surface defect states, while the time-resolved studies suggest that the enhanced radiative rate of the intrinsic states is responsible for the improvement of the QY, in addition to the reduced nonradiat...

Transient Spectroscopy of Glass-Embedded Perovskite Quantum Dots: Novel Structures in an Old Wrapping

Abstract Semiconductor doped glasses had been used by the research and engineering communities as color filters or saturable absorbers well before it was realized that their optical properties were defined by tiny specs of semiconductor matter known presently as quantum dots (QDs). Nowadays, the preferred type of QD samples are colloidal particles typically fabricated via organometallic chemical routines that allow for exquisite control of QD morphology, composition and surface properties. However, there is still a number of applications that would benefit from the availability of high-quality glass-based QD samples. These prospective applications include fiber optics, optically pumped lasers and amplifiers and luminescent solar concentrators (LSCs). In addition to being perfect optical materials, glass matrices could help enhance stability of QDs by isolating them from the environment and improving heat exchange with the outside medium. Here we conduct optical studies of a new type of all-inorganic CsPbBr3 perovskite QDs fabricated directly in glasses by high-temperature precipitation. These samples are virtually scattering free and exhibit excellent waveguiding properties which makes them well suited for applications in, for example, fiber optics and LSCs. However, the presently existing problem is their fairly low room-temperature emission quantum yields of only ca. 1%–2%. Here we investigate the reasons underlying the limited emissivity of these samples by conducting transient photoluminescence (PL) and absorption measurements across a range of temperatures from 20 to 300K. We observe that the low-temperature PL quantum yield of these samples can be as high as ~25%. However, it quickly drops (in a nearly linear fashion) with increasing temperature. Interestingly, contrary to traditional thermal quenching models, experimental observations cannot be explained in terms of a thermally activated nonradiative rate but rather suggest the existence of two distinct QD sub-ensembles of “emissive” and completely “nonemissive” particles. The temperature-induced variation in the PL efficiency is likely due to a structural transformation of the QD surfaces or interior leading to formation of extremely fast trapping sites or nonemissive phases resulting in conversion of emissive QDs into nonemissive. Thus, future efforts on improving emissivity of glass-based perovskite QD samples might focus on approaches for extending the range of stability of the low-temperature highly emissive structure/phase of the QDs up to room temperature.

(Invited) Aggregation-Induced Emission in Lamellar Solids of Colloidal Perovskite Quantum Wells

The outstanding excitonic properties, including photoluminescence quantum yield (η PL), of individual, quantum-confined semiconductor nanoparticles are often significantly quenched upon aggregation, representing the main obstacle towards scalable photonic devices. Here we report aggregation-induced emission (AIE) phenomena in the lamellar solids containing layer-controlled colloidal quantum wells (CQWs) of hybrid organic-inorganic lead bromide perovskites, resulting in anomalously high solid-state of up to 94%. Upon forming the QW solids, we observe an inverse correlation between exciton lifetime and , clearly distinct from that in typical quantum dot solid systems. Our multiscale theoretical analysis reveals that in a lamellar solid, the collective motion of the surface organic cations are more restricted to orient along the [100] direction, thereby inducing a more direct bandgap that facilitates radiative recombination. Using the QW solids, we demonstrate ultra-pure green emission by completely downconverting a blue GaN light emitting diode (LED) at room temperature, with a luminous efficacy higher than 90 lm/W at 5,000 cd/m2, which has never been reached in any nanomaterial assemblies by far [1]. [1] Jagielski et al., Science Advances, accepted manuscript (2017)

Cadmium telluride quantum dots induce apoptosis in human breast cancer cell lines

Semiconductor quantum dots (QDs), especially those containing cadmium, have undergone marked improvements and are now widely used nanomaterials in applicable biological fields. However, great concerns exist regarding their toxicity in biomedical applications. Because of the lack of sufficient data regarding the toxicity mechanism of QDs, this study aimed to evaluate the cytotoxicity of three types of QDs: CdTe QDs, high yield CdTe QDs, and CdTe/CdS core/shell QDs on two human breast cancer cell lines MDA-MB468 and MCF-7. The breast cancer cells were treated with different concentrations of QDs, and cell viability was evaluated via MTT assay. Hoechst staining was applied for observation of morphological changes due to apoptosis. Apoptotic DNA fragmentation was visualized by the agarose gel electrophoresis assay. Flow cytometric annexin V/propidium iodide (PI) measurement was used for apoptosis detection. A significant decrease in cell viability was observed after QDs treatment ( p < 0.05). Apoptotic bodies and chromatin condensation was observed by Hoechst staining. DNA fragmentation assay demonstrated a DNA ladder profile in the exposed cells and also annexin V/PI flow cytometry confirmed apoptosis in a dose-dependent manner. Our results revealed that CdTe, high yield CdTe, and CdTe/CdS core/shell QDs induce apoptosis in breast cancer cell lines in a dose-dependent manner. This study would help realizing the underlying cytotoxicity mechanism, at least partly, of CdTe QDs and may provide information for the development of nanotoxicology and safe use of biological applications of QDs.

Quantum Dots based on Indium Phosphide (InP): the Effect of Chemical Modifications of the Organic Shell on Interaction with Cultured Cells of Various Origins

CdSe and CdTe-based semiconductor fluorescent nanocrystals, also called quantum dots (QDs), attract the attention of biologists due to their wide range of emission in a visible light interval, high fluorescence quantum yield and photostability. However, their application is limited because of possible toxicity of cadmium. Indeed, there is a probability of metal leakage from QDs cores as a result of damage of both inorganic and organic layers of shells covering QDs. An alternative to cadmium QDs could be nanostructures having as a core, for example, non-toxical indium phosphide (InP), also emitting in the visible region of the spectrum. At present, there is few works on the use of these particles in biology. In this study, a comparative analysis of the spectral-luminescent properties of two InP/ZnS-QDs samples coated with PEG carrying- COOH or -NH2 functional groups was performed. The obtained data were compared with the characteristics of CdSe/ZnS-QDs coated with PEG. The photophysical properties of all QDs in aqueous solution corresponded to the information claimed by manufacturers, but the fluorescence quantum yield of InP-based nanoparticles was found to be lower than that of CdSe-QDs. We also show that the photoluminescence of all types of QDs at pH 4.0 was lower than at pH 7.4, while the decrease in fluorescence intensity was minimal in the case of QDs-PEG-COOH. Studying the uptake of all three types of QDs by J774 macrophages, we found that the fluorescence spectra of internalized QDs do not change in comparison with those in solution. All three types of QDs after 24 hours of incubation were accumulated in the cells, but while QDs-NH2 and QDs without reactive groups were detected mainly in vesicular-like discrete structures, the QDs-COOH were diffusely distributed throughout the cytoplasm. This fact indicates different mechanisms of interaction with cell membranes. In nonphagocytic HeLa cells all types of QDs behaved similarly, but the overall level of cells fluorescence was much lower. This may be due to both reduced nonspecific uptake and possible quenching of QDs fluorescence in acidic endolysosomes. Cytofluorimetric analysis of propidium iodide accumulation showed that after 24 hours incubation with all studied types of QDs as well as in control (no QDs), the proportion of dead HeLa cells did not exceed 10%. Thus, it has been demonstrated that non-toxic InP-based QDs can be used as an effective tool for biological research.

Ratiometric fluorescence sensor for Fe3+ ions detection based on quantum dot-doped hydrogel optical fiber

We develop a novel ratiometric fluorescence sensor based on CdTe quantum dots (QDs) doped hydrogel optical fiber for selective and on-site detection of Fe3+ ions in real time. The hydrogel fiber is made of a core-cladding structure with a step-index profile to confine light within the core. Two types of QDs, the green emissive thioglycolic acid capped quantum dots (gQDs) and red emissive N-Acetyl-l-cysteine capped QDs (rQDs), are synthesized and incorporated in the core of the hydrogel fiber. The rQDs can be selectively quenched by the Fe3+ ions that diffuse into the hydrogel matrix while the gQDs are immune to Fe3+ ions and exhibit stable fluorescence emission. By ratiometric detection of the fluorescence intensities of the two QDs, quantitative and selective detection of Fe3+ ions is achieved in a linear range of 0–3.5 μM with a detection limit of 14 nM. The cladded hydrogel fiber doped with QDs enables efficient laser excitation and fluorescence collection in water. Our results reveal that the ratiometric sensing based on multi-QDs doped fiber can be feasibly applied for real-time and on-site analysis of heavy metal ions in aqueous environments.

Short-term assessment of cadmium toxicity and uptake from different types of Cd-based Quantum Dots in the model plant Allium cepa L.

We report on the toxicity and bioaccumulation of three different types of Cd-based quantum dots (QDs), dispersed in aqueous medium, for a model plant Allium cepa L. It is believed that encapsulation of nanoparticles should reduce their toxicity and increase their stability in different environments; in this work we studied how QD encapsulation affects their phytotoxicity. Core, core/shell, and core/shell/shell QDs (CdTe, CdTe/ZnS, and CdTe/CdS/ZnS QDs capped by 2-mercaptopropionic acid) were tested and CdCl2 was used as a positive control. After 24-h and 72-h exposure, total Cd content (MCd) and bioaccumulation factors (BAFs) were determined in all parts of A. cepa plants (roots, bulb, shoot), and the total length of the root system was monitored as a toxicity end-point. Measurements of total Cd content versus free Cd2+ content (with Differential Pulse Voltammetry, DPV) in exposure media showed differences in chemical stability of the three QD types. Correspondingly, selected QDs showed different toxicity for A. cepa and different Cd bioaccumulation patterns. CdTe QDs were the most toxic; their effect was similar to CdCl2 due to the release of free Cd2+, which was confirmed by the DPV measurements. Plants exposed to CdTe QDs also bioaccumulated the most Cd among all QD exposure groups. CdTe/ZnS QDs showed no toxicity and very low bioaccumulation of Cd in A. cepa; the main source of measured Cd in the plants were QDs adsorbed on their roots, which was confirmed by fluorescence microscopy. On the contrary, CdTe/CdS/ZnS QD toxicity and bioaccumulation patterns were similar to those of CdTe QDs and pointed to unstable CdS/ZnS shells.

The interactions of CdTe quantum dots with serum albumin and subsequent cytotoxicity: the influence of homologous ligands.

With spreading applications of fluorescent quantum dots (QDs) in biomedical fields in recent years, there is increasing concern over their toxicity. Among various factors, surface ligands play critical roles. Previous studies usually employed QDs with different kinds of surface ligands, but general principles were difficult to be obtained since it was hard to compare these surface ligands with varied chemical structures without common features. Herein, the physicochemical properties of two types of CdTe QDs were kept very similar, but different in the surface ligands with mercaptoacetic acid (TGA) and 3-mercaptopropionic acid (MPA), respectively. These two types of homologous ligands only had a difference in one methylene group (-CH2-). The interactions of the two types of CdTe QDs with bovine serum albumin (BSA), which was one of the main components of cell culture, were studied by fluorescence, UV-vis absorption, and circular dichroism spectroscopy. It was found that the fluorescence quenching of BSA by CdTe QDs followed a static quenching mechanism, and there was no obvious difference in the Stern-Volmer quenching constants and binding constants. The thermodynamic parameters of the two types of QDs were similar. BSA underwent conformational changes upon association with these QDs. By comparing the cytotoxicity of these two types of QDs, TGA-capped QDs were found to be less cytotoxic than MPA-capped QDs. Besides, in the presence of serum proteins, the cytotoxicity of the QDs was reduced. QDs in the absence of serum proteins had a higher internalization efficiency, compared with those in the medium with serum. To the best of our knowledge, this is a rare study focusing on surface ligands with such small variations at the biomolecular and cellular levels. These findings can provide new insights for the design and applications of QDs in complex biological media.

Terahertz resonance fluorescence and squeezing in quantum dots: Effects of external electric field and dimension

The resonance fluorescence and phase-dependent spectrum in a typical quantum dot under the influence of an external electric field with attention to intersubband transitions driven by a laser field is studied. Finding energy eigenvalues and functions of the system, optical transition rates and Rabi frequency are calculated and effects of an external electric field and quantum dimension on the resonance fluorescence, squeezing and population of energy levels are investigated. Results show the fluorescence characteristics in Terahertz region of electromagnetic radiation strongly depend on external field and quantum dot dimensions. It is possible to control the resonance fluorescence and related phenomena via external factors and precise engineering of the system.

One-pot synthesis of polythiol ligand for highly bright and stable hydrophilic quantum dots toward bioconjugate formation

A fast and efficient one-pot synthesis of thiol-terminated poly(vinylpirrolidone-co-maleic anhydride-co-ethylene glycol dimethacrylate) based heterobifunctional polymer (PTVP) has been developed. The polymer was used for the modification of quantum dots (QDs) to prepare water soluble and stable QDs with emission quantum yield as high as 80%. Using carbodiimide method, PTVP-capped red light-emitting QDs were conjugated to model monoclonal antibodies specific to glycoprotein B (gB) of Aujeszky’s disease virus (ADV) and successfully used in the lateral flow assay (LFA) for the detection of ADV gB in biological fluids. A comparative analysis of the sensitivity of the method was carried out using three types of QDs emitting in the red and far-red region.

Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry

Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach we show that indeed lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatio-temporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot the phonon emission is strongly concentrated along the direction of the smallest axis of the dot which is important for the use of phonons for the communication between different dots.

The interaction between human blood neutrophil granulocytes and quantum dots

For biomedical applications, it is important to know, which kinds of blood cells can capture quantum dots (QDs). The maximum accumulation of QDs was found for the monocyte fraction of leukocytes, the minimum binding of QDs was observed for lymphocytes. It was found that CdSe/ZnS-MPA QDs are actively absorbed by the cells and have more expressed toxicity. The classical mechanism of the phagocytosis of QDs was revealed for neutrophils, when the QDs are located in phagolysosomes. The capture of QDs by neutrophil granulocytes has resulted in a destruction of certain types of QDs. The interaction of the neutrophils with the QDs has resulted in the death of the cells by one of the following cell death mechanisms: necrosis, apoptosis, autophagy, NETos, or mummification. The aggregation of the QDs manifested as an increase of the hydrodynamic diameter of the QDs was found to occur under the influence of serum and under the influence of blood cells (lymphocytes and neutrophils) in a serum-free medium.

Facile In Situ Growth of Nanostructured Copper Sulfide Films Directly on FTO Coated Glass Substrates as Efficient Counter Electrodes for Quantum Dot Sensitized Solar Cells

AbstractWe report a facile chemical solution deposition method for fabricating nanostructured copper sulfide film directly on fluorine doped tin oxide (FTO) coated glass substrates and demonstrate its use as efficient counter electrodes in quantum dot based solar cells. A typical quantum dot sensitized solar cell with CdS sensitized photo‐anode using this counter electrode shows ∼25% improvement in the power conversion efficiency when compared to the reference device assembled with conventional thermally evaporated gold/FTO counter electrode. The superior electrocatalytic activity of the copper sulfide electrode is also substantiated by potentiostatic I−V curves and electrochemical impedance spectroscopy.

Fluorescent Determination of Copper(II) in Industrial Wastewater Using Thiol-Capped Cadmium Sulfide–Zinc Sulfide Quantum Dots as the Probe

ABSTRACTIn situ detection of Cu2+ ions in the effluent from thin-film transistor-liquid crystal display (TFT-LCD) manufacturing facility has been successfully achieved using thiol-capped CdS/ZnS quantum dots (QDs) as the fluorescence probes. Three types of ligands, including L-cysteine (LC), mercaptosuccinic acid (MSA), and thioglycolic acid (TGA), were used as capping agents for stabilizing and functionalizing the QDs. Fluorescence quenching of the QDs by Cu2+ ions was well fitted by the Stern–Volmer equation, indicating a static quenching process. Interaction between the Cu2+ ions and the thiol-based capping agents to form Cu–S bonding was responsible for the nonradiative decay. The thiol-capped probes exhibited low detection limits (0.016–0.063 mg L−1), high recovery (81.7–114.5%), good precision (relative standard deviation = 0.36–4.56%), and suitable accuracy for the detection of Cu2+ ions in the field samples, even though those that contained Ca2+, Mg2 +, Na+, K+, and ions, which were 300–16,600 times higher in concentration than the target. These results clearly verify the feasibility of using the QDs as an early warning system for assisting TFT-LCD manufacturing facilities in compliance with strict effluent standards (0.15 mg L−1). Among the three types of thiol-capped QDs, the TGA-capped probes were the most sensitive and the LC-capped probes exhibited the highest errors. Substantial loading of the small TGA ligands on the surface and competitive complexation of the amino groups with Cu2+ ions are responsible for the benefits and the consequences of the TGA- and LC-capped QDs for Cu2+ sensing, respectively.

Single-photon sources of visible light

We report on emission properties of single-photon sources of visible light, based on InAs/AlGaAs, CdTe/ZnTe, and CdSe/ZnSe quantum dot (QD) heterostructures grown by molecular beam epitaxy. For all types of QDs, the studies performed by micro-photoluminescence and photon correlation spectroscopies demonstrated the single-photon nature of emission with typical values of the second-order correlation function g(2)(0) less than 0.2 and allowed evaluation of sub-microsecond kinetics of blinking governed by local charging effects.