Optical Properties Of Quantum Dots Research Articles

Quantum dots-based fluoroimmunoassay for anti-Zika virus IgG antibodies detection

Zika virus (ZIKV) has been declared a public health emergency of international concern. ZIKV has been associated with some neurological disorders, and their long-term effects are not completely understood. The majority of the methods for ZIKV diagnosis are based on the detection of IgM antibodies, which are the first signs of immunological response. However, the detection of IgG antibodies can be an important approach for ZIKV past infection diagnosis, especially for pregnant women, helping the comprehension/treatment of this disease. There has been a growing interest in applying nanoparticles for efficient ZIKV or antibodies detection. Quantum dots (QD) are unique fluorescent semiconductor nanoparticles, highly versatile for biological applications. In the present study, we explored the special QD optical properties to develop an immunofluorescence assay for anti-ZIKV IgG antibodies detection. Anti-IgG antibodies were successfully conjugated with QDs and applied in a fluorescence sensing nanoplatform. After optimization using IgG antibodies, the conjugates were employed to detect anti-ZIKV IgG antibodies in polystyrene microplates sensitized with ZIKV envelope E protein. The nanoplatform was able to detect anti-ZIKV IgG antibodies in a concentration at least 100-fold lower than the amount expected for protein E immune response. Moreover, conjugates were able to detect the antibodies for at least 4 months. Thus, our results showed that this QDs-based fluoroimmunoplatform can be considered practical, simple and promising to detect Zika past infections and/or monitoring immune response in vaccine trials.

Lifetime Enhancement of a Circulated Cooling Perovskite Quantum Dots Colloidal Solution System for Laser Illuminations

Perovskite quantum dots (QDs) attracted a lot of attention recently due to their high light conversion efficiency, and high color purity. However, perovskite materials are sensitive to heat. High temperature will cause serious quenching problem of the perovskite QDs. In order to solve the QDs thermal quenching problem without destroying their optical characters. A circulating quantum dots colloidal solution converter (CQD-converter) was developed. A closed loop pump tube coated with Teflon was utilized to prevent perovskite QDs from the external environment. A peristaltic pump was utilized to drive the QDs colloidal solution through a Peltier cooler for dissipating the heat of the QDs colloidal solution. The lifetime of the perovskite QDs can be significantly improved under a 450nm laser excitation. The effects of temperature of the Peltier cooler and flow velocity on the optical properties of QDs were also investigated. Compared to the static quantum dots colloidal solution (SQD-converter), which quenched after 7 min, the optical properties were maintained after 600 min for the CQD-converter.

Optical Properties of Quantum Dots with a Core–Multishell Structure

In the last decade, colloidal semiconductor nanocrystals (quantum dots) have been not only studied fundamentally but also applied in photovoltaics, optoelectronics, and biomedicine. Beginning with simple approaches to the deposition of protective shells, e.g., ZnS on CdSe cores, searches for ways to increase the quantum yield of photoluminescence of quantum dots have resulted now in the development of new types of quantum dots characterized not only by record high extinction coefficients but also by high photoluminescence quantum yields. In this work, the optical properties of core–multishell quantum dots have been analyzed. These quantum dots have been specially designed to reach the maximum possible localization of excited charge carriers inside luminescent cores, which makes it possible to reach a photoluminescence quantum yield close to 100%. Core–multishell quantum dot samples with a shell thickness of 3–7 monolayers have been fabricated. Changes in the characteristics of optical transitions in such quantum dots with an increase in the number of layers of the shell have been studied. The effect of the thickness of the shell on the optical properties of prepared quantum dots has been analyzed. In particular, analysis of photoluminescence lifetimes of such quantum dots has revealed a possible alternative mechanism of radiation of core–multishell quantum dots based on the slow charge carrier transfer from the excited outer layer of the CdS shell to the CdSe core.

Research on fluorescence lifetime dynamics of quantum dot by single photons modulation spectrum

Fluorescence lifetime is an important characteristic parameter of quantum dot, which plays an important role in studying the optical properties of quantum dot. As a common method to obtain fluorescence lifetime, fluorescence decay curve fitting has been broadly accepted. The least squares fitting to the fluorescence decay curve is performed by using the exponential decay function to obtain fluorescence lifetime with taking the instrument response function into account. However, since the fluorescence decay curve inevitably involves noise photons such as dark counts and stray photons, there is a certain error in the fluorescence lifetime obtained by the method. In order to reduce the error and improve the accuracy of the results, enough photons are required. Nevertheless, too many photons will result in low efficiency of lifetime analysis and temporal resolution, and therefore this method can hardly extract dynamic information on a smaller temporal scale. In this paper, we propose a new method of obtaining the fluorescence lifetime of quantum dot, namely the single photons modulation spectrum. The basic idea is based on the relationship between the fluorescence lifetime and the signal amplitude of pulse repetition frequency in a single dynamic process. The experimental results show that the fluctuation errors and deviation errors of lifetime obtained by our method are significantly lower than those of the previous method when the same number of photons is used. Therefore, high-accuracy fluorescence lifetime can be obtained. When the fluctuation error is 5%, the accuracy is increased by more than one order of magnitude. And to obtain the fluorescence lifetime of the same error level, the number of photons required for our method is much smaller than that of the previous one, which indicates that our method can effectively suppress the disturbance of noise photons and enables the lifetime measurement with high efficiency and temporal resolution. When the fluctuation error and deviation error are both 5%, the efficiency and temporal resolution are increased by more than four times. Finally, real-time lifetime trajectory corresponding to the photoluminescence intensity time trajectory is obtained by our method, where rich dynamic information can be obtained on a sub-second temporal scale. The method of obtaining fluorescence lifetime with powerful anti-noise capability, high efficiency and temporal resolution proposed in this paper can play an important role in studying the fluorescence dynamics of single quantum systems.

Quantum Dots in Biomedical Applications

Semiconducting nanocrystals, more commonly known as quantum dots, possess unique size and shape dependent optoelectronic properties. In recent years, these unique properties have attracted much attention in the biomedical field to enable real-time tissue imaging (bioimaging), diagnostics, single molecule sensors, and drug delivery, among many other areas. The optical properties of quantum dots can be tuned by size and composition, and their small size and high surface area make them excellent candidates for intracellular tracking, diagnostics, in vivo imaging, and therapeutic delivery. We discuss recent advances and challenges in the molecular design of quantum dots are discussed, along with applications of quantum dots as drug delivery vehicles, theranostic agents, single molecule sensors, and real-time in vivo deep tissue imaging agents. We present a detailed discussion of the biodistribution and toxicity of quantum dots, and highlight recent advances to improve long-term stability in biological buffers, increase quantum yield following bioconjugation, and improve clearance from the body. Last, we present an outlook on future challenges and strategies to further advance translation to clinical application.

Photoluminescence enhancement of colloidal CdSe/ZnS quantum dots embedded in polyvinyl alcohol after 2 MeV proton irradiation: crucial role of the embedding medium

The growing interest on the use of colloidal Quantum Dots (QDs) in scintillation and dosimetry applications in comparison with organic fluorophores relies in their narrower and tunable photoluminescence (PL) emission, easier chemical processability and higher cross-section for ionizing radiation. In this context, a deep understanding of the role of the embedding medium on the QD optical properties in unirradiated and irradiated samples represents an important issue. In this paper, we present the optical characterization of colloidal core-shell CdSe/ZnS QDs embedded in polyvinyl alcohol (PVOH) and irradiated with 2 MeV protons at different fluences. The characterization of the samples, performed by both steady-state and time-resolved PL measurements, indicates a damage of the QDs at the lowest fluence (1013 H+cm−2), demonstrated by a quenching of the QD PL intensity and by a shortening of the QD lifetime. At the middle fluence (5 × 1013 H+cm−2) a partial recovering of the QD optical properties are observed, due to energy transfer phenomena between radiation-induced PL defects in the PVOH, acting as donors, and the QDs, acting as acceptors. The higher concentration of PVOH PL defects in the most irradiated sample (1014 H+cm−2) led to an enhancement of the QD PL intensity in comparison with the unirradiated sample, highlighting the crucial role of the embedding medium in the post-irradiation QD optical response.

Detection of hydroquinone with a novel fluorescence probe based on the enzymatic reaction of graphite phase carbon nitride quantum dots

This paper developed a sensitive method for detecting hydroquinone by combining the unique optical properties of quantum dots and the specificity of enzymatic reactions. The interesting results shown that the fluorescence of graphite phase carbon nitride quantum dot (g-CNQDs) was quenched directly by benzoquinone or indirectly by hydroquinone (H2Q), and the possible quenching mechanism was proposed. Quinone might generate by catalyzing the oxidation of H2Q with horseradish peroxidase (HRP) in the presence of hydrogen peroxide. The intermediate quinone could effectively quench the fluorescence of g-CNQDs quantum dots. Therefore, a novel fluorescence probe based on g-CNQDs Quantum Dots was successfully used to detect H2Q by strongly quenching the fluorescence of g-CNQDs Quantum Dots which mediated by horseradish peroxidase enzymes. The detection limit was as low as 0.04 μM (S/N = 3), and the linear range was 0.5–11.6 μM. This kind of quantum dot-enzyme system has the advantages of simple operation, no modification of quantum dots, low cost, high sensitivity and short detection time.

Pressure dependent optical properties of quantum dot with spin orbit interaction and magnetic field

In this paper, a detailed investigation of the effects of the interplay of temperature, hydrostatic pressure, Rashba spin orbit interaction, and external magnetic field on the optical properties for quantum dot is presented. We obtained the exact wavefunctions and energy levels of a harmonic potential quantum dots taking Rashba spin orbit interaction into account. We have obtained the linear and nonlinear absorption coefficients and relative refractive index change for varying incident photon energies using density matrix theory. Counter intuitive red shift in the absorption coefficient peaks with increase in hydrostatic pressure is demonstrated. The role of temperature and hydrostatic pressure on variation of effective charge carrier mass is investigated.

A comparison of optical properties of disc-like and spherical quantum dots

The optical properties of quantum dots (QDs) are of interest to many researchers. In this study, the optical coeefficients analyzed include the optical absorption, the refractive index; both the linear and nonlinear cases together with the electric field effect. The electronic structures of the disc-like and spherical QDs are calculated by using the effective-mass approximation. The results show that the total change in the refractive index and the optical absorption increase with increasing QD size, the peaks are shifted with the changing QD size. The nonlinear optical properties increase with the external electric field and the optical intensity. Comparison of QD types shows that the peaks are red-shifted for the disc-like QD and lower than those in the spherical QD case.

Modifications of the optical properties of quantum dots on liposome encapsulation for applications in theranostic liposomes

Semiconductor quantum dots have been extensively used for biomedical applications as efficient biomarkers. At the same time, liposome encapsulation may open other applications of QDs: the possibility of liposome labeling to stimulate the pathway to specific organs as efficient and specific biomarkers. Due to this, the optical properties of QDs after liposomal encapsulation are very important to many applications, for example, in biosensors or theranostic liposomes. The commercial-acquired CdSe/ZnS core/shell quantum dots of two different emission wavelengths (530 and 640 nm) were encapsulated in lecithin liposomes, and characterized by Atomic Force Microscopy, Transmission Electron Microscopy, Dynamic Light Scattering, Photoluminescence, and Raman Spectroscopy. The important changes in optical properties at liposome encapsulation of the studied QDs are demonstrated and discussed.

Ligand-Mediated Photobrightening and Photodarkening of CdSe/ZnS Quantum Dot Ensembles

Variation of the steady-state optical properties of quantum dots (QDs) caused by photoinduced charge transfer is a widely known phenomenon which hinders QD applications requiring long-term stability of the optical signal, for example, bioimaging, single-photon sources, molecular tracking, and lasing. Intense light irradiation may provoke QD photodarkening, when their photoluminescence (PL) quantum yield (QY) is reduced, or photobrightening, when the QY increases and QD PL becomes brighter. In order to understand the nature of these processes and to determine the optimal operating conditions for QDs with different core sizes and shell thicknesses, we have systematically studied the photodarkening and photobrightening phenomena for different wavelengths and intensities of irradiation. The results have shown that changes in the core size only slightly alter the effect of light irradiation on the QD optical properties, whereas the irradiation wavelength and shell thickness are the major factors that determine...

The investigation of InGaAs quantum dot growth peculiarities for GaAs intermediate band solar cells

In this work the growth peculiarities of InGaAs quantum dots (QDs) on GaAs surface have been investigated by metal-organic vapor-phase epitaxy (MOVPE). The influence of the main structural parameters, such as the amount of deposited InGaAs material and the thickness of the GaAs cap layer, on the optical properties of QDs has been considered. For these parameters the optimal values at which achieved the best photoluminescence intensity of QDs embedded into the matrix of the GaAs-based light-emitting structure have been established. The possibility of using several layers of QDs with the preservation of the optical properties of the investigated structures has been demonstrated. The design of solar cell (SC) based on GaAs with QD arrays in the active area has been proposed. It was shown that 20 layers of QDs embedded into the proposed SC structure contribute to the photogenerated current up to 0.97 mA/cm2 for AM0 spectra and up to 0.77 mA/cm2 for AM1.5D spectra, while maintaining the high quality of the p-n junction.

Radiation-induced optical change of ion-irradiated CdSeS/ZnS core-shell quantum dots embedded in polyvinyl alcohol

Semiconductor quantum dots (QDs) are receiving increasing interest for the production of scintillator detectors and dosimeters. For this reason, the investigation of the effects of ionizing radiation on the optical properties of QDs has become of great importance. In this paper, we present the optical characterization of colloidal CdSeS/ZnS core-shell quantum dots (QDs) embedded in a polyvinyl alcohol (PVA) matrix and irradiated with 2 MeV H+ and He+ ions at different fluences. With steady-state luminescence measurements, we investigate the ion irradiation effects on the luminescence spectrum of the irradiated samples. With time-resolved luminescence measurements, acquired with a Time Correlated Single Photon Counting (TCSPC) system, we evaluate the radiation-induced change in the QD charge carrier dynamics. Luminescence spectra show the appearance of new features related to damage of the PVA host. Time-resolved measurements highlight a shortening of the QD luminescence time constants as the ion fluence increases.

Comment on the paper “The optical properties of quantum dots in anisotropic media” by Singh et al., J. Mol. Liq. 241 (2017) 1009–1012

The present comment concerns some doubtful results reported by Singh et al. [1].

Exciton-phonon coupling channels in a ‘strain-free’ GaAs droplet epitaxy single quantum dot

We examine the temperature-dependent excitonic transition energy shift of strain-free GaAs droplet epitaxy (DE) quantum dots (QDs). Interestingly the statistical investigation of QD optical properties enables us to observe three distinct temperature dispersions for four series of DE QDs. We present comparative analyses of the exciton-phonon coupling mechanisms employing various empirical to multi-oscillator models associated with each QD-specific phonon dispersion spectrum. The systematic investigation of such QD exciton-phonon coupling is crucial for fine control of local defects in engineered quantum dot single-photon sources.

The anticoagulant properties of cadmium telluride quantum dots.

The size‐dependent optical properties of quantum dots (QDs) are frequently exploited for use in medical imaging and labelling applications. Similarly, presented here, they also elicit profound size‐dependent anticoagulant properties. Cadmium telluride quantum dot (QDs) (3.2 nm) were shown to have a dramatic anticoagulant effect centred on around the intrinsic coagulation pathway, compared to their 3.6 nm counterparts. Several clinically relevant diagnostic tests were carried out over a concentration range of the QDs and demonstrated that the 3.2 nm QDs elicited their response on the intrinsic pathway as a whole, yet the activity of the individual intrinsic coagulation factors was not affected. The mechanism appears also to be strongly influenced by the concentration of calcium ions and not cadmium ions leached from the QDs. Static and shear‐based primary haemostasis assays were also carried out, demonstrating a profound anticoagulant effect which was independent of platelets and phospholipids. The data presented here suggest that the physical–chemical properties of the QDs may have a role in the modulation of haemostasis and the coagulation cascade, in a yet not fully understood mechanism. This study has implications for the use of similar QDs as diagnostic or therapeutic tools in vivo, and for the occupational health and safety of those working with such materials.

"Turn on" room-temperature phosphorescent biosensors for detection of hyaluronic acid based on manganese-doped ZnS quantum dots.

Biosensors based on excellent optical properties of quantum dots (QDs) nanohybrids are efficient for biological detection. In this work, a room-temperature phosphorescent (RTP) PDAD–Mn–ZnS QDs biosensor was constructed with poly(diallyldimethylammonium chloride) (PDAD) as the modifier of MPA-capped Mn–ZnS QDs, and used to detect hyaluronic acid (HA). The newly-added HA induced severe electrostatic interaction with PDAD–Mn–ZnS QDs, leading to the aggregation between PDAD–Mn–ZnS QDs and HA and thereby enhancing RTP. The enhancement of RTP was proportional to the HA concentrations within certain ranges. On this basis, a high-performance HA sensor was built and this sensor had a detection limit of 0.03 μg mL−1 and a detection range of 0.08–2.8 μg mL−1. This proposed RTP sensor can avoid interferences from the background fluorescence or scattering light of the matrix that are encountered in spectrofluorometry. Thus, this biosensor is potentially suitable for detection of HA in real samples without complicated pretreatment.

Quantum dot–Cramoll lectin as novel conjugates to glycobiology

The optical properties of quantum dots (QDs) make them useful tools for biology, especially when combined with biomolecules such as lectins. QDs conjugated to lectins can be used as nanoprobes for carbohydrate expression analysis, which can provide valuable information about glycosylation changes related to cancer and pathogenicity of microorganisms, for example. In this study, we evaluated the best strategy to conjugate Cramoll lectin to QDs and used the fluorescent labeling of Candida albicans cells as a proof-of-concept. Cramoll is a mannose/glucose–binding lectin with unique biological properties such as immunomodulatory, antiparasitic, and antitumor activities. We probed covalent coupling and adsorption as conjugation strategies at different pH values. QDs conjugated to Cramoll at pH7.0 showed the best labeling efficiency in the fluorescence microscopy analysis. Moreover, QD-Cramoll conjugates remained brightly fluorescent and preserved identical biological activity according to hemagglutination assays. Flow cytometry revealed that approximately 17% of C. albicans cells were labeled after incubation with covalent conjugates, while approximately 92% of cells were labeled by adsorption conjugates (both at pH7.0). Inhibition assays confirmed QD-Cramoll specificity, which reduced the labeling to at most 3%. Therefore, the conjugates obtained by adsorption (pH7.0) proved to be promising and versatile fluorescent tools for glycobiology.

Focus on microscopy, imaging, and nanotechnology

Focus on microscopy, imaging, and nanotechnology

Influence of the heterostructure design on the optical properties of GaN and Al0.1Ga0.9N quantum dots for ultraviolet emission

The optical properties of AlyGa1-yN quantum dots (QDs), with y = 0 or y = 0.1, in an AlxGa1−xN matrix are studied. The influence of the QD layer design is investigated pointing out the correlations between the QD structural and optical properties. In a first part, the role of the epitaxial strain in the dot self-assembling process is studied by fabricating GaN QD layers on different AlxGa1−xN layers with 0.5 ≤ x ≤ 0.7. Photoluminescence (PL) measurements show the main influence of the increase of the internal electric field (Fint) on the QD optical response inducing a strong red shift in the emission energy as x increases. Time resolved combined with temperature dependent PL measurements enabled the estimation of the QD internal quantum efficiencies at low temperature showing values around 50%. In addition, a PL integrated intensity ratio up to 74% is shown, between 300 and 9 K. In the second part, the design of Al0.1Ga0.9N QDs was investigated, by varying the Al0.1Ga0.9N amount deposited. An increase of the transition energy (from 3.65 eV up to 3.83 eV) is obtained while decreasing the deposited amount. Calculations of the ground state transition energies as a function of the Al0.1Ga0.9N dot height give a value of Fint around 2.0 ± 0.5 MV/cm. Therefore, the propensity of Al0.1Ga0.9N dots to emit at much higher energies than GaN dots (a PL shift of ∼1 eV using a low excitation power) is seen as the consequence of the reduced Fint together with their smaller sizes.