Optical Properties Of Quantum Dots Research Articles

Nanoimaging: photophysical and pharmaceutical characterization of poly-lactide-co-glycolide nanoparticles engineered with quantum dots

Quantum dots (QDs) and polymeric nanoparticles (NPs) are considered good binomials for the development of multifunctional nanomedicines for multimodal imaging. Fluorescent imaging of QDs can monitor the behavior of QD-labeled NPs in both cells and animals with high temporal and spatial resolutions. The comprehension of polymer interaction with the metallic QD surface must be considered to achieve a complete chemicophysical characterization of these systems and to describe the QD optical properties to be used for their unequivocal identification in the tissue. In this study, by comparing two different synthetic procedures to obtain polymeric nanoparticles labeled with QDs, we investigated whether their optical properties may change according to the formulation methods, as a consequence of the different polymeric environments. Atomic force microscopy, transmission electron microscopy, confocal and fluorescence lifetime imaging microscopy characterization demonstrated that NPs modified with QDs after the formulation process (post-NPs-QDs) conserved the photophysical features of the QD probe. In contrast, by using a polymer modified with QDs to formulate NPs (pre-NPs-QDs), a significant quenching of QD fluorescence and a blueshift in its emission spectra were observed. Our results suggest that the packaging of QDs into the polymeric matrix causes a modification of the QD optical properties: these effects must be characterized in depth and carefully considered when developing nanosystems for imaging and biological applications.

A comparative study about toxicity of CdSe quantum dots on reproductive system development of mice and controlling this toxicity by ZnS coverage

Objective(s): Medicinal benefits of quantum dots have been proved in recent years but there is little known about their toxicity especially in vivo toxicity. In order to use quantum dots in medical applications, studies ontheir in vivo toxicity is important. Materials and Methods: CdSe:ZnS quantum dots were injected in 10, 20, and 40 mg/kg doses to male mice10 days later, mice were sacrificed and five micron slides were prepared structural and optical properties of quantum dots were evaluated using XRD. Results: Histological studies of testis tissue showed high toxic effect of CdSe:ZnS in 40 mg/kg group. Histological studies of epididymis did not show any effect of quantum dots in terms of morphology and tube structure. Mean concentration of LH and testosterone and testis weight showed considerable changes in mice injected with 40 mg/kg dose of CdSe:ZnS compared to control group. However, FSH and body weight did not show any difference with control group. Conclusion: Although it has been reported that CdSe is highly protected from the environment by its shell, but this study showed high toxicity for CdSe:ZnS when it is used in vivo which could be suggested that shell could contribute to increased toxicity of quantum dots. Considering lack of any previous study on this subject, our study could potentially be used as an basis for further extensive studies investigating the effects of quantum dots toxicity on development of male sexual system.

Preparation and evaluation of vitamin A nanosuspension as a novel ocular drug delivery

Objective(s): The field of nanotechnology is rapidly expanding .The development quantum dots quantum dot (QDs), show great promise for treatment and diagnosis of cancer and targeted drug delivery little data on the toxicity of QDs, especially for in vivo applications, are available. As a result, concerns exist over their toxicity for in vivo applications. Then, cytotoxic effects of cadmium selenide (CdSe) quantum dots on organs development before maturity were studied in this study. Materials and Methods: One month old male Mice treated by injection of CdSe at the doses of 10, 20 and 40 mg/kg. Structural and optical properties of quantum dots were studied by XRD, UV-Vis absorption spectrum and Scanning Tunneling Microscopy and the number of cells in seminiferous tubes of various groups were analyzed using SPSS 16 program (one way ANOVA test). Results: Histological studies of testis tissue showed high toxicity of cdse in the dose of 40 mg/kg which followed by decrease in lamina propria thickness, destruction in interstitial tissue, deformation of seminiferoustubes, and reduction in number cells. Also histological study of lung tissue showed in 20 and 40 mg/kg doses destruction in interstitial and epithelium tissues. Conclusion: On the whole, this study showed high toxicity of cdse on development of testis and lung tissues, even in low doses considering lack of literature review in this field, this study can be an introduction to researches about toxicity effect of quantum dots on development of organs.

Nanocomposites Based on CdS Quantum Dots for Laser Control Devices

Here we report about study the novel class of nanocomposite for optical control devices. It was observed that nanocomposite based on cadmium sulfide quantum dots in silica matrix can change its optical properties under irradiation of UV-light. These changes are expressed as increasing of optical absorbance coefficient and not only decreasing of luminescence intensity but in some cases red-shifting of maximum. Dependence of quantum dot optical properties upon the kind of matrix and polarization degree of modifying radiation was obtained.

Preparation and Effect of Lighting on Structures and Properties of GSH Capped ZnSe QDs.

L-glutathione (GSH) capped ZnSe quantum dots (QDs) were prepared by microwave-assisted aqueous synthesis. Then, the resulting QDs were illuminated under dark, ultraviolet light and incandescent light, respectively. Thereby effect of lighting on the structures and properties of QDs were studied systematically. It was revealed that particle size and element content of QDs took a sharp change after irradiation, while the crystal structure maintains nearly unaffected. Comparing to the ZnSe QDs under dark condition, counterparts irradiated by UV light possessed outstanding sphericity, size distribution and dispersion. And the content of sulfur (S) in ZnSe QDs irradiated by UV light was much higher relatively. The effect of lighting on vibration peaks of O-H was considerable. However, this effect was observed to be weak on other chemical bonds. The possible explanation ascribes to photo-chemical interactions can occur between S-H and O-H bonds on the surface of GSH ligand. The lighting induced GSH to occur photocatalytic oxidation on the surface of ZnSe QDs, which improved the optical properties of QDs. The effects of lighting rely on irradiation types, the sequence is UV light, incandescent light and dark from high to low.

Formation of GaN quantum dots by molecular beam epitaxy using NH3 as nitrogen source

Self-assembled GaN quantum dots (QDs) in AlxGa1−xN (0.3 ≤ x ≤ 1) were grown on c-plane sapphire and Si (111) substrates by molecular beam epitaxy using ammonia as nitrogen source. The QD formation temperature was varied from 650 °C to 800 °C. Surprisingly, the density and size of QDs formed in this temperature range are very similar. This has been explained by considering together experimental results obtained from reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence to discuss the interplay between thermodynamics and kinetics in the QD formation mechanisms. Finally, possible ways to better control the QD optical properties are proposed.

Controlling the spatial distribution of quantum dots in nanofiber for light-harvesting devices

The ability to control inter-dot or inter-molecule spacing of functional moieties in solid-state devices has long been studied for both fundamental and technological reasons. In this study, we present a new strategy for controlling the distance between quantum dots (QDs) based on one-dimensional spatial confinement in a polymer nanofiber template. This reliable technique allows for the isolation of QDs at a sufficient distance in a thin film and retains their monomeric character, with distinct spectra from aggregates (~30-nm shift) and monoexponential photoluminescence decay, indicating the suppression of inter-dot interactions. We successfully developed light-harvesting devices by incorporating QDs in nanofibers as an auxiliary light harvester, improving the performance of these devices from 5.9 to 7.4%. This strategy offers a viable path of controlling the arrangements of various functional moieties in solid-state devices. By packing quantum dots evenly in polymer nanofibres, a Korean team has found a way to boost the performance of artificial light harvesters. The high-intensity optical properties of quantum dots make them ideal for devices such as lasers and photosensors, but such effects are lost when the tiny dots aggregate together. To prevent unwanted clustering, Dongho Kim from Yonsei University in Seoul and co-workers used electrospinning techniques to embed quantum dots into poly(methyl methacrylate) nanofibres. Electron microscopy images and spectroscopic measurements showed this approach isolated the dots retaining their monomeric characteristics and that their separations were determined by the nanofibre diameter— a result that supports using this strategy to manipulate other moieties into useful spatial arrangements. Incorporating the hybrid material in a dye-sensitized solar cell revealed that the dots raised the light-harvesting efficiency from 5.9% to 7.4%. Confining quantum dots (QDs) into one-dimensional polymer nanostructures, we develop an inter-dot spacing control technique by which we can effectively isolate QDs in the solid-state film. The resultant isolated QDs in this nanostructure have clear monomeric features caused by attenuation of several problematic interactions, such as self-quenching. By incorporating isolated QD as an auxiliary light harvester, we can improve the performance of light-harvesting devices due to its additional absorption and efficient energy transfer. This study provides a general strategy that could be potentially useful for the spatial control of other functional moieties in various devices.

Quantum dots-based tissue and in vivo imaging in breast cancer researches: current status and future perspectives.

As the most common malignant tumor for females, breast cancer (BC) is a highly heterogeneous disease regarding biological behaviors. Precisely targeted imaging on BC masses and biomarkers is critical to BC detection, treatment, monitoring, and prognostic evaluation. As an important imaging technique, quantum dots (QDs)-based imaging has emerged as a promising tool in BC researches owe to its outstanding optical properties. However, few reviews have been specifically devoted to discussing applications of QDs-based imaging in BC researches. This review summarized recent promising works in QDs-based tissue and in vivo imaging for BC studies. Physicochemical and optical properties of QDs and its potential applications were briefly described first. Then QDs-based imaging studies in BC were systematically reviewed, including tissue imaging for studying biomarkers interactions, and evaluating prognostic biomarkers, in vivo imaging for mapping axillary lymphatic system, showing BC xenograft tumor, and detecting BC metastases. At last, the future perspectives with special emphasis on the potential clinical applications have also been discussed. Potential applications of QDs-based imaging on clinical BC in the future are mainly focused on tissue study, especially in BC molecular pathology due to its optimal optical properties and quantitative information capabilities on multiple biomarkers.

Enhancement of the optical properties from quantum dots doped in soft matter by surface passivation

The photoluminescence quantum efficiency of quantum dots (QDs) at room temperature was markedly enhanced about 2 times by surface treatment of the nanocrystals, and the original lasing emission peak position and narrow line width were maintained. We report an investigation of the impact of surface passivation on the optical properties of QDs. Thiol coating was used to passivate the surface states that the luminescence efficiency of QDs can be improved.

Photoluminescence of nanocomposites of liquid-crystalline polymers and cadmium selenide quantum dots

The role of specific interactions between a polymer matrix and incorporated quantum dots is one of the critical problems for understanding the effect of the polymer matrix on the optical properties of quantum dots in a nanocomposite material and for creating new photonic materials and related instruments. In this study, cadmium selenide quantum dots have been incorporated into a liquid-crystalline polymer via the interaction of carboxyl groups of the polymer with the quantum-dot surfaces through ionic bonds. From the data of transmission electron microscopy, it has been shown that this interaction provides the localization of quantum dots in the environment of the liquid-crystalline phase of the polymer. Various features of photoluminescent properties have been observed and interpreted in terms of the emission recombination of excitons in CdSe quantum dots, light reabsorption by quantum dots, the effect of the electronic states on the surface CdSe-liquid crystal, and the energy transfer from quantum dots to the polymer liquid-crystalline matrix.

Quantum dot-based concentric FRET configuration for the parallel detection of protease activity and concentration.

Protease expression, activity, and inhibition play crucial roles in a multitude of biological processes; however, these three aspects of their function are difficult for any one bioanalytical probe to measure. To help address this challenge, we report a multifunctional concentric Förster resonance energy transfer (FRET) configuration that combines two modes of biorecognition using aptamers and peptide substrates coassembled to a central semiconductor quantum dot (QD). The aptamer is sensitive to the concentration of protease and the peptide is sensitive to its hydrolytic activity. The role of the QD is to serve as a nanoscale scaffold and initial donor for energy transfer with both Cyanine 3 (Cy3) and Alexa Fluor 647 (A647) fluorescent dyes associated with the aptamer and peptide, respectively. Using thrombin as a model protease, we show that a ratiometric analysis of the emission from the QD, Cy3, and A647 permits discrimination between thrombin and thrombin-like activity, and distinguishes between active, reversibly inhibited, and irreversibly inhibited thrombin. Reliable quantitative results were obtained from a kinetic analysis of the changes in FRET. This concentric FRET format, which capitalizes on both the physical and optical properties of QDs, should be adaptable to other protease targets for which both peptide substrates and binding aptamers are known. It is thus expected to become valuable a tool for the real-time analysis of protease activity and regulation.

PbSe-Based Colloidal Core/Shell Heterostructures for Optoelectronic Applications.

Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review focuses on the structures consisting of a PbSe core coated with a PbSexS1–x (0 ≤ x ≤ 1) or CdSe shell. The former-type shells were epitaxially grown on the PbSe core, while the latter-type shells were synthesized using partial cation-exchange. The influence of the QD composition and the ambient conditions, i.e., exposure to oxygen, on the QD optical properties, such as radiative lifetime, Stokes shift, and other temperature-dependent characteristics, was investigated. The study revealed unique properties of core/shell heterostructures of various compositions, which offer the opportunity of fine-tuning the QD electronic structure by changing their architecture. A theoretical model of the QD electronic band structure was developed and correlated with the results of the optical studies. The review also outlines the challenges related to potential applications of colloidal PbSe-based heterostructures.

Spatially resolved In and As distributions in InGaAs/GaP and InGaAs/GaAs quantum dot systems

InGaAs quantum dots (QDs) on GaP are promising for monolithic integration of optoelectronics with Si technology. To understand and improve the optical properties of InGaAs/GaP QD systems, detailed measurements of the QD atomic structure as well as the spatial distributions of each element at high resolution are crucial. This is because the QD band structure, band alignment, and optical properties are determined by the atomic structure and elemental composition. Here, we directly measure the inhomogeneous distributions of In and As in InGaAs QDs grown on GaAs and GaP substrates at the nanoscale using energy dispersive x-ray spectral mapping in a scanning transmission electron microscope. We find that the In distribution is broader on GaP than on GaAs, and as a result, the QDs appear to be In-poor using a GaP matrix. Our findings challenge some of the assumptions made for the concentrations and distributions of In within InGaAs/GaAs or InGaAs/GaP QD systems and provide detailed structural and elemental information to modify the current band structure understanding. In particular, the findings of In deficiency and inhomogeneous distribution in InGaAs/GaP QD systems help to explain photoluminescence spectral differences between InGaAs/GaAs and InGaAs/GaP QD systems.

Singlet oxygen-generating from fluorescence probes based on denatured bovine serum albumin-conjugated CdTe quantum dots and photosensitizer Chlorin e6

Based on the excellent optical properties of quantum dots (QDs), a simple and efficient method was proposed and established to produce a singlet oxygen activating QDs-denatured Bovine Serum Albumin (dBSA)-Chlorin e6 (Ce6) bioprobe. In this work, a quick synthesis of water-soluble CdTe QDs was accomplished and showed a good linear fit between synthetic heating duration and its maximum fluorescence emission wavelength. Moreover, dBSA which is a convenient and widely used agent was employed as a bridge to conjugate the selective CdTe QDs with a suitable emitting wavelength and photosensitizer Ce6, simply using N-ethyl-N-(3-dimethylaminopropyl) carbodiimide and N-hydroxy succinimide as coupling agents. UV–Vis, fluorescence, and IR spectroscopy confirmed the successful conjugation of QDs and Ce6. The as-produced QDs-dBSA-Ce6 bioconjugates demonstrated an effective fluorescence resonance energy transfer efficiency of as high as 0.90, which also proved to be well conserved of its singlet oxygen-generating in oxidation–extraction photometry tests and might be a potential bioprobe in the research of photo dynamic therapy.

Surface oxidation behaviors of Cd-rich CdSe quantum dot phosphors at high temperature.

The optical properties of quantum dots (QDs) are altered by exposure to air and light; upon such exposure, the quantum yield is typically reduced. Improved understanding of surface oxidation and oxide-layer behavior, both of which influence the photoluminescence of QDs, is necessary for advancing the use of QDs. In this study, the oxide layer properties of QDs are investigated. The QDs are synthesized and subsequently oxidized by heat treatment in atmospheric conditions, and the luminescence properties of the resultant QDs are investigated. The emission properties of QDs are characterized by photoluminescence. The composition and bonding structure of oxidized CdSe QDs are investigated by X-ray photoelectron spectroscopy (XPS). The XRD peaks of oxidized CdSe QDs match CdSe and CdO peaks. CdO is formed by partial oxidation of CdSe QDs. Transmission electron microscopy (TEM) image is confirmed morphology of oxidation before and after of CdSe QDs.

Capping layer growth rate and the optical and structural properties of GaAsSbN-capped InAs/GaAs quantum dots

Changing the growth rate during the heteroepitaxial capping of InAs/GaAs quantum dots (QDs) with a 5 nm-thick GaAsSbN capping layer (CL) strongly modifies the QD structural and optical properties. A size and shape transition from taller pyramids to flatter lens-shaped QDs is observed when the CL growth rate is decreased from 1.5 to 0.5 ML/s. This indicates that the QD dissolution processes taking place during capping can be controlled to some extent by the GaAsSbN CL growth rate, with high growth rates allowing a complete preservation of the QDs. However, the dissolution processes are shown to have a leveling effect on the QD height, giving rise to a narrower size distribution for lower growth rates. Contrary to what could be expected, these effects are opposite to the strong blue-shift and improvement of the photoluminescence (PL) observed for higher growth rates. Nevertheless, the PL results can be understood in terms of the strong impact of the growth rate on the Sb and N incorporation into the CL, which results in lower Sb and N contents at higher growth rates. Besides the QD-CL band offsets and QD strain, the different CL composition alters the band alignment of the system, which can be transformed to type-II at low growth rates. These results show the key role of the alloyed CL growth parameters on the resulting QD properties and demonstrate an intricate correlation between the PL spectra and the sample morphology in complex QD-CL structures.

A NOVEL ANTI-ESTROGEN RECEPTOR TARGETED WATER-SOLUBLE QDs FOR BREAST CANCER CELL IMMUNOFLUORESCENT LABELING

This research is aimed to develop a novel kind of biomarker based on water-soluble quantum dots (QDs) conjugated with estrogen receptor (ER) for the detection of breast cancer (BC). To achieve the purpose, hydrophobic octadecylamine-coated QDs were encapsulated with amphiphilic biocompatible centipede-like polymer p(aspartate)- Na -graft-p(ethylene glycol)-dodecylamine (PASP- Na -g-PEG-DDA), and then modified with ER monoclonal antibodies, which is one of the most popular biomarkers for the detection and management of breast cancer worldwide. The targeted QDs kept the original optical property of QDs. The cytotoxicity in vitro experiments showed that QDs-ER probes had no obvious toxic side effects. Remarkably, confocal laser scanning microscopy (CLSM) revealed that the localized fluorescence appeared around the nucleus of human breast cancer cell MCF7 (ER positive) compared with that of human breast cancer cell MBA-MD-231 (ER negative). According to the above analysis, this new kind of probe has great potential in the diagnosis of breast tumor in vitro in future clinical application.

CdSe/CdS Core/Shell Quantum Dots Synthesized with Water Soluble Polymer for Potential Biosensor Applications

Quantum dots (QDs) are very promising advanced materials due to their nanoscale dimensions and properties of quantum confinement. Among the most promising applications of QDs, the use as biomaterials is highlighted, especially as optical biosensors and biomarkers. In this work CdSe-CdS core-shell nanoparticles were obtained through colloidal aqueous route at room temperature. The biocompatible polymer poly (vinyl alcohol) modified with carboxyl groups (PVA-COOH) was used as a stabilizing agent. The effect of growing CdS shell on the quantum properties and dimensions of CdSe nanoparticles (core-shell structure) was studied by UV-vis spectroscopy, photoluminescence (PL) and transmission electron microscopy (TEM). The results showed the influence of the growth of the CdS shell layers in the optical properties of quantum dots. Based on the results it can be stated that conjugated systems of CdS/CdSe-PVA-COOH were obtained and exhibited enhanced photoluminescent behavior, an essential property to use this system in biosensing devices.

Application advances in optical imaging of inorganic fluorescent nano-materials-quantum dots

Optical imaging is one of the molecular imaging modalities,and it consists of three imaging methods (fluorescence,bioluminescence and diffusion imaging).For fluorescence imaging,quantum dots (QDs) are inorganic semiconductor nanocrystals with a diameter from 2 to 100 nm.Compared with organic fluorescent dye,QDs have several unique optical properties,such as wide and continuous excitation spectra,narrow and symmetrical emission spectrum,strong fluorescence intensity and high resistance to photobleaching.This article reviews the optical properties of QDs and their development in the field of molecular imaging from in vitro and in vivo applications,as well as the limitations and problems. Key words: Quantum dots; Nanotechnology; Optical imaging; Trends

Chemical basis of interactions between engineered nanoparticles and biological systems.

Chemical basis of interactions between engineered nanoparticles and biological systems.