Application Of Semiconductor Quantum Dots Research Articles

Fluorescent Quantum Dots and Its Composites for Highly Sensitive Detection of Heavy Metal Ions and Pesticide Residues: A Review

Quantum dots nanomaterials have attracted extensive interest for fluorescence chemical sensors due their attributes, such as excellent optical characteristics, quantum size effects, interface effects, etc. Moreover, the fluorescence properties of quantum dots can be adjusted by changing their structure, size, morphology, composition, doping, and surface modification. In recent years, quantum dots nanomaterials have been considered the preferred sensing materials for the detection of heavy metal ions and pesticide residues by the interactions between quantum dots and various analytes, showing excellent sensitivity, selectivity, and interference, as well as reducing the cost of equipment compared with traditional measurement methods. In this review, the applications and sensing mechanisms of semiconductor quantum dots and carbon-based quantum dots are comprehensively discussed. The application of semiconductor quantum dots, carbon quantum dots, graphene quantum dots, and their nanocomposites that are utilized as fluorescence sensors are discussed in detailed, and the properties of various quantum dots for heavy metal ion and pesticide residue determination are also presented. The recent advances in and application perspectives regarding quantum dots and their composites are also summarized.

Electrochemiluminescence of Semiconductor Quantum Dots and Its Biosensing Applications: A Comprehensive Review.

Electrochemiluminescence (ECL) is the chemiluminescence triggered by electrochemical reactions. Due to the unique excitation mode and inherent low background, ECL has been a powerful analytical technique to be widely used in biosensing and imaging. As an emerging ECL luminophore, semiconductor quantum dots (QDs) have apparent advantages over traditional molecular luminophores in terms of luminescence efficiency and signal modulation ability. Therefore, the development of an efficient ECL system with QDs as luminophores is of great significance to improve the sensitivity and detection flux of ECL biosensors. In this review, we give a comprehensive summary of recent advances in ECL using semiconductor QDs as luminophores. The luminescence process and ECL mechanism of semiconductor QDs with various coreactants are discussed first. Specifically, the influence of surface defects on ECL performance of semiconductor QDs is emphasized and several typical ECL enhancement strategies are summarized. Then, the applications of semiconductor QDs in ECL biosensing are overviewed, including immunoassay, nucleic acid analysis and the detection of small molecules. Finally, the challenges and prospects of semiconductor QDs as ECL luminophores in biosensing are featured.

(Invited) Quantum Well Architecture to Realize High Optical Gain Lasing Media

Photonic applications of semiconductor quantum dots (QDs) had significant drawbacks due to their ultrafast Auger decay of multiple excitons. These nonradiative processes have hindered the performance of electroluminescent and lasing devices. The emergence of the colloidal quantum well (QW) architecture where semiconductor quantum shell with an inverted QD geometry has led to suppressed Auger recombination. Ultra long biexciton lifetime (>10 ns) and large biexciton quantum yields has been achieved through spatial separation promoted by the QW geometry. Moreover, architecture induced exciton-exciton repulsions have led to the splitting of exciton and biexciton optical transitions which resulted in the single exciton gain mode along with the biexciton gain mode. High biexciton lifetime and the longest reported single exciton gain lifetime (>6 ns) has rendered this geometry a worthy candidate for the development of optically and electrically pumped gain media

Quantum Shells Boost the Optical Gain of Lasing Media.

Auger decay of multiple excitons represents a significant obstacle to photonic applications of semiconductor quantum dots (QDs). This nonradiative process is particularly detrimental to the performance of QD-based electroluminescent and lasing devices. Here, we demonstrate that semiconductor quantum shells with an "inverted" QD geometry inhibit Auger recombination, allowing substantial improvements to their multiexciton characteristics. By promoting a spatial separation between multiple excitons, the quantum shell geometry leads to ultralong biexciton lifetimes (>10 ns) and a large biexciton quantum yield. Furthermore, the architecture of quantum shells induces an exciton-exciton repulsion, which splits exciton and biexciton optical transitions, giving rise to an Auger-inactive single-exciton gain mode. In this regime, quantum shells exhibit the longest optical gain lifetime reported for colloidal QDs to date (>6 ns), which makes this geometry an attractive candidate for the development of optically and electrically pumped gain media.

Construction and Application of Semiconductor Quantum Dots and Carbon Dots Based 0D/2D Heterojunction Photocatalysts

Construction and Application of Semiconductor Quantum Dots and Carbon Dots Based 0D/2D Heterojunction Photocatalysts

Tuning CdTe quantum dots reactivity for multipoint detection of mercury(II), silver(I) and copper(II)

In this work we tuned the surface chemistry of distinctly-sized CdTe quantum dots (QDs), by using a variety of capping ligands with distinctive functional moieties, and combined them in multi-QDs probing solutions for Hg2+, Cu2+ and Ag+. Upon the individual interaction of the distinctly-capped QDs with each of the abovementioned metal ions, several parameters such as Stern-Volmer constants, equilibrium binding constants, the red-shift magnitude and photoluminescence (PL) lifetime values were thoroughly evaluated.Due to their great reactivity, selectivity could become a major issue in the application of semiconductor quantum dots in chemical analysis. Therefore, the combination in the same analysis of multiple QDs, capped with distinct ligands and emitting at different wavelengths, was exploited to guarantee a specific analyte-response profile. When coupled with chemometrics, for data analysis and processing, the developed approach provided enhanced selectivity and accuracy. In fact, the obtained results of all the partial least squares (PLS) models coefficient of determination of cross-validation (R2CV) close to 1, root mean square error of calibration (RMSEC) and root mean square error of cross-validation (RMSECV) values ranging 0.0094–0.15 and 0.013–0.19 mg L−1, respectively. demonstrated the possibility to perform accurate predictions of Hg2+ and Cu2+. Additionally, the sensitivity of the developed models was also calculated and allowed us to conclude which combination of distinctly-capped QDs assured a more sensitive quantification of Cu2+ (sensitivity = 653 L−1 mg for 3-mercaptopropionic acid (MPA)/MPA conjugated probe) and Hg2+ (sensitivity = 14,017 L−1 mg for reduced glutathione (GSH)/MPA-conjugated probe).

Combined Computational and Experimental Study of CdSeS/ZnS Nanoplatelets: Structural, Vibrational, and Electronic Aspects of Core-Shell Interface Formation.

In the past few years, core-shell nanoparticles have opened new perspectives for the optoelectronic applications of semiconductor quantum dots. In particular, it has become possible to localize electrons in either part of these heterostructures. Understanding and controlling this phenomenon require a thorough characterization of the interfaces. In this study, we prepared quasi-2D CdSeS/ZnS core-shell nanoplatelets (NPLs) by colloidal atomic layer deposition. This technique allows fine control over the quantum confinement, the surfaces, and the interfaces. The layer-by-layer formation of a the ZnS shell around the CdSeS core was monitored using UV-vis absorption, XRD, and Raman spectroscopy. The measured band gaps and structural distortions were compared with results obtained from density functional theory (DFT) calculations. Modeling has also shown that 34% of the photoexcited electrons are delocalized into the ZnS shell. The herein presented combined modeling and experimental characterization strategy is of general interest since it can be applied to a large choice of layered semiconductor heterostructures in optoelectronics. The present approach paves the way for the synthesis of nanocrystals with precisely engineered properties for light-emitting diodes and solar cells.

Site-Controlled Single-Photon Emitters Fabricated by Near-Field Illumination.

Many of the most advanced applications of semiconductor quantum dots (QDs) in quantum information technology require a fine control of the QDs' position and confinement potential, which cannot be achieved with conventional growth techniques. Here, a novel and versatile approach for the fabrication of site-controlled QDs is presented. Hydrogen incorporation in GaAsN results in the formation of N-2H and N-2H-H complexes, which neutralize all the effects of N on GaAs, including the N-induced large reduction of the bandgap energy. Starting from a fully hydrogenated GaAs/GaAsN:H/GaAs quantum well, the NH bonds located within the light spot generated by a scanning near-field optical microscope tip are broken, thus obtaining site-controlled GaAsN QDs surrounded by a barrier of GaAsN:H (laterally) and GaAs (above and below). By adjusting the laser power density and exposure time, the optical properties of the QDs can be finely controlled and optimized, tuning the quantum confinement energy over more than 100 meV and resulting in the observation of single-photon emission from both the exciton and biexciton recombinations. This novel fabrication technique reaches a position accuracy <100 nm and it can easily be applied to the realization of more complex nanostructures.

Deciphering hot- and multi-exciton dynamics in core-shell QDs by 2D electronic spectroscopies.

Although the harnessing of multiple and hot excitons is a prerequisite for many of the groundbreaking applications of semiconductor quantum dots (QDs), the characterization of their dynamics through conventional spectroscopic techniques is cumbersome. Here, we show how a careful analysis of 2DES maps acquired in different configurations (BOXCARS and pump-probe geometry) allows the tracking and visualization of intraband Auger relaxation mechanisms, driving the hot carrier cooling, and interband bi- and tri-exciton recombination dynamics. The results obtained on archetypal core-shell CdSe/ZnS QDs suggest that, given the global analysis of the resulting datasets, 2D electronic spectroscopy techniques can successfully and efficiently dispel the intertwined dynamics of fast and ultrafast recombination processes in nanomaterials. Hence, we propose this analysis scheme to be used in future research on novel quantum confined systems.

Expanded Quantum Dot-Based Concentric Förster Resonance Energy Transfer: Adding and Characterizing Energy-Transfer Pathways for Triply Multiplexed Biosensing

Concentric Forster resonance energy transfer (cFRET) is an emerging application of semiconductor quantum dots (QDs) that takes advantage of their excellent photoluminescence (PL) properties, small size, and versatile surface area. To date, cFRET configurations have combined QDs with only two fluorescent dyes, limiting multiplexed bioanalysis to two targets. Here, we expanded cFRET to create a triply multiplexed configuration that comprised a central QD assembled with multiple copies of three different peptide sequences labeled with one of three different fluorescent dyes. These dyes were Alexa Fluor 555 (A555), either Cyanine 3.5 (Cy3.5) or Atto 594 (At594), and Alexa Fluor 647 (A647). The expanded cFRET configuration had double the number of FRET pathways of previous systems, with three competitive pathways from the QD to the dyes and three sequential pathways between the dyes. The quenching efficiencies for QD and dye PL in the full three-acceptor cFRET configuration were successfully predicted from rat...

Application of semiconductor quantum dots in bioimaging and biosensing.

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing. We analyze the biologically relevant properties of QDs focusing on the following topics: QD surface treatment and stability, labeling of cellular structures and receptors with QDs, incorporation of QDs in living cells, cytotoxicity of QDs and influence of the biological environment on the biological and optical properties of QDs. Initially, we consider utilization of QDs as agents in high-resolution bioimaging techniques that can provide information at the molecular levels. The diverse range of modern live-cell QD-based imaging techniques with resolution far beyond the diffraction limit of light is examined. In each technique, we discuss the pros and cons of QD use and deliberate how QDs can be further engineered to facilitate their application in the respective imaging techniques and to produce significant improvements in resolution. Then we review QD-based point-of-care bioassays, bioprobes, and biosensors designed in different formats ranging from analytic biochemistry assays and ELISA, to novel point-of-care smartphone integrated QD-based biotests. Here, a wide range of QD-based fluorescence bioassays with optical transduction, elecrochemiluminescence and photoelectrochemical assays are discussed. Finally, this review provides an analysis of the prospects of application of QDs in selected important areas of biology.

One-pot aqueous synthesis of germanium-doped cadmium sulfide quantum dots as fluorescent probes for cell imaging

Water-soluble germanium-doped cadmium sulfide quantum dots (Ge:CdS q-dots) were successfully synthesized by a facile one-pot method, and used as fluorescent probes for labeling live MCF-7 cells. The optical properties of the q-dots and several key parameters of the synthesis conditions were studied, and the mechanism of these parameters was also discussed. After doping with germanium, the PL intensity increased 50%, while improving the photostability and fluorescence quantum yield. Furthermore, the toxicity of CdS quantum dot decreased after doping with germanium due to its low toxicity, which greatly improved the CdS quantum dots biocompatibility. Then the doped quantum dots modified with folic acid (FA) to use as fluorescent probes, which expanded the application of semiconductor quantum dots in the biomedical field.

Biomedical Applications of Quantum Dots, Nucleic Acid-Based Aptamers, and Nanostructures in Biosensors.

This review is a survey of the biomedical applications of semiconductor quantum dots, nucleic acid-based aptamers, and nanosensors as molecular biosensors. It focuses on the detection of analytes in biomedical applications using (1) advances in molecular beacons incorporating semiconductor quantum dots and nanoscale quenching elements; (2) aptamer-based nanosensors on a variety of platforms, including graphene; (3) Raman scattering and surface-enhanced Raman scattering (SERS) using nanostructures for enhanced SERS spectra of biomolecules, including aptamers; and (4) the electrical and optical properties of nanostructures incorporated into molecular beacons and aptamer-based nanosensors. Research done at the University of Illinois at Chicago (UIC) is highlighted throughout since it emphasizes the specific approaches taken by the bioengineering department at UIC.

Application of semiconductor quantum dots to white-light-emitting diodes

Based on the electro-optical energy transfer process, the pseudo-spectral-luminous efficiency function (QD) of quantum dots (QDs) is introduced, the equations of chromaticity coordinates, luminous efficiency, and the QDs' mass of the white-light-emitting devices with CdSe, CuInS2 or CdS:Mn QDs are obtained, and the calculated results are in agreement with the experimental data. For a certain luminescent peak wavelength, when the full width at half maximum of the QD's photoluminescence becomes larger, the QD value becomes smaller while the chromaticity coordinates become more different from those of the corresponding monochromatic light. It is indicated that the color rendering index (CRI) of the devices is strongly dependent on the photoluminescent position and width of the QDs, and the CRI value can be increased towards 98 when a certain kind of CdS:Mn QDs is added into the traditional white-light LEDs.

Recent advances in the field of bionanotechnology: an insight into optoelectric bacteriorhodopsin, quantum dots, and noble metal nanoclusters.

Molecular sensors and molecular electronics are a major component of a recent research area known as bionanotechnology, which merges biology with nanotechnology. This new class of biosensors and bioelectronics has been a subject of intense research over the past decade and has found application in a wide variety of fields. The unique characteristics of these biomolecular transduction systems has been utilized in applications ranging from solar cells and single-electron transistors (SETs) to fluorescent sensors capable of sensitive and selective detection of a wide variety of targets, both organic and inorganic. This review will discuss three major systems in the area of molecular sensors and electronics and their application in unique technological innovations. Firstly, the synthesis of optoelectric bacteriorhodopsin (bR) and its application in the field of molecular sensors and electronics will be discussed. Next, this article will discuss recent advances in the synthesis and application of semiconductor quantum dots (QDs). Finally, this article will conclude with a review of the new and exciting field of noble metal nanoclusters and their application in the creation of a new class of fluorescent sensors.

The contribution of the capillary endothelium to blood clearance and tissue deposition of anionic quantum dots in vivo

The increasing interest in biomedical applications of semiconductor quantum dots (QDs) is closely linked to the use of surface modifications to target specific sites of the body. The immense surface area of vascular endothelium is a possible interaction platform with systemically administered QDs. Therefore, the aim of this study was to investigate the microvascular distribution of neutral, cationic, and anionic QDs in vivo. QDs with carboxyl-, amine- and polyethylene glycol surface coatings were injected into the blood circulation of mice. In vivo microscopy of the cremaster muscle, two-photon microscopy of skeletal and heart muscle, as well as quantitative fluorescence measurements of blood, excreta, and tissue samples were performed. Transmission electron microscopy was used to detect QDs at the cellular level. The in vitro association of QDs with cultured endothelial cells was investigated by flow cytometry and confocal microscopy. Anionic QDs exhibited a very low residence time in the blood stream, preferably accumulated in organs with a prominent mononuclear phagocytic component, but were also found in other tissues with low phagocytic properties where they were predominantly associated with capillary endothelium. This deposition behavior was identified as a new, phagocyte-independent principle contributing to the rapid clearance of anionic QDs from the circulation.

Spin-polarization dynamics in electrically excited single InGaAs quantum dots

Potential applications of semiconductor quantum dots include spin memory and quantum information processing devices. For these, a rapid spin-initialization process would be desirable. In this contribution, we demonstrate nanosecond-pulsed electrical spin-injection into quantum dots embedded in a spin light-emitting diode. As inferred from time-resolved electroluminescence experiments, the circular polarization degree of the emitted light exhibits a peak at the beginning of the electroluminescence signal, indicating that the spin-initialization is more efficient in pulsed operation than under constant-current excitation. Results for the quantum-dot ensemble, the wetting layer states, and for single quantum dots are presented. We attribute these observations to energy-dependent spin-relaxation processes in the device.

Use of the Semiconductor Nanotechnologies &amp;#x201C;Quantum Dots&amp;#x201D; for in vivo Cancer Imaging

Non-invasive in vivo imaging offers great potential to facilitate translational drug development research at the animal testing phase. The emerging luminescent nanoparticles or quantum dots provide a new type of biological agents that can improve these applications. The advantages of luminescent nanoparticles for biological applications include their high quantum yield, color availability, good photo-stability, large surface-to-volume ratio, surface functionality, and small size. These properties could improve the sensitivity of biological detection and imaging by at least 10- to 100-fold and make them an exceptional tool for live-cell imaging. In this review patents on applications of semiconductor quantum dots for in vivo imaging are discussed.

Doped Carbon Nanoparticles as a New Platform for Highly Photoluminescent Dots

There have been rapid advances in the development and applications of semiconductor quantum dots (QDs) represented by CdSe/ZnS. However, a serious limitation of these QDs is the necessary use of toxic heavy metals. It is reported here that small carbon nanoparticles doped with inorganic salts serve as a highly promising new platform for brightly photoluminescent dots. The photoluminescent carbon dots with the carbon core doped with ZnO (C(ZnO)-Dots) or ZnS (C(ZnS)-Dots) in aqueous solutions are competitive to the commercially available CdSe/ZnS QDs in luminescence brightness.

New physics and devices based on self-assembled semiconductor quantum dots

Self-assembled semiconductor quantum dots (QDs) exhibit fully quantized electronic states and high radiative efficiencies. This makes them highly suitable both for fundamental physics studies of zero-dimensionality, atomic-like semiconductor systems and applications in a range of novel electro-optical devices. This review discusses recent important advances in the study and application of semiconductor QDs. Using a wide range of optical spectroscopy techniques, it is possible to obtain a detailed understanding of the electronic structure and dynamical carrier processes. Such an understanding is required for the implementation of a wide range of QD-based devices.