Surface Of Quantum Dots Research Articles

Anomalous photoluminescence of InAs surface quantum dots: intensity enhancement and strain control by underlying quantum dots

Strain control and photoluminescence (PL) enhancement of InAs surface quantum dots (SQDs), exposed to ambient conditions, have been achieved by introducing underlying buried quantum dots (BQDs). The PL wavelength has been tuned from 1270 to as long as 1780 nm, redshifted as the size of the SQDs is reduced. This is in strong contrast to standard QDs, in which blueshift is observed from smaller QDs following basic quantum mechanics. Here, smaller SQDs, both in height and base area, as observed by atomic force microscopy, were obtained with wider GaAs spacer thickness between the SQDs and BQDs. The result strongly suggests that strain and related effects dominate the electronic properties of the SQDs rather than their size, and that a change in the complex strain field occurs through the spacer. The underlying BQDs also serve as effective carrier reservoirs. A PL intensity enhancement of 17 fold was observed as the GaAs spacer thickness was reduced from 150 to 10 nm. A large portion of the photoexcited carriers is initially captured and stored in the BQDs. When sufficient carriers are transferred to fill non-radiative surface states, the excess may be transferred to the SQDs enhancing the luminescence.

Semiconductor Quantum Dots as Target Analytes: Properties, Surface Chemistry and Detection.

Since the discovery of Quantum Dots (QDs) by Alexey I. Ekimov in 1981, the interest of researchers in that particular type of nanomaterials (NMs) with unique optical and electrical properties has been increasing year by year. Thus, since 2009, the number of scientific articles published on this topic has not been less than a thousand a year. The increasing use of QDs due to their biomedical, pharmaceutical, biological, photovoltaics or computing applications, as well as many other high-tech uses such as for displays and solid-state lighting (SSL), has given rise to a considerable number of studies about its potential toxicity. However, there are a really low number of reported studies on the detection and quantification of QDs, and these include ICP–MS and electrochemical analysis, which are the most common quantification techniques employed for this purpose. The knowledge of chemical phenomena occurring on the surface of QDs is crucial for understanding the interactions of QDs with species dissolved in the dispersion medium, while it paves the way for a widespread use of chemosensors to facilitate its detection. Keeping in mind both human health and environmental risks of QDs as well as the scarcity of analytical techniques and methodological approaches for their detection, the adaptation of existing techniques and methods used with other NMs appears necessary. In order to provide a multidisciplinary perspective on QD detection, this review focused on three interrelated key aspects of QDs: properties, surface chemistry and detection.

Co2P/CoP quantum dots surface heterojunction derived from amorphous Co3O4 quantum dots for efficient photocatalytic H2 production

Amorphous/crystalline heterostructures show excellent potential in the hydrogen evolution reaction (HER) as they can significantly facilitate surface adsorption and redox reactions. Herein, a unique amorphous Co2P/crystalline CoP quantum dots (Co2P/CoP QDs) Type-II surface heterojunction was derived from amorphous Co3O4 QDs via phosphorization. The intimate contact between Co2P QDs and CoP QDs was conducive to charge transfer, thereby promoting surface reaction kinetics. The unique structure and properties were beneficial to providing more active sites and controlling the electronic structures thus making amorphous/crystalline composites show superior photocatalytic hydrogen (H2) production performance. Additionally, the amorphous Co2P QDs had a plethora of unsaturated bonds and abundant defects; the disordered structure led to increased active sites that promoted surface reaction kinetics. Due to the synergistic effect of the quantum confinement of QDs and the surface heterojunction, the charge transfer efficiency of Co2P/CoP QDs was extremely high, and high H2 evolution activity and photostability were achieved. The maximum H2 generation rate over the Co2P/CoP QDs composite reached 11.88 mmol h−1 g−1 with an apparent quantum efficiency (AQE) of 3.88 % at 420 nm, which is roughly 20-times that of the pure Co3O4 QDs. In addition, high photostability was realized; even the photocatalyst that stood for a week reached initial photoactivity. This work offers a novel idea for reasonably establishing amorphous/crystalline photocatalysts to achieve efficient H2 evolution.

Multifunctional probe based on modified Ag&Mn:ZnInS QDs for dual-mode fluorescence and magnetic resonance imaging of intracellular glutathione

Glutathione (GSH) plays vital roles in a variety of biological processes, and the development of simple and effective GSH detection method is an important research topic. Herein, a multifunctional probe based on Ag&Mn:ZnInS quantum dots (QDs) was developed for bimodal imaging of GSH. MnO2, as an efficient fluorescence quencher, was in-situ grown on the surface of QDs, and then modified with hyaluronic acid (HA) to improve the stability and targeted recognition capability of the probe due to the binding between HA and CD44 receptors. After MnO2 was deconstructed by GSH, the fluorescence of the probe was recovered and the generated Mn2+ could serve as good magnetic resonance imaging (MRI) contrast agent. Moreover, the near-infrared emission probe was successfully employed in living cell and zebrafish imaging due to its low toxicity and high anti-biological interference performance. This strategy provides a simple dual-mode fluorescence/MRI imaging of GSH, which may have a broad application in biological detection.

In Situ Ligand‐Exchange in Solid Quantum Dots Film Enables Stacked White Light‐Emitting Diodes

AbstractSolution‐processed white quantum dot light‐emitting diodes (WQLEDs) hold great promise for lighting and backlight applications. Stacked blue/green/red quantum dots (QDs) films as an emitting layer through the layer‐by‐layer deposition offer a simple way to realize WQLEDs. However, the redissolution issue rising from the deposition of the adjacent QDs layers prevents the fabrication of high‐quality multilayer emissive layers. Here, a ligand exchange strategy is developed to improve the solvent‐resistance of the QDs films by exposing the QDs films in a trace acid environment. The dissociated hydrions from the acid protonate the aliphatic ligands and desorb them away from QDs’ surface, leaving space for inorganic ions to anchor onto the QDs’ surface. Importantly, the trace acid does not destroy the morphological properties of QDs films and reserves their initial photoluminescence efficiency. In addition, the charge transporting ability of the QDs is enhanced on account of the replaced inorganic ligands. As result, the stacked WQLEDs display pure white emission with Commission International de I'Eclairage coordinates of (0.34, 0.33), and impressive external quantum efficiency of 9.1% has been demonstrated. This solid‐phase ligands exchange strategy provides an alternative way to engineer the surface of QDs for efficient optoelectronics.

A Nanobody-on-Quantum Dot Displacement Assay for Rapid and Sensitive Quantification of the Epidermal Growth Factor Receptor (EGFR).

Biosensing approaches that combine small, engineered antibodies (nanobodies) with nanoparticles are often complicated. Here, we show that nanobodies with different C‐terminal tags can be efficiently attached to a range of the most widely used biocompatible semiconductor quantum dots (QDs). Direct implementation into simplified assay formats was demonstrated by designing a rapid and wash‐free mix‐and‐measure immunoassay for the epidermal growth factor receptor (EGFR). Terbium complex (Tb)‐labeled hexahistidine‐tagged nanobodies were specifically displaced from QD surfaces via EGFR‐nanobody binding, leading to an EGFR concentration‐dependent decrease of the Tb‐to‐QD Förster resonance energy transfer (FRET) signal. The detection limit of 80±20 pM (16±4 ng mL−1) was 3‐fold lower than the clinical cut‐off concentration for soluble EGFR and up to 10‐fold lower compared to conventional sandwich FRET assays that required a pair of different nanobodies.

Nondestructive Direct Photolithography for Patterning Quantum Dot Films by Atomic Layer Deposition of ZnO

AbstractColloidal quantum dot‐based light‐emitting diodes (QD‐LEDs) are one of the potential future self‐emissive displays owing to their large‐scale solution‐processibility and high color purity. For the industrial application of QD‐LEDs, high‐performance QD‐LED and high‐resolution patterning of quantum dot (QD) films are required. Photolithography is an ideal tool for patterning QD films. Previously, the high‐resolution patterning of QD films using direct photolithography by ultra‐thin atomic layer deposition of ZnO on the QD surface is reported. The patterning process is acceptable for Cd‐based QD films, but the photoresist severely deteriorates the photoluminescence (PL) intensity of InP‐based QD films owing to the presence of sulfonic groups in the photoactive compound. Herein, a non‐destructive direct photolithography process for QD film patterning using a negative photoresist that does not affect the PL intensities of Cd‐ and InP‐based QD films is reported. The effect of the photoresist is also verified by a PL lifetime study. Extremely bright Cd‐ and InP‐based QD films are successfully patterned using a softer photoresist, and micropatterning of InP‐based QD films is reported for the first time in this work using photolithography. A QD electroluminescence device is also successfully fabricated using the patterning method.

A Nanobody‐on‐Quantum Dot Displacement Assay for Rapid and Sensitive Quantification of the Epidermal Growth Factor Receptor (EGFR)

AbstractBiosensing approaches that combine small, engineered antibodies (nanobodies) with nanoparticles are often complicated. Here, we show that nanobodies with different C‐terminal tags can be efficiently attached to a range of the most widely used biocompatible semiconductor quantum dots (QDs). Direct implementation into simplified assay formats was demonstrated by designing a rapid and wash‐free mix‐and‐measure immunoassay for the epidermal growth factor receptor (EGFR). Terbium complex (Tb)‐labeled hexahistidine‐tagged nanobodies were specifically displaced from QD surfaces via EGFR‐nanobody binding, leading to an EGFR concentration‐dependent decrease of the Tb‐to‐QD Förster resonance energy transfer (FRET) signal. The detection limit of 80±20 pM (16±4 ng mL−1) was 3‐fold lower than the clinical cut‐off concentration for soluble EGFR and up to 10‐fold lower compared to conventional sandwich FRET assays that required a pair of different nanobodies.

Surface plasmon-enhanced aptamer-based fluorescence detection of cocaine using hybrid nanostructure of cadmium-free ZnSe/In2S3 core/shell quantum dots and gold nanoparticles

Cocaine abuse remains a global public health problem and a contributing factor to various social problems. In this work, we report on the development of a novel amphiphilic polymer (A-polym)-functionalized cadmium-free ZnSe/In2S3 core/shell quantum dots (QDs)-cationic cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticle (AuNP) fluorescence nanoprobe for cocaine. ZnSe/In2S3 QDs were synthesized using the classic organometallic synthetic route for group II – VI semiconductor QDs and was surface-capped with organophosphorous-based ligands and organic-based stabilizers. A-polym, synthesized using an anhydride-capped polymer backbone and a nucleophilic agent, was used as a capping agent to coat and stabilize the QDs surface. The A-polym-coated QDs was electrostatically linked to cationic cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticles (AuNPs) to form an A-polym-QDs-AuNP nanohybrid. The electrostatic interaction between the A-polym-coated QDs and CTAB-AuNPs quenched the fluorescence emission of the bound QDs. An MNS 4.1 anticocaine thiolated DNA aptamer (Aptm) was adsorbed on the A-polym-QDs-AuNP surface to form an Aptm-A-polym-QDs-AuNP nanoprobe. Upon interaction of cocaine with the Aptm-A-polym-QDs-AuNP nanoprobe, the fluorescence of the bound QDs was remarkably enhanced based on localized surface plasmon resonance-induced fluorescence emission signal. In general, the QDs functioned as the fluorophore reporter, CTAB-AuNP as a plasmon amplifier and the Aptm as the receptor. Under optimum reaction conditions, cocaine was selectively and quantitatively detected with a detection limit of 0.8 nM. Selectivity was achieved against other drugs and cocaine metabolites. The efficacy of the Aptm-A-polym-QDs-AuNP nanoprobe to detect cocaine in adulterated cocaine samples was successfully achieved.

C3N4 and C3N5 Nanosheets As Passivation Layers and Carrier Extractors for Inorganic Semiconductor Nanowires and Quantum Dots

Inorganic semiconductor nanowires and quantum dots made of chalcogenides, III-V semiconductors and halide perovskites offer exciting potential for optoelectronic devices. The orthogonalization possible in nanowires between the normally competing processes of charge generation and charge separation have been used to project very high operating performance exceeding that of thin films and single crystals in light harvesting devices such as solar cells, photodetectors, photocatalysts and photoelectrolyzers. Likewise, inorganic quantum dots with size-tunable absorption and emission spectra are excellent candidates for light emitting devices as well as light harvesting devices. However, the practical performance of inorganic nanowire based optoelectronic devices has significantly lagged theoretical predictions. A major reason for the discrepancy between theory and experiment is the presence of surface traps and defects in nanowires and quantum dots, which exhibit a large surface area to volume ratio. Several chemical treatments and annealing regimens have been employed to heal surface defects in nanowires and quantum dots. One popular strategy involves wrapping nanowires and/or quantum dots with a thin coating of a molecular monolayer (e.g. alkanethiols) or an atomic layer deposited conformal oxide. While such core-shell architectures are frequently effective in reducing surface defects, the surface passivation is invariably accompanied by a deterioration in optoelectronic properties due to the difficulty experienced by charge carriers in tunneling through the thin shell layer. The resulting trade-off between surface passivation and carrier extraction limits performance improvements in light harvesting devices. Thus there is a strong need for passivating layers that do not negatively impact carrier extraction.Herein, we show that graphitic carbon nitride coatings are highly effective in passivating the surfaces of inorganic nanowires and quantum dots while preserving excellent carrier transport and extraction. Three illustrative examples are provided together with in-depth spectroscopic and electrical characterization:(1) Cesium lead bromide (CsPbBr3) quantum dots passivated by g-C3N4 nanosheets and performing spectacularly as CO2 photoreduction catalysts and water-splitting photoanodes(2) The double helical ternary semiconductor SnIP passivated by g-C3N4 nanosheets which experienced a remarkable improvement in photoelectrochemical performance(3) Cadmium sulfide (CdS) nanowires passivated by C3N5 nanosheets resulting in a superior photocatalytic performance

Fundamental Charge Transfer Dynamics in 2D TMDCs for Use in Novel Heterostructures

Efficient transfer of charge carriers and/or excitons between small organic molecules and two-dimensional (2D) semiconductor interfaces is being explored for applications in photovoltaics and quantum information processing.Interfaces of small molecules and 2D semiconductors such as graphene, nanocrystals, quantum dots and transition metal dichalcogenides (TMDCs) are capable of charge, energy, and spin singlet transfer. The long excited state lifetimes of spin triplet excitons makes triplet exciton transfer across such interfaces advantageous for exciton harvesting and photon upconversion. However, to date, triplet energy transfer between physisorbed small molecules and monolayer TMDCs has only been reported in a single study. To our knowledge, the process where photoexcitation of a TMDC/organic interface yields triplet excitons in the TMDC layer has not been reported. In quantum dot (QD) systems, direct covalent attachment of organic molecules to QD surfaces has shown to facilitate triplet energy transfer across the QD/molecule interface, but this covalent approach has not been widely applied to TMDC/molecule interfaces.Here we present a systematic study of covalently functionalized TMDC/molecule interfaces employing synthetically tailored thiolated acenes. We create tunable amounts of sulfur vacancies, which allows for subsequent covalent acene functionalization. We study the impact of covalent bonding on the charge transfer (CT) dynamics of TMDC/organic interfaces with energy level offsets suitable for charge and energy transfer (ET) as well as triplet acceptance and sensitization. We characterize the interfaces with a variety of steady-state and time-resolved spectroscopic techniques and initial results show success in selective isolation of CT vs ET pathways. Figure 1

Thermally Processed Quantum-Dot Polypropylene Composite Color Converter Film for Displays

Quantum dots (QDs) have attracted much attention as one of the most promising candidates for next-generation display materials. However, stability is still a big challenge for QDs. Herein, we encapsulated QDs in a thermoplastic polypropylene (PP) matrix by thermal processing technology to prepare a stabler color conversion film for the first time. Thermal processing technology expands the packaging materials of QDs from traditional soluble polymers to thermoplastic polymers such as PP with easy processing and a low cost. We showed that the QDs in the PP film exhibited longer-lasting stability than the traditional PMMA film. After 216 h of blue light accelerated aging test, the QDs maintained more than 90% of the initial performance in the PP film but dropped to less than 25% in the PMMA film. Moreover, the reasons for the improved stability have been further discussed. It was found that the PP-H film not only possessed better barriers to moisture and oxygen, but the absence of ester groups also led to a milder environment around the QDs. The results show that ester groups have stronger electronegativity and easily cause the ligands on the surface of QDs to fall off, which lead to performance degradation.

Detection of Cd2+ in Aqueous Solution by the Fluorescent Probe of CdSe/CdS QDs Based on OFF-ON Mode.

The detection of heavy metals in aqueous solutions has always attracted much attention from all over the world. A fluorescent probe of CdSe/CdS core-shell quantum dots (QDs) was designed to detect trace Cd2+ in aqueous solutions using the OFF–ON mode rapidly and efficiently, likely based on adsorption and desorption reactions between ethylenediaminetetraacetic acid disodium salt (EDTA) and CdSe/CdS QDs. In the OFF mode, the optical shielding function of EDTA results in fluorescence quenching owing to the strong adsorption ability of EDTA with Cd2+ on the sites of CdSe/CdS QDs surface. In the ON mode, the introduction of Cd2+ promotes the desorption of EDTA from the EDTA-CdSe/CdS QDs and restores the fluorescence intensity. There were two linear response ranges which were 0.1–20 µmol/L and 20–90 µmol/L for the EDTA-CdSe/CdS system to detect Cd2+. The detection limit was 6 nmol/L, and the standard deviation was below 4% for the detection of Cd2+ concentration in tap water.

Fluorescence Detection of Cancer Stem Cell Markers Using a Sensitive Nano-Aptamer Sensor.

Antigen CD133 is a glycoprotein present on the surface of cancer stem cells (CSCs), which is a key molecule to regulate the fate of stem cells and a functional marker of stem cells. Herein, a novel fluorescence “turn-on” nano-aptamer sensor for quantifying CD133 was designed using hybridization between CD133-targeted aptamers and partially complementary paired RNA (ssRNA), which were modified on the surface of quantum dots (QDs) and gold nanoparticles (AuNPs), respectively. Owing to the hybridization of aptamers and ssRNA, the distance between QDs and AuNPs was shortened, which caused fluorescence resonance energy transfer (FRET) between them, and the florescence of QDs was quenched by AuNPs. When CD133 competitively replaced ssRNA and was bound to aptamers, AuNPs-ssRNA could be released, which led to a recovery of fluorescent signals of QDs. The increase in the relative value of fluorescence intensity was investigated to linearly correlate with the CD133 concentration in the range of 0–1.539 μM, and the detection limit was 6.99 nM. In confocal images of A549 cells, the CD133 aptamer sensor was further proved applicable in lung cancer cell samples with specificity, precision, and accuracy. Compared with complicated methods, this study provided a fresh approach to develop a highly sensitive and selective detection sensor for CSC markers.

Doping of superalkali and superhalogen on graphene quantum dot surfaces to enhance nonlinear optical response: An efficient strategy for fabricating novel electro-optical materials

Graphene quantum dots are evolving as a popular novel class of organic nonlinear optical (NLO) materials, with applications in optoelectronics, nanocomposites, and many other areas. Tetragonal graphene quantum dots (T-GQDs) doped with superalkalis (Li3O, Li4N) and superhalogens (BeF3, BF4) have been investigated here with regard to their geometrical, thermodynamic, electronic, and NLO properties by means of density functional theory (DFT) calculations at the B3LYP level. Computational studies reflect the high stability of these complexes, and indicate interaction with the dopants at the top of a cavity. Interaction energies of dopant molecules suggest the feasibility of their complexation on a T-GQD sheet, with an isomer of BF4@T-GQD showing the highest interaction energy (Eint) of −97.15 kcal mol−1. HOMO-LUMO energy gaps (EH-L) yield the lowest band gap (0.23 eV) for an isomer of Li3O@T-GQD, which in turn enhances the NLO response. A significant increase in NLO response is noted for all of the reported complexes, particularly for superalkali-doped Li4N@T-GQD, which displays a first hyperpolarizability (βo) of 4.5 × 104 a.u. Moreover, absorption phenomena prove that the resultant complexes retain viable deep-ultraviolet (UV) transparency. Natural bond order (NBO) and density of states (DOS) analyses further verify charge transfer and the establishment of new states in the complexes. All of the results manifest the distinction of superalkali- and superhalogen-doping on T-GQD, with superalkali being an electron-donating entity and superhalogen showing electron-withdrawing behavior. We conclude that superalkali-doped Li4N@T-GQD and superhalogen-doped BF4@T-GQD complexes (isomers f and l) may serve as excellent alternatives to current NLO materials. Hence, this study may pave the way for the fabrication of thermally stable graphene quantum dot complexes as valuable precursors for highly efficient NLO materials.

Development of tumor-specific liposomes containing quantum dots-photosensitizer conjugate used for radiotherapy

This study aims to develop a multifunctional liposomal radiosensitizer to destroy more tumor cells by using lower radiation doses compared to clinically used 6 MV X-ray doses. To achieve this aim, first Chlorine-e6 (Ce6) was covalently bound to functional groups of outer surfaces of quantum dots (QDs) through EDC/NHS reactions. Then, QDs-Ce6 conjugate loaded, nanosized, PEG-coated, and tumor-specific folic acid-modified immunoliposome dispersions were prepared by film method. Enhanced anti-proliferation activity of free and liposomal conjugate against 4T1 (murine breast cancer) cell lines was investigated at different X-ray doses (5, 10, 15, and 20 Gy). As a result, the best radiosensitizer effect was observed at a 5 Gy X-ray dose and it was found that following the X-ray irradiation, immunoliposome dispersions containing QDs-Ce6 conjugate killed 26.8 ± 1.7% more cancer cells than radiation alone.

Dual-channel fluorescent imaging of reactive oxygen species in living cells based on Ce(III) modified quantum dots with oxidation triggered phosphatase-like activity

The two-wavelength fluorescent sensing and imaging of reactive oxygen species (ROS) was demonstrated using Ce(III) ions modified fluorescent quantum dots (QDs). After the addition of ROS, the Ce(III) on the surface of QDs was transformed to Ce(IV) which exhibits phosphatase-like catalytic activity. The Ce(IV)/QDs can catalyze the hydrolysis of 4-methylumbelliferyl phosphate (4-MUP) to generate blue emission. On the other hand, ROS had only slight effect on the red fluorescent signal of QDs. Based on this phenomenon, the ratiometric fluorescent detection of ROS (ClO-, H2O2, and ONOO-) was successfully performed by using Ce(III)/QDs/4-MUP system. The two fluorescent emission peaks (450 nm and 620 nm) were well-separated, which holds the advantages such as high selectivity and accuracy. Finally, the Ce(III)/QDs/4-MUP system was successfully used for dual-channel fluorescent ROS imaging in HeLa and RAW264.7 cells.

Quantum Dot-Antibody Conjugates for Immunofluorescence Studies of Biomolecules and Subcellular Structures.

Quantum dots, or nanoscale semiconductors, are one of the most important materials for various research and development purposes. Due to their advantageous photoluminescence and electronic properties, namely, their unique photostability, high brightness, narrow emission spectra from visible to near-infrared wavelengths, convey them significant advantages over widely used fluorochromes, including organic dyes, fluorescent probes. Quantum dots are a unique instrument for a wide range of immunoassays with antibodies. The paper provides an overview of the developed and already applied methods of quantum dot surface modification, quantum dots conjugation to different antibodies (non-covalent, direct covalent linkage or with the use of special adapter molecules), as well as practical examples of recent quantum dot-antibody applications in the immunofluorescence microscopy for cell and cell structure imaging, fluorescent assays for biomolecules detection and in diagnostics of various diseases. The review presents advantages of quantum dot-antibody conjugation technology over the existing methods of immunofluorescence studies and a forward look into its potential prospects in biological and biomedical research.

In situ-Synthesized cadmium sulfide quantum dots in pore-forming protein and polysaccharide matrices for optical biosensing applications

The main limitation for practical implementation of quantum dots-based sensors and biosensors is the possible contamination of sensing media with quantum dots (QDs) moved out from the sensor structure, being critical for living systems measurements. Numerous efforts have addressed the challenge of pre-synthesized QDs incorporation into porous matrix provide, on the one hand, proper fixation of quantum dots in its volume and preserving a free analyte transfer from the sensing media to them - on the other hand. Here, we propose an alternative insight into this problem. Instead of using preliminary synthesized particles for doping a matrix, we have in situ synthesized cadmium sulfide QDs in porous biopolymeric matrices, both in an aqueous solution and on a mica substrate. The proposed technique allows obtaining QDs in a matrix acting simultaneously as a ligand passivating surface defects and preventing QDs aggregation. The conjugates were used as a photoluminescence sensor for the metal ions and glutathione detection in an aqueous media. Different kinds of sensor responses have been found depending on the analyte nature. Zinc ions' presence initiates the intraband QDs emission increases due to the reduction of non-radiative processes. The presence of copper ions, in contrast, leads to a gradual photoluminescence decrease due to the formation of the non-luminescent copper-based alloy in the QDs structure. Finally, the presence of glutathione initiates a ligand exchange process followed by some QDs surface treatment enhancing defect-related photoluminescence. As a result, three different kinds of sensor responses for three analytes allow claiming development of a new selective QD-based sensor suitable for biomedical applications.

Size Engineering of Trap Effects in Oxidized and Hydroxylated ZnSe Quantum Dots.

Environmentally friendly blue-emitting ZnSe quantum dots (QDs) are in high demand for next-generation light-emitting devices. Yet, they suffer longstanding optical instability issues under aerobic conditions. Herein, we have demonstrated the existence of oxidization or hydroxylation on the QD surface when QDs are subjected to oxygen exposure, which potentially introduces highly localized in-gap states. Those states result in a dense number of surface-related, weak-intensity "dark" exciton states at the emission edge. Remarkably, there exists a critical diameter (Dc ≈ 8.5 nm) at which the deepest trap level reaches resonance with the highest occupied molecular orbital state. Beyond this critical diameter, the effects of those trap states are minimized, and the emission edge is dominated by high-intensity, bulk-to-bulk-like "bright" exciton states. The present work provides a novel strategy for designing highly stable QD emitters via size engineering, which are broadly applicable to other closely related QD systems.