Surface Modification Of Quantum Dots Research Articles

(Invited) Photocatalytic H2 Evolution Activity of Anisotropic-Shaped ZnSe-AgInSe2 Solid Solution Quantum Dots with a Near-IR-Responsivity

Semiconductor nanocrystals, often referred to as quantum dots (QDs), exhibit unique physicochemical properties due to the quantum size effect when their size is less than 10 nm. In our previous works, we successfully synthesized Zn-Ag-In-S (ZAIS) solid solution QDs with a tunable energy gap (Eg) and then reported the photocatalytic activity for H2 evolution depending on their morphology and particle composition [1,2]. However, ZAIS QDs have limited light absorption with wavelengths less than ca. 600 nm, restricting their utilization of near-infrared light in solar light. In this study, we report the preparation of near-IR-responsive QD photocatalysts with use of Zn-Ag-In-Se (ZAISe) solid solution semiconductors. Precise controls over their morphology and particle composition enabled to vary their photocatalytic H2 evolution activity.ZAISe QDs with different compositions and particle shapes (sphere or rod) were synthesized by thermal decomposition of corresponding metal acetates and selenourea in a mixture solution of oleylamine and dodecane thiol at 250 oC. The chemical composition of QDs was controlled by varying the Zn fraction in metal precursors, ensuring nearly stoichiometric composition.The obtained QDs with a rod shape had lengths varying from ca. 10 to 100 nm, correlating with an increase in the Zn fraction. The onset wavelengths of absorption spectra of the ZAISe QDs were red-shifted from 500 nm to 900 nm with decreasing Zn fraction, indicating that the Eg of ZAISe QDs was controlled between visible and near-infrared wavelength regions.The QDs modified with dodecane thiol showed poor dispersibility in water and almost no photocatalytic activity for H2 evolution. In contrast, the surface modification of QDs with 3-mercaptopropionic acid enabled to uniformly disperse in an aqueous solution. The photocatalytic activity of ZAISe QDs was investigated for H2 evolution as a model reaction. The irradiation to ZAISe QDs in an aqueous solution containing Na2S and Na2SO3 as hole scavengers was carried out using Xe lamp light (λ> 350 nm). The H2 evolution rate exhibited a remarkable dependence on both the composition and particle shape of ZAISe QDs. The photocatalytic activity showed a tendency to increase with the enlargement of the Eg of QDs, probably due to the negative shift of conduction band minimum potential. The optimum H2 evolution activity was obtained with rod-shaped QDs having the Eg of 1.65 eV, being twice as large as that of spherical QDs with a similar Eg. This behavior can be attributed to the change of the crystal facets exposed on the QD surface. References Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, and T. Torimoto, J. Phys. Chem. C, 2015, 119, 24740-24749.Torimoto, Y. Kamiya, T. Kameyama, H. Nishi, T. Uematsu, S. Kuwabata, and T. Shibayama, ACS Appl. Mater. Interfaces 2016 , 8, 27151-27161.

Supramolecular Click Chemistry for Surface Modification of Quantum Dots Mediated by Cucurbit[7]uril.

Cucurbiturils (CBs), barrel-shaped macrocyclic molecules, are capable of self-assembling at the surface of nanomaterials in their native state, via their carbonyl-ringed portals. However, the symmetrical two-portal structure typically leads to aggregated nanomaterials. We demonstrate that fluorescent quantum dot (QD) aggregates linked with CBs can be broken-up, retaining CBs adsorbed at their surface, via inclusion of guests in the CB cavity. Simultaneously, the QD surface is modified by a functional tail on the guest, thus the high affinity host-guest binding (logKa > 9) enables a non-covalent, click-like modification of the nanoparticles in aqueous solution. We achieved excellent modification efficiency in several functional QD conjugates as protein labels. Inclusion of weaker-binding guests (logKa = 4-6) enables subsequent displacement with stronger binders, realising modular switchable surface chemistries. Our general "hook-and-eye" approach to host-guest chemistry at nanomaterial interfaces will lead to divergent routes for nano-architectures with rich functionalities for theranostics and photonics in aqueous systems.

Quantum Dot-Based Fluorometric Sensor for Hg(II) in Water Customizable for Onsite Visual Detection.

An easy naked-eye detection technique for mercuric ions in water using silanized quantum dots is demonstrated. Cadmium selenide quantum dots were synthesized and rendered water soluble by silica overcoating. The quantum dot emission was instantly turned off by the mercuric ions in the analyte, enabling visual detection. The emission quenching was associated with a concomitant bathochromic shift, both in the absorption and emission profiles. The underlying mechanism is a permanent surface modification of quantum dots by mercuric ions, altering the electronic structure and, in turn, the photophysical properties. The results confirmed the potential of this simple system to be customized for on-site visual detection of mercury contamination in water bodies, biological fluids, and soil with high selectivity and sensitivity.

Binding of Water‐Soluble CdSe Quantum Dots with Human Serum Albumin: Further Studies into their Effects on Dietary Polyphenol Binding and Sensing of Antibiotic Lomefloxacin

AbstractSynthesis of surface modified quantum dots (QDs) having potential biological activities are great important in biomedicinal chemistry. Here, we have synthesized mercapto propanoic acid (MPA) and thiolactic acid (TLA) coated water soluble cadmium selenide (CdSe) QDs having biological activity. Dispersion of QDs into a biological fluid can form protein corona. Hence, the binding of CdSe QDs with the carrier protein, human serum albumin (HSA) have been executed using spectroscopic methods. The binding affinity order of CdSe QDs‐HSA complexes were found in the order of 105 M−1 at 298 K. CdSe QDs are also affects the binding affinities of dietary polyphenols (naringin: NG and naringenin: NRG) towards HSA. The synthesized CdSe QDs was employed to sensing of antibiotic lomefloxacin by fluorescence quenching mechanism. The detection limit was found 0.70‐1.83 μg mL−1. The CdSe QDs also demonstrate the detection of lomefloxacin under uv light based on color change of the solutions.

Application of novel quantum dot-based molecularly imprinted fluorescence sensor in rapid detection

作为一种新型荧光纳米材料,量子点具有十分优异的光学特性,是分析化学、生物科学、医学等领域研究的热点标记材料。分子印迹聚合物是能够进行特异性识别和选择性吸附的“仿生”材料,它易于制备且具有较好的重现性和稳定性,因而分子印迹技术已成为具有广阔应用前景的识别技术。量子点基分子印迹荧光传感器结合了量子点和分子印迹技术的优势,由于其高选择性和高灵敏度,在环境监测、食品检测、生物分析等领域得到快速发展。但该传感器在应用中也还存在亲水性不足、识别单一、便携性不足等问题。该文引用了近5年来发表在American Chemical Society、Elsevier等数据库约20篇相关文献,对量子点基分子印迹荧光传感器的构建及该传感器在快速检测分析痕量物质中的应用进展进行了综述。首先根据荧光光谱图中发射峰个数的不同分别介绍了3种量子点基分子印迹荧光传感器的类型及相关识别机理,其次根据待测物的不同归纳介绍了近五年来该传感器在离子、有机小分子、生物大分子等检测分析中的最新研究进展,最后对当前该传感器在制备及应用中仍存在的问题进行了总结并对其发展趋势进行了展望。

51.3: Stable Quantum Dot Nanocomposites for Display Application

Quantum dots (QDs) are promising luminescent materials for display application owing to their excellent optical properties and easy processing. However, it is still challenging to achieve high efficiency and stability for QDs in practical LED application because of their high surface sensitivity to air, heat and moisture. Here we summary the recent developments in efficiency and stability enhancement of QDs in terms of surface chemistry, thermal management and light extraction of QDs in LED devices. We show that the QDs can withstand critical condition (85 °C/85 RH/high light density) with the properly designed surface encapsulation equipped with air‐barrier, thermal conductivity and optical scattering characteristics. The surface modification of QDs towards high compatibility with polymer matrices and micro/nano manufacturing is discussed. Finally, the performance and optical properties of the QD‐nanocomposites are summarized with a prospect for nano/micro‐LED display applications.

Study on the Photoluminescence Properties and First-Principles Calculations of L-cysteine Capped ZnS Quantum Dots

L-cysteine (L-cys) was used to coat ZnS quantum dots (QDs), which should benefit the improvement of water solubility and photoluminescence (PL) intensity of ZnS QDs. The impact of L-cys on the performances of ZnS QDs and the corresponding mechanism were discussed. It illustrated that L-cys modification didn’t change the crystal structure of ZnS QDs, and the mean diameter was enlarged as the content of L-cys was more. The results also displayed that the water solubility and PL intensity of samples coated with L-cys was better than that of the uncoated sample. The sample exhibited the maximal emission while the weight ratio of L-cys to QDs equaled 1.4:0.5, and it was 4.5 times as strong as ZnS sample. The result of the First-principles calculations indicated that L-cys shell layer is beneficial to prolong the lifetime of photon-generated carriers at surface location, which should lead to a reduction in the nonradiative recombination on the surface, and then the PL intensity will be enhanced. This work helps to investigate the surface modification of QDs modified by other organic compounds.

Surface Modification of a Stable CdSeZnS/ZnS Alloy Quantum Dot for Immunoassay

Quantum dots (QDs) are powerful materials in various bioapplications based on their excellent optical and electronic properties. For the application of various fields of QDs, surface modification of QDs is necessary. However, surface modification in QDs may result in a reduction in quantum yield (QY). This reduction of QY causes many weaknesses in the biological application of QDs. In this study, CdSeZnS/ZnS alloy QDs were used to prepare antibody-conjugated QDs for a sandwich immunoassay. The alloy QDs displayed a QY of 84.5% that was maintained at 83.0% (98.2% of QY was maintained) after surface modification with the anti-rabbit IgG as a model study. Surface-modified QDs successfully detected their corresponding target through antibody-antigen binding. The limit of detection was 1.1 × 10 2 ng mL-1 for rabbit IgG.

Synthesis of surface-modified quantum dots

The review discusses the main methods used to obtain surface-modified quantum dots, specifically silicon, heavy metal chalcogenide and pnictide semiconductor nanoparticles. Examples of transformation processes of the grafted layer are considered. The importance of surface modification of AIIBVI- and AIIIBV-type semiconductor nanoparticles for the practical application of quantum dots is shown. It was determined that the most promising areas of their practical application are biology, medicine, and pharmacology. Special attention is paid to the hydrophilization of quantum dots, because only these materials can be used in biomedical applications. Modification of the quantum dot surface with amino acids is considered.

Impact of Bis(imino)pyridine Ligands on Mesoscale Properties of CdSe/ZnS Quantum Dots

We investigate the effect of surface modification of CdSe/ZnS quantum dots (QDs) with bis(imino)pyridine (BIP) ligands. BIPs are a class of redox non-innocent ligands known to facilitate charge transfer in base metals on the molecular scale, but their behavior in nano- to meso-scale systems has been largely unexplored. Using electron microscopy, crystallography and ultrafast spectroscopy, we reveal that structure specific π-π stacking of the BIP molecules alters inter-dot separation in QD films, thereby leading to changes in optical and electronic properties. The three variations used are unsubstituted (BIP-H), dimethyl (BIP-Me) and diisopropyl (BIP-Ipr) bis(imino)pyridine, and when compared with the native octadecylamine (ODA) ligand, we find that both energy and charge transfer efficiencies between QDs are increased post-ligand exchange, the highest achieved through BIP-Ipr, despite its larger unit cell volume. We further investigate charge transfer from QD films to conducting (indium tin oxide, ITO) and semiconducting (zinc oxide, ZnO) substrates using time-resolved spectroscopy, and determine that the influence of the ligands is QD band gap dependent. In QDs with large band gap (2.3 eV) the BIP ligands facilitate charge transfer to both ITO and ZnO substrates, but in dots with small band gap (1.9 eV) they pose a hindrance when ZnO is used, resulting in reduced recombination rates. These results highlight the importance of investigating multiple avenues in order to optimize surface modification of QDs based on the end goal. Finally, we verify that BIP ligands hasten the rate of QD photo brightening under continuous illumination, allowing the ensemble to achieve stable emission faster than in their native configuration. Our study sets the stage for novel charge transfer systems in the meso and nanoscale, yielding a diverse selection of new surface ligands for applications such as conductive materials and energy production/storage devices employing QDs.

Quantum Dot Bioconjugates for Diagnostic Applications.

Quantum dots (QDs) are a special type of engineered nanomaterials with outstanding optoelectronic properties that make them as a very promising alternative to conventional luminescent dyes in biomedical applications, including biomolecule (BM) targeting, luminescence imaging and drug delivery. A key parameter to ensure successful biomedical applications of QDs is the appropriate surface modification, i.e. the surface of the nanomaterials should be modified with the appropriate functional groups to ensure stability in aqueous solutions and it should be conjugated with recognition elements capable of ensuring an efficient tagging of the BMs of interest. In this review we summarize the most relevant strategies used for surface modification of QDs and for their conjugation to BMs in preparation of their application in nanoplatforms for luminescent BM sensing and imaging-guided targeting. The applications of conjugations of photoluminescent QDs with different BMs in both in vitro and in vivo chemical sensing, immunoassays or luminescence imaging are reviewed. Recent progress in the application of functionalized QDs in ultrasensitive detection in bioanalysis, diagnostics and imaging strategies are reported. Finally, some key future research goals in the progress of bioconjugation of QDs for diagnosis are identified, including novel synthetic approaches, the need for exhaustive characterization of bioconjugates and the design of signal amplification schemes.

Atomic layer deposition for quantum dots based devices

Quantum dots (QDs) are promising candidates for the next-generation optical and electronic devices due to the outstanding photoluminance efficiency, tunable bandgap and facile solution synthesis. Nevertheless, the limited optoelectronic performance and poor lifetime of QDs devices hinder their further applications. As a gas-phase surface treatment method, atomic layer deposition (ALD) has shown the potential in QDs surface modification and device construction owing to the atomic-level control and excellent uniformity/conformality. In this perspective, the attempts to utilize ALD techniques in QDs modification to improve the photoluminance efficiency, stability, carrier mobility, as well as interfacial carrier utilization are introduced. ALD proves to be successful in the photoluminance quantum yield (PLQY) enhancement due to the elimination of QDs surface dangling bonds and defects. The QDs stability and devices lifetime are improved greatly through the introduction of ALD barrier layers. Furthermore, the carrier transport is ameliorated efficiently by infilling interstitial spaces during ALD process. Attributed to the ultra-thin and dense coating on the interface, the improvement on optoelectronic performance is achieved. Finally, the challenges of ALD applications in QDs at present and several prospects including ALD process optimization, in-situ characterization and computational simulations are proposed.

The Effect of Silicon-Organic Modifier of CdZnS/ZnS (GT) Quantum Dot with Wavelength 390 nm on cathodoluminescent mode

Surface modification of quantum Dots is very demanding to improve the optical properties of quantum Dots and it is generally carried out by depositing an organic or an inorganic layer on the quantum Dots. In this study the behavior of CdZnS/ZnS and CdZnS/ZnS (GT), both emitting at 390 nm, differ by silicon-organic additives studying in a vacuum chamber to find out their feature and to identify the luminescent of quantum Dots, under the action of electron bombardment to assess the capability of quantum Dots as phosphors for further use in vacuum electronics

Europium metal-organic framework for selective and sensitive detection of doxycycline based on fluorescence enhancement

Metal-organic framework is an extended coordination compound with repeating coordination entities and voids, which shows potential applications in gas storage, separation, catalysis, and etc. This work reports the synthesis of a new functional metal-organic framework of pyromellitic acid and europium, and its application in fluorescence sensing of doxycycline, a broad-spectrum polyketide antibiotic on the basis of fluorescence turn-on method. The metal-organic framework was initially non-fluorescent, however, with the addition of doxycycline, the system exhibited significant fluorescence enhancement at 526 nm and 617 nm, where both fluorescence intensities showed good linear correlations with the doxycycline concentration, suggesting the possibility for direct two-channel detection without any sensitization materials such as metal particles or surface-modified quantum dots. More interestingly, the unique fluorescence response of the system could discriminate doxycycline from other tetracycline antibiotics with high selectivity, and a limit of detection (LOD) was estimated to be 47 nM. It has been further demonstrated that the material has been successfully applied as sensing materials for selective determination of doxycycline in real samples of fish and urine.

Iron fluoride vertical nanosheets array modified with graphene quantum dots as long-life cathode for lithium ion batteries

We successfully built a unique architecture of FeF3·0.33H2O, a self-supported, binder-free vertical nanosheets array directly growing on Ti foil by a simple solvothermal approach and firstly use graphene quantum dots to surface modification. The high specific surface area of 2D nanosheets and high conductivity of graphene quantum dots provide an expressway for charge transfer and ion transport. This unique structural design endows a capacity of 161.5 mAh g−1 at 1 C and a capability of 117 mAh g−1 at a high current density of 4 Ag−1 (20 C). Graphene quantum dots surface modification can stabilize the structure and reduce possible side reactions, making the cycle performance greatly improved. Even cycled over 1000 times at 2 C the capacity attenuation rate is as low as 0.03% per cycle.

Enhanced Device Performance of Bulk Heterojunction (BHJ) Hybrid Solar Cells Based on Colloidal CdSe Quantum Dots (QDs) via Optimized Hexanoic Acid-Assisted Washing Treatment

As-synthesized colloidal quantum dots (QDs) are usually covered by an organic capping ligand. These ligands provide colloidal stability by preventing QDs agglomeration. However, their inherent electrical insulation properties deliver a problem for hybrid solar cell application, disrupting charge transfer, and electron transport in conjugated polymer/QDs photoactive blends. Therefore, a surface modification of QDs is crucial before QDs are integrated into solar cell fabrication. In this work, enhancement of power conversion efficiency (PCE) in bulk heterojunction (BHJ) hybrid solar cells based on hexadecylamine- (HDA-) capped CdSe quantum dots (QDs) has been achieved via a postsynthetic hexanoic acid washing treatment. The investigation of the surface modification was performed to find the optimum of washing time and their effect on solar cell devices performance. Variation of washing time between 16 and 30 min has been conducted, and an optimum washing time was found at 22 min, resulting in a high PCE of 2.81%. The efficiency enhancement indicates improved electron transport, contributing in an increased short-circuit current density of solar cell devices.

ATP Aptamer-Modified Quantum Dots with Reduced Glutathione/Adenosine Triphosphate Dual Response Features as a Potential Probe for Intracellular Drug Delivery Monitoring of Vesicular Nanocarriers.

Nanoparticles have great promise in drug delivery, but their functional mechanisms are very complicated. Monitoring the payloads or carriers by conventional labeling strategies may result in an inaccurate perception of the effectiveness of nano drug delivery systems (NDDSs). A GSH/ATP dual-responsive fluorescence enhancement probe was developed by manipulating the electron transfer pathways of surface-modified quantum dots (QDs). Because the intracellular concentrations of GSH and ATP are one hundred times greater than those in the extracellular environment, the intracellular drug release process could be observed by the fluorescence signal of this probe after it is loaded into NDDSs as drug simulants. As a proof-of-concept investigation, the intracellular drug release behaviors of classical liposomes were studied by loading this probe, and the observed results strongly support the known drug delivery mechanism of these systems. Although more studies are needed to investigate the in vivo performance of the probe, this study may encourage further investigations of other intracellular environment-responsive smart probes for deciphering the in vivo fate of NDDSs.

Facile Synthesis of Cu–In–S/ZnS Core/Shell Quantum Dots in 1-Dodecanethiol for Efficient Light-Emitting Diodes with an External Quantum Efficiency of 7.8%

CuInS2 quantum dots (QDs) are promising alternatives for user- and environment-friendly light-emitting diode (LED) applications, but the capping of electrically insulating ligands on QDs limits the device charge injection efficiency and results in poor LED performance. To solve the problem, in this work, we demonstrate the facile synthesis of Cu–In–S/ZnS (CIS/ZnS) core/shell QDs employing 1-dodecanethiol (DT) as the single ligand. The capping of QDs solely by DT not only enhances the colloidal stability of the QD ink by avoiding proton transfer between different kinds of ligands but also improves the electrical property of the QD films. By controlling the molar feed ratio of cations, the photoluminescence emission peak of the CIS/ZnS QDs is tunable from 530 to 710 nm. Because the QD surface chemistry is optimized, it becomes facile to perform QD surface modification for LED application. A QD LED prototype is fabricated using CIS/ZnS QDs as the emissive layer, which exhibits a maximum luminance of 4490 cd ...

Synthesis, characterization and energy transfer studies of fluorescent dye-labeled metal-chelating polymers anchoring pendant thiol groups for surface modification of quantum dots and investigation on their application for pH-responsive controlled release of doxorubicin.

We describe the synthesis of an end-functionalized fluorescent dye-labeled poly(N-(2-thiolethyl methacrylamide) as a metal chelating polymer with a very narrow size distribution and controllable molecular weights by reversible addition-fragmentation chain transfer polymerization. In following, we apply this water-soluble metal-chelating polymer for surface modification of cadmium telluride quantum dots (CdTe QDs) by ligand exchange method. The obtained poly(N-(2-thiolethyl methacrylamide)/CdTe QDs hybrid was fully characterized using Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TG) and transmission electron microscopy (TEM). The size of the prepared hybrid was estimated around 3.2 nm by TEM. Furthermore, we used this hybrid for improving the release performance of doxorubicin hydrochloride as a chemotherapeutic model drug. The in vitro release of doxorubicin was studied in pH 5.4 and 7.4, which release curves were nicely fitted by the Korsemeyer-Peppas equation and the release followed by non-Fickian diffusion or anomalous diffusion in pH 5.4. The synthesized fluorescent dye-labeled hybrid can be used as a donor-acceptor pair for fluorescence resonance energy transfer (FRET) experiments, so the energy transfer behavior between fluorescent dye as a donor and CdTe QDs as an acceptor were interrogated using Förster/fluorescence resonance energy transfer model, which the distance was found to be 3.95 nm. This present work has potential for both diagnostic and therapeutic aspects for cancer patients.

Assay of Single-Cell Apoptosis by Ensemble and Single-Molecule Fluorescence Methods: Annexin-V/Polyethylene Glycol-Functionalized Quantum Dots as Probes

Apoptosis plays a critical role in many biological processes and the etiology of various diseases of the immune system. The study of apoptosis would allow both improving the diagnosis of certain diseases and serving as a target of drug screening. In this paper, we developed a sensitive assay of single-cell apoptosis using semiconductor quantum dots (QDs) as fluorescent-labeling probes. The principle of this assay is based on the detection of phosphatidylserine (PS) exposed on the plasma membrane during the drug-induced apoptosis. The QD-labeled annexin V (AV) was prepared to specifically target PS on the membrane of apoptotic cells, and PS was detected by fluorescent imaging, flow cytometer, and single-molecule fluorescence correlation spectroscopy (FCS). We developed the procedures for conjugation of QDs to AV and for purification of their conjugates by gel chromatography. The obtained conjugates were characterized by FCS, capillary electrophoresis, and zeta potential analyzer. We studied the nonspecific adsorption of cells to different surface-modified QDs and found that the nonspecific adsorption effects were significantly reduced by modification of QDs with polyethylene glycol in the detection of apoptosis. In this assay, the results obtained by flow cytometry were consistent with the commercial test kit. Furthermore, a home-built single-molecule FCS system was developed for in situ study the drug-induced apoptosis. We observed the significant change in the diffusion coefficients of QDs on cells during the progress of cell apoptosis. Compared with conventional methods, the fluorescent methods represented here possess high sensitivity because of the use of high photo stability and brightness QDs as labeling probes and provide the temp-spatial information on a single apoptotic cell.