Temperature-dependent photoluminescence of highly luminescent water-soluble CdTe quantum dots

Highly luminescent water-soluble CdTe quantum dots(QDs) have been synthesized with an electrogenerated precursor.The obtained CdTe QDs can possess good crystallizability,high quantum yield(QY) and favorable stability.Furthermore,a detection system is designed firstly for the investigation of the temperature-dependent PL of the QDs.     

水溶性CdTe量子点的合成及其用于荧光猝灭法测定肌红蛋白

以3-巯基丙酸为稳定剂,合成了具有特殊光学性质的水溶性CdTe量子点,其最大发射波长位于544 nm.利用荧光光谱、紫外可见光谱及圆二色光谱法系统的研究了CdTe量子点与肌红蛋白(Mb)二者结合前后体系光谱的变化,从而证实了CdTe量子点与Mb之间静电结合反应的特征.在pH 7.0的PBS缓冲液中,用CdTe量子点作为荧光探针研究了肌红蛋白与量子点的相互作用,并基于肌红蛋白对CdTe量子点有显著的荧光猝灭作用,建立了肌红蛋白的快速检测方法.在最佳实验条件下,该体系荧光强度的猝灭程度(△F)与肌红蛋白质量浓度呈良好的线性关系,线性范围为0.3～24 μg/mL,检出限为0.13 μg/mL.该方法已对合成样品中肌红蛋白进行检测,并用于人体尿样中肌红蛋白的测定.     

Study on molecular interactions between proteins on live cell membranes using quantum dot-based fluorescence resonance energy transfer

Mouse anti-human CD71 monoclonal antibody (anti-CD71) was conjugated with red quantum dots (QDs; 5.3 nm, emission wavelength λ _em = 614 nm) and used to label HeLa cells successfully. Then green QD-labeled goat anti-mouse immunoglobulin G (IgG; the size of the green QDs was 2.2 nm; λ _em = 544 nm) was added to bind the red-QD-conjugated anti-CD71 on the cell surface by immunoreactions. Such interaction between anti-CD71 and IgG lasted 4 min and was observed from the fluorescence spectra: the fluorescence intensity of the “red” peak at 614 nm increased by 32%; meanwhile that of the “green” one at 544 nm decreased by 55%. The ratio of the fluorescence intensities (I _544 nm/I _614 nm) decreased from 0.5 to 0.2. The fluorescence spectra as well as cell imaging showed that fluorescence resonance energy transfer took place between these two kinds of QDs on the HeLa cells through interactions between the primary antibody and the secondary antibody.     

Sizes of water-soluble luminescent quantum dots measured by fluorescence correlation spectroscopy

In this paper, fluorescence correlation spectroscopy (FCS) was applied to measure the size of water-soluble quantum dots (QDs). The measurements were performed on a home-built FCS system based on the Stokes-Einstein equation. The obtained results showed that for bare CdTe QDs the sizes from FCS were larger than the ones from transmission electron microscopy (TEM). The brightness of QDs was also evaluated using FCS technique. It was found that the stability of the surface chemistry of QDs would be significantly improved by capping it with hard-core shell. Our data demonstrated that FCS is a simple, fast, and effective method for characterizing the fluorescent quantum dots, and is especially suitable for determining the fluorescent nanoparticles less than 10 nm in water solution.     

An alternative aqueous synthetic route to preparing CdTe quantum dots with tunable photoluminescence

An aqueous synthetic route has been developed for the preparation of mercaptosuccinic acid（MSA）-capped CdTe quantum dots （QDs） using TeO₂ as tellurium source and sodium borohydride as reductant.The size and the emission color of CdTe QDs can be tuned by varying the reflux time.The obtained QDs were characterized by photoluminescence（PL） spectroscopy,X-ray powder diffraction（XRD） and high-resolution transmission electron microscopy（HRTEM）.The results show that the CdTe QDs were of zinc-blende crystal structure in a sphere-like shape.     

Review of the synthesis and properties of colloidal quantum dots: the evolving role of coordinating surface ligands

This review highlights the developments in synthetic methods for colloidal quantum dots that have expanded the range of achievable sizes, shapes, materials, and surface chemistries over the past 30 years, and how these methods have enabled optimization of properties like photoluminescence quantum yield, monodisperse size distributions, and conductivity in the solid state.     

Ligand displacement-induced fluorescence switch of quantum dots for ultrasensitive detection of cadmium ions

This paper reports the construction of a simple CdTe quantum dots (QDs)-based sensor with 1,10-phenanthroline (Phen) as ligand, and the demonstration of a novel ligand displacement-induced fluorescence switch strategy for sensitive and selective detection of Cd²⁺ in aqueous phase. The complexation of Phen at the surface quenches the green photoluminescence (PL) of QDs dominated by a photoinduced hole transfer (PHT) mechanism. In the presence of Cd²⁺, the Phen ligands are readily detached from the surface of CdTe QDs, forming [Cd(Phen)₂(H₂O)₂]²⁺ in solution, and as a consequence the PL of CdTe QDs switches on. The detection limit for Cd²⁺ is defined as ∼0.01 nM, which is far below the maximum Cd²⁺ residue limit of drinking water allowed by the U.S. Environmental Protection Agency (EPA). Two consecutive linear ranges allow a wide determination of Cd²⁺ from 0.02 nM to 0.6 μM. Importantly, this CdTe QDs-based sensor features to distinctly discriminate between Cd²⁺ and Zn²⁺, and succeeds in real water samples. This extremely simple strategy reported here represents an attempt for the development of fluorescent sensors for ultrasensitive chemo/biodetection.     

Active cellular sensing with quantum dots: Transitioning from research tool to reality; a review

The application of luminescent semiconductor quantum dots (QDs) within a wide range of biological imaging and sensing formats is now approaching its 15th year. The unique photophysical properties of these nanomaterials have long been envisioned as having the potential to revolutionize biosensing within cellular studies that rely on fluorescence. However, it is only now that these materials are making the transition towards accomplishing this goal. With the idea of understanding how to actively incorporate QDs into different types of cellular biosensing, we review the progress in many of the areas relevant to achieving this goal. This includes the synthesis of the QDs themselves, with an emphasis on minimizing potential toxicity, along with the general methods for making these nanocrystalline structures stable in aqueous media. We next survey some methods for conjugating QDs to biomolecules to allow them to participate in active biosensing. Lastly, we extensively review many of the applications where QDs have been demonstrated in an active role in cellular biosensing. These formats cover a wide range of possibilities including where the QDs have contributed to: monitoring the cell's interaction with its extracellular environment; elucidating the complex molecular interplay that characterizes the plasma membrane; understanding how cells continuously endocytose and exocytose materials across the cellular membrane; visualizing organelle trafficking; and, perhaps most importantly, monitoring the intracellular presence of target molecules such as nucleic acids, nutrients, cofactors, and ions or, alternatively, intracellular responses to external changes in the environment. We illustrate these processes with examples from the recent literature and focus on what QDs can uniquely contribute along with discussing the benefits and liabilities of each sensing strategy. A perspective on where this field is expected to develop in both the near and long-term is also provided.     

水溶性CdSe量子点的合成及其作为荧光探针对大肠杆菌的快速检测

采用水相法以谷胱甘肽为稳定剂合成高稳定性的CdSe量子点,利用化学偶联剂的作用使得量子点表面基团与菌体之间的成功结合,对偶联的条件进行了优化.基于荧光分析法建立了一种快速简便的大肠杆菌检测定量分析方法.研究结果表明:合成的量子点具有稳定、荧光性能良好等突出优点.通过偶联剂量子点能与大肠杆菌结合,其荧光强度与大肠杆菌浓度...     

Ultrafine biocompatible chitosan nanoparticles encapsulating multi-coloured quantum dots for bioapplications

Owing to their excellent optical properties, luminescent semi-conductor quantum dots (QDs) have proven themselves to be an attractive choice in biological labeling. However, there exists the concern of cytotoxicity in using these heavy metal-based nanoparticles as molecular probes. In order to improve their general biocompatibility, CdSe/ZnS QDS are encapsulated in the natural biopolymer chitosan, forming monodisperse chitosan nanoparticles in the range of 60 nm in 1 single step. This straight forward method also allows for the synthesis of chitosan nanoparticles encapsulating multi-coloured QDs. In vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests on primary myoblast cells suggest that the cytotoxicity of the QDs is greatly reduced after chitosan encapsulation. At the same time, fluorescence confocal microscopy studies also prove that nanoparticles are small enough to be internalized into the myoblast cells. Our results show the ease of synthesizing biocompatible, nanometer-sized chitosan nanoparticles encapsulating QDs and their promise in biological applications such as ultra-sensitive bio-detection and labeling of biomolecules.     

Surface-modified CdS quantum dots as luminescent probes for sulfadiazine determination

A novel, sensitive and convenient determine technology based on the quenching of the fluorescence intensity of functionalized CdS quantum dots by sulfadiazine was proposed. Luminescent CdS semiconductor quantum dots (QDs) modified by thioglycollic acid (TGA) were synthesized with the microwave method. The modified CdS QDs are water-soluble, stable and highly luminescent. The possible mechanism for the reaction was also discussed. When sulfadiazine was added into the CdS QDs colloid solution, the surface of CdS QDs generates the electrostatic interaction in aqueous medium, which induces the quenching of fluorescence emission at 489 nm. Under optimum condition, the fluorescence intensity versus sulfadiazine concentration gave a linear response according Stern-Volmer equation with an excellent 0.9981 correlation coefficient. The linearity range of the calibration curve was 1.2 x 10(-5) to 2.13 x 10(-3) mol L(-1). The limit of detection (3delta) is 8.0 micromol L(-1). The relative standard deviation for five determinations of 0.13 x 10(-3)mol L(-1) sulfadiazine is 1.4%. The concentrations of sulfadiazine injections were determined by the proposed method with a satisfactory result.     

A novel fluorene-containing oligomer with relative high photoluminescence quantum efficiency

A novel oligomer (F1) based on 2,4-difluorobenzene and trifluorene was prepared and characterized. The experimental results showed that the new trifluorene containing 2,4-difluorobenzene had relative high photoluminescence quantum efficiency, up to 71.6%, compared with 42% of trifluorene (F0), and its maximum absorption and emission spectra took on some abnormal characteristics, which could both be attributed to the unique function of fluorine.     

Effect of graphene quantum dots on photoluminescence property of polyvinyl butyral nanocomposite

Design and development of new photoluminescence system are much in demand for various engineering and technological applications. The present investigation focused on the influence of graphene quantum dots (GQDs) dispersion in the polyvinyl butyral (PVB) matrix. The structural and chemical interaction of GQD‐dispersed PVB composites was confirmed by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), micro‐Raman spectroscopy, ultraviolet and visible (UV‐Vis), and photoluminescence (PL) techniques. Chemical interaction between the functional groups leads to PL quenching at 455 nm. Changes on crystallite size and interplanar spacing hinders on the structural properties of the nanocomposite. Raman spectroscopy reveals the decrease in D/G intensity ratio influenced by GQD loading wt% in the polymer system. The dispersion and occupied network of GQD in the PVB matrix was confirmed by optical polarizing microscopy (OPM), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Effect of electrical conductivity of composites as a function of temperature has been verified. Decrease in direct bandgap as a function of GQD loading confirms the promising PL properties of the prepared composite system. Thus GQD‐derived composites may further be developed as a membrane for improved PL property.     

Directing energy flow through quantum dots: towards nanoscale sensing

Nanoscale sensors can be created when an expected energetic pathway is created and then that pathway is either initiated or disrupted by a specific binding event. Constructing the sensor on the nanoscale could lead to greater sensitivity and lower limits of detection. To this end, quantum dots (QDs) can be considered prime candidates for the active components. Relative to organic chromophores, QDs have tunable spectral properties, show less susceptibility to photobleaching, have similar brightness, and have been shown to display electro-optical properties. In this review, we discuss recent articles that incorporate QDs into directed energy flow systems, some with the goal of building new and more powerful sensors and others that could lead to more powerful sensors. Figure     

Intercalation of quantum dots as the new signal acquisition and amplification platform for sensitive electrochemiluminescent detection of microRNA

Herein, we report on the development of a simple and sensitive biosensor for electrochemiluminescent (ECL) detection of microRNAs (miRNA) based on the intercalation of doxorubicin-conjugated quantum dot nanoparticles (Dox-QDs) into the DNA/RNA hybrids as the new signal acquisition and amplification platform. The thiolated DNA capture probes are self-assembled onto gold electrodes via   the formation of Au–S bonds. The sensing surface is then incubated in a target miRNA-containing buffer solution to form the double-stranded duplexes. In this case, massive Dox-QDs can intercalate into the base pairs of the hybrid duplexes, resulting in amplified ECL emissions due to their reactions with the coreactant S₂O₈²⁻${{\text{S}}_2{\text{O}}_8}^{2-}$ and the dissolved oxygen in the detection buffer. The increase in ECL intensity proportional to the amount of target miRNA in the testing samples serves as the quantitative basis. Different from traditional QDs-based methods such as labeling and embedding, our sensor involves the employment of the intercalation of the Dox-QDs as the signal acquisition and amplification platform. The combination of the QDs intercalation amplification with the high sensitivity of the ECL technique enables us to detect miRNA down to the low femtomolar level. Moreover, our method is also coupled with acceptable selectivity in discriminating the target miRNA and against its family members as well as other interference sequence, and can monitor miRNAs from human prostate carcinoma (22Rv1) cell lysates.     

CdSe/CdS量子点荧光猝灭法测定芹黄素的研究

以巯基乙酸为稳定剂,在水溶液中合成了具有特殊光学性质的水溶性CdSe/CdS量子点。以该量子点为荧光探针,基于荧光猝灭法对芹黄素进行了定量检测。考察了缓冲体系、反应时间、量子点浓度等多种因素的影响。实验结果表明,在0.001 mol/L、pH为6.80的KH2PO4-Na2HPO4缓冲液中,当量子点浓度为1.2×10^-4mol/L、反应时间为20 min时,该方法的线性范围为0.16-27.02μg/mL,其线性回归方程为F0/F=0.99665＋0.11067ρ（μg/mL）,相关系数r=0.998,检出限为0.13μg/mL,并用于合成样品的分析。     

Enhanced photoluminescence of water-soluble Mn-doped ZnS quantum dots by thiol ligand exchange

Hydrophobic Mn-doped ZnS quantum dots (Mn:ZnS d-dots) were made to be water soluble by coating a monolayer of mercaptopropionic acid (MPA). It is found that the PL efficiency of Mn:ZnS d-dots with various shell thicknesses were all improved after thiol (MPA) ligand exchange. We attribute their PL enhancement to the effective surface passivation induced by the thiol ligand and significantly decrease of holes transfer from d-dots to ligands. The PL QY of as-synthesized thiol-coated d-dots can reach as high as 50%. These efficient, stable, and water soluble d-dots are confirmed to be suitable for biomedical applications.     

Recent developments in analytical applications of quantum dots

This review discusses the application of quantum dots (QDs) to chemical and biological detection, for which they have excellent features, particularly size-dependent optical properties.We can summarize the main areas discussed in this review as follows:(1) QDs associated with enzyme-linked immunosorbent assay (ELISA), chip detection and capillary electrophoresis (CE) enhance the sensitivity and the speed of detection of residues;(2) QDs are applied with other techniques, including polymerase chain reaction (PCR), fluorescence resonance-energy transfer (FRET) analysis, fluorescence in-situ hybridization (FISH) and western blot analysis; and,(3) QDs combined with the above techniques can successfully detect DNA and protein.We also cover perspectives and challenges in analytical applications of QDs.     

Encapsulating of single quantum dots into polymer particles

Single semiconductor quantum dots were embedded into polymer particles with diameters below 0.1 μm by an emulsion polymerization procedure or via a secondary dispersion approach. The photoluminescence properties of the nanocrystals are retained upon encapsulation, as demonstrated by fluorescence confocal microscopy.

The polymeric characteristics and photoluminescence mechanism in polymer carbon dots: A review

A large amount of emerging research on carbon dots (CDs) has been gradually improving the understanding of their structures, properties and emission mechanism. Distinct from the dominating status of quantum confinement effect in quantum dots, CDs always suffer from the complicated optical properties, deriving from the large differences in raw materials and synthesis methods. The diverse concepts and species puzzle researchers and hinder the further study. Thus, there is an urgent need to unify the definition and clarify the confused relation of CDs. Herein, we classify the raw materials of CDs synthesis into small molecules and polymers, and discuss CDs from the aspects of raw materials. We believe that the polymer-like structures reserved in CDs are universal no matter from the condensation of small molecules or the direct inheritance of polymers. Moreover, many similarities are concluded between CDs and polymers through serious comparisons and enough evidences. The formation processes of CDs are mostly polymerization and the obtained CDs always possess polymeric characteristics, such as abundant reactive functional groups, polydispersity of products, highly crosslinked network structure and other similar properties to non-conjugated fluorescent polymers. Therefore, the new concept, polymer carbon dots (PCDs), is put forward to generalize all kinds of CDs based on the summary of related reports. Besides, the complicated influence factors of photoluminescence (PL) are discussed and mainly classified as molecule state, carbon core state, surface state and crosslink enhanced emission (CEE) effect. In general, this review puts forward PCDs as a unified definition of reported CDs, and summarizes the polymeric characteristics of PCDs from formation process and product properties, as well as simultaneously illustrates the PL mechanism.