Recent advances in the use of near-infrared quantum dots as optical probes for bioanalytical,imaging and solar cell application

Near-infrared quantum dots (NIR QDs) represent a powerful material and diagnostic tool owing to their long emission wavelength which extends into the near-infrared region where permeation depths are much larger and where the intrinsic absorbance and autofluorescence of tissue is much smaller compared to shortwave emitting QDs. We are reviewing here recent (2008–2013) methods for the preparation of NIR QDs, their (bio)chemical modifications, and their applications. The article is subdivided into the following sections: (a) Synthesis of NIR QDs; (b) modification of NIR QDs and probe preparation; (c) applications of NIR QDs (with subsections on fluorescence quenching and fluorescence enhancement-based bioanalytical detection, on fluorescence bioimaging, on uses in photovoltaic cells and solar cells, and on molecular detection based on electrogenerated chemiluminescence). We finally make conclusions and discuss current challenges, trends, and future applications. The review contains 119 references. Figure

This review systematically presents the development, preparation methods, modifications and bioapplications of Near-infrared quantum dots (NIR QDs). The review contains 126 references.     

聚合物/量子点纳米复合材料的制备

量子点具有优异的光电性能,聚合物具有性质稳定、质轻、可加工性好等优点;将聚合物和量子点复合可综合两者的优点,同时还可使量子点的稳定性得以大幅度提高。得到的聚合物/量子点纳米复合材料应用领域广;其制备方法主要有简单易操作的直接分散法、在聚合物中原位生成量子点的原位生成法、在有量子点存在的聚合场所引发有机单体聚合的原位聚合法、层-层组装法以及在量子点表面直接修饰聚合物的表面直接修饰法。本文就这些制备方法进行了概要综述,并对各种方法的特点进行了总结。     

In vitro and intracellular sensing by using the photoluminescence of quantum dots

Quantum dots (QDs) have attracted increasing attention due to their unique physical and chemical properties. This article introduces recent advances in using QDs’ photoluminescence (PL) for in vitro and intracellular sensing analytes, in particular ions, and biomolecules from the last 3 years. Different sensing strategies are demonstrated and compared for increasing the detecting/sensing selectivity. The perspectives for in vitro and intracellular sensing based on QDs’ PL are also discussed.     

Study of fluorescence quenching and dialysis process of CdTe quantum dots, using ensemble techniques and fluorescence correlation spectroscopy

Luminescence properties of quantum dots (QDs) are closely related to their surface structure and chemical properties. In this work some ensemble techniques and fluorescence correlation spectroscopy (FCS) were used to study the fluorescence quenching and dialysis process of CdTe QDs. It is found that when some heavy metal ions, such as silver ions (Ag+), quench QDs, the free Ag+ ions bind with bare Te atoms and form the AgTe structure on the surface. The FCS experimental results show that the quenching process is not the gradual reduction of fluorescence intensity of single QDs, but the decrease in the number of bright QDs with the addition of Ag+ ions. In other words, the bright QDs turn into dark directly in the quenching process. It is observed that some dark QDs converse into the bright QDs in the dialysis experiments and the dialysis process can improve the brightness per QDs. Furthermore, the results of FCS and fluorescence spectroscopy illustrate that the increase of the fluorescence quantum yield (QY) is mainly attributed to the removal of excess unreacted Cd-MPA complex and the possible chemical change of the QDs surface in the dialysis process. These new results can help us to further understand the complex surface structure of water-soluble QDs, improve their surface chemical features, and expand their applications in some fields.     

近红外量子点的研究进展

量子点具有优异的光学性能及丰富的表面化学性质,在生物医学分析领域具有较好应用前景。近红外窗口生物成像所具有的背景干扰小、穿透深度大等特点,使得近红外量子点在生物成像应用中更具优势。本文介绍了近红外量子点从早期含Cd、含Pb量子点到近年来新型无Cd、无Pb量子点的发展历程,以及其在生物医学成像领域的应用,着重介绍了新型低毒性近红外量子点的研究进展。     

Instant visual detection of trinitrotoluene particulates on various surfaces by ratiometric fluorescence of dual-emission quantum dots hybrid

To detect trace trinitrotoluene (TNT) explosives deposited on various surfaces instantly and on-site still remains a challenge for homeland security needs against terrorism. This work demonstrates a new concept and its utility for visual detection of TNT particulates on various package materials. The concept takes advantages of the superior fluorescent properties of quantum dots (QDs) for visual signal output via ratiometric fluorescence, the feasibility of surface grafting of QDs for chemical recognition of TNT, and the ease of operation of the fingerprint lifting technique. Two differently sized CdTe QDs emitting red and green fluorescences, respectively, have been hybridized by embedding the red-emitting one in silica nanoparticles and covalently linking the green-emitting one to the silica surface, respectively, to form a dual-emissive fluorescent hybrid nanoparticle. The fluorescence of red QDs in the silica nanoparticles stays constant, whereas the green QDs functionalized with polyamine can selectively bind TNT by the formation of Meisenheimer complex, leading to the green fluorescence quenching due to resonance energy transfer. The variations of the two fluorescence intensity ratios display continuous color changes from yellow-green to red upon exposure to different amounts of TNT. By immobilization of the probes on a piece of filter paper, a fingerprint lifting technique has been innovated to visualize trace TNT particulates on various surfaces by the appearance of a different color against a yellow-green background under a UV lamp. This method shows high selectivity and sensitivity with a detection limit as low as 5 ng/mm(2) on a manila envelope and the attribute of being seen with the naked eye.     

Composition-dependent fluorescence emission of ternary Cd-In-S alloyed quantum dots

This communication describes a new type of alloyed Cd-In-S quantum dots (CdIS QDs) with ultra small particle size and broadly tunable fluorescence emission from 450 to 700 nm. The band gap of CdIS QDs was mainly controlled by their composition rather than their particle size. The CdIS-ZnS core-shell nanocrystals exhibited significantly improved optical properties and chemical stabilities, with the PL quantum yield (QY) of up to 60%.     

Capillary electrophoresis of quantum dots: Minireview

It has been already three decades, since the fluorescent nanocrystals called quantum dots (QDs) appeared and attracted attention of a broad scientific community. Their excellent not only optical but also electronic properties predetermined QDs for utilization in a variety of areas. Besides lasers, solar cells, and/or computers, QDs have established themselves in the field of (bio)chemical labeling as well as medical imaging. However, due to the numerous application possibilities of QDs, there are high demands on their properties that need to be precisely controlled and characterized. CE with its versatile modes and possibilities of detection was found to be an effective tool not only for characterization of QDs size and/or surface properties but also for monitoring of their interactions with other molecules of interest. In this minireview, we are giving short insight in analysis of QDs by CE, and summarizing the advantages of this method for QDs characterization.     

量子点敏化太阳能电池研究进展

量子点敏化太阳能电池(QDSCs)因其制备成本低、工艺简单及量子点(QDs)本身的优异性能(如尺寸效应、多激子效应)等优点,近年来受到广泛关注。在此类电池中,无机半导体量子点敏化剂作为吸光材料,其自身的光电性质、制备方法、表面缺陷、化学稳定性及其在TiO₂光阳极上的敏化方法等是影响电池性能的关键。本文综述了无机半导体量子点敏化剂(包括窄带隙二元量子点、多元合金量子点及Type-Ⅱ核壳量子点)的最新研究进展,重点介绍了胶体量子点的制备方法;分类阐释了量子点在TiO₂光阳极表面的沉积与敏化方法,特别是双官能团辅助自组装吸附法;总结了针对提高电子注入效率和减少复合的量子点表面修饰方法;最后简要介绍了QDSCs的电解质和对电极的研究进展。     

Amino‐Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g‐C3N4 for Enhanced Photocatalytic CO2 Reduction

Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these obstacles, we anchored CsPbBr₃ QDs (CPB) on NH_x‐rich porous g‐C₃N₄ nanosheets (PCN) to construct the composite photocatalysts via N?Br chemical bonding. The 20 CPB‐PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h^?1 g^?1 in acetonitrile/water for photocatalytic reduction of CO₂ to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr₃ QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.     

Luminescent properties of water-soluble denatured bovine serum albumin-coated CdTe quantum dots

Chemically reduced bovine serum albumin (BSA) has been used to modify the surface of water-soluble CdTe quantum dots (QDs). It is demonstrated that the denatured BSA (dBSA) can be conjugated to the surface of CdTe QDs and thereby efficiently improve the chemical stability and the photoluminescence quantum yield (PL QY) of the QDs. It is inferred that a shell-like complex structure CdTe(x)(dBSA)(1-x) will form on the surface of the CdTe "core", resulting in the enhancement of PL intensity and the blue shift of the PL peak. This study of the effects of pH and dBSA concentration on optical properties of dBSA-coated QDs suggests that, at pH 6-9, the solution of dBSA-coated CdTe QDs can keep substantial stability and fluorescent brightness, whereas further increase of pH value leads to a dramatic decrease in PL QY and chemical stability. On the other hand, too high or too low initial dBSA concentration in the QD solution results in a decrease of PL QY for dBSA-coated CdTe QDs. This study provides a new approach of preparing stable water-soluble QDs with high PL QY and controllable luminescent colors for biological labeling applications.     

Immobilization of Distinctly Capped CdTe Quantum Dots onto Porous Aminated Solid Supports

Immobilization of quantum dots (QDs) onto solid supports could improve their applicability in the development of sensing platforms and solid‐phase reactors by allowing the implementation of reusable surfaces and the execution of repetitive procedures. As the reactivity of QDs relies mostly on their surface chemistry, immobilization could also limit the disruption of solution stability that could prevent stable measurements. Herein, distinct strategies to immobilize QDs onto porous aminated supports, such as physical adsorption and the establishment of chemical linking, were evaluated. This work explores the influence of QD capping and size, concentration, pH, and contact time between the support and the QDs. Maximum QD retention was obtained for physical adsorption assays. Freundlich and Langmuir isotherms were used to analyze the equilibrium data. Gibbs free energy, enthalpy, and entropy were calculated and the stability of immobilized QDs was confirmed.     

Characterization and separation of semiconductor quantum dots and their conjugates by capillary electrophoresis

Semiconductor quantum dots (QDs) are very important luminescent nanomaterials with a wide range of potential applications. Currently, QDs as labeling probes are broadly used in bioassays, including immunoassay, DNA hybridization, and bioimaging, due to their excellent physical and chemical properties, such as broad excitation spectra, narrow and size‐dependent emission profiles, long fluorescence life time, and good photostability. The characterization of QDs and their conjugates is crucial for their wide bioapplications. CE has become a powerful tool for the separation and characterization of QDs and their conjugates. In this review, some CE separation models of QDs are first introduced, mainly including CZE, CGE, MEKC, and ITP. And then, some key applications, such as the measurements of size, surface charge, and concentration of QDs and the characterization of QDs conjugates (e.g. QD–protein, QD–DNA, QD–small molecule), are also described. Finally, future perspectives are discussed.     

Stable Perovskite Quantum Dots Coated with Superhydrophobic Organosilica Shells for White Light‐Emitting Diodes

Metalammonium lead perovskite (MAPbX₃, MA=CH₃NH₃⁺; X=Cl, Br, I) quantum dots (QDs) have attracted tremendous attention due to their outstanding optical properties. However, they usually suffer from poor stability towards water or moisture, which seriously limits their practical applications. Here, we report a simple and effective approach to improve the stability of MAPbBr₃ QDs by encapsulating them with superhydrophobic fluorinated organosilica (FSiO₂) shells. The water‐resistant stability of the superhydrophobic MAPbBr₃ QDs/FSiO₂ is significantly enhanced and they display strong fluorescence even after immersion in water for 12 hours. This method is readily extended to prepare superhydrophobic MAPbBr_2.4Cl_0.6 QDs/FSiO₂ and MAPbI₃ QDs/FSiO₂ powders. These superhydrophobic MAPbX₃ QDs/FSiO₂ can be further used to fabricate white light‐emitting diodes (LEDs) with comparable color to pure white emission.     

How Quantum Dots Aggregation Enhances Förster Resonant Energy Transfer

As luminescent quantum dots (QDs) are known to aggregate themselves through their chemical activation by carbodiimide chemistry and their functionalization with biotin molecules, we investigate both effects on the fluorescence properties of CdTe QDs and their impact on Förster Resonant Energy Transfer (FRET) occurring with fluorescent streptavidin molecules (FA). First, the QDs fluorescence spectrum undergoes significant changes during the activation step which are explained thanks to an original analytical model based on QDs intra-aggregate screening and inter-QDs FRET. We also highlight the strong influence of biotin in solution on FRET efficiency, and define the experimental conditions maximizing the FRET. Finally, a free-QD-based system and an aggregated-QD-based system are studied in order to compare their detection threshold. The results show a minimum concentration limit of 80 nM in FA for the former while it is equal to 5 nM for the latter, favouring monitored aggregation in the design of QDs-based biosensors.     

Enhanced chemiluminescence from reactions between CdTe/CdS/ZnS quantum dots and periodate

A novel chemiluminescence (CL) performance of CdTe/CdS/ZnS quantum dots (QDs) with periodate (KIO₄) was studied. Effects of concentration and pH on the CL system were investigated. Electron spin resonance (ESR) and the effects of radical scavenger analysis were employed for identification of intermediate species. The CL spectra for this system showed only one maximum emission peak centered around 620 nm, which was similar with photoluminescence (PL) spectra of CdTe/CdS/ZnS QDs. The CL of CdTe/CdS/ZnS QDs was induced by direct chemical oxidation and the possible mechanism could be explained by radiative recombination of injected holes and electrons. This investigation not only provided new sight into the optical characteristics of CdTe/CdS/ZnS QDs, but also broadened their potential optical utilizations.     

有机体系中II–VI族量子点的制备及其合成机理

量子点由于其量子效应而具有既不同于体相材料又有别于一般分子的优异光学性能,因此在生物医学领域,特别是在生物标记中具有良好的应用前景。II–VI族量子点由于其荧光发射波长几乎覆盖了整个可见光区而引起人们的关注,其中在有机体系中合成油溶性II–VI族量子点具有反应产物稳定,量子产率高,并且可以制备性能更加优异的核–壳结构的量子点（CdSe/ZnS, CdSe/CdS等）等优点,因此在过去的十几年中被广泛而深入地研究。本文重点综述了在有机体系中,单分散、高荧光性能II–VI族量子点的制备方法——高温热解法及其合成机理的研究进展,并对今后的研究方向作了展望。     

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ~170% and attained a saturation value after ~100 min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200 °C) and pressures (~120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation.     

Preparation of liposomes loaded with quantum dots, fluorescence resonance energy transfer studies, and near-infrared in-vivo imaging of mouse tissue

We report on a simple, fast and convenient method to engineer lipid vesicles loaded with quantum dots (QDs) by incorporating QDs into a vesicle-type of lipid bilayer using a phase transfer reagent. Hydrophilic CdTe QDs and near-infrared (NIR) QDs of type CdHgTe were incorporated into liposomes by transferring the QDs from an aqueous solution into chloroform by addition of a surfactant. The QD-loaded liposomes display bright fluorescence, and the incorporation of the QDs into the lipid bilayer leads to enhanced storage stability and reduced sensitivity to UV irradiation. The liposomes containing the QD were applied to label living cells and to image mouse tissue in-vivo using a confocal laser scanning microscope, while NIR images of mouse tissue were acquired with an NIR fluorescence imaging system. We also report on the fluorescence resonance energy transfer (FRET) that occurs between the CdTe QDs (the donor) and the CdHgTe QDs (the acceptor), both contained in liposomes. Based on these data, this NIR FRET system shows promise as a tool that may be used to study the release of drug-loaded liposomes and their in vivo distribution.

Purification of denatured bovine serum albumin coated CdTe quantum dots for sensitive detection of silver(I) ions

CdTe quantum dots (QDs) were synthesized in aqueous solution with 3-mercaptopropionic acid as the stabilizer. Chemically reduced bovine serum albumin (BSA) was used to modify the surface of the QDs. Experimental results showed that the denatured BSA (dBSA) could be effectively conjugated to the surface of CdTe QDs. Column chromatography was used to purify the conjugates and determine the optimal ratio of dBSA to QDs. Further experimental results showed that the conjugation of QDs by dBSA efficiently improved the photoluminescence quantum yield, the chemical stability of QDs and their stability against photobleaching. A facile and sensitive method for determination of silver(I) ions was proposed based on the fluorescence quenching of the dBSA–QDs. Under the optimal conditions, the relative fluorescence intensity decreased linearly with the concentration of the silver(I) ions in the range 0.08–10.66 μM. The detection limit was 0.01 μM. This study provides a new method for the detection of metal cations. Figure In this work, denatured BSA was used to modify the surface of CdTe QDs by a simple and rapid method. And the conjugates of dBSA-QDs were purified by column of Sephadex G-100. After the purification of the conjugates, the sensitivity was greatly increased as silver (I) ions probe.