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.     

油溶性CuInS2/ZnS量子点的制备及其温敏性聚丙烯酰胺胶束介导的水相转移

采用非热注法成功制备了高质量的油溶性CuInS2/ZnS核壳量子点,量子点的荧光发射峰在可见光到近红外范围内可调(550～800 nm),且荧光量子产率最高达80%。本文进一步利用具有温敏特性的聚丙烯酰胺胶束作相转移剂,成功地将油溶性的CuInS2/ZnS核壳量子点转移入水相。水相中自组装形成的CuInS2/ZnS量子点-胶束复合物不仅具有良好的荧光性质,而且胶束原有的灵敏的热响应性被保留。这些研究初步表明,无镉的低毒的CuInS2/ZnS量子点可作为纳米胶束的荧光示踪探针。     

油溶性CuInS2/ZnS量子点的制备及其温敏性聚丙烯酰胺胶束介导的水相转移

采用非热注法成功制备了高质量的油溶性CuInS₂/ZnS核壳量子点, 量子点的荧光发射峰在可见光到近红外范围内可调(550~800 nm), 且荧光量子产率最高达80%。本文进一步利用具有温敏特性的聚丙烯酰胺胶束作相转移剂, 成功地将油溶性的CuInS₂/ZnS核壳量子点转移入水相。水相中自组装形成的CuInS₂/ZnS量子点-胶束复合物不仅具有良好的荧光性质, 而且胶束原有的灵敏的热响应性被保留。这些研究初步表明, 无镉的低毒的CuInS₂/ZnS量子点可作为纳米胶束的荧光示踪探针。     

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.     

一锅合成绿色到近红外发射的CdTe量子点

以3-巯基丙酸(MPA)为稳定剂,采用水相合成法制备了从绿色到近红外发射的CdTe量子点。系统研究了反应液pH值、镉和碲的物质的量之比及镉和3-巯基丙酸的物质的量之比等实验条件对CdTe量子点体系的发射波长和荧光量子产率的影响。在pH值为10.5,且nCd2+∶nTe2-∶nMPA=1∶0.05∶1.1的条件下,回流0.5 h,CdTe量子点体系在569 nm波长处的荧光量子产率达到30.8%;在7 h的回流时间内,制备的量子点的波长覆盖范围为525～730 nm。分别用X射线粉末衍射、透射电镜和红外光谱对CdTe量子点的晶体结构、形貌及表面基团进行表征。     

PbS/CdS Core–Shell Quantum Dots Suppress Charge Transfer and Enhance Triplet Transfer

A sub‐monolayer CdS shell on PbS quantum dots (QDs) enhances triplet energy transfer (TET) by suppressing competitive charge transfer from QDs to molecules. The CdS shell increases the linear photon upconversion quantum yield (QY) from 3.5 % for PbS QDs to 5.0 % for PbS/CdS QDs when functionalized with a tetracene acceptor, 5‐CT . While transient absorption spectroscopy reveals that both PbS and PbS/CdS QDs show the formation of the 5‐CT triplet (with rates of 5.91±0.60 ns⁻¹ and 1.03±0.09 ns⁻¹ respectively), ultrafast hole transfer occurs only from PbS QDs to 5‐CT . Although the CdS shell decreases the TET rate, it enhances TET efficiency from 60.3±6.1 % to 71.8±6.2 % by suppressing hole transfer. Furthermore, the CdS shell prolongs the lifetime of the 5‐CT triplet and thus enhances TET from 5‐CT to the rubrene emitter, further bolstering the upconverison QY.     

Controlled aging of PbS colloidal quantum dots under mild conditions

A new controlled aging methodology was developed for the synthesis of PbS colloidal quantum dots (QDs), applying larger PbS QDs as a starting material for smaller QDs by application of environmentally friendly oleic acid and oleylamine as reagents. This simple and mild procedure provides a possible strategy for tailoring the size-dependent properties of PbS QDs.     

Reversible surface electronic traps in PbS quantum dot solids induced by an order-disorder phase transition in capping molecules

The electronic properties of semiconductor quantum dots (QDs) are critically dependent on the nature of the ligand molecules on their surfaces. Here we show the reversible formation of surface electronic trap states in the model system of solid thin films of PbS QDs capped with thiol molecules. As the temperature was increased from cryogenic to room temperature, we discovered a phase transition in the fluorescence spectra from excitonic emission to trap emission. The critical temperature (T(c)) of the phase transition scales with molecular length and in each case is close to the bulk melting temperature of the capping molecules. We conclude that an order-disorder transition in the molecular monolayer above T(c) introduces surface mobility and the formation of a disordered atomic lead layer at the QD/capping molecule interface, leading to electronic trap formation.     

超声电化学快速制备近红外CdTe量子点与细胞成像

针对当前水溶性量子点合成路线复杂、量子产率低的现状, 在无需N₂保护的条件下, 采用简便的超声电化学方法快速合成了CdTe量子点前驱体;并对不同条件下制得的前驱体加热回流, 得到水溶性、高质量的近红外CdTe量子点。产物的形貌、结构和组成通过高分辨透射电子显微镜(HRTEM)、X-射线粉末衍射(XRD)等手段进行了表征。考察了超声电化学参数和回流条件对量子点荧光性质的影响。通过控制电流脉冲宽度、反应时间、反应温度等参数, 实现了CdTe量子点前驱体的可控制备;通过调节加热回流条件得到不同荧光发射波长的量子点;选用602 nm近红外发射波长的CdTe量子点标记了子宫颈癌细胞(Hela), 并采用共聚焦技术实现了肿瘤细胞的显微成像观察。和传统的量子点合成方法相比, 超声电化学方法具有合成路线简单、参数易调可控的特点;为高品质量子点的快速制备提供了新的思路, 拓展了超声电化学在纳米材料制备领域的应用。     

Highly luminescent CdSe/Cd(x)Zn(1-x)S quantum dots coated with thickness-controlled SiO2 shell through silanization

A silanization technique of hydrophobic quantum dots (QDs) was applied to SiO(2)-coated CdSe/Cd(x)Zn(1-x)S QDs to precisely control the SiO(2) shell thickness and retain the original high photoluminescence (PL) properties of the QDs. Hydrophobic CdSe/Cd(x)Zn(1-x)S core-shell QDs with PL peak wavelengths of 600 and 652 nm were prepared by a facile organic route by using oleic acid (OA) as a capping agent. The QDs were silanized by using partially hydrolyzed tetraethyl orthosilicate by replacing surface OA. These silanized QDs were subsequently encapsulated in a SiO(2) shell by a reverse micelles synthesis. The silanization plays an important role for the QDs to be coated with a homogeneous SiO(2) shell and retain a high PL efficiency in water. Transmission electron microscopy observation shows that the shells are 1-9 nm with final particle sizes of 10-25 nm, depending on the initial QD size. In the case of short reaction time (6 h), the QDs were coated with a very thin SiO(2) layer because no visible SiO(2) shell was observed but transferred into the water phase. The silica coating does not change the PL peak wavelength of the QDs. The full width at half-maximum of PL was decreased 4 nm after coating for QDs emitting at both 600 and 652 nm. The PL efficiency of the SiO(2)-coated is up to 40%, mainly determined by the initial PL efficiency of the underlying CdSe/Cd(x)Zn(1-x)S QDs.     

Graphdiyne:Structure of Fluorescent Quantum Dots

Graphdiyne (GDY) as an emerging two‐dimensional carbon allotrope exhibits excellent performance in energy chemistry, catalytic chemistry, optoelectronics, electronics, etc. because of the unique structure combining an sp‐ and sp²‐hybrid carbon network. However, the poor solubility of pristine GDY is a major obstacle to its applications in many fields. Proposed here is a facile strategy to control the preparation of GDY quantum dots (GDY‐Py QDs), in which pyrene groups are covalently linked to GDY by using a Sonogashira cross‐coupling reaction. The as‐prepared GDY‐Py QDs, with an average diameter of about 3±0.1 nm, show superior dispersibility in many organic solvents and water. The GDY‐Py QDs display not only bright fluorescent with a high relative quantum yield (QY) of 42.82 %, but they are also well‐behaved as contrast agents in cell imaging. The GDY‐Py QDs are bestowed with high stability and non‐cytotoxicity, and exhibit long fluorescent times, and have potential for optical imaging and biomedical applications.     

超声电化学快速制备近红外CdTe量子点与细胞成像

针对当前水溶性量子点合成路线复杂、量子产率低的现状,在无需N2保护的条件下,采用简便的超声电化学方法快速合成了CdTe量子点前驱体;并对不同条件下制得的前驱体加热回流,得到水溶性、高质量的近红外CdTe量子点。产物的形貌、结构和组成通过高分辨透射电子显微镜(HRTEM)、X-射线粉末衍射(XRD)等手段进行了表征。考察了超声电化学参数和回流条件对量子点荧光性质的影响。通过控制电流脉冲宽度、反应时间、反应温度等参数,实现了CdTe量子点前驱体的可控制备;通过调节加热回流条件得到不同荧光发射波长的量子点;选用602 nm近红外发射波长的CdTe量子点标记了子宫颈癌细胞(Hela),并采用共聚焦技术实现了肿瘤细胞的显微成像观察。和传统的量子点合成方法相比,超声电化学方法具有合成路线简单、参数易调可控的特点;为高品质量子点的快速制备提供了新的思路,拓展了超声电化学在纳米材料制备领域的应用。     

水溶性量子点的制备及应用

高量子产率的水溶性量子点在众多领域如发光晶体、薄膜光激发器件,尤其是生物荧光标记中展现出巨大的潜在应用价值.量子点荧光明亮、稳定,激发光谱宽,发射光谱窄,且发射波长可通过改变材料的粒径大小和组成来调控,因而在生物样本尤其是活组织的多色成像中极为有用,能有效避免因样本自身发光和光散射导致的信号干扰.量子点的研究已成为一门新兴的交叉科学,是目前最有吸引力的研究领域之一.近年来,水溶性量子点作生物荧光标记物的研究取得了长足的进展.本文简述了量子点的结构特征及光学特性,重点综述了水溶性量子点的制备方法及应用研究进展,特别是它在生物、医学中作荧光探针的最新研究.     

Synthesis of cysteamine-coated CdTe quantum dots and its application in mercury (II) detection

High-quality cysteamine-coated CdTe quantum dots (CA-CdTe QDs) were successfully synthesized in aqueous phase by a facile one-pot method. Through hydroxylamine hydrochloride-promoted kinetic growth strategy, water-soluble CA-CdTe QDs could be obtained conveniently in a conical flask by a stepwise addition of raw materials. The photoluminescence quantum yield (PL QY) of the obtained QDs reached 9.2% at the emission peak of 520 nm. The optical property and the morphology of the QDs were characterized by UV–vis absorption spectra, photoluminescence spectra (PL) and transmission electron microscopy (TEM) respectively. Furthermore, the fluorescence of the resultant QDs was quenched by copper (II) (Cu²⁺) and mercury (II) (Hg²⁺) meanwhile. It is worthy of note that to separately detect Hg²⁺, cyanide ion could be used to eliminate the interference of Cu²⁺. Under the optimal conditions, the response was linearly proportional to the logarithm of Hg²⁺ concentration over the range of 0.08–3.33 μM with a limit of detection (LOD) of 0.07 μM.     

Microwave-assisted Synthesis of CdTe Quantum Dots Using 3-Mercaptopropionic Acid as Both a Reducing Agent and a Stabilizer

In this paper, a facile synthetic approach to prepare CdTe quantum dots(QDs) with high luminescence via a one-pot microwave irradiation reaction route using 3-mercaptopropionic acid(MPA) as both a sodium tellurite reducer and a capping molecule was described, and the mechanism of the formation of CdTe QDs was elucidated. In this approach, CdTe QDs with six different emission wavelengths of 553, 567, 577, 595, 608 and 615 nm were obtained via changing the refluxing time and the quantum yields(QY) of these QDs were 40.6%, 55.3%, 63.6%, 43.4%, 37.4% and 29.7%, respectively. The characterization results of X-ray powder diffraction(XRD) and transmission electron microscopy(TEM) indicate that the obtained QDs have a pure cubic zinc blended structure with a spherical shape. No toxic gases were released during the preparation process, indicating that the method is relatively fast, cheap and environmentally friendly.     

Study the damage of DNA molecules induced by three kinds of aqueous nanoparticles

In this paper, the interaction of DNA molecules with aqueous CdTe quantum dots (CdTe QDs), CdTe/SiO₂ composite nanoparticles (CdTe/SiO₂ NPs), and Mn-doped ZnSe quantum dots (Mn:ZnSe d-dots) was studied with ethidium bromide as a probe. The purpose of this work was to study the damage of DNA molecules induced by these three kinds of water-soluble nanoparticles. It was found that ionic strength, pH value and UV irradiation influenced the PL emission properties of CdTe QDs, CdTe/SiO₂ NPs and Mn:ZnSe d-dots, and also influenced the interaction of DNA molecules with them. Among the three kinds of nanoparticles, DNA molecules were most easily damaged by CdTe QDs whether in the dark or under UV irradiation. The CdTe/SiO₂ NPs led to much less DNA damage when compared with CdTe QDs, as a silica overcoating layer could isolate the QDs from the external environment. Mn:ZnSe d-dots as a new class of non-cadmium doped QDs demonstrated almost no damage for DNA molecules, which have great potentials as fluorescent labels in the applications of biomedical assays, imaging of cells and tissues, even in vivo investigations.     

Catalytic Molecular Imaging of MicroRNA in Living Cells by DNA‐Programmed Nanoparticle Disassembly

Molecular imaging is an essential tool for disease diagnostics and treatment. Direct imaging of low‐abundance nucleic acids in living cells remains challenging because of the relatively low sensitivity and insufficient signal‐to‐background ratio of conventional molecular imaging probes. Herein, we report a class of DNA‐templated gold nanoparticle (GNP)–quantum dot (QD) assembly‐based probes for catalytic imaging of cancer‐related microRNAs (miRNA) in living cells with signal amplification capacity. We show that a single miRNA molecule could catalyze the disassembly of multiple QDs with the GNP through a DNA‐programmed thermodynamically driven entropy gain process, yielding significantly amplified QD photoluminescence (PL) for miRNA imaging. By combining the robust PL of QDs with the catalytic amplification strategy, three orders of magnitude improvement in detection sensitivity is achieved in comparison with non‐catalytic imaging probe, which enables facile and accurate differentiation between cancer cells and normal cells by miRNA imaging in living cells.     

Photoluminescence investigation of MPA–ZnS QDs interaction with selenite ion

The interaction between water-soluble zinc sulfide quantum dots (ZnS QDs) and selenite ion was investigated by photoluminescence method. The water-soluble ZnS QDs were synthesized using a simple and fast procedure based on the co-precipitation of nanoparticles in an aqueous solution in the presence of 3-mercaptopropionic acid (MPA), as the capping agent. Fluorescence intensity for MPA–ZnS QDs, with a strong fluorescent emission at about 430 nm, decreased in the presence of selenite. The influence of the effective parameters including pH and temperature was investigated. The results showed that under the optimum conditions, the fluorescence intensity change of QDs was linearly proportional to the selenite concentration in the range 4.0 × 10^?5–7.2 × 10^?4 mol L^?1. Moreover, the quenching mechanism was discussed to be a static quenching procedure.     

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.     

Fine tuning of the morphology of copper oxide nanostructures and their application in ambient degradation of methylene blue

A low-cost, green, and reproducibly non-injection one-pot synthesis of high-quality CdS quantum dots (QDs) is reported. The synthesis was performed in the open air by mixing precursors cadmium stearate and S powder into a new solvent N-oleoylmorpholine. An overlapped nucleation-growth stage followed by a dominated growth stage was observed. The resulting QDs exhibited well-resolved absorption fine substructure and a dominant band-edge emission with a narrow size distribution (the full width at half maximum (fwhm) was only 22-24nm). The maximum photoluminescence (PL) quantum yield (QY) was as high as 46.5%. Highly monodispersed CdS QDs with tunable sizes and similar PL fwhm and QYs could also be obtained from the CdS QDs in a large-scale synthesis. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs with high crystallinity had a cubic structure. A significant PL improvement and a continuous QY increase for the CdS QDs were observed during a long storage time in air and in a glovebox under room temperature. A slow surface reconstruction was proposed to be the cause for the PL enhancement of CdS QDs.