Preparation and characterization of thiacalix[4]arene coated water-soluble CdSe/ZnS quantum dots as a fluorescent probe for Cu2+ ions

Highly fluorescent water-soluble CdSe/ZnS (core/shell) quantum dots (QDs) as a fluorescent Cu2+ ion probe were synthesized using thiacalix[4]arene carboxylic acid (TCC) as a surface coating agent. Hydrophobic trioctylphosphine oxide (TOPO) capped CdSe/ZnS QDs were overcoated with TCC in tetrahydrofuran at room temperature, and deprotonation of the carboxyl groups of TCC resulted in the formation of water-soluble QDs. The surface structure of the QDs was characterized by using transmission electron microscopy (TEM) and fluorescence correlation spectroscopy (FCS). TEM images showed that TCC-coated QDs were monodispersed with the particle size (core-shell moiety) of approximately 5 nm. Hydrodynamic diameter of the TCC-coated QDs was determined to be 8.9 nm by FCS, showing that the thickness of the surface organic layer of the QDs was approximately 2 nm. These results indicate that the surface layer of TCC-coated QDs forms a bilayer structure consisting of TOPO and TCC molecules. TCC-coated CdSe/ZnS QDs were highly fluorescent (quantum yield, 0.21) compared to the QDs surface-modified with mercaptoacetic acid and mercaptoundecanoic acid. Fluorescence of the TCC-coated QDs was effectively quenched by Cu2+ ions even in the presence of other transition metal ions such as Cd2+, Zn2+, Co2+, Fe2+, and Fe3+ ions in the same solution. The Stern-Volmer plot for the fluorescence quenching by Cu2+ ions showed a linear relationship up to 30 microM of Cu2+ ions. The ion selectivity of TCC-coated QDs was determined by measurements of fluorescence responses towards biologically important transition metal ions (50 microM) including Fe2+, Fe3+, Co2+>Zn2+, Cd2+. The fluorescence of TCC-coated QDs was almost insensitive to other biologically important ions such as Na+, K+, Mg2+, and Ca2+, suggesting that TCC-coated QDs can be used as a fluorescent Cu2+ ion probe for biological samples. A possible quenching mechanism by Cu2+ ions was also discussed on the basis of a Langmuir-type adsorption isotherm.     

水稳定的镁掺杂ZnO量子点:一锅法合成及细胞成像应用

一锅法合成了镁掺杂的ZnO量子点,利用APTES对其进行表面包覆,并采用XRD、TEM、UV-Vis、PL和FTIR等对材料进行了表征。结果表明镁掺杂能明显增强荧光发光强度,在合适的掺杂浓度(30%)下其量子产率由11%增加到33%。通过APTES的表面包覆使镁掺杂的ZnO量子点具有良好的水溶性和荧光稳定性,可用于MCF-7细胞成像研究。     

水稳定的镁掺杂ZnO量子点:一锅法合成及细胞成像应用

一锅法合成了镁掺杂的ZnO量子点, 利用APTES对其进行表面包覆, 并采用XRD、TEM、UV-Vis、PL和FTIR等对材料进行了表征。结果表明镁掺杂能明显增强荧光发光强度, 在合适的掺杂浓度(30%)下其量子产率由11%增加到33%。通过APTES的表面包覆使镁掺杂的ZnO量子点具有良好的水溶性和荧光稳定性, 可用于MCF-7细胞成像研究。     

Host–Guest Interaction of Chaperonin GroEL and Water‐Soluble CdTe Quantum Dots and its Size‐Selective Inclusion

Some nanoparticles, such as quantum dots (QDs), are widely used in the biological and biomedical fields due to their unique optical properties. However, little is currently known about the interaction between these nanoparticles and biomolecules. Herein, we systemically investigated the interaction between chaperonin GroEL and water‐soluble CdTe QDs based on fluorescence correlation spectroscopy (FCS), capillary electrophoresis, and fluorescence spectrometry. We observed that some water‐soluble CdTe QDs were able to enter the inner cavity of GroEL and formed an inclusion complex after the activation of chaperonin GroEL with ATP. The inclusion of GroEL was size‐selective to QDs and only small QDs were able to enter the inner cavity. The inclusion could suppress the fluorescence quenching of the QDs. Meanwhile, we evaluated the association constant between chaperonin GroEL and CdTe QDs by FCS. Our results further demonstrated that FCS was a very useful tool for study of the interaction of QDs and biomolecules.     

Fluorescent quantum dots for microbial imaging

QDs (Semiconductor QDs, CDs, SiQDs, and Pdots) are used in imaging microorganisms including viruses, bacteria, and fungi.     

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.     

叶酸受体靶向CdS量子点应用于HepG2细胞成像研究

0引言量子点(quantum dots,QDs)又称半导体纳米晶体(semiconductor nanocrystal),是一种由Ⅱ-Ⅵ族或Ⅲ-Ⅴ族元素组成的尺寸在2￣20nm之间,稳定的微     

Preparation of High‐Performance Water‐Soluble Quantum Dots for Biorecognition through Fluorescence Resonance Energy Transfer

An improved method for the synthesis of high‐performance and water‐soluble quantum dots (QDs) involving the encapsulation of mercaptosuccinic acid coated QDs (MSA‐QDs) with poly(diallyldimethylammonium chloride) (PDDA) followed by their direct photoactivation with fluorescent radiation near 295 K to yield PDDA‐coated QDs (PDDA‐QDs) has been demonstrated. The quantum yield (QY) of the PDDA‐QDs was significantly improved from 0.6 (QY of MSA‐QDs) to 48 %. By using this synthetic strategy, highly photoluminescent PDDA‐QDs of varied size were readily prepared. The surface properties of PDDA‐QDs and MSA‐QDs were extensively characterized. The highly luminescent and positively charged PDDA‐QDs serve as a useful and convenient tool for protein adsorption. With a Δ⁵‐3‐ketosteroid isomerase adsorbed PDDA‐QD complex, the biorecognition of steroids was demonstrated through the application of fluorescent resonance energy transfer.     

Highly fluorescent streptavidin-coated CdSe nanoparticles: preparation in water, characterization, and micropatterning

CdSe quantum dots (QDs) with a high fluorescence quantum yield of 25% and a narrow size distribution were synthesized in a single step in water using glutathione as a stabilizing molecule. The exceptional optical properties enabled for the first time the detection of in-water-prepared single quantum dots at room temperature. For application as fluorescent bioanalytical probes, the QDs were coated with streptavidin. These QDs self-assemble with high contrast on micropatterned biotin while preserving their optical properties and their capability to bind in addition biotinylated molecules, a prerequisite for the development of novel supramolecular structures and bioassays.     

Selective capturing and detection of Salmonella typhi on polycarbonate membrane using bioconjugated quantum dots

Present work demonstrates the utilization of surface modified polycarbonate (PC) membrane as solid phase and antibody conjugated CdSe/ZnS quantum dots (QDs) as fluorescent label for the sensitive and selective detection of Salmonella typhi (S. typhi) in water in a period of 2.5 h. PC membrane was surface modified with glycine and activated by EDC/NHS for immobilization of S. typhi specific IgG. Antibody immobilized porous PC membrane was incubated with bacteria contaminated water for immunocapturing of S. typhi. Antibody conjugated QDs were also prepared by using carbodiimide chemistry. Both modified PC membrane and quantum dots were characterized by using various modern analytical tools. It was estimated that 1.95 molecules of QDs were successfully bio-conjugated per unit of IgG. PC membrane with captured bacteria was incubated with prepared IgG conjugated QDs for the formation of sandwich complex. Analysis of the regions of interest (ROI) in fluorescent micrographs showed that newly developed method based on PC and fluorescent QDs has 100 times higher detection sensitivity (100 cells/mL) as compared with detection using conventional dye (FITC) based methods.     

Fluorescent II-VI semiconductor quantum dots in living cells: nonlinear microspectroscopy in an optical tweezers system

In this work we used a setup consisting of an optical tweezers combined with a nonlinear microspectroscopy system to perform scanning microscopy and obtain emission spectra using two photon excited (TPE) luminescence of captured single living cells labeled with core-shell fluorescent semiconductor quantum dots (QDs). The QDs were obtained via colloidal synthesis in aqueous medium with an adequate physiological resulting pH. Sodium polyphosphate was used as the stabilizing agent. The results obtained show the potential presented by this system as well as by these II-VI fluorescent semiconductor quantum dots to perform spectroscopy in living trapped cells in any neighborhood and dynamically observe the cell chemical reactions in real time.     

In-situ encapsulation of quantum dots into polymer microspheres

We have incorporated fluorescent quantum dots (QDs) into polystyrene microspheres using functionalized oligomeric phosphine (OP) ligands. We find that a uniform distribution of quantum dots is loaded inside each polymer bead. Some local close-packing of quantum dots in the beads is attributed to the self-polymerization of the functionalized ligands. The presence of quantum dots disturbs the nucleation and growth processes during the formation of polymer microspheres and results in a wider size distribution of the quantum dot-embedded polystyrene beads than for the control without dots. The change in quantum efficiency of the quantum dots before (approximately 20%) and after (12%) loading into the beads substantiates the protection of oligomeric phosphine ligands yet indicates that the properties of these quantum dots are still affected during processing.     

水合肼还原二氧化碲水相合成CdTe量子点

以巯基乙酸为稳定剂, 氯化镉为镉源, 二氧化碲为碲源, 水合肼为还原剂, 一步合成了CdTe量子点. 研究了反应时间、 碲与镉的摩尔比及巯基乙酸与镉的摩尔比等实验条件对CdTe量子点生长过程的影响. 采用荧光光谱、 X射线粉末衍射和透射电子显微镜等对量子点的性能进行了表征. 结果表明, 反应时间及反应物的相对用量对量子点的生长和荧光光谱有明显影响, 所得CdTe量子点具有立方晶型, 发光颜色从绿色到红色连续可调, 荧光量子产率可达26%.     

Forming highly fluorescent near-infrared emitting PbS quantum dots in water using glutathione as surface-modifying molecule

We present a new facile procedure for transferring oil-soluble oleic acid-capped NIR-emitting PbS quantum dots (QDs) into water, using hydrophilic thiol ligands as the surface-modifying agents of the primary capping molecules (oleic acid). The influence of exchange of the primary capping molecules with five different types of thiol molecules is investigated. The results show that highly fluorescent water-soluble PbS QDs are obtained using glutathione as a surface-modifying agent (photoluminescence quantum yield (PL QY), >30%); significantly less fluorescent water-soluble QDs were obtained using l-cysteine (PL QY, ~5%); with other three thiol molecules, PbS QDs lose almost completely their fluorescence in aqueous solution. This striking difference among the five thiol molecules may be attributed to the difference in the molecular structure. Next, we explored systematically the conditions of QD water solubilization, storage stability, photostability and cytotoxicity and tested further the resulting water-soluble PbS QDs for the imaging of living animals. The preliminary results from these studies illustrate that our synthesis procedure is very facile and that the as-prepared water-soluble PbS QDs are stable and low-cytotoxic and will be an important potential probe in the imaging of living animals due to free carboxyl and amino groups on the external surface of the QDs.     

Average Arrival Time: an Alternative Approach for Studying Fluorescent Behavior of Single Quantum Dots?

Due to photoluminescence intermittency of single colloidal quantum dots (QDs), the traditional exponential fluorescence lifetime analysis is not perfect to characterize QDs' fluorescent emission behavior. In this work we used the time-tagged time-resolved (TTTR) mode to record the fluorescent photons from single QDs. We showed that this method is compatible with the traditional lifetime analysis. In addition, by constructing the trajectory over time and the distribution of average arrival time (AAT) of the fluorescent photons, more details about the emission behavior of QDs were revealed.     

Oligomeric PEG-phospholipids for solubilization and stabilization of fluorescent nanocrystals in water

Water soluble fluorescent nanocrystals were obtained by encapsulation of hydrophobic quantum dots (QDs) with amphiphilic phospholipids derived from the ring opening metathesis of norbornene-based monomers. The robustness of the newly coated quantum dots was assessed by comparative studies under various ionic conditions which indicated an overall enhancement of their fluorescence stability.     

基于量子点的荧光共振能量转移

研究了具有相反电荷的两种量子点间的荧光共振能量转移.分别以巯基乙酸(TGA)和十六烷基三甲基溴化胺(CTMAB)修饰发射绿色和红色荧光的CdSe/ZnS量子点,使其由油溶性变为水溶性,且表面带相反的电荷,并对修饰后的水相量子点进行琼脂糖凝胶电泳、荧光成像、量子产率等系列表征.对两种量子点间的荧光共振能量转移现象进行研究.结果表明: 在激发波长为400 nm时,两种量子点在磷酸盐缓冲溶液(pH 7.5)中具有较好的荧光共振能量转移效率(猝灭效率0.54,增强效率0.27).     

Studies on bioconjugation of quantum dots using capillary electrophoresis and fluorescence correlation spectroscopy

In this paper, we systematically investigated the conjugation of quantum dots (QDs) with certain biomolecules using capillary electrophoresis (CE) and fluorescence correlation spectroscopy (FCS) methods. Commercial QDs and aqueous-synthesized QDs in our lab were used as labeling probes, certain bio-macromolecules, such as proteins, antibodies, and enzymes, were used as mode samples, and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysulfo-succinimide (Sulfo-NHS) were used as linking reagents. We studied the effects of certain factors such as the isoelectric points (pIs) of bio-macromolecules and buffer pH on the bioconjugation of QDs, and found that the pIs of bio-macromolecules played an important role in the conjugation reaction. By the optimization of the buffer pH some proteins with different pIs were efficiently conjugated with QDs using EDC and Sulfo-NHS as linking agents. Furthermore, we on-line investigated the kinetic process of QDs-bioconjugation by FCS and found that the conjugation reaction of QDs with protein was rapid and the reaction process almost completed within 10 min. We also observed that QDs conjugated with proteins were stable for at least 5 days in phosphate buffer. Our work described here will be very helpful for the improvement of the QDs conjugation efficiency in bioapplications.     

Biotin-modified glutathione as a functionalized coating for bioconjugation of CdTe-based quantum dots

In this study, biotin-conjugated glutathione was synthesized using peptide bonding of the biotin carboxy group and amino group of the γ-glutamic acid to prepare an alternative coating for CdTe quantum dots (QDs). This type of coating combines the functionality of the biotin with the fluorescent properties of the QDs to create a specific, high-affinity fluorescent probe able to react with avidin, streptavidin and/or neutravidin. Biotin-functionalized glutathione-coated CdTe QDs were prepared by a simple one-step method using Na? TeO? and CdCl?. Obtained QDs were separated from the excess of the biotin-conjugated glutathione by CE employing 300?mM borate buffer with pH 7.8 as a background electrolyte. The detection of sample components was performed by the photometric detection at 214?nm and LIF employing Ar? ion laser (488?nm).     

CdSe量子点荧光增敏法测定甘草酸

以巯基乙酸为稳定剂水相法一步合成了CdSe量子点,并以此量子点为荧光探针,基于甘草酸(GL)对量子点的荧光增强效应,建立了一种简便、快速、灵敏测定GL的分析方法,同时对GL与CdSe量子点的反应机理进行了初步探讨.考察了多种因素对GL测定的影响.结果表明,在pH 7.4的Na2 HPO4 - NaH2 PO4缓冲溶液中...