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1.
Inorganic cesium lead halide perovskites have evoked wide popularity because of their excellent optoelectronic properties, high photoluminescence (PL) quantum yield (PLQY), and narrowband emission. Here, cesium lead bromide (CsPbBr3) quantum dots (QDs) were synthesized via the ligand-assisted re-precipitation method. Post-synthesis treatment of CsPbBr3 QDs using antimony tribromide improved the PL stability and optoelectronic properties of the QDs. In addition, the PLQY of the post-treated sample was enhanced to 91% via post-treatment, and the luminescence observed was maintained for 8 days. The post-synthesis treatment ensured defect passivation and improved the stability of CsPbBr3 perovskite QDs. High-resolution transmission electron microscopy revealed the presence of more ordered, uniform-sized CsPbBr3 QDs after post-synthesis treatment, and the uniformity of the sample improved as the day passed. The formation of a mixed crystal phase was observed from X-ray diffraction in both as-synthesized, as well as post-treated QDs samples with the possibility of a polycrystalline nature in the post-treated CsPbBr3 QDs as per the selected area electron diffraction pattern. The X-ray photoelectron spectroscopy spectra confirmed the presence of antimony and the possibility of defect passivation in the post-treated samples. These QDs can act as potential candidates in various optoelectronic applications such as photodetectors and light-emitting diodes due to their high PLQY and longer lifetime. 相似文献
2.
Simultaneously improving the stability and photoluminescence quantum yield (PLQY) of all inorganic perovskite nanocrystals (NCs) is crucial for their practical utilization in various optoelectronic devices. Here, CsPbBr3 NCs coated with polyethersulfone (PES) were prepared via an in-situ co-precipitation method. The sulfone groups in PES bind to undercoordinated lead ion (Pb2+) on the CsPbBr3 NCs, resulting in significant reduction of surface defects, thus enhancing the PLQY from 74.2% to 88.3%. Meanwhile, the PES-coated NCs exhibit high water resistance and excellent heat and light stability, maintaining over 85% of the initial PL intensity under thermal aging (70°C, 4 h) and continuous 365 nm ultraviolet (UV) light irradiation (24 W, 8 h) conditions. By contrast, the PL intensity of the control NCs dramatically dropped to less than 40%. Finally, a diode emitting bright white light was fabricated utilizing the PES-coated CsPbBr3 NCs, which exhibits a color gamut of ~110% NTSC standard. 相似文献
3.
Mohammed Ali Al-Duais Zuhair M. Mohammedsaleh Hamza S. Al-Shehri Yahya S. Al-Awthan Suhair A. Bani-Atta Ali A. Keshk Syed Khalid Mustafa Adel D. Althaqafy Jozaa N. Al-Tweher Hatem A. Al-Aoh Chellasamy Panneerselvam 《Luminescence》2022,37(4):633-641
In the present work, an improved class of protein functionalized fluorescent 2D Ti3C2 MXene quantum dots (MXene QDs) was prepared using a hydrothermal method. Exfoliated 2D Ti3C2 sheets were used as the starting precursor and transport protein bovine serum albumin (BSA) was used to functionalize the MXene QDs. BSA-functionalized MXene QDs exhibited excellent photophysical property and stability at various physiological parameters. High-resolution transmission electron microscopy analysis showed that the BSA@MXene QDs were quasispherical in shape with a size of ~2 nm. The fluorescence intensity of BSA@MXene QDs was selectively quenched in the presence of Fe3+ ions. The mechanism of fluorescence quenching was further substantiated using time-resolved fluorescence and Stern–Volmer analysis. The sensing assay showed a linear response within the concentration range 0–150 μM of Fe3+ ions with excellent limit of detection. BSA@MXene QDs probe showed good selectivity toward ferric ions even in the presence of other potential interferences. The practical applicability of BSA@MXene QDs was further tested in real samples for Fe3+ ion quantification and the sensor had good recovery rates. The cytotoxicity studies of the BSA@MXene QDs toward the human glioblastoma cells revealed that BSA@MXene QDs are biocompatible at lower doses and showed significant cytotoxicity at higher dosages. 相似文献
4.
Jingtao Huang Yi-Lin Hu Jin-Zhou Liu Hai-Chi Zhang Qiu-E Cao Rong Sheng Li Jian Ling 《Luminescence》2024,39(1):e4615
By using the method of low-temperature crystallization, CsPbBr3 perovskite nanocrystals (PNCs) coated with trifluoroacetyl lysine (Tfa-Lys) and oleamine (Olam) were synthesized in aqueous solution. The structure of the CsPbBr3 PNCs was characterized by many methods, such as ultraviolet (UV)-visible absorption spectrophotometer, fluorescence spectrophotometer, transmission electron microscopy (TEM), and X-ray diffraction (XRD) pattern. The fluorescence emission of the CsPbBr3 PNCs is stable in water for about 1 day at room temperature. It was also found that the fluorescence of the PNCs could be obviously and selectively quenched after the addition of mercury ion (Hg2+), allowing a visual detection of Hg2+ by the naked eye under UV light illumination. The fluorescence quenching rate (I0/I) has a good linear relationship with the addition of Hg2+ in the concentration range 0.075 to 1.5 mg/L, with a correlation coefficient (R2) of 0.997, and limit of detection of 0.046 mg/L. The fluorescence quenching mechanism of the PNCs was determined by the fluorescence lifetime and X-ray photoelectron spectroscopy (XPS) of the PNCs. Overall, the synthesis method for CsPbBr3 PNCs is simple and rapid, and the as-prepared PNCs are stable in water that could be conveniently used for selective detection of Hg2+ in the water environment. 相似文献
5.
Fengzhao Yang Zhancheng Xu Jinjie Wang Feng Zan Chaoqing Dong Jicun Ren 《Luminescence》2013,28(3):392-400
In this study, we report for the first time a one‐pot approach for the synthesis of new CdSeTeS quaternary‐alloyed quantum dots (QDs) in aqueous phase by microwave irradiation. CdCl2 was used as a Cd precursor during synthesis, NaHTe and NaHSe were used as Te and Se precursors and mercaptopropionic acid (MPA) was used as a stabilizer and source of sulfur. A series of quaternary‐alloyed QDs of different sizes were prepared. CdSeTeS QDs exhibited a wide emission range from 549 to 709 nm and high quantum yield (QY) up to 57.7 %. Most importantly, the quaternary‐alloyed QDs possessed significantly long fluorescence lifetimes > 100 ns as well as excellent photostability. Results of high‐resolution transmission electron microscopy (HRTEM), energy dispersive X‐ray spectroscopy (EDX) and powder X‐ray diffraction (XRD) spectroscopy showed that the nanocrystals possessed a quaternary alloy structure with good crystallinity. Fluorescence correlation spectroscopy (FCS) showed that QDs possessed good water solubility and monodispersity in aqueous solution. Furthermore, CdSeTeS QDs were modified with alpha‐thio‐omega‐carboxy poly(ethylene glycol) (HS‐PEG‐COOH) and the modified QDs were linked to anti‐epidermal growth factor receptor (EGFR) antibodies. QDs with the EGFR antibodies as labeling probes were successfully applied to targeted imaging for EGFR on the surface of SiHa cervical cancer cells. We believe that CdSeTeS QDs can become useful probes for in vivo targeted imaging and clinical diagnosis. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
6.
Yaqian Zheng Yanyu Duan Yun Ye Xingke Zheng Aochen Du Enguo Chen Sheng Xu Tailiang Guo 《Luminescence》2024,39(2):e4691
The preparation of perovskite quantum dots (PQDs) using an in situ inkjet printing method is beneficial for improving the problems of aggregation and photoluminescence (PL) quenching during long-term storage. However, the stability of PQDs prepared using this method is still not ideal, and the morphology of in situ-printed patterns needs to be optimized. To address these problems, this study introduced polymethyl methacrylate (PMMA) into the process of in situ inkjet printing of PQDs and explored the effect of PMMA on the in situ patterning effect of PQDs. The results showed that using a mixed precursor solution containing a small amount of PMMA as the printing ink can slow down the shrinkage process of ink droplets and improve the uniformity of film formation. As the printing substrate, PMMA provided a suitable high-viscosity environment for the in situ growth of PQDs. This could effectively suppress the coffee ring effect. In addition, the interaction between the C=O=C group in PMMA and metal ion Pb2+ in the CsPbBr3 precursor molecules was favourable to enhancing the density of PQDs. The prepared PMMA-coated CsPbBr3 quantum dots (QDs) pattern had high stability and could maintain at 90.08% PL intensity after 1 week of exposure to air. 相似文献
7.
It is a challenging task to prepare well‐dispersed and highly luminescent quantum dots (QDs) powder and a new strategy is reported in this article. Sodium carboxymethyl starch (CMS‐Na) was employed in this work to prepare the QDs–starch composite. Ultraviolet (UV) light shows that the blank starches had no fluorescence, while the QDs‐starches were highly luminescent. Scanning electron microscopy (SEM) observation shows that the QDs–starch composite has the typical particle morphology with the diameter around 200 nm. Energy dispersive X‐ray spectroscopy (EDX) results show that there are intensive tellurium (Te) and cadmium (Cd) element signals. Combined fluorescent lifetime and steady‐state spectrometer show that the QDs–starch quantum yields (QYs) increase when the QDs loading increases from 1 × 10?6 mol/g to 2 × 10?6 mol/g, but when the loadings further increase, the QYs decrease slightly. For the red colour (λem = 660 nm) QDs, the QYs can reach to as high as 28.2%, and for the other colour QDs they can also have the QYs above 22%. Time‐resolved photobleaching experiments show that the fluorescent QDs–starch composite has a half‐decay time of 40.23 s. These results indicate that the CMS‐Na is a promising QDs dispersant to obtain high QY QD composites. 相似文献
8.
Amit Jaiswal Pallab Sanpui Arun Chattopadhyay Siddhartha Sankar Ghosh 《Plasmonics (Norwell, Mass.)》2011,6(1):125-132
Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment
friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra
having an absorbance edge at 300 nm and emission maxima (λ
emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process.
The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K
sv value of 9 × 109 M−1. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism
was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as
confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag
NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence
measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence
in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm. 相似文献
9.
A facile method was developed for the preparation of water soluble β‐Cyclodextrin (β‐CD)‐modified CdSe quantum dots (QDs) (β‐CD‐QDs) by directly replacing the oleic acid ligands on the QDs surface with β‐CD in an alkaline aqueous solution. The as‐prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulphite acid ion and carbonic acid ion, affect the fluorescence of β‐CD‐QDs. Among them, H2PO4– exhibited the largest quenching effect. For the polyprotic acids (HO)3AO, the effect of acidic anions on the fluorescence of β‐CD‐QDs was in the order: monoanion (HO)2AO2– > dianion (HO)AO32– >> trianion AO43–. After photoactivation for several days in the presence of anions at alkaline pH, the β‐CD‐QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the β‐CD‐QDs was investigated further. It was found that Ag+, Hg2+ and Co2+ have significant quenching effect on the fluorescence of the β‐CD‐QDs. The Stern–Volmer quenching constants increased in the order: Hg2+ < Co2+ <Ag+. The adsorption model of metal ions on β‐CD‐QDs was explored. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
Realizing efficient solid‐state luminescence is of great important to expand quantum dots (QDs) application fields. This work reports the preparation of CdTe@BaCO3 composite by a one‐pot precipitation method. Both steady‐state PL and PL decay characteristics in either solid‐state or colloid solution show no obvious difference, mainly benefited from the effective protection of BaCO3 on QDs from the external environment. By utilizing green and red CdTe QDs as dual‐color emission centers, precise emitting‐color control from green (0.312, 0.667) to red (0.691, 0.292) could be achieved in CdTe@BaCO3 composite by adjusting volume ratio of CdTe solution precursor. Our results demonstrate that this composite material shows bright solid‐state luminescence and facile adjustment of the emitting color in QDs‐based composite is feasible, which could offer new path to design color‐tunable luminescent materials for future optoelectronic applications. 相似文献
11.
Core–shell structured CdTe/CdS@SiO2@CdTe@SiO2 composite fluorescent spheres: Synthesis and application for Cd2+ detection
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Core–shell structured quantum dot (QD)–silica fluorescent nanoparticles have attracted a great deal of attention due to the excellent optical properties of QDs and the stability of silica. In this study, core–shell structured CdTe/CdS@SiO2@CdTe@SiO2 fluorescent nanospheres were synthesized based on the Stöber method using multistep silica encapsulation. The second silica layer on the CdTe QDs maintained the optical stability of nanospheres and decreased adverse influences on the probe during subsequent processing. Red‐emissive CdTe/CdS QDs (630 nm) were used as a built‐in reference signal and green‐emissive CdTe QDs (550 nm) were used as a responding probe. The fluorescence of CdTe QDs was greatly quenched by added S2?, owing to a S2?‐induced change in the CdTe QDs surface state in the shell. Upon addition of Cd2+ to the S2?‐quenched CdTe/CdS@SiO2@CdTe@SiO2 system, the responding signal at 550 nm was dramatically restored, whereas the emission at 630 nm remained almost unchanged; this response could be used as a ratiometric ‘off–on’ fluorescent probe for the detection of Cd2+. The sensing mechanism was suggested to be: the newly formed CdS‐like cluster with a higher band gap facilitated exciton/hole recombination and effectively enhanced the fluorescence of the CdTe QDs. The proposed probe shows a highly sensitive and selective response to Cd2+ and has potential application in the detection of Cd2+ in environmental or biological samples. 相似文献
12.
Jing Wang Fengjuan Song Yongling Ai Shanwen Hu Zhizhou Huang Wenying Zhong 《Luminescence》2019,34(2):205-211
In this study, we developed a novel simple fluorescence resonance‐energy transfer (FRET) system between two‐color CdTe quantum dots (QDs) assisted by cetyltrimethylammonium bromide (CTAB). Mercaptopropionic (MPA)‐capped CdTe QDs serving as both donors and acceptors were successfully synthesized by changing the refluxing time in aqueous solution. CTAB micelles formed in water and minimized the distance between the donors and acceptors significantly by electrostatic interactions, improving FRET efficiency. Several factors that affected the fluorescence spectra of the FRET system were investigated. The prepared FRET system was feasible as an effective fluorescent probe to detect Hg(II) in aqueous solution. At pH 7.0, a linear relationship between the quenched fluorescence intensity of orange‐emitting acceptors (QDs(A)) and Hg(II) concentration was acquired in the range 5–250 nmol/L with a detection limit of 1.95 nmol/L. The developed method showed excellent analytical performance for Hg(II) with high sensitivity and acceptable selectivity, reproducibility and stability. This finding indicated that the method has a promising potential application for environmental monitoring. This study demonstrated the great promise of QDs for expedient, low‐cost and high‐sensitivity detection of Hg(II). 相似文献
13.
Hybrid SiO2‐coated CdTe/CdSe quantum dots (QDs) were prepared using CdTe/CdSe QDs prepared by hydrothermal synthesis. A CdSe interlayer made CdTe/CdSe cores with unique type II heterostructures. The hybrid SiO2‐coated CdTe/CdSe QDs revealed excellent photoluminescence (PL) properties compared with hybrid SiO2‐coated CdTe QDs. Because of the existence of spatial separations of carriers in the type II CdTe/CdSe core/shell QDs, the hybrid QDs had a relatively extended PL lifetime and high stability in phosphate‐buffered saline buffer solutions. This is ascribed to the unique components and stable surface state of hybrid SiO2‐coated CdTe/CdSe QDs. During the stabilization test in phosphate‐buffered saline buffer solutions, both static and dynamic quenching occurred. The quenching mechanism of the hybrid QDs was not suited with the Stern–Volmer equation. However, the relative stable surface of CdTe/CdSe QDs resulted in lower degradation and relative high PL quantum yields compared with hybrid SiO2‐coated CdTe QDs. As a result, hybrid SiO2‐coated CdTe/CdSe QDs can be used in bioapplications. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
14.
It is of great significance to develop an effective method for methyl parathion (MP) detection. Herein, a novel nitrogen-doped titanium carbide quantum dots (N-Ti3C2 QDs) was prepared and used to construct a simple and sensitive fluorescence sensing platform of MP by making use of inner filter effect (IFE). The prepared N-Ti3C2 QDs can exhibit strong blue fluorescence at 434 nm. Meanwhile, MP could hydrolyze to produce p-nitrophenol (p-NP) under alkaline conditions, which showed a characteristic ultraviolet-visible (UV-visible) absorption peak at 405 nm, resulting in the fluorescence of N-Ti3C2 QDs is effectively quenched by p-NP. In addition, the investigation of time-resolved fluorescence decays indicated that the corresponding quenching mechanism of p-NP on N-Ti3C2 QDs is due to the IFE. After optimizing the conditions, the as-developed fluorescence sensing platform displayed wide detection range (0.1–30 μg mL−1) and low detection limit (0.036 μg mL−1) for MP, and it was also successfully applied for MP analysis in real water samples, thus it is expected that this simple, sensitive and enzyme-free sensing platform shows great applications. 相似文献
15.
The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd2+ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360 nm and a broad emission spectra between 450 and 650 nm when excited at 370 nm, both characteristic of CdS QDs. Average sizes of 6 and 10 nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H2S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5–5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms. 相似文献
16.
Yan Liu 《Journal of biomolecular structure & dynamics》2013,31(1):90-91
Achieving DNA-functionalized semiconductor quantum dots (QDs) that are robust enough to be compatible with the DNA nanotechnology that withstand precipitation at high temperature and ionic strength is a challenge. Here we report a method that facilitates the synthesis of stable core/shell (1–20 monolayers) QD-DNA conjugates in which the end part (5–10 nucleotides) of the phosphorothiolated oligonucleotides is embedded within the shell of the QD. These reliable QD-DNA conjugates exhibit excellent chemical, colloidal and photonic stability over a wide pH range (4–12) and at high salt concentrations (>100?mM Na+ or Mg2+), bright fluorescence emission with quantum yields of upto 70%, and broad spectral tunability with emission ranging from UV to NIR (360–800?nm). The assembly of these different QDs into DNA origami in a well-controlled pattern was demonstrated (Deng, Samanta, Nangreave, Yan, & Liu, 2012). We also used DNA origami as a platform to co-assemble a gold nanoparticle with 20?nm diameter (AuNP) and an organic fluorophore (TAMRA) and studied the distance dependent plasmonic interactions between the particle and the dye using steady state fluorescence and lifetime measurements. Greater fluorescence quenching was found at smaller inter-particle distances, which was accompanied by an enhancement of the decay rate. We further fabricated 20?nm and 30?nm AuNP homodimers with different inter-particle distances using DNA origami scaffolds and positioned a Cy3 fluorophore between the AuNPs in both the assemblies. Up to 50% enhancement of the Cy3 fluorescence quantum efficiency was observed for the dye between the 30?nm AuNPs. These results are in good agreement with the theoretical simulations (Pal et al., 2013). 相似文献
17.
Zhaoyong Jin Chuangwei Liu Zaichun Liu Jingrui Han Yanfeng Fang Yaqian Han Yusheng Niu Yuping Wu Chenghua Sun Yuanhong Xu 《Liver Transplantation》2020,10(22)
To enable an efficient and cost‐effective electrocatalytic N2 reduction reaction (NRR) the development of an electrocatalyst with a high NH3 yield and good selectivity is required. In this work, Ti3C2Tx MXene‐derived quantum dots (Ti3C2Tx QDs) with abundant active sites enable the development of efficient NRR electrocatalysts. Given surface functional groups play a key role on the electrocatalytic performance, density functional theory calculations are first conducted, clarifying that hydroxyl groups on Ti3C2Tx offer excellent NRR activity. Accordingly, hydroxyl‐rich Ti3C2Tx QDs (Ti3C2OH QDs) are synthesized as NRR catalysts by alkalization and intercalation. This material offers an NH3 yield and Faradaic efficiency of 62.94 µg h?1 mg?1cat. and 13.30% at ?0.50 V, respectively, remarkably higher than reported MXene catalysts. This work demonstrates that MXene catalysts can be mediated through the optimization of both QDs sizes and functional groups for efficient ammonia production at room temperature. 相似文献
18.
A novel fluorescence assay system for glucose was developed with thioglycollic acid (TGA)‐capped CdTe quantum dots (QDs) as probes. The luminescence quantum yield of the TGA‐capped CdTe QDs was highly sensitive to H2O2 and pH. In the presence of glucose oxidase, glucose is oxidized to yield, gluconic acid and H2O2. H2O2 and H+ (dissociated from gluconic acid) intensively quenched the fluorescence of QDs. The experimental results showed that the quenched fluorescence was proportional to the glucose concentration within the range of 0.01–5.0 mm under optimized experimental conditions. Compared with most of the existing methods, this newly developed system possesses many advantages, including simplicity, low cost, high flexibility, and good sensitivity. Furthermore, no complicated chemical modification of QDs and enzyme immobilization was needed in this system. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
19.
Reliable and General Route to Inverse Opal Structured Nanohybrids of Carbon‐Confined Transition Metal Sulfides Quantum Dots for High‐Performance Sodium Storage
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Xiang Hu Jingchun Jia Genxiang Wang Junxiang Chen Hongbing Zhan Zhenhai Wen 《Liver Transplantation》2018,8(25)
Sodium‐ion batteries (SIBs) have recently attracted increasing attention as the promising alternative to lithium‐ion batteries due to their multiple advantages of abundant reserves and low cost. However, the development of highly desirable anode materials suitable for SIBs is still hampered by a rather low capacity, poor rate capability, and cycling stability. Herein, a deliberate design to implement reliable and simple fabrication of an inverse opal structured nanohybrid of carbon‐confined various transition metal sulfides quantum dots (QDs) is presented. Comprehensive characterizations demonstrate that the hybrids hold a 3D architecture with uniform dispersion of QDs in a conductive carbon matrix that in turn encapsulates these quantum dots. With Co9S8 as an example, such a unique architecture, when applied as the anode of SIBs, endows the hybrids with multiple advantages including a high reversible specific capacity, extraordinary high rate capability, and excellent durability over 2000 cycles charging–discharging process. 相似文献
20.
Single-molecule imaging is an important tool for understanding the mechanisms of biomolecular function and for visualizing the spatial and temporal heterogeneity of molecular behaviors that underlie cellular biology 1-4. To image an individual molecule of interest, it is typically conjugated to a fluorescent tag (dye, protein, bead, or quantum dot) and observed with epifluorescence or total internal reflection fluorescence (TIRF) microscopy. While dyes and fluorescent proteins have been the mainstay of fluorescence imaging for decades, their fluorescence is unstable under high photon fluxes necessary to observe individual molecules, yielding only a few seconds of observation before complete loss of signal. Latex beads and dye-labeled beads provide improved signal stability but at the expense of drastically larger hydrodynamic size, which can deleteriously alter the diffusion and behavior of the molecule under study.Quantum dots (QDs) offer a balance between these two problematic regimes. These nanoparticles are composed of semiconductor materials and can be engineered with a hydrodynamically compact size with exceptional resistance to photodegradation 5. Thus in recent years QDs have been instrumental in enabling long-term observation of complex macromolecular behavior on the single molecule level. However these particles have still been found to exhibit impaired diffusion in crowded molecular environments such as the cellular cytoplasm and the neuronal synaptic cleft, where their sizes are still too large 4,6,7.Recently we have engineered the cores and surface coatings of QDs for minimized hydrodynamic size, while balancing offsets to colloidal stability, photostability, brightness, and nonspecific binding that have hindered the utility of compact QDs in the past 8,9. The goal of this article is to demonstrate the synthesis, modification, and characterization of these optimized nanocrystals, composed of an alloyed HgxCd1-xSe core coated with an insulating CdyZn1-yS shell, further coated with a multidentate polymer ligand modified with short polyethylene glycol (PEG) chains (Figure 1). Compared with conventional CdSe nanocrystals, HgxCd1-xSe alloys offer greater quantum yields of fluorescence, fluorescence at red and near-infrared wavelengths for enhanced signal-to-noise in cells, and excitation at non-cytotoxic visible wavelengths. Multidentate polymer coatings bind to the nanocrystal surface in a closed and flat conformation to minimize hydrodynamic size, and PEG neutralizes the surface charge to minimize nonspecific binding to cells and biomolecules. The end result is a brightly fluorescent nanocrystal with emission between 550-800 nm and a total hydrodynamic size near 12 nm. This is in the same size range as many soluble globular proteins in cells, and substantially smaller than conventional PEGylated QDs (25-35 nm). 相似文献