Single-molecule quantum-dot fluorescence resonance energy transfer.

Colloidal semiconductor quantum dots are promising for single-molecule biological imaging due to their outstanding brightness and photostability. As a proof of concept for single-molecule fluorescence resonance energy transfer (FRET) applications, we measured FRET between a single quantum dot and a single organic fluorophore Cy5. DNA Holliday junction dynamics measured with the quantum dot/Cy5 pair are identical to those obtained with the conventional Cy3/Cy5 pair, that is, conformational changes of individual molecules can be observed by using the quantum dot as the donor.     

Characterization of the Self-Assembly of Glutathione Stabilized Cadmium Selenide–Zinc Sulfide Quantum Dots with a Cyanine5-Labeled Peptide by Capillary Electrophoresis and Fluorescence

Capillary electrophoresis with fluorescence detection was used to characterize the self-assembly of cadmium selenide–zinc sulfide quantum dots and a cyanine5-labeled peptide (cyanine5-EAAAAAHHHHHH). The self-assembly was driven by metal-affinity forces to allow characterization by Förster resonance energy transfer. The Förster resonance energy transfer signal increased with the ratio of cyanine5-EAAAAAHHHHHH to quantum dots and reached a plateau at a ratio of 32:1. This method illustrates the application of quantum dot-based bioanalysis.     

Application of Scanning Tunneling Microscopy and Spectroscopy in the Studies of Colloidal Quantum Qots

Colloidal quantum dots display remarkable optical and electrical characteristics with the potential for extensive applications in contemporary nanotechnology. As an ideal instrument for examining surface topography and local density of states (LDOS) at an atomic scale, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) has become indispensable approaches to gain better understanding of their physical properties. This article presents a comprehensive review of the research advancements in measuring the electronic orbits and corresponding energy levels of colloidal quantum dots in various systems using STM and STS. The first three sections introduce the basic principles of colloidal quantum dots synthesis and the fundamental methodology of STM research on quantum dots. The fourth section explores the latest progress in the application of STM for colloidal quantum dot studies. Finally, a summary and prospective is presented.     

Light Harvesting and White‐Light Generation in a Composite of Carbon Dots and Dye‐Encapsulated BSA‐Protein‐Capped Gold Nanoclusters

Several strategies have been adopted to design an artificial light‐harvesting system in which light energy is captured by peripheral chromophores and it is subsequently transferred to the core via energy transfer. A composite of carbon dots and dye‐encapsulated BSA‐protein‐capped gold nanoclusters (AuNCs) has been developed for efficient light harvesting and white light generation. Carbon dots (C‐dots) act as donor and AuNCs capped with BSA protein act as acceptor. Analysis reveals that energy transfer increases from 63 % to 83 % in presence of coumarin dye (C153), which enhances the cascade energy transfer from carbon dots to AuNCs. Bright white light emission with a quantum yield of 19 % under the 375 nm excitation wavelength is achieved by changing the ratio of components. Interesting findings reveal that the efficient energy transfer in carbon‐dot–metal‐cluster nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.     

Luminescence quenching in self-assembled adducts of [Ru(dpp)3]2+ complexes and CdTe nanocrystals

We have investigated chloroform solutions containing tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) and CdTe nanocrystal quantum dots (5.6 nm diameter). The electronic levels of these two components are such that the Ru complex can act as an energy donor towards the quantum dot, which can thus behave as an energy acceptor. Steady-state and time-resolved spectroscopic experiments indicate that the Ru complexes and the CdTe nanocrystals self-assemble to give stable 1?:?1 adducts, in which the luminescence of the former units is strongly quenched. Such a quenching can be ascribed to either energy transfer to the CdTe quantum dot, or to electron transfer from the CdTe valence band to the excited Ru complex. However, no supporting evidence for the occurrence of photoinduced energy transfer in the adduct could be found. The CdTe luminescence is also slightly quenched in the presence of the ruthenium complex. The strong association of the metal complexes with the nanocrystals suggests that self-assembly strategies may be effectively employed to achieve surface functionalization of semiconductor quantum dots with molecular units.     

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

The observed resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules [Zenkevich et al., J. Phys. Chem. B 109 (2005) 8679] is studied computationally by ab initio electronic structure and quantum dynamics approaches. The system harvests light in a broad energy range and can transfer the excitation from the dot through the porphyrin to oxygen, generating singlet oxygen for medical applications. The geometric structure, electronic energies, and transition dipole moments are derived by density functional theory and are utilized for calculating the Förster coupling between the excitons residing on the quantum dot and the porphyrin. The direction and rate of the irreversible exciton transfer is determined by the initial photoexcitation of the dot, the dot–porphyrin coupling and the interaction to the electronic subsystem with the vibrational environment. The simulated electronic structure and dynamics are in good agreement with the experimental data and provide real-time atomistic details of the energy transfer mechanism.     

Observation of enhanced energy transfer in individual quantum dot-oligophenylene vinylene nanostructures

The temporal and spectral properties of luminescence from individual CdSe quantum dot-oligophenylene vinylene nanostructures (single quantum dots with conjugated organic ligands coordinated to the surface) are profoundly modified relative to blended films of the same components. These kinds of composite quantum dot-conjugated organic systems have attracted significant interest as a way to improve efficiency in photovoltaic device applications. By direct functionalization of the dot surface with the conjugated organic ligands, we realize a significant enhancement in energy transfer and luminescence stability.     

Luminescence of Hybrid Nanostructures of InP@ZnS Colloidal Quantum Dots and <Emphasis Type="Italic">meso</Emphasis>-Tetra(3-pyridyl)porphyrin Molecules

The formation of hybrid nanostructures consisting of InP@ZnS colloidal quantum dots and mesotetra(3-pyridyl)porphyrin molecules adsorbed on the quantum dots has been studied. In such nanostructures, strong quenching of quantum dot luminescence and an increase in the emission intensity of porphyrin are observed due to nonradiative resonance energy transfer from colloidal quantum dots to porphyrin.     

Designed Long‐Lived Emission from CdSe Quantum Dots through Reversible Electronic Energy Transfer with a Surface‐Bound Chromophore

The size‐tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface‐bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self‐assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer.     

半导体荧光量子点标记技术

生命体系中化学、生物信息的活体、原位、实时、动态和高灵敏获取,是当前生命科学研究中迫切需要解决的关键问题之一,发展相关的新技术与新方法至关重要。半导体荧光量子点因其优异的荧光特性可望在解决此类难题中发挥重要作用而日益受到关注。本文将根据我们课题组多年来的研究工作经验,就半导体荧光量子点标记技术的相关基础问题、在生物医学领域中的应用以及发展前景等做简要评述。     

Electrochemical properties of CdSe and CdTe quantum dots

Semiconductor nanocrystal quantum dots (QDs), owing to their unique opto-electronic properties determined by quantum confinement effects, have been the subject of extensive investigations in different areas of science and technology in the past two decades. The electrochemical behaviour of QDs, particularly for CdSe and CdTe nanocrystals, has also been explored, although to a lesser extent compared to the optical properties. Voltammetric measurements can be used to probe the redox levels available for the nanocrystals, which is an invaluable piece of information if these systems are involved in electron transfer processes. Electrochemical data can also foster the interpretation of the spectroscopic properties of QDs, and give insightful information on their chemical composition, dimension, and surface properties. Hence, electrochemical methods constitute in principle an effective tool to probe the quality of QD samples in terms of purity, size dispersion, and surface defects. The scope of this critical review is to discuss the results of electrochemical studies carried out on CdSe and CdTe core and core-shell semiconductor nanocrystals of spherical shape. Examples of emerging or potential applications that exploit electroactive quantum dot-based systems will also be illustrated.     

硅烯量子点二聚物的等离激元激发

基于含时密度泛函理论,研究了随着间距改变时硅烯量子点二聚物的等离激元激发特性。沿垂直于硅烯所在平面方向激发时,在一定间距范围内,硅烯量子点二聚物中形成了长程电荷转移激发模式。参与长程电荷转移激发的π电子主要在两个量子点之间运动。该等离激元模式随着间隙的减小发生蓝移。此外,在不同间距时,体系中还有两个等离激元共振带,分别位于7和15 eV附近。沿平行于硅烯所在平面方向激发时,由于两个量子点之间的耦合,在低能     

In‐capillary probing of quantum dots and fluorescent protein self‐assembly and displacement using Förster resonance energy transfer

Herein, a Förster resonance energy transfer system was designed, which consisted of CdSe/ZnS quantum dots donor and mCherry fluorescent protein acceptor. The quantum dots and the mCherry proteins were conjugated to permit Förster resonance energy transfer. Capillary electrophoresis with fluorescence detection was used for the analyses for the described system. The quantum dots and mCherry were sequentially injected into the capillary, while the real‐time fluorescence signal of donor and acceptor was simultaneously monitored by two channels with fixed wavelength detectors. An effective separation of complexes from free donor and acceptor was achieved. Results showed quantum dots and hexahistidine tagged mCherry had high affinity and the assembly was affected by His₆‐mCherry/quantum dot molar ratio. The kinetics of the self‐assembly was calculated using the Hill equation. The microscopic dissociation constant values for out of‐ and in‐capillary assays were 10.49 and 23.39 μM, respectively. The capillary electrophoresis with fluorescence detection that monitored ligands competition assay further delineated the different binding capacities of histidine containing peptide ligands for binding sites on quantum dots. This work demonstrated a novel approach for the improvement of Förster resonance energy transfer for higher efficiency, increased sensitivity, intuitionistic observation, and low sample requirements of the in‐capillary probing system.     

Synthesis of surface-modified quantum dots

The review discusses the main methods used to obtain surface-modified quantum dots, specifically silicon, heavy metal chalcogenide and pnictide semiconductor nanoparticles. Examples of transformation processes of the grafted layer are considered. The importance of surface modification of A^IIB^VI- and A^IIIB^V-type semiconductor nanoparticles for the practical application of quantum dots is shown. It was determined that the most promising areas of their practical application are biology, medicine, and pharmacology. Special attention is paid to the hydrophilization of quantum dots, because only these materials can be used in biomedical applications. Modification of the quantum dot surface with amino acids is considered.

     

Fluorescence correlation spectroscopy using quantum dots: advances, challenges and opportunities

Semiconductor nanocrystals (quantum dots) have been increasingly employed in measuring the dynamic behavior of biomacromolecules using fluorescence correlation spectroscopy. This poses a challenge, because quantum dots display their own dynamic behavior in the form of intermittent photoluminescence, also known as blinking. In this review, the manifestation of blinking in correlation spectroscopy will be explored, preceded by an examination of quantum dot blinking in general.     

Biocompatible quantum dots for biological applications

Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, size-tunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots.     

Fluorescence and Sensing Applications of Graphene Oxide and Graphene Quantum Dots: A Review

Graphene oxide and graphene quantum dots are attractive fluorophores that are inexpensive, nontoxic, photostable, water‐soluble, biocompatible, and environmentally friendly. They find extensive applications in fluorescent biosensors and chemosensors, in which they serve as either fluorophores or quenchers. As fluorophores, they display tunable photoluminescence emission and the “giant red‐edge effect”. As quenchers, they exhibit a remarkable quenching efficiency through either electron transfer or Förster resonance energy transfer (FRET) process. In this review, the origin of fluorescence and the mechanism of excitation wavelength‐dependent fluorescence of graphene oxide and graphene quantum dots are discussed. Sensor design strategies based on graphene oxide and graphene quantum dots are presented. The applications of these sensors in health care, the environment, agriculture, and food safety are highlighted.     

Synthesis and electronic properties of semiconductor nanoparticles/quantum dots

This review examines recent work on the synthesis, characterisation and potential applications of semiconductor nanoparticles (quantum dots). Recent advances in single quatum dot spectroscopy is also reviewed.     

Effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure

We study the effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure. The CdSe quantum dots are anchored on the surface of ZnO nanocolumns through either aliphatic linker of 3-aminopropyl trimethoxysilane (APS) or aromatic linker of p-aminophenyl trimethoxysilane (APhS). X-ray photoelectron spectroscopy is used to confirm the bifunctional linker bound onto CdSe quantum dots and onto the ZnO nanocolumns. The TEM study reveals a CdSe quantum dot shell of about 15 nm coated on the ZnO nanocolumns. The photoluminance (PL) spectroscopy and time-resolved PL spectroscopy of ZnO nanocolumn-linker-CdSe quantum dots reflects that the photo-induced electron transfer across the interface of ZnO and CdSe through the aromatic APhS is more efficient than the aliphatic APS. This study demonstrates that through the usage of appropriate surface linker, the charge transfer rate across the interfaces of donor/acceptor (D/A) heterostructure can be improved for potential photovoltaic cell applications.     

Förster Resonance Energy Transfer Investigations Using Quantum‐Dot Fluorophores

F?rster resonance energy transfer (FRET), which involves the nonradiative transfer of excitation energy from an excited donor fluorophore to a proximal ground-state acceptor fluorophore, is a well-characterized photophysical tool. It is very sensitive to nanometer-scale changes in donor-acceptor separation distance and their relative dipole orientations. It has found a wide range of applications in analytical chemistry, protein conformation studies, and biological assays. Luminescent semiconductor nanocrystals (quantum dots, QDs) are inorganic fluorophores with unique optical and spectroscopic properties that could enhance FRET as an analytical tool, due to broad excitation spectra and tunable narrow and symmetric photoemission. Recently, there have been several FRET investigations using luminescent QDs that focused on addressing basic fundamental questions, as well as developing targeted applications with potential use in biology, including sensor design and protein conformation studies. Herein, we provide a critical review of those developments. We discuss some of the basic aspects of FRET applied to QDs as both donors and acceptors, and highlight some of the advantages offered (and limitations encountered) by QDs as energy donors and acceptors compared to conventional dyes. We also review the recent developments made in using QD bioreceptor conjugates to design FRET-based assays.