Quantum Dot Hybrid Research Articles

ZnO QUANTUM DOT HYBRID LUMINESCENT RESISTS FOR NANOIMPRINT LITHOGRAPHY

We report the preparation of ZnO quantum dot hybrid luminescent resists for nanoimprint lithography. Photoluminescence spectra indicate that ZnO QDs@AMONIL have a significant increase in the luminescent intensity, an obvious blue-shift of emission peak and the Stoke's shift, revealing that ZnO QDs@AMONIL have dramatic luminescent property change instead of inhibiting or only preserving the optical properties of pure ZnO QDs. The fabrication of two-dimensional (2D) photonic crystal structure on the ZnO QDs@AMONIL by UV-based nanoimprint lithography is demonstrated at last, which confirms the luminescent ZnO QDs@AMONIL reliable processing capabilities in wavelength-scale and envisions its promising applications in the optoelectronic micro-/nanodevices.

Quantum Dots Acting as Energy Acceptors with Organic Dyes as Donors in Solution

Quantum dots (QDs) usually act as energy donors in Förster resonant energy transfer (FRET) in various application fields. We report, for the first time, a FRET process from a conventional naphthalimide chromophore 1 to CdSe/ZnS core/shell QDs (acting as energy acceptors) in (1)-QDs hybrid system in solution. This FRET process is supported by various spectroscopies, such as steady-state and time-resolved photoluminescence (PL) as well as PL excitation spectra. The highest energy transfer efficiency is estimated to be about 0.37. Interestingly, the role of QDs in FRET can be specifically reversed (from energy acceptors to energy donors) with the use of QDs with larger band-gaps.

Photoelectronic characterization of IgG antibody molecule–quantum dot hybrid asbiosensing probe

Quantum dot (QD)-based biomolecule hybrids have recently attracted much attention inspecifically identifying and labeling target proteins. In this study, QD encapsulated withimmunoglobulin antibodies, as a labeling building block in biosensors, was investigated toclarify the most efficient configuration and photoluminescence behavior. Boththe biological recognition capacity and photoluminescence emitting signal of theantibody-coupled nanocrystal were validated through a photoelectrical characterizationprocedure. Derivation of the optimum number of antibody molecules to be packedonto the QD surface yielded the highest binding capacity for the target antigen.During formation of the bioactive layer, the intrinsic photoluminescence responseof the QDs significantly decreased due to photoinduced hole transfer accordingto their rearranged electronic structure. The thorough study of this assemblyprovides a validation approach for the careful titration of biosensor probes foroptimal reaction kinetics. Furthermore, it contributes to the development of aneffective tool for the application and interpretation of QD-based labeling techniques.

Controlled photoluminescence from self-assembled semiconductor–metal quantum dothybrid array films

Thin films of hybrid arrays of cadmium selenide quantum dots and polymer grafted goldnanoparticles have been prepared using a BCP template. Controlling the dispersion andlocation of the respective nanoparticles allows us to tune the exciton–plasmon interactionin such hybrid arrays and hence control their optical properties. The observedphotoluminescence of the hybrid array films is interpreted in terms of the dispersion andlocation of the gold nanoparticles and quantum dots in the block copolymer matrix.

CdSe quantum dot (QD) and molecular dye hybrid sensitizers for TiO2 mesoporous solar cells: working together with a common hole carrier of cobalt complexes

Redox couples based on cobalt complexes were found to be effective in regenerating both inorganic CdSe quantum dot- and organic dye-sensitizers. The hybrid sensitizer composed of CdSe QD and ruthenium sensitizer (Z907Na) dye showed a maximum power conversion efficiency of 4.76% on using cobalt(o-phen)(3)(2+/3+) as a common redox mediator.

Plasmonic (thermal) electromagnetically induced transparency in metallicnanoparticle–quantum dot hybrid systems

We study the application of an infrared laser to control heat dissipation in a metallicnanoparticle when it is in the vicinity of a semiconductor quantum dot. The infrared laseris considered to be near-resonant with two of the conduction states of the quantum dot,coherently mixing them together. Via exciton–plasmon coupling, this processnormalizes the internal field of the metallic nanoparticle, forming a plasmonic(thermal) electromagnetically induced transparency. When this process happensthe metallic nanoparticle becomes nearly completely non-dissipative around itsplasmon frequency, while it remains strongly dissipative at other frequencies. Weshow that, by adjusting the intensity of the infrared laser, one can control thetransparency window width and optical Stark shift associated with such a process.

Stepwise Self‐Assembly of P3HT/CdSe Hybrid Nanowires with Enhanced Photoconductivity

A facile approach to prepare poly(3-hexylthiophene) (P3HT)/cadmium selenide quantum dot (CdSe QD) hybrid coaxial nanowires by a stepwise self-assembly process is reported. P3HT nanowires of ≈20 nm diameter are first prepared by self-assembly in a poor solvent such as cyclohexanone, and then as-prepared CdSe QDs are deposited compactly onto the P3HT nanowires by non-covalent interactions between P3HT and CdSe. When illuminated with white light, the hybrid nanowires show enhanced photoconductivity compared with the pristine P3HT nanowires and the blended nanocomposites.

The inhibition of optical excitations and enhancement of Rabi flopping in hybrid quantumdot–metallic nanoparticle systems

We study the inhibition of optical excitation and enhancement of Rabi flopping andfrequency in semiconductor quantum dots via plasmonic effects. This is done bydemonstrating that the interaction of a quantum dot with a laser field in the vicinity of ametallic nanoparticle can be described in terms of optical Bloch equations with aplasmically normalized Rabi frequency. We show that in the weak-field regime plasmoniceffects can suppress the interband transitions, inhibiting exciton generation. In thestrong-field regime these effects delay the response of the quantum dot to the laser field andenhance Rabi flopping. We relate these to the conversion of Rabi frequency from a realquantity into a complex and strongly frequency-dependent quantity as plasmoniceffects become significant. We show that, within the strong-field regime, in thewavelength range where real and imaginary parts of this frequency reach their maxima,a strongly frequency-dependent enhancement of carrier excitation can happen.

Virus imaging: Small 6/2009

The cover picture shows a fluorescence image of a living Vero cell being “infected” by capsid–quantum-dot (QD) hybrid nanoparticles through caveolae-mediated endocytosis. The hybrid nanoparticles are constructed by self-assembly of the major capsid protein of simian virus 40 (SV40) in the presence of QDs. When incubated with living cells, they are found to mimic the early infection steps of wild-type SV40, which confirms the feasibility of tracing viruses with encapsidated QDs in living cells. QD encapsidation may serve as a new strategy for ultrasensitive intracellular or in vivo imaging of viral behaviors and targeted nanoparticle delivery as well. For more information, please read the Full Paper “Imaging Viral Behaviors in Mammalian Cells with Self-Assembled Capsid–Quantum-Dot Hybrid Particles” by X.-E. Zhang et al. beginning on page 718.

Energy Transfer within Ultralow Density Twin InAs Quantum Dots Grown by Droplet Epitaxy

Ultralow density (approximately 10(6)/cm(2)) of twin InAs quantum dot (QD) hybrid structure was grown by a droplet epitaxy technique. The photoluminescence (PL) from ensemble and individual twin InAs QD structures showed a bimodal behavior and an energy transfer between the well-separated (approximately 190 nm) twin QDs, which was supposedly due to the special wetting ring that built the channel for exciton transfer. This research demonstrates a novel approach to fabricate lateral InAs QD pairs as the candidate for a laterally coupled QD molecule.

Energy transfer in hybrid quantum dot light-emitting diodes

Energy transfer in a host-guest system consisting of a blue-emitting poly(2,7-spirofluorene) (PSF) donor and red-emitting CdSe∕ZnS core shell quantum dots (QDs) as acceptor is investigated in solid films, using time-resolved optical spectroscopy, and in electroluminescent diodes. In the QD:PSF composite films, the Förster radius for energy transfer is found to be 4–6nm. In electroluminescent devices lacking an electron transport layer, the electroluminescence (EL) spectrum of the QD:PSF polymer composite is similar to the photoluminescence (PL), giving evidence for energy transfer from PSF to the QDs. The addition of an electron transport layer between the emitting layer and the cathode results in a significant change in the EL spectrum and a considerable improved device performance, providing almost pure monochromatic emission at 630nm with a luminance efficiency of 0.32cd∕A. The change in spectrum signifies that the electron transport layer changes the dominant pathway for QD emission from energy transfer from the polymer host to direct electron-hole recombination on the QDs.

Facile fabrication of multi-colors high fluorescent/superparamagnetic nanoparticles

We developed a novel method to prepare multi-colors high fluorescent/superparamagnetic nanoparticles (FMNPs) employing hydrophobic multi-color quantum dots (QDs) and hydrophobic Fe 3O 4 (MNPs) via ultrasonic emulsification method. This structural procedure was simple, one-off, and timesaving. Different-sizes FMNPs with encoding single/multi-color QDs and MNPs were achieved. Analysis with transmission electron microscopy (TEM) and particle size analyzer demonstrated that the as-prepared samples were spherical, uniform in size distribution; Ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurement showed the FMNPs had good optical properties, lacking of fluorescence resonance energy transfer (FRET) inside FMNPs; vibrating sample magnetometer (VSM) indicated that FMNPs were superparamagnetic. These results indicate that the as-prepared FMNPs have potential of serving as a hybrid of QDs and MNPs in bioanalysis communities.

Direct Light‐Driven Modulation of Luminescence from Mn‐Doped ZnSe Quantum Dots

Quantum dot (QD) nanocrystals remain at the forefront of fluorescence microscopy as they have the advantages of enhanced photostability, high quantum yield, and macromolecular size. Furthermore, the ability to tune the QD fluorescence, either by changing their size or by doping, allows for multiplexed imaging. The range of applications extends well beyond the realm of microscopy: QDs may also play a major role in developing novel photonic devices including lasers, light-emitting diodes, and displays. Despite significant advancements in nanocrystal research, the inability to directly modulate the fluorescence from QDs has precluded their implementation in several areas. In particular, emerging far-field diffraction-unlimited microscopy techniques uniquely benefit from the capability to reversibly modulate/switch fluorescent ensembles from a bright “on” state to a dark “off” state. This activation must occur as a response to optical stimuli which do not contain spectral components within the excitation kernel of the fluorescent markers. With the need for optical control over QD fluorescence, indirect methods have been conceived by using hybrid QD structures that incorporate a photochromic activator/quencher. Although the concept has been clearly established, hybrid QD structures suffer from inherent drawbacks, such as inadequate photostability, limited fluorescence quenching, and sensitivity to local environment/ solvent. Herein we report on the direct light-driven modulation of QD fluorescence. The mechanism for the fluorescence modulation relies only on internal electronic transitions within Mn-doped ZnSe quantum dots (Mn-QDs). It is demonstrated that the fluorescence of the QD can be reversibly depleted with efficiencies of over 90% by using continuous-wave optical intensities of approximately 1.9 MWcm . Time-domain measurements during the modulation indicate that the number of fluorescent on–off cycles exceeds 10 before a significant reduction in the fluorescence quantum efficiency occurs. Such robust nanometric probes having remotely controllable optical transitions are useful in many areas of research, particularly in far-field nanoscopy based on reversible saturable or switchable optical fluorescence transitions (RESOLFT). Consequently, we show that implementation of Mn-QDs for imaging leads to an increase in the resolution by a factor of 4.4 over that of confocal microscopy. A schematic diagram of the electronic transitions involved in light-modulated fluorescence from Mn-QDs is shown in Figure 1a. Initially, electrons are photoexcited from the

XPS studies of DNA–cation-interacted self-assembled HgTe quantum dots formed underelectrodeposition and their resultant biomolecular recognition application

DNA interactions with multivalent cations, leading to wrapping around the cations andthermodynamically stable structure formation, followed by electrodeposition, have yieldeda narrow size distributed single-crystalline HgTe–DNA quantum dot (QD) hybrid system.The mechanisms of the DNA interactions resulting in self-assembled HgTe QDs throughphosphate–cation linkages and superstructure formation by nitrogen base interactions havebeen established by their respective binding energy shifts as evidenced from x-rayphotoelectron spectroscopic studies. The photoluminescence peak position associated withHgTe QD single stranded DNA is red shifted in the presence of its conjugate andsuggests the system as a potential optical probe for biomolecular recognitionapplications.

Fluorescent resonance energy transfer based detection of biological contaminants through hybrid quantum dot–quencher interactions

A nanoscale sensor employing fluorescent resonance energy transfer interactions between fluorescent quantum dots (QDs) and organic quencher molecules can be used for the multiplexed detection of biological antigens in solution. Detection occurs when the antigens to be detected displace quencher-labelled inactivated (or dead) antigens of the same type attached to QD-antibody complexes through equilibrium reactions. This unquenches the QDs, allowing detection to take place through the observation of photoluminescence in solution or through the fluorescence imaging of unquenched QD complexes trapped on filter surfaces. Multiplexing can be accomplished by using several different sizes of QDs, with each size QD labelled with an antibody for a different antigen, providing the ability to detect several types of antigens or biological contaminants simultaneously in near real-time with high specificity and sensitivity.

Bulk Synthesis of Transparent and Homogeneous Polymeric Hybrid Materials with ZnO Quantum Dots and PMMA

In situ sol-gel polymerization is demonstrated for fabricating transparent poly(methyl methacrylate) (PMMA)-ZnO quantum dot (QD)- hybrid materials in bulk dimension. The transparent PMMA-ZnO QD hybrid materials exhibit enhanced UV-shielding effects in the entire UV range, even at concentrations as low as 0.02 wt %.

Red light emitting solid state hybrid quantum dot–near-UV GaN LED devices

We produced core–shell (CdSe)ZnSe quantum dots by direct colloidal chemical synthesisand the surface-passivation method—an overcoating of the core CdSe with alarger-bandgap material ZnSe. The (CdSe)ZnSe quantum dots(QDs) play the role of acolour conversion centre. We call these quantum dots nanophosphors. We fabricated redlight emitting hybrid devices of (CdSe)ZnSe QDs and a near-UV GaN LED by combiningred light emitting (CdSe)ZnSe quantum dots (as a colour conversion centre) with anear-UV(NUV) GaN LED chip (as an excitation source). A few good red phosphors havebeen known for UV excitation wavelengths, and red phosphors for UV excitation have beensought for a long time. Here we tested the possibility of using (CdSe)ZnSe QDs as rednanophosphors for UV excitation. The fabricated red light emitting hybrid device of(CdSe)ZnSe and a NUV GaN LED chip showed a good luminance. We demonstrated thatthe (CdSe)ZnSe quantum dots were promising red nanophosphors for NUV excitation andthat a red LED made of QDs and a NUV excitation source was a highly efficient hybriddevice.

Peptide-mediated surface-immobilized quantum dot hybrid nanoassemblies with controlled photoluminescence

Combinatorially selected peptides and peptide–organic conjugates were used as linkers with controlled structural and organizational conformations to attach quantum dots (QDs) at addressable distances from a metal surface. This study demonstrates an approach towards nanophotonics by integrating inorganic, organic, and biological constructs to form hybrid nanoassemblies through template-directed self-assembly. Peptide–organic-linked QD arrays showed stronger fluorescence than peptide-linked QD arrays. We attribute this difference primarily to the increased number density of QDs on peptide–organic-linked QD arrays.

Maltose-binding protein: a versatile platform for prototyping biosensing

The bacterial periplasmic-binding protein (PBP) superfamily members, in particular the maltose-binding protein, have been used extensively to prototype a variety of biosensing platforms. Although quite diverse at the primary sequence level, this protein superfamily retains the same basic two-domain structure, and upon binding a recognized ligand almost all PBPs undergo a conformational change to a closed structure. This process forms the basis for most, but not all, PBP-based biosensor signal transduction. Many direct detection or reagentless sensing modalities have been utilized with maltose-binding protein for both in vitro and in vivo detection of target compounds. Signal transduction modalities developed to date include direct fluorescence, electrochemical detection, fluorescence resonance energy transfer (FRET)-based detection, surface-tethered FRET sensing, hybrid quantum dot FRET sensing, and enzymatic detection, each of which have different benefits, potential applications and limitations.

Third-order nonlinear optical properties of hybrid films of biopolymer-CdSe/ZnS core-shell quantum dots

Biopolymer_CdSe/ZnS core_shell quantum dot hybrid films were prepared using self_assembly technique. Compared with the absorbance spectrum, the photoluminescence excited by laser with λ=395nm has Stokes shift. The third_order nonlinear optical properties of biopolymer_CdSe/ZnS film were studied by Z_scan setup with femtosecond laser at 790nm. It is found that the nonlinear absorptive signal partially originates from Cde/ZnS quantum dots while the nonlinear refractive signal partially originates from biopolymer chitosan. The magnitudes of them are measured to be β＝6.5×10-6cm/W and n2＝1.5×10-10cm2/W, respectively.