Showing papers by "Moungi G. Bawendi published in 2011"
TL;DR: In vivo circulationHalf-life and intratumoral diffusion measurements indicate that the multistage nanoparticles exhibited both the long circulation half-life necessary for the EPR effect and the deep tumor penetration required for delivery into the tumor's dense collagen matrix.
Abstract: Current Food and Drug Administration-approved cancer nanotherapeutics, which passively accumulate around leaky regions of the tumor vasculature because of an enhanced permeation and retention (EPR) effect, have provided only modest survival benefits. This suboptimal outcome is likely due to physiological barriers that hinder delivery of the nanotherapeutics throughout the tumor. Many of these nanotherapeutics are ≈100 nm in diameter and exhibit enhanced accumulation around the leaky regions of the tumor vasculature, but their large size hinders penetration into the dense collagen matrix. Therefore, we propose a multistage system in which 100-nm nanoparticles “shrink” to 10-nm nanoparticles after they extravasate from leaky regions of the tumor vasculature and are exposed to the tumor microenvironment. The shrunken nanoparticles can more readily diffuse throughout the tumor's interstitial space. This size change is triggered by proteases that are highly expressed in the tumor microenvironment such as MMP-2, which degrade the cores of 100-nm gelatin nanoparticles, releasing smaller 10-nm nanoparticles from their surface. We used quantum dots (QD) as a model system for the 10-nm particles because their fluorescence can be used to demonstrate the validity of our approach. In vitro MMP-2 activation of the multistage nanoparticles revealed that the size change was efficient and effective in the enhancement of diffusive transport. In vivo circulation half-life and intratumoral diffusion measurements indicate that our multistage nanoparticles exhibited both the long circulation half-life necessary for the EPR effect and the deep tumor penetration required for delivery into the tumor's dense collagen matrix.
941 citations
Patent•
10 Jun 2011TL;DR: A nanocrystal capable of light emission includes a nanoparticle having photoluminescence having quantum yields of greater than 30% as mentioned in this paper, which is the state of the art.
Abstract: A nanocrystal capable of light emission includes a nanoparticle having photoluminescence having quantum yields of greater than 30%.
535 citations
TL;DR: CdS quantum dots were bound onto crystalline P3HT nanowires through solvent-assisted grafting and ligand exchange, leading to controlled organic-inorganic phase separation and an improved maximum power conversion efficiency of 4.1% under AM 1.5 solar illumination.
Abstract: Quantum dots show great promise for fabrication of hybrid bulk heterojunction solar cells with enhanced power conversion efficiency, yet controlling the morphology and interface structure on the nanometer length scale is challenging. Here, we demonstrate quantum dot-based hybrid solar cells with improved electronic interaction between donor and acceptor components, resulting in significant improvement in short-circuit current and open-circuit voltage. CdS quantum dots were bound onto crystalline P3HT nanowires through solvent-assisted grafting and ligand exchange, leading to controlled organic–inorganic phase separation and an improved maximum power conversion efficiency of 4.1% under AM 1.5 solar illumination. Our approach can be applied to a wide range of quantum dots and polymer hybrids and is compatible with solution processing, thereby offering a general scheme for improving the efficiency of nanocrystal hybrid solar cells.
435 citations
TL;DR: The tumor microenvironment limits the uniform penetration of nanotherapeutics by slowing or halting their transport through hydrodynamic and steric hindrance, and overcoming these physiological barriers in tumors is an outstanding challenge for nanomedicine.
Abstract: Nanomedicine has offered new hope for cancer treatment.[1] Nanotherapeutics exhibit many advantages over small-molecule chemotherapeutics, including diminished systemic toxicity and improved circulation times. Unfortunately, non-uniformly leaky vasculature[2] and a dense interstitial structure[3] hinder their effective delivery to tumors.[4] These physiological abnormalities make transvascular transport—movement from vessels to the interstitium—and interstitial transport—movement through the interstitium to target cells—heterogeneous.[4a] Hence the tumor microenvironment limits the uniform penetration of nanotherapeutics by slowing or halting their transport through hydrodynamic and steric hindrance.[2a,3a,5] Overcoming these physiological barriers in tumors is an outstanding challenge for nanomedicine.
384 citations
01 Oct 2011
TL;DR: In this article, the tumor microenvironment limits the uniform penetration of nanotherapeutics by slowing or halting their transport through hydrodynamic and steric hindrance, which is an outstanding challenge for nanomedicine.
Abstract: Nanomedicine has offered new hope for cancer treatment.[1] Nanotherapeutics exhibit many advantages over small-molecule chemotherapeutics, including diminished systemic toxicity and improved circulation times. Unfortunately, non-uniformly leaky vasculature[2] and a dense interstitial structure[3] hinder their effective delivery to tumors.[4] These physiological abnormalities make transvascular transport—movement from vessels to the interstitium—and interstitial transport—movement through the interstitium to target cells—heterogeneous.[4a] Hence the tumor microenvironment limits the uniform penetration of nanotherapeutics by slowing or halting their transport through hydrodynamic and steric hindrance.[2a,3a,5] Overcoming these physiological barriers in tumors is an outstanding challenge for nanomedicine.
372 citations
TL;DR: It is demonstrated that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO(3) interlayer between the PbS colloidal quantum dot film and the top-contact anode.
Abstract: The ability to engineer interfacial energy offsets in photovoltaic devices is one of the keys to their optimization. Here, we demonstrate that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO3 interlayer between the PbS colloidal quantum dot film and the top-contact anode. Through a combination of current–voltage characterization, circuit modeling, Mott–Schottky analysis, and external quantum efficiency measurements performed with bottom- and top-illumination, these enhancements are shown to stem from the elimination of a reverse-bias Schottky diode present at the PbS/anode interface. The incorporation of the high-work-function MoO3 layer pins the Fermi level of the top contact, effectively decoupling the device performance from the work function of the anode and resulting in a high open-circuit voltage (0.59 ± 0.01 V) for a range of different anode materials. Corresponding increases in short-circuit current...
282 citations
TL;DR: In this article, the biexciton to exciton (X) to ground photoluminescence cascade of single colloidal semiconductor nanocrystals (NCs) under weak excitation in a g(2) photon correlation measurement is observed and the normalized amplitude of the cascade feature is equal to the ratio of the BX to X fluorescence quantum yields.
Abstract: Biexciton properties strongly affect the usability of a light emitter in quantum photon sources and lasers but are difficult to measure for single fluorophores at room temperature due to luminescence intermittency and bleaching at the high excitation fluences usually required. Here, we observe the biexciton (BX) to exciton (X) to ground photoluminescence cascade of single colloidal semiconductor nanocrystals (NCs) under weak excitation in a g(2) photon correlation measurement and show that the normalized amplitude of the cascade feature is equal to the ratio of the BX to X fluorescence quantum yields. This imposes a limit on the attainable depth of photon antibunching and provides a robust means to study single emitter biexciton physics. In NC samples, we show that the BX quantum yield is considerably inhomogeneous, consistent with the defect sensitivity expected of the Auger nonradiative recombination mechanism. The method can be extended to study X,BX spectral and polarization correlations.
204 citations
01 Dec 2011
TL;DR: The design and synthesis of a compact and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand with strong binding affinity to SPIONs is reported, which exhibits small hydrodynamic diameters, and stability with respect to time, pH, and salinity.
Abstract: National Institutes of Health (U.S.) (MIT-Harvard Center for Cancer Nanotechnology Excellence Grant 1U54-CA126642)
195 citations
TL;DR: The finding of bulklike CM in NCs suggests that the main promise of quantum confinement is to boost the photovoltage at which carriers can be extracted, and research directions that may result in effective use of CM in a solar cell are discussed.
Abstract: This article presents a perspective on the experimental and theoretical work to date on the efficiency of carrier multiplication (CM) in colloidal semiconductor nanocrystals (NCs). Early reports on CM in NCs suggested large CM efficiency enhancements. However, recent experiments have shown that CM in nanocrystalline samples is not significantly stronger, and often is weaker, than in the parent bulk when compared on an absolute photon energy basis. This finding is supported by theoretical consideration of the CM process and the competing intraband relaxation. We discuss the experimental artifacts that may have led to the apparently strong CM estimated in early reports. The finding of bulklike CM in NCs suggests that the main promise of quantum confinement is to boost the photovoltage at which carriers can be extracted. With this in mind, we discuss research directions that may result in effective use of CM in a solar cell.
183 citations
TL;DR: The study builds on previous InP nanocrystal synthetic and mechanistic work to probe the significant experimental parameters involved in InPnanocrystal syntheses and finds that the growth of Inp nanocrystals is dominated by the aging regime, which is consistent with a model of InP Nanocrystal growth where nanocystal growth is dominatedBy nonmolecular processes such as coalescence from nonmolescular InP species and interparticle ripening processes.
Abstract: Indium phosphide (InP) nanocrystals are of significant interest for use in optoelectronic devices, specifically as a replacement for CdSe nanocrystals in commercial applications. However, the current mechanistic understanding and synthetic procedures for InP nanocrystals has not yet reached the same level as for CdSe nanocrystal synthesis. Using a truly continuous three-stage microfluidic reactor to precisely tune reaction conditions in the mixing, aging, and sequential growth regimes, our study described here builds on previous InP nanocrystal synthetic and mechanistic work to probe the significant experimental parameters involved in InP nanocrystal syntheses. We find that the growth of InP nanocrystals is dominated by the aging regime, which is consistent with a model of InP nanocrystal growth where nanocrystal growth is dominated by nonmolecular processes such as coalescence from nonmolecular InP species and interparticle ripening processes. The InP growth model is in contrast to the molecular-based growth of nanocrystals as observed in CdSe and PbSe nanocrystals. We observe that the size of InP nanocrystals is predominantly dependent on the concentration of free fatty acid in solution and the aging temperature. Other experimental parameters such as injection temperature and particle concentration do not appear to significantly affect InP nanocrystal size or size distributions. In addition, we probe the ability to grow larger InP nanocrystals through the sequential injection of precursors in the third stage of the microfluidic reactor. The use of high temperatures and high pressures in a continuous microfluidic system allows for a wide selection of solvents, precursors, and ligand systems, providing a vastly increased parameter space to explore synthetic conditions. The utilization of low-molecular-weight solvents at high pressures offers supercritical conditions tunable from liquid to gaslike, providing high diffusion rates, improved mixing, and the ability to solubilize various compounds inaccessible by solvents employed in traditional nanocrystal syntheses. The use of a supercritical solvent in a microfluidic reactor results in narrower residence time distributions, producing homogeneous reaction conditions ideal for nanocrystal synthesis. Microfluidic systems allow precise control over reaction conditions and reproducibility as a result of rigorous control of heat and mass transfer. In addition, the microfluidic system can be utilized for fast screening of reaction parameters with in situ reaction monitoring. Figure 1 illustrates our truly continuous three-stage silicon-based microfluidic system consisting of mixing, aging, and sequential injection stages operating at a pressure of 65 bar,
137 citations
TL;DR: The synthesis of Cd(3)As(2) colloidal quantum dots luminescent from 530 to 2000 nm is presented, expanding the availability of high quality infrared emitters.
Abstract: We present the synthesis of Cd3As2 colloidal quantum dots luminescent from 530 to 2000 nm. Previous reports on quantum dots emitting in the infrared are primarily limited to the lead chalcogenides and indium arsenide. This work expands the availability of high quality infrared emitters.
TL;DR: A modular method is demonstrated to assemble three different cyanine J-aggregates onto CdSe nanowires, resulting in a photodetector that is color-sensitized in three specific, narrow absorption bands.
Abstract: J-aggregates are ordered clusters of coherently coupled molecular dyes,(1) and they have been used as light sensitizers in film photography due to their intense absorptions. Hybrid structures containing J-aggregates may also have applications in devices that require spectral specificity, such as color imaging or optical signaling.(2) However the use of J-aggregates in optoelectronic devices has posed a long-standing challenge(3, 4) due to the difficulty of controlling aggregate formation and the low charge carrier mobility of many J-aggregates in solid state. In this paper, we demonstrate a modular method to assemble three different cyanine J-aggregates onto CdSe nanowires, resulting in a photodetector that is color-sensitized in three specific, narrow absorption bands. Both the J-aggregate and nanowire device components are fabricated from solution and the sensitizing wavelength is switched from blue to red to green, using only solution-phase exchange of the J-aggregates on the same underlying device.
20 Jun 2011
TL;DR: A technique for motion and size estimation of non-line-of-sight (NLOS) moving objects in cluttered environments using a time of flight camera and multipath analysis and compute the upper bound on the size of the target by backprojecting the extremas of the time profiles.
Abstract: We present a technique for motion and size estimation of non-line-of-sight (NLOS) moving objects in cluttered environments using a time of flight camera and multipath analysis. We exploit relative times of arrival after reflection from a grid of points on a diffuse surface and create a virtual phased-array. By subtracting space-time impulse responses for successive frames, we separate responses of NLOS moving objects from those resulting from the cluttered environment. After reconstructing the line-of-sight scene geometry, we analyze the space of wavefronts using the phased array and solve a constrained least squares problem to recover the NLOS target location. Importantly, we can recover target's motion vector even in presence of uncalibrated time and pose bias common in time of flight systems. In addition, we compute the upper bound on the size of the target by backprojecting the extremas of the time profiles. Ability to track targets inside rooms despite opaque occluders and multipath responses has numerous applications in search and rescue, medicine and defense. We show centimeter accurate results by making appropriate modifications to a time of flight system.
TL;DR: Electroluminescence is demonstrated by local generation of charge that eliminates the need for injection of charge carriers from the device electrodes and a mechanism for the charge generation and electroluminecence is suggested that is consistent with time-averaged and time-resolved observations.
Abstract: The high degree of morphological and energetic disorder inherent to many nanosized materials places limitations on charge injection into and transport rates through thin films of these materials We demonstrate electroluminescence achieved by local generation of charge that eliminates the need for injection of charge carriers from the device electrodes We show electroluminescence from thin films of nanoscale materials that do not support direct current excitation and suggest a mechanism for the charge generation and electroluminescence that is consistent with our time-averaged and time-resolved observations
TL;DR: An average improvement in the external quantum efficiency (EQE) from 1.8% to 21% across the near UV is realized using an LDS layer consisting of PbS/CdS core/shell QDs embedded in PMMA.
Abstract: A colloidal quantum dot (QD) luminescent down-shifting (LDS) layer is used to sensitize an InGaAs short wavelength infrared photodetector to the near UV spectral band. An average improvement in the external quantum efficiency (EQE) from 1.8% to 21% across the near UV is realized using an LDS layer consisting of PbS/CdS core/shell QDs embedded in PMMA. A simple model is used to fit the experimental EQE data. A UV sensitive InGaAs imaging array is demonstrated and the effect of the LDS layer on the optical resolution is calculated. The bandwidth of the LDS detector under UV illumination is characterized and shown to be determined by the photoluminescence lifetime of the QDs.
07 Aug 2011
TL;DR: Inspired by the classic high speed photography art of Harold Edgerton, this camera has the game changing ability to capture objects moving at the speed of light.
Abstract: How will the world look with a one trillion frame per second camera? Although such a camera does not exist today, we converted high end research equipment to produce conventional movies at 0.5 trillion (5· 1011) frames per second, with light moving barely 0.6 mm in each frame. Our camera has the game changing ability to capture objects moving at the speed of light. Inspired by the classic high speed photography art of Harold Edgerton [Kayafas and Edgerton 1987] we use this camera to capture movies of several scenes.
22 Dec 2011
TL;DR: Several advances in high-detection efficiency superconducting nanowire single photon detectors (SNSPDs) including multi-layer optical structures and multi-element geometries make them uniquely suited to applications in the short-wave infrared as mentioned in this paper.
Abstract: Several advances in high-detection-efficiency superconducting nanowire single photon detectors (SNSPDs) including multi-layer optical structures and multi-element geometries make them uniquely suited to applications in the short-wave infrared.
TL;DR: In this article, an ultra-fast imaging system capable of capturing images with picosecond time resolution or movies with a frame rate of 5x10^11 frames per second was presented.
Abstract: We present an ultra-fast imaging system capable of capturing images with picosecond time resolution or movies with a frame rate of 5x10^11 frames per second.
TL;DR: By combining the wide electronic tunability of nanocrystals with the excellent one-dimensional charge transport characteristics obtainable in nanowires, this work is able to increase photocurrent extraction from a nanocrystal solid by 2-3 orders of magnitude.
Abstract: Synthetic methods yielding highly uniform colloidal semiconductor nanocrystals with controlled shapes and sizes are now available for many materials. These methods have enabled geometrical control ...
Patent•
23 Mar 2011TL;DR: In this paper, polyimidazole ligands (PILs) incorporating pendant imidazoles moieties for nanocrystal binding and either sulfonatebetaine, carboxy betaine, or phosphocholine-betaine for water-solubilization were developed.
Abstract: In this invention, polyimidazole ligands (PILs) incorporating pendant imidazole moieties for nanocrystal binding and either sulfonatebetaine, carboxybetaine, or phosphocholinebetaine moieties for water-solubilization have been developed. Greatly enhanced stability of nanocrystals (both over time and in wide pH range) was achieved by incorporating multi-dentate imidazole moieties which provide strong coordination of the ligand to the nanocrystal surface and prevent aggregation of nanocrystals. Synthesis of betaine PILs was developed by modifying the synthesis of recently developed PEG containing poly imidazole ligands (PEG PILs). These nanocrystals are compact, water soluble, and biocompatible.
Patent•
11 Mar 2011
TL;DR: In this article, the authors present bio-orthoganl and modular conjugation methods for efficient coupling of organic compounds to quantum dots. But they do not provide any details of their experiments.
Abstract: The present disclosure provides for bio-orthoganl and modular conjugation methods for efficient coupling of organic compounds to quantum dots.
TL;DR: A multistage nanoparticle delivery system in which 100-nm gelatin nanoparticles “shrink” to 10-nm nanoparticles after they extravasate from the tumor vasculature and are exposed to the tumor microenvironment, allowing enhanced penetration into the tumor parenchyma and reduction of the likelihood for tumor regression and enhancement of the drug9s therapeutic efficacy.
Abstract: Background: Through the enhanced permeation and retention (EPR) effect, current FDA-approved cancer nanotherapeutics accumulate preferentially around leaky regions of the tumor vasculature due to their large size – typically ∼100 nm in diameter. However, these extravasated large nanocarriers localize mostly at the tumor periphery and might not be able to effectively distribute throughout the tumor due to the dense collagen matrix in the tumor interstitum. The resulting heterogeneous distribution of therapeutic are likely responsible for the modest survival benefits of current nanomedicine. Methods: To overcome these physiological barriers to drug delivery in tumors, we have developed a multistage nanoparticle delivery system (QDGelNP) in which 100-nm nanoparticles “shrink” to 10-nm nanoparticles after they extravasate from the tumor vasculature and are exposed to the tumor microenvironment, allowing enhanced penetration into the tumor parenchyma. This “shrinkage” is preferentially triggered in the tumor by proteases, such as MMP-2, which are highly expressed and/or activated in the tumor microenvironment. These proteases degrade the cores of 100-nm gelatin nanoparticles, releasing smaller 10-nm nanoparticles from their surfaces. We used quantum dots (QD) as a model system for the 10-nm particles because their fluorescence can be monitored in vivo to test the validity of our approach. Results: In vivo blood circulation half-life measurement indicates that our QDGelNPs exhibited the long circulation half-life (22.0 ± 3.4 hours) necessary for the EPR effect. In vitro MMP-2 activation of QDGelNPs was characterized using gel filtration chromatography, fluorescence correlation spectroscopy, and collagen gel diffusion; these experiments revealed that the size change was efficient (50% activation in 1.5 hrs using 0.16 μM MMP-2) and effective in the enhancement of diffusive transport in dense collagen matrices (∼1 mm penetration in 12 hrs, D = ∼2.3 × 10−7 cm2s−1). To test whether tumor secreted MMP-2 can change the size of QDGelNPs in vivo, we intratumorally administered QDGelNPs into MMP-2 expressing tumors (HT-1080) grown in mouse dorsal skin chamber transparent window models and monitored interstitial distribution of QDs by intravital microscopy. At 6 hrs post-injection, the QDGelNPs penetrated up to ∼300 μm into the surrounding tumor tissue (Deff = ∼2.2 × 10-8 cm2s−1), whereas 100-nm single-stage control nanoparticles were confined mostly at the injection site. These data confirmed our QDGelNPs’ capacity to penetrate the tumor9s dense collagen matrix for delivery deep into solid tumors. Conclusion: We have successfully developed a multistage nanoparticle delivery system. Such delivery systems provide a promising approach to improving the delivery of anticancer agents into solid tumors and, as a result, reduction of the likelihood for tumor regression and enhancement of the drug9s therapeutic efficacy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 548. doi:10.1158/1538-7445.AM2011-548
Patent•
28 Feb 2011
TL;DR: In this article, the size distribution of the quantum dots 14, 18 and 22 is chosen to allow light of a particular color to be emitted therefrom. But, the number of quantum dots required to be overcoated to increase photoluminescence is limited.
Abstract: PROBLEM TO BE SOLVED: To provide an electronic device comprising a population of quantum dots embedded in a host matrix and a primary light source which causes the dots to emit secondary light of a selected color, and such a device. SOLUTION: The size distribution of the quantum dots 14, 18 and 22 is chosen to allow light of a particular color to be emitted therefrom. The light emitted from the device may be of either a monochromatic color, or a mixed (polychromatic) color, and may consist solely of light emitted from the dots themselves, or of a mixture of light emitted from the dots and light emitted from the primary source. The dots desirably are composed of an undoped semiconductor such as CdSe, and may optionally be overcoated to increase photoluminescence. COPYRIGHT: (C)2011,JPO&INPIT
TL;DR: In this article, the exact nature of the morphology of contact printed and self-assembled quantum dot light emitting devices on typical organic materials is investigated and the QDs are substantially pressed into the organic material, to a somewhat greater extent when contact printed compared to selfassembled structures.
Abstract: Quantum dot light emitting devices (QD-LEDs) con-sist of a monolayer of QDs sandwiched between a hole transporting layer (HTL) and electron transporting layer (ETL) of organic materials These hybrid devices emit with the narrow bandwidth characteristic of the QDs The precise position of the QD layer, relative to the interface between the ETL and HTL, can affect the quantum efficiency of the device on the scale of 10 nm or less
Motivated by this observation, the exact nature of the morphology of contact printed and self-assembled QDs on typical organic materials is investigated The QDs are substantially pressed into the organic material, to a somewhat greater extent when contact printed compared to self-assembled structures Measured device characteristics from samples made with the two methods are consistent with these observations (© 2011 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
12 Jun 2011
TL;DR: In this article, quantum dots and chalcogenide glasses form the basis for photoluminescent films which are fabricated in microcavities to enhance light emission for coupling into waveguides.
Abstract: Quantum dots and chalcogenide glasses form the basis for photoluminescent films which are fabricated in microcavities to enhance light emission for coupling into waveguides.
Patent•
11 Mar 2011
TL;DR: The authors concerne des procedes de conjugaison bio-orthogonale et modulaire for le couplage efficace de composes organiques a des boites quantiques.
Abstract: La presente invention concerne des procedes de conjugaison bio-orthogonale et modulaire pour le couplage efficace de composes organiques a des boites quantiques.