Co-reporter:J. Scott Niezgoda;Amy Ng;Jonathan D. Poplawsky;James R. McBride;Stephen J. Pennycook;Sra J. Rosenthal
Advanced Functional Materials 2016 Volume 26( Issue 6) pp:895-902
Publication Date(Web):
DOI:10.1002/adfm.201503839
The delicate influence of properties such as high surface state density and organic–inorganic boundaries on the individual quantum dot electronic structure complicates pursuits toward forming quantitative models of quantum dot thin films ab initio. This report describes the application of electron beam-induced current (EBIC) microscopy to depleted-heterojunction colloidal quantum dot photovoltaics (DH-CQD PVs), a technique which affords one a “map” of current production within the active layer of a PV device. The effects of QD sample size polydispersity as well as layer thickness in CQD active layers as they pertain to current production within these PVs are imaged and explained. The results from these experiments compare well with previous estimations, and confirm the ability of EBIC to function as a valuable empirical tool for the design and betterment of DH-CQD PVs. Lastly, extensive and unexpected PbS QD penetration into the mesoporous TiO2 layer is observed through imaging of device cross sections by energy-dispersive X-ray spectroscopy combined with scanning transmission electron microscopy. The possible effects of this finding are discussed and corroborated with the EBIC studies on similar devices.
Co-reporter:Dr. J. Scott Niezgoda; Sra J. Rosenthal
ChemPhysChem 2016 Volume 17( Issue 5) pp:645-653
Publication Date(Web):
DOI:10.1002/cphc.201500758
Abstract
The field of semiconductor plasmonics has grown rapidly since its outset, only roughly six years ago, and now includes many crystalline substances ranging from GeTe to wide-bandgap transition-metal oxides. One byproduct of this proliferation is the sea of differing synthetic methods to realize localized surface plasmon resonances (LSPRs) based on the studied material. Strategies vary widely from material to material, but all have the common goal of introducing extremely high carrier densities to the semiconductor system. This doping results in tunable, size-quantized, and on/off-switchable LSPR modes, which are a complete departure from traditional metal-nanoparticle-based plasmon resonances. This Minireview will provide an overview of the current state of nanocrystal and quantum-dot plasmonics and the physical basis thereof, however its main purpose is to summarize the methods for realizing LSPRs in the various syntheses and systems that have been reported to date.
Co-reporter:Noah J. Orfield, James R. McBride, Feng Wang, Matthew R. Buck, Joseph D. Keene, Kemar R. Reid, Han Htoon, Jennifer A. Hollingsworth, and Sandra J. Rosenthal
ACS Nano 2016 Volume 10(Issue 2) pp:1960
Publication Date(Web):February 5, 2016
DOI:10.1021/acsnano.5b05876
Physical variations in colloidal nanostructures give rise to heterogeneity in expressed optical behavior. This correlation between nanoscale structure and function demands interrogation of both atomic structure and photophysics at the level of single nanostructures to be fully understood. Herein, by conducting detailed analyses of fine atomic structure, chemical composition, and time-resolved single-photon photoluminescence data for the same individual nanocrystals, we reveal inhomogeneity in the quantum yields of single nonblinking “giant” CdSe/CdS core/shell quantum dots (g-QDs). We find that each g-QD possesses distinctive single exciton and biexciton quantum yields that result mainly from variations in the degree of charging, rather than from volume or structure inhomogeneity. We further establish that there is a very limited nonemissive “dark” fraction (<2%) among the studied g-QDs and present direct evidence that the g-QD core must lack inorganic passivation for the g-QD to be “dark”. Therefore, in contrast to conventional QDs, ensemble photoluminescence quantum yield is principally defined by charging processes rather than the existence of dark g-QDs.Keywords: correlation; heterogeneity; nanocrystal atomic structure; nanocrystal quantum dot; quantum yield;
Co-reporter:Toshia L. Wrenn, James R. McBride, Jeremy W. Mares, and Sandra J. Rosenthal
Chemistry of Materials 2015 Volume 27(Issue 11) pp:3817
Publication Date(Web):May 19, 2015
DOI:10.1021/acs.chemmater.5b01201
Co-reporter:Oleg Kovtun, Dhananjay Sakrikar, Ian D. Tomlinson, Jerry C. Chang, Xochitl Arzeta-Ferrer, Randy D. Blakely, and Sandra J. Rosenthal
ACS Chemical Neuroscience 2015 Volume 6(Issue 4) pp:526
Publication Date(Web):March 8, 2015
DOI:10.1021/cn500202c
The presynaptic, cocaine- and amphetamine-sensitive dopamine (DA) transporter (DAT, SLC6A3) controls the intensity and duration of synaptic dopamine signals by rapid clearance of DA back into presynaptic nerve terminals. Abnormalities in DAT-mediated DA clearance have been linked to a variety of neuropsychiatric disorders, including addiction, autism, and attention deficit/hyperactivity disorder (ADHD). Membrane trafficking of DAT appears to be an important, albeit incompletely understood, post-translational regulatory mechanism; its dysregulation has been recently proposed as a potential risk determinant of these disorders. In this study, we demonstrate a link between an ADHD-associated DAT mutation (Arg615Cys, R615C) and variation on DAT transporter cell surface dynamics, a combination only previously studied with ensemble biochemical and optical approaches that featured limited spatiotemporal resolution. Here, we utilize high-affinity, DAT-specific antagonist-conjugated quantum dot (QD) probes to establish the dynamic mobility of wild-type and mutant DATs at the plasma membrane of living cells. Single DAT-QD complex trajectory analysis revealed that the DAT 615C variant exhibited increased membrane mobility relative to DAT 615R, with diffusion rates comparable to those observed after lipid raft disruption. This phenomenon was accompanied by a loss of transporter mobilization triggered by amphetamine, a common component of ADHD medications. Together, our data provides the first dynamic imaging of single DAT proteins, providing new insights into the relationship between surface dynamics and trafficking of both wild-type and disease-associated transporters. Our approach should be generalizable to future studies that explore the possibilities of perturbed surface DAT dynamics that may arise as a consequence of genetic alterations, regulatory changes, and drug use that contribute to the etiology or treatment of neuropsychiatric disorders.Keywords: amphetamine; Attention deficit/hyperactivity disorder; cocaine; dopamine transporter; membrane dynamics; single quantum dot tracking
Co-reporter:Noah J. Orfield, James R. McBride, Joseph D. Keene, Lloyd M. Davis, and Sandra J. Rosenthal
ACS Nano 2015 Volume 9(Issue 1) pp:831
Publication Date(Web):December 18, 2014
DOI:10.1021/nn506420w
In a size regime where every atom counts, rational design and synthesis of optimal nanostructures demands direct interrogation of the effects of structural divergence of individuals on the ensemble-averaged property. To this end, we have explored the structure–function relationship of single quantum dots (QDs) via precise observation of the impact of atomic arrangement on QD fluorescence. Utilizing wide-field fluorescence microscopy and atomic number contrast scanning transmission electron microscopy (Z-STEM), we have achieved correlation of photoluminescence (PL) data and atomic-level structural information from individual colloidal QDs. This investigation of CdSe/CdS core/shell QDs has enabled exploration of the fine structural factors necessary to control QD PL. Additionally, we have identified specific morphological and structural anomalies, in the form of internal and surface defects, that consistently vitiate QD PL.Keywords: core/shell quantum dots; correlation; nanocrystal atomic structure; nanocrystal quantum dots; semiconductor nanocrystals; single nanocrystal microscopy; single nanocrystal spectroscopy;
Co-reporter:J. Scott Niezgoda, Eugene Yap, Joseph D. Keene, James R. McBride, and Sandra J. Rosenthal
Nano Letters 2014 Volume 14(Issue 6) pp:3262-3269
Publication Date(Web):May 5, 2014
DOI:10.1021/nl500645k
A synthetic approach has recently been developed which results in CuxInyS2 quantum dots (QDs) possessing localized surface plasmon resonance (LSPR) modes in the near-infrared (NIR) frequencies.1 In this study, we investigate the potential benefits of near-field plasmonic effects centered upon light absorbing nanoparticles in a photovoltaic system by developing and verifying nonplasmonic counterparts as an experimental control. Simple QD-sensitized solar cells (QD-SSCs) were assembled which show an 11.5% relative increase in incident photon conversion efficiency (IPCE) achieved in the plasmon-enhanced devices. We attribute this increase in IPCE to augmented charge excitation stemming from near-field “antenna” effects in the plasmonic CuxInyS2 QD-SSCs. This study represents the first of its kind; direct interrogation of the influence of plasmon-on-semiconductor architectures with respect to excitonic absorption in photovoltaic systems.
Co-reporter:Joseph D. Keene, James R. McBride, Noah J. Orfield, and Sandra J. Rosenthal
ACS Nano 2014 Volume 8(Issue 10) pp:10665
Publication Date(Web):September 9, 2014
DOI:10.1021/nn504235w
Interaction of charge carriers with the surface of semiconductor nanocrystals plays an integral role in determining the ultimate fate of the excited state. The surface contains a dynamic ensemble of trap states that can localize excited charges, preventing radiative recombination and reducing fluorescence quantum yields. Here we report quasi-type-II band alignment in graded alloy CdSxSe1–x nanocrystals revealed by femtosecond fluorescence upconversion spectroscopy. Graded alloy CdSxSe1–x quantum dots are a compositionally inhomogeneous nano-heterostructure designed to decouple the exciton from the nanocrystal surface. The large valence band offset between the CdSe-rich core and CdS-rich shell separates the excited hole from the surface by confining it to the core of the nanocrystal. The small conduction band offset, however, allows the electron to delocalize throughout the entire nanocrystal and maintain overlap with the surface. Indeed, the ultrafast charge carrier dynamics reveal that the fast 1–3 ps hole-trapping process is fully eliminated with increasing sulfur composition and the decay constant for electron trapping (∼20–25 ps) shows a slight increase. These findings demonstrate progress toward highly efficient nanocrystal fluorophores that are independent of their surface chemistry to ultimately enable their incorporation into a diverse range of applications without experiencing adverse effects arising from dissimilar environments.Keywords: CdSxSe1−x; core/shell; graded alloy; nanocrystal spectroscopy; quasi-type-II; ultrafast fluorescence upconversion;
Co-reporter:Amy Ng, Jonathan D. Poplawsky, Chen Li, Stephen J. Pennycook, and Sandra J. Rosenthal
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 5) pp:856-860
Publication Date(Web):February 9, 2014
DOI:10.1021/jz402752k
Scanning electron microscopy (SEM) electron beam-induced current (EBIC) studies were performed on the cross-section of a nanocrystal-based hybrid bulk heterojunction photovoltaic device. Using these techniques, the short circuit carrier collection efficiencies are mapped with a better than 100 nm resolution. Electronically deficient and proficient regions within the photoactive layer are determined. The results show that only a fraction of the CdSe nanorod:P3HT layer (P3HT = poly-3(hexylthiophene)) at the Al cathode interface shows primary collection of charged carriers, in which the photoactivity decreases exponentially away from the interface. The recombination losses of the photoactive layer away from this interface prove that the limiting factor of the device is the inability for electrons to percolate between nanoparticles; to alleviate this problem, an interparticle network that conducts the electrons from one nanorod to the next must be established. Furthermore, the EBIC technique applied to the nanocrystalline device used in this study is the first measurement of its kind and can be applied toward other similar architectures.Keywords: CdSe; EBIC; electron beam-induced current; nanocrystal; P3HT; photovoltaic; SEM;
Co-reporter:Sarah M. Harrell, James R. McBride, and Sandra J. Rosenthal
Chemistry of Materials 2013 Volume 25(Issue 8) pp:1199
Publication Date(Web):February 15, 2013
DOI:10.1021/cm303318f
Nanocrystals exhibit useful properties not found in their bulk counterparts; however, a subclass of nanocrystals that consist of diameters on the order of 2 nm or less further exhibit unique properties. As synthetic methodologies of nanocrystals have matured, greater emphasis has been made on controlling the early stages of the reaction in order to gain access to these sub-2 nm species. This review provides an overview of ultrasmall and magic-sized nanocrystals, and the diverse chemical means to obtain them. Due to their small size and their resultant properties, these ultrasmall and magic-sized nanocrystals have a distinct advantage in many applications including achieving renal clearance for the purpose of biological imaging, producing simple and high-quality white LEDs, and controlling the growth of nanocrystals to produce various morphologies.Keywords: magic-sized; nanocrystal; synthesis; ultrasmall;
Co-reporter:Oleg Kovtun, Xochitl Arzeta-Ferrer and Sandra J. Rosenthal
Nanoscale 2013 vol. 5(Issue 24) pp:12072-12081
Publication Date(Web):14 Aug 2013
DOI:10.1039/C3NR02019C
Biomolecule detection using quantum dots (Qdots), nanometer-sized semiconductor crystals, effectively addresses the limitations associated with conventional optical and biochemical techniques, as Qdots offer several key advantages over traditional fluorophores. In this minireview, we discuss the role of Qdots as a central nanoscaffold for the polyvalent assembly of multifunctional biomolecular probes and describe recent advances in Qdot-based biorecognition. Specifically, we focus on Qdot applications in target-based, drug screening assays and real-time active biosensing of cellular processes.
Co-reporter:James R. McBride, Timothy J. Pennycook, Stephen J. Pennycook, and Sandra J. Rosenthal
ACS Nano 2013 Volume 7(Issue 10) pp:8358
Publication Date(Web):October 15, 2013
DOI:10.1021/nn403478h
Understanding the precise nature of a surface or interface is a key component toward optimizing the desired properties and function of a material. For semiconductor nanocrystals, the surface has been shown to modulate fluorescence efficiency, lifetime, and intermittency. The theoretical picture of a nanocrystal surface has included the existence of an undefined mixture of trap states that arise from incomplete passivation. However, our recent scanning transmission electron microscope movies and supporting theoretical evidence suggest that, under excitation, the surface is fluctuating, creating a dynamic population of surface and subsurface states. This possibility challenges our fundamental understanding of the surface and could have far-reaching ramifications for nanoparticle-based technologies. In this Perspective, we discuss the current theories behind the optical properties of nanocrystals in the context of fluxionality.Keywords: fluorescence intermittency; nanocrystal; nanoparticle; surface dynamics; trap states
Co-reporter:Jerry C. Chang and Sandra J. Rosenthal
The Journal of Physical Chemistry Letters 2013 Volume 4(Issue 17) pp:2858-2866
Publication Date(Web):August 8, 2013
DOI:10.1021/jz401071g
This Perspective describes recent progress in single quantum dot techniques, with an emphasis on their applications in exploring membrane dynamics and cellular mechanisms. In these cases, conventional population measurements, such as fluorescence recovery after photobleaching, yield only a mean value on an ensemble or bulk collection of molecules, where the behavior of individual proteins and vehicles is missing. In recent years, the single quantum dot imaging approach has been introduced as a subcategory of single molecule fluorescent techniques to reveal single protein/vehicle dynamics in real time. One of the major advantages of using single quantum dots is the high signal-to-noise ratio originating from their unique photophysical properties such as extraordinarily high molar extinction coefficients and large effective Stokes shifts. In addition to a brief overview on the principle of single quantum dot imaging techniques, we highlight recent discoveries and discuss future directions in the field.
Co-reporter:Teresa E. Rosson ; Sarah M. Claiborne ; James R. McBride ; Benjamin S. Stratton
Journal of the American Chemical Society 2012 Volume 134(Issue 19) pp:8006-8009
Publication Date(Web):May 7, 2012
DOI:10.1021/ja300132p
A simple treatment method using formic acid has been found to increase the fluorescence quantum yield of ultrasmall white light-emitting CdSe nanocrystals from 8% to 45%. Brighter white-light emission occurs with other carboxylic acids as well, and the magnitude of the quantum yield enhancement is shown to be dependent on the alkyl chain length. Additionally, the nanocrystal luminescence remains enhanced relative to the untreated nanocrystals over several days. This brightened emission opens the possibility for even further quantum yield improvement and potential for use of these white-light nanocrystals in solid-state lighting applications.
Co-reporter:J. Scott Niezgoda, Melissa A. Harrison, James R. McBride, and Sandra J. Rosenthal
Chemistry of Materials 2012 Volume 24(Issue 16) pp:3294
Publication Date(Web):July 30, 2012
DOI:10.1021/cm3021462
The burgeoning field of thin film quantum dot photovoltaics has made considerable strides toward efficient and inexpensive forms of third generation solar cells. However, these technologies have largely been based upon toxic metal-containing materials, limiting their foreseeable applications. Here we present a synthesis of nontoxic and stable CuxInyS2 quantum dots with tunable size and band gap. Interestingly, this synthesis leads to the presence of a broad-band and size-dependent absorption peak in the infrared (IR), attributed to localized surface plasmon resonances (LSPRs). Due to the sensitivity of their LSPR peak to quantum dot size and solvent refractive index, these quantum dots provide an attractive candidate for tunable plasmon resonance applications. And, if these LSPRs are found to be coupled with excitonic transitions, they may result in sizable increases in photovoltaic efficiency.Keywords: CuInS2; low toxicity; photovoltaics; quantum dots; surface plasmon;
Co-reporter:Oleg Kovtun, Emily J. Ross, Ian D. Tomlinson and Sandra J. Rosenthal
Chemical Communications 2012 vol. 48(Issue 44) pp:5428-5430
Publication Date(Web):05 Apr 2012
DOI:10.1039/C2CC31951A
Here we present the development and validation of a flow cytometry-based dopamine transporter (DAT) binding assay that uses antagonist-conjugated quantum dots (QDs). We anticipate that our QD-based assay is of immediate value to the high throughput screening of novel DAT modulators.
Co-reporter:Jerry C. Chang and Sandra J. Rosenthal
ACS Chemical Neuroscience 2012 Volume 3(Issue 10) pp:737
Publication Date(Web):August 1, 2012
DOI:10.1021/cn3000845
Lipid rafts are cholesterol-enriched subdomains in the plasma membrane that have been reported to act as a platform to facilitate neuronal signaling; however, they are suspected to have a very short lifetime, up to only a few seconds, which calls into question their roles in biological signaling. To better understand their diffusion dynamics and membrane compartmentalization, we labeled lipid raft constituent ganglioside GM1 with single quantum dots through the connection of cholera toxin B subunit, a protein that binds specifically to GM1. Diffusion measurements revealed that single quantum dot-labeled GM1 ganglioside complexes undergo slow, confined lateral diffusion with a diffusion coefficient of ∼7.87 × 10–2 μm2/s and a confinement domain about 200 nm in size. Further analysis of their trajectories showed lateral confinement persisting on the order of tens of seconds, comparable to the time scales of the majority of cellular signaling and biological reactions. Hence, our results provide further evidence in support of the putative function of lipid rafts as signaling platforms.Keywords: lipid rafts; membrane dynamics; Quantum dot; single-molecule imaging; trafficking
Co-reporter:Melissa A. Harrison;Amy Ng;Anthony B. Hmelo;Sra J. Rosenthal
Israel Journal of Chemistry 2012 Volume 52( Issue 11-12) pp:1063-1072
Publication Date(Web):
DOI:10.1002/ijch.201200040
Abstract
Semiconductor nanocrystals of CdSSe exhibiting chemical composition gradients are synthesized via a facile, one-pot synthesis. Varying degrees of gradation are observed as growth temperatures are manipulated to alter rates of reactivity for anionic precursors. Stoichiometries, with growth time and change in temperature, are determined using Rutherford backscattering spectroscopy to demonstrate chemical composition gradients. Sizes and structures of compositionally graded CdSSe nanocrystals are determined using transmission electron microscopy and X-ray diffraction techniques, respectively. We employ absorption spectroscopy and photoluminescence techniques to elucidate the corresponding optical properties. Nanocrystals with chemical composition gradients demonstrating enhanced luminescence efficiency could be the key to improved nanocrystal optical performance.
Co-reporter:Jerry C. Chang ; Ian D. Tomlinson ; Michael R. Warnement ; Hideki Iwamoto ; Louis J. DeFelice ; Randy D. Blakely ◆
Journal of the American Chemical Society 2011 Volume 133(Issue 44) pp:17528-17531
Publication Date(Web):October 4, 2011
DOI:10.1021/ja204301g
The serotonin (5-hydroxytryptamine, 5-HT) transporter (SERT) protein plays a central role in terminating 5-HT neurotransmission and is the most important therapeutic target for the treatment of major depression and anxiety disorders. We report an innovative, versatile, and target-selective quantum dot (QD) labeling approach for SERT in single Xenopus oocytes that can be adopted as a drug-screening platform. Our labeling approach employs a custom-made, QD-tagged indoleamine derivative ligand, IDT318, that is structurally similar to 5-HT and accesses the primary binding site with enhanced human SERT selectivity. Incubating QD-labeled oocytes with paroxetine (Paxil), a high-affinity SERT-specific inhibitor, showed a concentration- and time-dependent decrease in QD fluorescence, demonstrating the utility of our approach for the identification of SERT modulators. Furthermore, with the development of ligands aimed at other pharmacologically relevant targets, our approach may potentially form the basis for a multitarget drug discovery platform.
Co-reporter:Sandra J. Rosenthal, Jerry C. Chang, Oleg Kovtun, James R. McBride, Ian D. Tomlinson
Chemistry & Biology 2011 Volume 18(Issue 1) pp:10-24
Publication Date(Web):28 January 2011
DOI:10.1016/j.chembiol.2010.11.013
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.
Co-reporter:Oleg Kovtun, Ian D. Tomlinson, Dhananjay S. Sakrikar, Jerry C. Chang, Randy D. Blakely, and Sandra J. Rosenthal
ACS Chemical Neuroscience 2011 Volume 2(Issue 7) pp:370
Publication Date(Web):April 26, 2011
DOI:10.1021/cn200032r
The presynaptic dopamine (DA) transporter is responsible for DA inactivation following release and is a major target for the psychostimulants cocaine and amphetamine. Dysfunction and/or polymorphisms in human DAT (SLC6A3) have been associated with schizophrenia, bipolar disorder, Parkinson’s disease, and attention-deficit hyperactivity disorder (ADHD). Despite the clinical importance of DAT, many uncertainties remain regarding the transporter’s regulation, in part due to the poor spatiotemporal resolution of conventional methodologies and the relative lack of efficient DAT-specific fluorescent probes. We developed a quantum dot-based labeling approach that uses a DAT-specific, biotinylated ligand, 2-β-carbomethoxy-3-β-(4-fluorophenyl)tropane (IDT444), that can be bound by streptavidin-conjugated quantum dots. Flow cytometry and confocal microscopy were used to detect DAT in stably and transiently transfected mammalian cells. IDT444 is useful for quantum-dot-based fluorescent assays to monitor DAT expression, function, and plasma membrane trafficking in living cells as evidenced by the visualization of acute, protein-kinase-C (PKC)-dependent DAT internalization.Keywords: cocaine analogue; dopamine transporter; live cell imaging; Quantum dot; single-cell analysis; trafficking
Co-reporter:Ian D. Tomlinson, Hideki Iwamoto, Randy D. Blakely, Sandra J. Rosenthal
Bioorganic & Medicinal Chemistry Letters 2011 Volume 21(Issue 6) pp:1678-1682
Publication Date(Web):15 March 2011
DOI:10.1016/j.bmcl.2011.01.102
Quantum dot conjugates of compounds capable of inhibiting the serotonin transporter (SERT) could form the basis of fluorescent probes for live cell imaging of membrane bound SERT. Additionally, quantum dot-SERT antagonist conjugates may be amenable to fluorescence-based, high-throughput assays for this transporter. This Letter describes the synthesis of SERT-selective ligands amenable to conjugation to quantum dots via a biotin–streptavidin binding interaction. SERT selectivity and affinity were incorporated into the ligand via a tetrahydropyridine or cyclohexylamine derivative and the affinity of these compounds for SERT was measured by their ability to produce SERT-dependent currents in Xenopus laveis oocytes.
Co-reporter:Albert D. Dukes III, Philip C. Samson, Joseph D. Keene, Lloyd M. Davis, John P. Wikswo, and Sandra J. Rosenthal
The Journal of Physical Chemistry A 2011 Volume 115(Issue 16) pp:4076-4081
Publication Date(Web):February 22, 2011
DOI:10.1021/jp1109509
We report the observation of broad-spectrum fluorescence from single CdSe nanocrystals. Individual semiconductor nanocrystals typically have a narrower emission spectrum than that of an ensemble. However, our experiments show that the ensemble white-light emission observed in ultrasmall CdSe nanocrystals is the result of many single CdSe nanocrystals, each emitting over the entire visible spectrum. These results indicate that each white-light-emitting CdSe nanocrystal contains all the trap states that give rise to the observed white-light emission.
Co-reporter:Michael A. Schreuder, Kai Xiao, Ilia N. Ivanov, Sharon M. Weiss and Sandra J. Rosenthal
Nano Letters 2010 Volume 10(Issue 2) pp:573-576
Publication Date(Web):January 11, 2010
DOI:10.1021/nl903515g
We report white light-emitting diodes fabricated with ultrasmall CdSe nanocrystals, which demonstrate electroluminescence from a size of nanocrystals (<2 nm) previously thought to be unattainable. These LEDs have excellent color characteristics, defined by their pure white CIE color coordinates (0.333, 0.333), correlated color temperatures of 5461−6007 K, and color rendering indexes as high as 96.6. The effect of high voltage on the trap states responsible for the white emission is also described.
Co-reporter:Albert D. Dukes III, James R. McBride, and Sandra J. Rosenthal
Chemistry of Materials 2010 Volume 22(Issue 23) pp:6402
Publication Date(Web):November 17, 2010
DOI:10.1021/cm102370a
We report the observation of quantized growth in magic-sized CdSe and CdTe nanocrystals that utilize diisooctylphosphinic acid as the surface passivating ligand. The interaction between the diisooctylphosphinic acid and the coordinating solvent, hexadecylamine, results in the growth of only certain allowed sizes of nanocrystals. Magic-sized CdSe nanocrystals were synthesized with band edge absorption peaks at 414, 446, and 490 nm. Magic-sized CdTe nanocrystals were synthesized with band edge absorption peaks at 445 and 483 nm. The synthesis detailed here allows for the isolation of larger magic-sized nanocrystals than has been previously reported. The emission of diisooctylphosphinic acid-capped magic-sized nanocrystals is low, with a quantum yield of less than 1%. Photoluminescence excitation scans revealed a significantly reduced emission from absorption at the band edge. The diameter for the smallest CdSe magic-size was 1.7 nm, and the diameter for the smallest CdTe magic-size was 1.8 nm, as determined by transmission electron microscopy.
Co-reporter:James R. McBride, Albert D. Dukes III, Michael A. Schreuder, Sandra J. Rosenthal
Chemical Physics Letters 2010 Volume 498(1–3) pp:1-9
Publication Date(Web):30 September 2010
DOI:10.1016/j.cplett.2010.08.052
Ultrasmall nanocrystals are a growing sub-class of traditional nanocrystals that exhibit new properties at diameters typically below 2 nm. In this review, we define what constitutes an ultrasmall nanoparticle while distinguishing between ultrasmall and magic-size nanoparticles. After a brief overview of ultrasmall nanoparticles, including ultrasmall gold clusters, our recent work is presented covering the optical properties, structure, and application of ultrasmall CdSe nanocrystals. This unique material has potential application in solid state lighting due to its balanced white emission. This section is followed by a discussion on the blurring boundary between what can be considered a nanoparticle and a molecule.Graphical abstractResearch highlights► Ultrasmall nanoparticles exhibit unique properties. ► Ultrasmall CdSe nanocrystals emit broad-spectrum white light. ► Surface emission is dependent on ligand electronegativity. ► Ultrasmall CdSe can be utilized as a white-light source.
Co-reporter:
Nature Nanotechnology 2009 4(1) pp:
Publication Date(Web):2009-01-01
DOI:10.1038/nnano.2008.386
Lattice strain has long been avoided in the world of quantum dots, but it is now being used to tune the colour of light emitted by these structures
Co-reporter:Rebecca L. Orndorff and Sandra J. Rosenthal
Nano Letters 2009 Volume 9(Issue 7) pp:2589-2599
Publication Date(Web):June 9, 2009
DOI:10.1021/nl900789e
High affinity peptide neurotoxins are effective agents for integrating technological advances with biological inquiries. Both chlorotoxin (CTX) and dendrotoxin-1 (DTX-1) are peptide neurotoxins demonstrated to bind targets expressed by glioma cancer cells and are suitable ligands for quantum dot (QD) live cell investigations. Here, we present dual labeling of endogenously expressed cellular proteins within living cells utilizing high affinity peptide neurotoxins conjugated to QDs. Multiplexing experiments reveal quantifiable evidence that CTX and DTX-1 conjugated QDs may potentially be used as a live assessment of markers toward identification of cancer cell presence.
Co-reporter:Michael J. Bowers II ; James R. McBride ; Maria D. Garrett ; Jessica A. Sammons ; Albert D. Dukes III ; Michael A. Schreuder ; Tony L. Watt ; Andrew R. Lupini ; Stephen J. Pennycook
Journal of the American Chemical Society 2009 Volume 131(Issue 16) pp:5730-5731
Publication Date(Web):April 2, 2009
DOI:10.1021/ja900529h
White-light emission from ultrasmall CdSe nanocrystals offers an alternative approach to the realization of solid-state lighting as an appealing technology for consumers. Unfortunately, their extremely small size limits the feasibility of traditional methods for nanocrystal characterization. This paper reports the first images of their structure, which were obtained using aberration-corrected atomic number contrast scanning transmission electron microscopy (Z-STEM). With subangstrom resolution, Z-STEM is one of the few available methods that can be used to directly image the nanocrystal’s structure. The initial images suggest that they are crystalline and approximately four lattice planes in diameter. In addition to the structure, for the first time, the exciton dynamics were measured at different wavelengths of the white-light spectrum using ultrafast fluorescence upconversion spectroscopy. The data suggest that a myriad of trap states are responsible for the broad-spectrum emission. It is hoped that the information presented here will provide a foundation for the future development and improvement of white-light-emitting nanocrystals.
Co-reporter:James R. McBride, Andrew R. Lupini, Michael A. Schreuder, Nathanael J. Smith, Stephen J. Pennycook and Sandra J. Rosenthal
ACS Applied Materials & Interfaces 2009 Volume 1(Issue 12) pp:2886
Publication Date(Web):November 3, 2009
DOI:10.1021/am900608j
One consistent limitation for high-resolution imaging of small nanoparticles is the high background signal from the amorphous carbon support film. With interest growing for smaller and smaller nanostructures, state of the art electron microscopes are becoming necessary for rudimentary tasks, such as nanoparticle sizing. As a monolayer of carbon, free-standing graphene represents the ultimate support film for nanoparticle imaging. In this work, conventional high-resolution transmission electron microscopy (HRTEM) and aberration-corrected scanning transmission electron microscopy (STEM) were used to assess the benefits and feasibility of few-layer graphene support films. Suspensions of few-layer graphene to produce the support films were prepared by simple sonication of exfoliated graphite. The greatest benefit was observed for conventional HRTEM, where lattice resolved imaging of sub 2 nm CdSe nanocrystals was achieved. The few-layer graphene films were also used as a support film for Cs-corrected STEM and electron energy loss spectroscopy of CuInSe2 nanocrystals.Keywords: aberration-corrected scanning transmission electron microscopy; cadmium selenide; copper indium selenide,; few-layer graphene; graphene; nanocrystal; nanoparticle; transmission electron microscopy
Co-reporter:Michael A. Schreuder, James R. McBride, Albert D. Dukes III, Jessica A. Sammons and Sandra J. Rosenthal
The Journal of Physical Chemistry C 2009 Volume 113(Issue 19) pp:8169-8176
Publication Date(Web):2017-2-22
DOI:10.1021/jp900300t
Pinned emission from ultrasmall (<1.7 nm) CdSe nanocrystals is dominated by surface trap state emission. In sharp contrast to bulk defect emission, optical properties of the nanocrystal can be tuned through surface chemistry. We demonstrate the ability to alter this pinned emission from 2.79 to 2.91 eV by varying the phosphonic acid ligand. The blue shifting emission is attributed to the increased electronegativity of shorter chain length ligands. Further, the quantum yield of these nanocrystals can be enhanced by increasing the chain length of the ligand. These results indicate that for ultrasmall nanocrystals, the surface ligands play the dominant role in the emission properties.
Co-reporter:Michael A. Schreuder, Jonathan D. Gosnell, Nathanael J. Smith, Michael R. Warnement, Sharon M. Weiss and Sandra J. Rosenthal
Journal of Materials Chemistry A 2008 vol. 18(Issue 9) pp:970-975
Publication Date(Web):24 Jan 2008
DOI:10.1039/B716803A
White-light emitting ultra-small CdSe nanocrystals present exciting possibilities in the area of solid-state lighting technology. In this work, thirteen dissimilar polymers were examined as potential encapsulants for these single-sized nanocrystals. Films of the encased nanocrystals were characterized in terms of nanocrystal aggregation and changes to the nanocrystals' natural emission. The Hildebrand and Hansen solubility parameters of each encapsulant were found to be correlated to the quality of nanocrystal encapsulation achieved. Encapsulants with cyclosiloxane or bisphenol-A type epoxy structures caused extensive aggregation of the nanocrystals at low loading levels (<0.5% w/w) due to the solubility difference between the polymer structure and the nanocrystals' ligands. Of the encapsulants tested, the most robust, color stable, and homogenous encapsulation was obtained using a biphenylperfluorocyclobutyl polymer. In this polymer, nanocrystal loading levels up to 18% w/w were achieved. White-light emitting CdSe nanocrystals encapsulated in the biphenylperfluorocyclobutyl polymer were coated on various UV-LEDs creating a white light source with chromaticity coordinates of (0.324, 0.322) and a high color-rendering index of 93.
Co-reporter:Michael R. Warnement, Ian D. Tomlinson, Jerry C. Chang, Michael A. Schreuder, Courtney M. Luckabaugh and Sandra J. Rosenthal
Bioconjugate Chemistry 2008 Volume 19(Issue 7) pp:1404
Publication Date(Web):June 5, 2008
DOI:10.1021/bc800104n
Modifications of the quantum dot (QD) surface are routinely performed via covalent biomolecule attachment, and poly(ethylene glycol) (PEG) derivatization has previously been shown to limit nonspecific cellular interactions of QD probes. Attempts to functionalize ampiphilic QDs (AMP-QDs) with custom PEG derivatives having a hydrophobic terminus resulted in self-assembly of these PEG ligands to the AMP-QD surface in the absence of covalent coupling reagents. We demonstrate, via electrophoretic characterization techniques, that these self-assembled PEG-QDs exhibit improved passivation in biological environments and are less susceptible to unwanted protein adsorption to the QD surface. We highlight the artifactual fluorescent response protein adsorption can cause in biological assays, and discuss considerations for improved small molecule presentation to facilitate specific QD interactions.
Co-reporter:Arun Narayanaswamy;James McBride;Laura A. Swafford
Journal of Porous Materials 2008 Volume 15( Issue 1) pp:21-27
Publication Date(Web):2008 February
DOI:10.1007/s10934-006-9047-5
A fast and reliable synthetic route for preparing contaminant-free porous TiO2 with a wormhole-like framework and close packed macropores is demonstrated based on a sol-gel process involving acid hydrolysis of an alkoxide in the presence of a cationic surfactant. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements have been used to characterize the porous structure and the crystallinity. The XRD patterns, TEM and scanning electron microscopy (SEM) images confirm that these materials have disordered wormhole-like topology with close-packed nearly hexagonal macropores. The mesopore diameters and surface area of titanium dioxide, evaluated from the N2-sorption isotherms, indicate average pore diameters of about 7 and 6 nm and surface areas of about 100 and 335 m2/g, for as-prepared and calcined samples at 400°C.
Co-reporter:Maria Danielle Garrett, Albert D. Dukes III, James R. McBride, Nathanael J. Smith, Stephen J. Pennycook and Sandra J. Rosenthal
The Journal of Physical Chemistry C 2008 Volume 112(Issue 33) pp:12736-12746
Publication Date(Web):July 23, 2008
DOI:10.1021/jp803708r
The effect of surface trap states on band edge recombination in CdSe, CdS and CdSxSe1−x alloy nanocrystals has been determined using fluorescence upconversion spectroscopy. These measurements reveal that there is both a size and composition dependence on the short-lived (τ1) and long-lived (τ2) components of fluorescence lifetime at the band edge. An increase in nanocrystal diameter, ranging from 23 to 60 Å, is accompanied by an increase in τ1. This behavior is explained by the decrease in accessible trap sites through a reduction in surface-to-volume ratio. Similarly, τ2 is found to increase with increasing nanocrystal size. However, with increasing sulfur concentration in the alloy nanocrystals, both a reduction in the magnitude of τ1 and a reversal in the trend for τ2 are observed. These changes in lifetimes associated with the addition of sulfur are explained by increased trapping on the nanocrystal surface. These results indicate that carrier dynamics may be controlled not only through size, but also through composition of the nanocrystals. Compositional variation has been shown not only to affect carrier dynamics, but also to affect the optical properties of nanocrystals. An increase in the Stokes shift is observed for CdSxSe1−x alloy nanocrystals as compared to CdSe and CdS nanocrystals. This indicates that the Stokes shift is highly influenced by the nonlinear effects of alloying.
Co-reporter:Sandra J. Rosenthal, James McBride, Stephen J. Pennycook, Leonard C. Feldman
Surface Science Reports 2007 Volume 62(Issue 4) pp:111-157
Publication Date(Web):30 April 2007
DOI:10.1016/j.surfrep.2007.02.001
Nanostructures, with their very large surface to volume ratio and their non-planar geometry, present an important challenge to surface scientists. New issues arise as to surface characterization, quantification and interface formation. This review summarizes the current state of the art in the synthesis, composition, surface and interface control of CdSe nanocrystal systems, one of the most studied and useful nanostructures.
Co-reporter:Ian D. Tomlinson, Michael R. Warnerment, John N. Mason, Matthew J. Vergne, David M. Hercules, Randy D. Blakely, Sandra J. Rosenthal
Bioorganic & Medicinal Chemistry Letters 2007 Volume 17(Issue 20) pp:5656-5660
Publication Date(Web):15 October 2007
DOI:10.1016/j.bmcl.2007.07.061
Quantum dots consisting of a cadmium selenide core encapsulated in a shell of cadmium doped zinc sulfide have the potential to revolutionize fluorescent imaging of live cell cultures. In order to utilize these fluorescent probes it is necessary to functionalize them with biologically active ligands. In this paper we report the design and synthesis of a ligand that has a high affinity for the serotonin transporter (SERT) that may be conjugated to quantum dots.(i) 3-(1,2,3,6-Tetrahydro-pyridin-4yl)-1H-indole, cesium carbonate, 37.5%; (ii) hydrazine monohydrate, 34.6%; (iii) Boc-NH-PEG-NHS-3400, 100%; (iv) TFA, 100%.
Co-reporter:Michael A. Schreuder, Jonathan D. Gosnell, Nathanael J. Smith, Michael R. Warnement, Sharon M. Weiss and Sandra J. Rosenthal
Journal of Materials Chemistry A 2008 - vol. 18(Issue 9) pp:NaN975-975
Publication Date(Web):2008/01/24
DOI:10.1039/B716803A
White-light emitting ultra-small CdSe nanocrystals present exciting possibilities in the area of solid-state lighting technology. In this work, thirteen dissimilar polymers were examined as potential encapsulants for these single-sized nanocrystals. Films of the encased nanocrystals were characterized in terms of nanocrystal aggregation and changes to the nanocrystals' natural emission. The Hildebrand and Hansen solubility parameters of each encapsulant were found to be correlated to the quality of nanocrystal encapsulation achieved. Encapsulants with cyclosiloxane or bisphenol-A type epoxy structures caused extensive aggregation of the nanocrystals at low loading levels (<0.5% w/w) due to the solubility difference between the polymer structure and the nanocrystals' ligands. Of the encapsulants tested, the most robust, color stable, and homogenous encapsulation was obtained using a biphenylperfluorocyclobutyl polymer. In this polymer, nanocrystal loading levels up to 18% w/w were achieved. White-light emitting CdSe nanocrystals encapsulated in the biphenylperfluorocyclobutyl polymer were coated on various UV-LEDs creating a white light source with chromaticity coordinates of (0.324, 0.322) and a high color-rendering index of 93.
Co-reporter:Oleg Kovtun, Emily J. Ross, Ian D. Tomlinson and Sandra J. Rosenthal
Chemical Communications 2012 - vol. 48(Issue 44) pp:NaN5430-5430
Publication Date(Web):2012/04/05
DOI:10.1039/C2CC31951A
Here we present the development and validation of a flow cytometry-based dopamine transporter (DAT) binding assay that uses antagonist-conjugated quantum dots (QDs). We anticipate that our QD-based assay is of immediate value to the high throughput screening of novel DAT modulators.
