Benjamin D. Mangum

Bio: Benjamin D. Mangum is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Quantum dot & Nanocrystal. The author has an hindex of 15, co-authored 24 publications receiving 2233 citations. Previous affiliations of Benjamin D. Mangum include University of Utah.

The Tol2kit: a multisite gateway-based construction kit for Tol2 transposon transgenesis constructs.

Abstract: Transgenesis is an important tool for assessing gene function. In zebrafish, transgenesis has suffered from three problems: the labor of building complex expression constructs using conventional subcloning; low transgenesis efficiency, leading to mosaicism in transient transgenics and infrequent germline incorporation; and difficulty in identifying germline integrations unless using a fluorescent marker transgene. The Tol2kit system uses site-specific recombination-based cloning (multisite Gateway technology) to allow quick, modular assembly of [promoter]-[coding sequence]-[3' tag] constructs in a Tol2 transposon backbone. It includes a destination vector with a cmlc2:EGFP (enhanced green fluorescent protein) transgenesis marker and a variety of widely useful entry clones, including hsp70 and beta-actin promoters; cytoplasmic, nuclear, and membrane-localized fluorescent proteins; and internal ribosome entry sequence-driven EGFP cassettes for bicistronic expression. The Tol2kit greatly facilitates zebrafish transgenesis, simplifies the sharing of clones, and enables large-scale projects testing the functions of libraries of regulatory or coding sequences.

New Insights into the Complexities of Shell Growth and the Strong Influence of Particle Volume in Nonblinking “Giant” Core/Shell Nanocrystal Quantum Dots

Abstract: The growth of ultra-thick inorganic CdS shells over CdSe nanocrystal quantum dot (NQD) cores gives rise to a distinct class of NQD called the “giant” NQD (g-NQD). g-NQDs are characterized by unique photophysical properties compared to their conventional core/shell NQD counterparts, including suppressed fluorescence intermittency (blinking), photobleaching, and nonradiative Auger recombination. Here, we report new insights into the numerous synthetic conditions that influence the complex process of thick-shell growth. We show the individual and collective effects of multiple reaction parameters (noncoordinating solvent and coordinating-ligand identities and concentrations, precursor/NQD ratios, precursor reaction times, etc.) on determining g-NQD shape and crystalline phase, and the relationship between these structural features and optical properties. We find that hexagonally faceted wurzite g-NQDs afford the highest ensemble quantum yields in emission and the most complete suppression of blinking. Signif...

Suppressed Blinking and Auger Recombination in Near-Infrared Type-II InP/CdS Nanocrystal Quantum Dots

Abstract: Nonblinking excitonic emission from near-infrared and type-II nanocrystal quantum dots (NQDs) is reported for the first time. To realize this unusual degree of stability at the single-dot level, novel InP/CdS core/shell NQDs were synthesized for a range of shell thicknesses (∼1–11 monolayers of CdS). Ensemble spectroscopy measurements (photoluminescence peak position and radiative lifetimes) and electronic structure calculations established the transition from type-I to type-II band alignment in these heterostructured NQDs. More significantly, single-NQD studies revealed clear evidence for blinking suppression that was not strongly shell-thickness dependent, while photobleaching and biexciton lifetimes trended explicitly with extent of shelling. Specifically, very long biexciton lifetimes—up to >7 ns—were obtained for the thickest-shell structures, indicating dramatic suppression of nonradiative Auger recombination. This new system demonstrates that electronic structure and shell thickness can be employed...

Disentangling the effects of clustering and multi-exciton emission in second-order photon correlation experiments.

Abstract: In single particle spectroscopy, the degree of observed fluorescence anti-bunching in a second-order cross correlation experiment is indicative of its bi-exciton quantum yield and whether or not a particle is well isolated. Advances in quantum dot synthesis have produced single particles with bi-exciton quantum yields approaching unity. Consequently, this creates uncertainty as to whether a particle has a high bi-exciton quantum yield or if it exists as a cluster. We report on a time-gated anti-bunching technique capable of determining the relative contributions of both multi-exciton emission and clustering effects. In this way, we can now unambiguously determine if a particle is single. Additionally, this time-gated anti-bunching approach provides an accurate way for the determination of bi-exciton lifetime with minimal contribution from higher order multi-exciton states.

Energy Transfer from an Individual Quantum Dot to a Carbon Nanotube

Abstract: Precision measurements of resonant energy transfer from isolated quantum dots (QDs) to individual carbon nanotubes (CNTs) exhibit unique features due to the one-dimensional nature of CNTs In particular, excitons can be created at varying distances from the QD at different locations along the CNT length This leads to large variations in energy transfer length scales for different QDs and a novel saturation of the energy transfer efficiency at ∼96%, seemingly independent of CNT chirality

Recent Advances in Two-Dimensional Materials beyond Graphene

Abstract: The isolation of graphene in 2004 from graphite was a defining moment for the “birth” of a field: two-dimensional (2D) materials In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement Here, we review significant recent advances and important new developments in 2D materials “beyond graphene” We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (ie, silicene, phosphorene, etc) and transition metal carbide- and carbon nitride-based MXenes We then discuss the doping and functionalization of 2

High cleavage efficiency of a 2A peptide derived from porcine teschovirus-1 in human cell lines, zebrafish and mice.

Abstract: When expression of more than one gene is required in cells, bicistronic or multicistronic expression vectors have been used. Among various strategies employed to construct bicistronic or multicistronic vectors, an internal ribosomal entry site (IRES) has been widely used. Due to the large size and difference in expression levels between genes before and after IRES, however, a new strategy was required to replace IRES. A self-cleaving 2A peptide could be a good candidate to replace IRES because of its small size and high cleavage efficiency between genes upstream and downstream of the 2A peptide. Despite the advantages of the 2A peptides, its use is not widespread because (i) there are no publicly available cloning vectors harboring a 2A peptide gene and (ii) comprehensive comparison of cleavage efficiency among various 2A peptides reported to date has not been performed in different contexts. Here, we generated four expression plasmids each harboring different 2A peptides derived from the foot-and-mouth disease virus, equine rhinitis A virus, Thosea asigna virus and porcine teschovirus-1, respectively, and evaluated their cleavage efficiency in three commonly used human cell lines, zebrafish embryos and adult mice. Western blotting and confocal microscopic analyses revealed that among the four 2As, the one derived from porcine teschovirus-1 (P2A) has the highest cleavage efficiency in all the contexts examined. We anticipate that the 2A-harboring cloning vectors we generated and the highest efficiency of the P2A peptide we demonstrated would help biomedical researchers easily adopt the 2A technology when bicistronic or multicistronic expression is required.

Zebrafish heart regeneration occurs by cardiomyocyte dedifferentiation and proliferation

Abstract: Although mammalian hearts show almost no ability to regenerate, there is a growing initiative to determine whether existing cardiomyocytes or progenitor cells can be coaxed into eliciting a regenerative response. In contrast to mammals, several non-mammalian vertebrate species are able to regenerate their hearts, including the zebrafish, which can fully regenerate its heart after amputation of up to 20% of the ventricle. To address directly the source of newly formed cardiomyocytes during zebrafish heart regeneration, we first established a genetic strategy to trace the lineage of cardiomyocytes in the adult fish, on the basis of the Cre/lox system widely used in the mouse. Here we use this system to show that regenerated heart muscle cells are derived from the proliferation of differentiated cardiomyocytes. Furthermore, we show that proliferating cardiomyocytes undergo limited dedifferentiation characterized by the disassembly of their sarcomeric structure, detachment from one another and the expression of regulators of cell-cycle progression. Specifically, we show that the gene product of polo-like kinase 1 (plk1) is an essential component of cardiomyocyte proliferation during heart regeneration. Our data provide the first direct evidence for the source of proliferating cardiomyocytes during zebrafish heart regeneration and indicate that stem or progenitor cells are not significantly involved in this process.

A molecular atlas of cell types and zonation in the brain vasculature

Abstract: Cerebrovascular disease is the third most common cause of death in developed countries, but our understanding of the cells that compose the cerebral vasculature is limited Here, using vascular sin

Compact high-quality CdSe–CdS core–shell nanocrystals with narrow emission linewidths and suppressed blinking

Abstract: High particle uniformity, high photoluminescence quantum yields, narrow and symmetric emission spectral lineshapes and minimal single-dot emission intermittency (known as blinking) have been recognized as universal requirements for the successful use of colloidal quantum dots in nearly all optical applications. However, synthesizing samples that simultaneously meet all these four criteria has proven challenging. Here, we report the synthesis of such high-quality CdSe-CdS core-shell quantum dots in an optimized process that maintains a slow growth rate of the shell through the use of octanethiol and cadmium oleate as precursors. In contrast with previous observations, single-dot blinking is significantly suppressed with only a relatively thin shell. Furthermore, we demonstrate the elimination of the ensemble luminescence photodarkening that is an intrinsic consequence of quantum dot blinking statistical ageing. Furthermore, the small size and high photoluminescence quantum yields of these novel quantum dots render them superior in vivo imaging agents compared with conventional quantum dots. We anticipate these quantum dots will also result in significant improvement in the performance of quantum dots in other applications such as solid-state lighting and illumination.