Keith A. Brown

Bio: Keith A. Brown is an academic researcher from Boston University. The author has contributed to research in topics: Dielectrophoresis & Nanolithography. The author has an hindex of 32, co-authored 105 publications receiving 2759 citations. Previous affiliations of Keith A. Brown include International Institute of Minnesota & Northwestern University.

Universal noble metal nanoparticle seeds realized through iterative reductive growth and oxidative dissolution reactions.

Abstract: Control over nanoparticle shape and size is commonly achieved via a seed-mediated approach, where nanoparticle precursors, or seeds, are hypothesized to act as templates for the heterogeneous nucleation of anisotropic products. Despite the wide variety of shapes that have been produced via this approach, high yield and uniformity have been more difficult to achieve. These shortcomings are attributed to limited structural control and characterization of the initial distribution of seeds. Herein, we report how iterative reductive growth and oxidative dissolution reactions can be used to systematically control seed structural uniformity. Using these reactions, we verify that seed structure dictates anisotropic nanoparticle uniformity and show that iterative seed refinement leads to unprecedented noble metal nanoparticle uniformities and purities for eight different shapes produced from a single seed source. Because of this uniformity, the first nanoparticle optical extinction coefficients for these eight shapes were analytically determined.

Building superlattices from individual nanoparticles via template-confined DNA-mediated assembly

Abstract: DNA programmable assembly has been combined with top-down lithography to construct superlattices of discrete, reconfigurable nanoparticle architectures on a gold surface over large areas. Specifically, the assembly of individual colloidal plasmonic nanoparticles with different shapes and sizes is controlled by oligonucleotides containing “locked” nucleic acids and confined environments provided by polymer pores to yield oriented architectures that feature tunable arrangements and independently controllable distances at both nanometer- and micrometer-length scales. These structures, which would be difficult to construct by other common assembly methods, provide a platform to systematically study and control light-matter interactions in nanoparticle-based optical materials. The generality and potential of this approach are explored by identifying a broadband absorber with a solvent polarity response that allows dynamic tuning of visible light absorption.

Human T cell lymphotropic virus type I Tax protein trans-activates interleukin 15 gene transcription through an NF-κB site

Abstract: Interleukin 15 (IL-15) mRNA is expressed in a wide variety of tissue types. However, with the exception of some T cell lines, IL-15 transcript expression has not been described in T cells. Herein we demonstrate that IL-15 mRNA can be detected in freshly isolated normal T cells and T cell lines. Furthermore, its expression is 3- to 4-fold higher in human T cell lymphotropic virus type I (HTLV-I)-infected T cells. By using reporter constructs bearing the 5′ regulatory region of the IL-15 gene, we observed a positive correlation between HTLV-I Tax protein expression and IL-15 promoter activity in HTLV-I-infected T cells. Additionally, by using a Jurkat T cell transfectant that expresses Tax under an inducible promoter, we demonstrated that the expression of IL-15 mRNA increased 3-fold as Tax was expressed, suggesting that the Tax protein activates IL-15 transcription. An NF-κB consensus sequence is located at the −75 and −65 region of the IL-15 5′ regulatory region. Mutations in the NF-κB motif or deletion of this sequence abrogated the promoter activity in both HTLV-I-positive and Jurkat Tax-transfectant cells. These data represent evidence for trans-activation of the IL-15 gene by the HTLV-I Tax protein through an NF-κB motif and suggest a potential role for IL-15 in HTLV-I-associated diseases such as adult T cell leukemia and HTLV-I-associated myopathy/tropical spastic paraparesis.

Strong Coupling between Plasmonic Gap Modes and Photonic Lattice Modes in DNA-Assembled Gold Nanocube Arrays

Abstract: Control of both photonic and plasmonic coupling in a single optical device represents a challenge due to the distinct length scales that must be manipulated. Here, we show that optical metasurfaces with such control can be constructed using an approach that combines top-down and bottom-up processes, wherein gold nanocubes are assembled into ordered arrays via DNA hybridization events onto a gold film decorated with DNA-binding regions defined using electron beam lithography. This approach enables one to systematically tune three critical architectural parameters: (1) anisotropic metal nanoparticle shape and size, (2) the distance between nanoparticles and a metal surface, and (3) the symmetry and spacing of particles. Importantly, these parameters allow for the independent control of two distinct optical modes, a gap mode between the particle and the surface and a lattice mode that originates from cooperative scattering of many particles in an array. Through reflectivity spectroscopy and finite-difference...

Nucleotide sequence of the leader region of the phenylalanine operon of Escherichia coli.

Abstract: The pheA structural gene of the phenylalanine operon of Escherichia coli is preceded by a transcribed leader region of about 170 nucleotide pairs. In vitro transcription of plasmids and restriction fragments containing the phe promoter and leader region yields a major RNA transcript about 140 nucleotides in length. This transcript, pheA leader RNA, has the following features: (i) a potential ribosome binding site and AUG translation start codon about 20 nucleotides from its 5′ end; (ii) 14 additional in phase amino acid codons and a UGA stop codon after the AUG; 7 of these 14 are Phe codons; (iii) a 3′-OH terminus about 140 nucleotides from the 5′ end (transcription termination occurs in an A·T-rich region which is subsequent to a G·C-rich region; just beyond the site of transcription termination there is a sequence corresponding to a ribosome binding site and the AUG translation start codon of the pheA structural gene); (iv) a sequence which would permit extensive intrastrand stable hydrogen bonding. In addition to G·C-rich stem structures, highly analogous to those proposed for the leader RNAs of the tryptophan operons of E. coli and Salmonella typhimurium [Lee, F. & Yanofsky, C. (1977) Proc. Natl. Acad. Sci. USA 74, 4365-4369], there is also extensive base-pairing possible between the phe codon region and a more distal region of the leader transcript. The roles of synthesis of the Phe-rich leader peptide and secondary structure of the leader transcript in the regulation of transcription termination at the attenuator of the phe operon are discussed.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

Activators and target genes of Rel/NF-kappaB transcription factors.

Abstract: Sixteen years have passed since the description of the nuclear factor-кB (NF-кB) as a regulator of к light-chain gene expression in murine B lymphocytes (Sen & Baltimore, 1986a) During that time, over 4,000 publications have appeared, characterizing the family of Rel/NF-кB transcription factors involved in the control of a large number of normal and pathological cellular processes The physiological functions of NF-кB proteins include immunological and inflammatory responses, developmental processes, cellular growth and modulating effects on apoptosis In addition, these factors are activated in a number of diseases, including cancer, arthritis, acute and chronic inflammatory states, asthma, as well as neurodegenerative and heart diseases

Self-Assembly of Colloidal Nanocrystals: From Intricate Structures to Functional Materials

Abstract: Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape. These Brownian objects readily order into superlattices. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. This process is often driven by both interparticle interactions and the influence of the assembly environment. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micro...