Miguel Jose Yacaman

Bio: Miguel Jose Yacaman is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Scanning transmission electron microscopy & Nanoparticle. The author has an hindex of 19, co-authored 39 publications receiving 8009 citations. Previous affiliations of Miguel Jose Yacaman include University of Connecticut.

The bactericidal effect of silver nanoparticles

Abstract: Nanotechnology is expected to open new avenues to fight and prevent disease using atomic scale tailoring of materials. Among the most promising nanomaterials with antibacterial properties are metallic nanoparticles, which exhibit increased chemical activity due to their large surface to volume ratios and crystallographic surface structure. The study of bactericidal nanomaterials is particularly timely considering the recent increase of new resistant strains of bacteria to the most potent antibiotics. This has promoted research in the well known activity of silver ions and silver-based compounds, including silver nanoparticles. The present work studies the effect of silver nanoparticles in the range of 1-100 nm on Gram-negative bacteria using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Our results indicate that the bactericidal properties of the nanoparticles are size dependent, since the only nanoparticles that present a direct interaction with the bacteria preferentially have a diameter of approximately 1-10 nm.

Interaction of silver nanoparticles with HIV-1

Abstract: The interaction of nanoparticles with biomolecules and microorganisms is an expanding field of research. Within this field, an area that has been largely unexplored is the interaction of metal nanoparticles with viruses. In this work, we demonstrate that silver nanoparticles undergo a size-dependent interaction with HIV-1, with nanoparticles exclusively in the range of 1–10 nm attached to the virus. The regular spatial arrangement of the attached nanoparticles, the center-to-center distance between nanoparticles, and the fact that the exposed sulfur-bearing residues of the glycoprotein knobs would be attractive sites for nanoparticle interaction suggest that silver nanoparticles interact with the HIV-1 virus via preferential binding to the gp120 glycoprotein knobs. Due to this interaction, silver nanoparticles inhibit the virus from binding to host cells, as demonstrated in vitro.

The role of twinning in shape evolution of anisotropic noble metal nanostructures

Abstract: Nanotechnology provides the ability to engineer the properties of materials by controlling their size and shape. Among the most interesting nanostructures are anisotropic noble metal nanocrystals such as nanorods and nanowires. Nevertheless, the production of such crystals in a controlled fashion remains as a challenging task, and many available colloidal techniques produce a mixture of morphologies. In cases where high yields of a particular anisotropic structure have been produced, the growth mechanism has been primarily explained in terms of the presence of surfactants or capping agents that regulate the growth of the crystal in a particular direction. However, the growth mechanism should also consider nucleation and kinetics, and not only thermodynamics or physical restrictions imposed by the surface stabilizing agent. In this work, we present several examples of anisotropic noble metal nanocrystals obtained by different methods. Finally, the important role of twinning in determining the habit of the final morphology is discussed.

Corrosion at the Nanoscale: The Case of Silver Nanowires and Nanoparticles

Abstract: Metal nanostructures, such as nanoparticles and nanowires, have been proposed as building blocks for several applications in nanofabrication and nanoelectronics However, even when atmospheric corrosion is common in metals, there is a lack of information about the stability of those nanostructures against such phenomenon Therefore, we decided to study the atmospheric corrosion of silver nanowires and nanoparticles synthesized by the polyol method using poly(vinylpyrrolidone) (PVP) as the capping agent by different techniques, including transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) After synthesis and purification, the silver nanostructures were deposited on different substrates and exposed to laboratory air at ambient conditions The structural changes in the samples were monitored by TEM as a function of time for a period of time of 24 weeks Our results demonstrated that these silver nanostructures are susceptible to atmospheric corrosion and that, in most cases, a

The single-layered morphology of supported MoS2-based catalysts—The role of the cobalt promoter and its effects in the hydrodesulfurization of dibenzothiophene

Abstract: In order to completely resolve the morphology of supported hydrodesulfurization (HDS) catalysts, synchrotron X-ray scattering studies of silica- and alumina-supported MoS2 catalysts have been carried out and compared to results previously reported for their cobalt-promoted counterparts [J. Catal. 225 (2004) 288]. The present study is mainly centered on the structural role of cobalt and of support interactions and on their influence on the morphology and catalytic properties of these transition metal sulfide catalysts. Results showed that cobalt promoter strongly enhances the stacking height of MoS2 layers. However this effect is counterbalanced by hydrodesulfurization conditions that favor in an opposite way the formation of single slabs. Single slab morphology suggests that the vast majority of the sites on MoS2 layers are “rim” sites able to perform both hydrogenation and CS bond cleavage steps. Moreover, the complete determination of the morphology of these catalysts allowed correlation of structural and catalytic properties for both supported MoS2 and CoMo catalysts. This approach led us to examine the respective influences of the MoS2 slab morphology and of support interactions on activity and selectivity properties of HDS MoS2-based catalysts.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Abstract: Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Does the antibacterial activity of silver nanoparticles depend on the shape of the nanoparticle? A study of the Gram-negative bacterium Escherichia coli.

Abstract: In this work we investigated the antibacterial properties of differently shaped silver nanoparticles against the gram-negative bacterium Escherichia coli, both in liquid systems and on agar plates. Energy-filtering transmission electron microscopy images revealed considerable changes in the cell membranes upon treatment, resulting in cell death. Truncated triangular silver nanoplates with a {111} lattice plane as the basal plane displayed the strongest biocidal action, compared with spherical and rod-shaped nanoparticles and with Ag+ (in the form of AgNO3). It is proposed that nanoscale size and the presence of a {111} plane combine to promote this biocidal property. To our knowledge, this is the first comparative study on the bactericidal properties of silver nanoparticles of different shapes, and our results demonstrate that silver nanoparticles undergo a shape-dependent interaction with the gram-negative organism E. coli.

Nanomaterials and nanoparticles: Sources and toxicity

Abstract: This review is written with the goal of informing public health concerns related to nanoscience, while raising awareness of nanomaterials toxicity among scientists and manufacturers handling them. We show that humans have always been exposed to nanoparticles and dust from natural sources and human activities, the recent development of industry and combustion-based engine transportation profoundly increasing anthropogenic nanoparticulate pollution. The key to understanding the toxicity of nanoparticles is that their minute size, smaller than cells and cellular organelles, allows them to penetrate these basic biological structures, disrupting their normal function. Among diseases associated with nanoparticles are asthma, bronchitis, lung cancer, neurodegenerative diseases (such as Parkinson`s and Alzheimer`s diseases), Crohn`s disease, colon cancer. Nanoparticles that enter the circulatory system are related to occurrence of arteriosclerosis, and blood clots, arrhythmia, heart diseases, and ultimately cardiac death. We show that possible adverse effects of nanoparticles on human health depend on individual factors such as genetics and existing disease, as well as exposure, and nanoparticle chemistry, size, shape, and agglomeration state. The faster we will understand their causes and mechanisms, the more likely we are to find cures for diseases associated with nanoparticle exposure. We foresee a future with better-informed, and hopefully more cautious manipulation of engineered nanomaterials, as well as the development of laws and policies for safely managing all aspects of nanomaterial manufacturing, industrial and commercial use, and recycling.