Showing papers by "Paul Matsudaira published in 2016"

Multi-step nucleation of nanocrystals in aqueous solution

Abstract: Nucleation and growth of solids from solutions impacts many natural processes and are fundamental to applications in materials engineering and medicine. For a crystalline solid, the nucleus is a nanoscale cluster of ordered atoms, which forms through mechanisms that are still poorly understood. These mechanisms have important consequences on the morphology and nucleation rates of the resultant crystals but it is unclear whether a nucleus forms spontaneously from solution in a single step or through multiple steps. Using in-situ electron microscopy, we observe and quantify how gold and silver nanocrystals nucleate from a supersaturated aqueous gold and silver solution in three distinct steps: (I) spinodal decomposition into solute-rich and solute-poor liquid phases, (II) nucleation of amorphous gold nanoclusters within the gold-rich liquid phase, followed by (III) crystallization of these amorphous clusters. Our ab-initio calculations on gold nucleation suggest that these steps might be associated with strong gold-gold atom coupling and water-mediated metastable gold complexes. The understanding of intermediate steps in nuclei formation has important implications for the formation and growth of both crystalline and amorphous materials.

Desorption-Mediated Motion of Nanoparticles at the Liquid–Solid Interface

Abstract: Nanoparticles (NPs) confined in thin layers of liquid within liquid cells used for in situ transmission electron microscopy (TEM) move very slowly, in contrast to free particles in bulk liquid. The reason is still poorly understood. Here, we tracked gold NPs moving in water at the liquid–solid interface with in situ TEM at rates of 100 frames per second. The recorded motion exhibited three key features: (1) it was made up of sustained sequences of “sticky” motion where NPs only moved a few nanometers each time; (2) sporadic long “flights” where the NPs traveled tens to hundreds of nanometers between frames; and (3) “flights” are accompanied by intermittent, fast pivoted rotations. Trajectory analysis shows that the displacements follow a truncated Levy distribution, pointing to desorption-mediated motion of NPs at the liquid–solid interface. We further associate pivoted rotations with a transient “weakly adsorbed” state between desorption and adsorption of NPs. The frequency of desorption was also control...

Hopping Diffusion of Gold Nanoparticles Observed with Liquid Cell TEM

Abstract: The diffusion of nanoparticles in the microfluidic cells used for liquid cell transmission electron microscopy (TEM) have always been found to be much slower [1-6], often by several orders of magnitude, when compared with bulk diffusion. While this highly suppressed motion is serendipitous for the atomic resolution imaging of nanoparticle nucleation and coalescence events, we still lack a compelling explanation for this anomalous phenomena. Here, we report results from our experiments tracking the motion of Au nanoparticles in water, using a combination of energy filtered imaging and image acquisition at frame rates of 100 Hz.

Real time observation of gold nanoparticle aggregation dynamics on a 2D membrane

Abstract: The dynamics of particles confined to the solid-liquid interface is the key to understand the mechanism behind many physical, chemical and biological systems, such as self-assembly, electro-catalysis, and a vast variety of macromolecules on lipid membranes. Recent studies have revealed that the classic Brownian diffusion model and DLVO model have both failed to predict the behaviors regarding the nanoscale interfacial systems, where the surface effects will dominate and regulate the particle motion [1]. It’s reported by several authors that nanoparticles on a surface will be damped 10 -3 -10 -9 times slower than Brownian self-diffusion [2-4]. But how the surface takes effect in particle dynamics is still not fully understood. Thus, a detailed analysis of particle motion could give us more information about the role of surface in regulating particle motion.

A method to quantify co-localization in biological images

Abstract: Quantitative co-localization analysis with fluorescent microscopy is a common approach to assess the spatial co-ordination of molecules and thus to understand their functions in biological processes. However, the co-localization analysis results might not be consistent due to various imaging conditions and different quantification methods used. We propose a novel method to separate a co-localization event into two aspects: co-occurrence and intensity correlation, which are usually combined as one parameter in other quantitative co-localization analyses. By examining co-localization through both co-occurrence and intensity correlation, the co-localization analysis provides accurate and interpretable results. Furthermore, the co-occurrence pixels can be visualized in an additional image channel to provide an intuitive impression of the quantity and locations of the co-localization events occurring.