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Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2018)

Abstract

The Use of Liquid Phase Transmission Electron Microscopy for Quantifying Interactions Between Colloidal Nanoparticles and Visualizing Their Self-Assembled Structures

By

Hoduk Cho

Doctor of Philosophy in Chemistry

University of California, Berkeley

Professor A. Paul Alivisatos, Chair

This dissertation demonstrates the application of liquid phase transmission electron microscopy for quantifying interactions between colloidal nanoparticles and visualizing their self-assembled structures in their native solution state. Over a decade ago, the first liquid cells that could successfully enclose a thin layer of liquid while maintaining compatibility with the high vacuum conditions inside an electron microscope were developed. Subsequent commercialization of this technology by several companies greatly increased its accessibility and the research field has expanded rapidly as a result. The ability to directly visualize real-time nanoscale dynamics in solution has enabled researchers in physics, chemistry, biology, and materials science to investigate previously unexplored scientific phenomena. Thus far, the vast majority of research in this field has made use of the highly perturbative effect of the electron beam to initiate the dynamic process under study. Although this approach has yielded fruitful knowledge and insights, it has not been straightforward to extrapolate the conclusions formed from these studies to experiments conducted outside of the electron microscope. The effects of electron beam irradiation are still poorly understood, and ways to counteract them are limited. A more widespread application of liquid phase transmission electron microscopy would only be realized if the influence of the electron beam were well-known and could be tuned in a predictable manner. By understanding and controlling the effects of the electron beam on the encapsulated specimen during the imaging process, it will be possible to extract information relating to the behavior of colloidal nanoparticles in solution that can be generalizable to experiments carried out in the wet lab.

Chapter 1 introduces the basic concepts of nanoparticle self-assembly, interparticle interactions at the nanoscale, DNA-mediated nanoparticle assembly, liquid phase transmission electron microscopy, and radiation-induced effects that accompany electron microscopy imaging in liquid. Chapter 2 illustrates how the individual trajectories of nanoparticles moving in solution, obtained using liquid phase transmission electron microscopy, can be utilized for quantitative analysis of their interparticle interactions. Chapter 3 describes how the damaging effects of electron beam irradiation on DNA-assembled nanoparticles can be mitigated with the use of graphene and its derivatives as biocompatible radical scavengers. Chapter 4 summarizes the seminal findings that are reported in this dissertation and provides a brief outlook for the future.

    Cover page: The Use of Liquid Phase Transmission Electron Microscopy for Quantifying Interactions Between Colloidal Nanoparticles and Visualizing Their Self-Assembled Structures
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2015)
    We present two examples of the use of liquid cells to study colloidal inorganic nanocrystals using in situ transmission electron microscopy. The first uses a liquid cell to quantify the interaction potential between pairs of colloidal nanocrystals, and the second demonstrates direct imaging of nanocrystal growth and structure in the liquid cell.
      Cover page: Spiers Memorial Lecture New tools for observing the growth and assembly of colloidal inorganic nanocrystals
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2017)
      One of the key challenges facing liquid-phase transmission electron microscopy (TEM) of biological specimens has been the damaging effects of electron beam irradiation. The strongly ionizing electron beam is known to induce radiolysis of surrounding water molecules, leading to the formation of reactive radical species. In this study, we employ DNA-assembled Au nanoparticle superlattices (DNA-AuNP superlattices) as a model system to demonstrate that graphene and its derivatives can be used to mitigate electron beam-induced damage. We can image DNA-AuNP superlattices in their native saline environment when the liquid cell window material is graphene, but not when it is silicon nitride. In the latter case, initial dissociation of assembled AuNPs was followed by their random aggregation and etching. Using graphene-coated silicon nitride windows, we were able to replicate the observation of stable DNA-AuNP superlattices achieved with graphene liquid cells. We then carried out a correlative Raman spectroscopy and TEM study to compare the effect of electron beam irradiation on graphene with and without the presence of water and found that graphene reacts with the products of water radiolysis. We attribute the protective effect of graphene to its ability to efficiently scavenge reactive radical species, especially the hydroxyl radicals which are known to cause DNA strand breaks. We confirmed this by showing that stable DNA-AuNP assemblies can be imaged in silicon nitride liquid cells when graphene oxide and graphene quantum dots, which have also recently been reported as efficient radical scavengers, are added directly to the solution. We anticipate that our study will open up more opportunities for studying biological specimens using liquid-phase TEM with the use of graphene and its derivatives as biocompatible radical scavengers to alleviate the effects of radiation damage.
        Cover page: The Use of Graphene and Its Derivatives for Liquid-Phase Transmission Electron Microscopy of Radiation-Sensitive Specimens
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2015)
        We demonstrate a generalizable strategy to use the relative trajectories of pairs and groups of nanocrystals, and potentially other nanoscale objects, moving in solution which can now be obtained by in situ liquid phase transmission electron microscopy (TEM) to determine the interaction potentials between nanocrystals. Such nanoscale interactions are crucial for collective behaviors and applications of synthetic nanocrystals and natural biomolecules, but have been very challenging to measure in situ at nanometer or sub-nanometer resolution. Here we use liquid phase TEM to extract the mathematical form of interaction potential between nanocrystals from their sampled trajectories. We show the power of this approach to reveal unanticipated features of nanocrystal-nanocrystal interactions by examining the anisotropic interaction potential between charged rod-shaped Au nanocrystals (Au nanorods); these Au nanorods assemble, in a tip-to-tip fashion in the liquid phase, in contrast to the well-known side-by-side arrangements commonly observed for drying-mediated assembly. These observations can be explained by a long-range and highly anisotropic electrostatic repulsion that leads to the tip-selective attachment. As a result, Au nanorods stay unassembled at a lower ionic strength, as the electrostatic repulsion is even longer-ranged. Our study not only provides a mechanistic understanding of the process by which metallic nanocrystals assemble but also demonstrates a method that can potentially quantify and elucidate a broad range of nanoscale interactions relevant to nanotechnology and biophysics.
          Cover page: Interaction Potentials of Anisotropic Nanocrystals from the Trajectory Sampling of Particle Motion using in Situ Liquid Phase Transmission Electron Microscopy
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