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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2017)

Dynamic materials have always held the interest of scientists because they change their properties in response to some stimulus. Being able to program the desired material properties before and after a stimulus is important to many sensing technologies. One interesting class of materials are termed ‘metamaterials’ because they interact with light in exotic ways that naturally occurring materials do not. These engineered materials are able to interact with light (or other frequencies of electromagnetic waves) in novel ways is due to the low symmetry arrangement of their components. In order to achieve the low symmetry arrangement, lithographic techniques are commonly used to fabricate these materials, because lithography can arrange nanoscale components in arbitrary patterns. However, most lithographed materials are static and do not react to external chemical stimuli. This dissertation lays out a novel approach to rationally assemble dynamic metamaterials by combining lithographic techniques with DNA mediated self-assembly, which imparts a responsive, organic component to the metamaterial.

Integrating DNA into a metamaterial allows for several advancements over lithographed-only metamaterials. First it allows for sub-nanometer control over the spacing of the constituent components. Second, DNA is responsive to a wide variety of stimuli—such as other DNA strands, salt, proteins, certain organic molecules, and temperature. Depending on the stimuli, one could then program a single metamaterial to respond in divergent ways to different chemical stimuli.

The model metamaterial examined here is a three nanorod system that exhibits a property known as electromagnetically induced transparency (EIT). Two rods are defined with lithography, and the third is assembled with DNA. This hybrid organic-inorganic structure behaves in accordance to plasmon hybridization theory and finite difference time domain (FDTD) simulations. Finally, external chemical stimuli, such as removing sodium cations or dehydrating the DNA, can cause the components to either decouple or couple more strongly, causing the EIT effect to either disappear or become enhanced, respectively. This assembly method allows for creating of dynamic metamaterials that can be predictably perturbed in order to change their desired optical properties.

    Cover page: Integration of Lithography and DNA Mediated Self-Assembly for the Synthesis of Responsive Metamaterials
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2018)
    Metamaterials are architectures that interact with light in novel ways by virtue of symmetry manipulation, and have opened a window into studying unprecedented light-matter interactions. However, they are commonly fabricated via lithographic methods, are usually static structures, and are limited in how they can react to external stimuli. Here we show that by combining lithographic techniques with DNA-based self-assembly methods, we can construct responsive plasmonic metamaterials that exhibit the plasmonic analog of an effect known as electromagnetically induced transparency (EIT), which can dramatically change their spectra upon motion of their constituent parts. Correlative scanning electron microscopy measurements, scattering dark-field microscopy, and computational simulations are performed on single assemblies to determine the relationship between their structures and spectral responses to a variety of external stimuli. The strength of the EIT-like effect in these assemblies can be tuned by precisely controlling the positioning of the plasmonic nanoparticles in these structures. For example, changing the ionic environment or dehydrating the sample will change the conformation of the DNA linkers and therefore the distance between the nanoparticles. Dark-field spectra of individual assemblies show peak shifts of up to many tens of nanometers upon DNA perturbations. This dynamic metamaterial represents a stepping stone toward state-of-the-art plasmonic sensing platforms and next-generation dynamic metamaterials.
      Cover page: Hybrid Lithographic and DNA-Directed Assembly of a Configurable Plasmonic Metamaterial That Exhibits Electromagnetically Induced Transparency
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2016)
      Tools capable of imaging and perturbing mechanical signaling pathways with fine spatiotemporal resolution have been elusive, despite their importance in diverse cellular processes. The challenge in developing a mechanogenetic toolkit (i.e., selective and quantitative activation of genetically encoded mechanoreceptors) stems from the fact that many mechanically activated processes are localized in space and time yet additionally require mechanical loading to become activated. To address this challenge, we synthesized magnetoplasmonic nanoparticles that can image, localize, and mechanically load targeted proteins with high spatiotemporal resolution. We demonstrate their utility by investigating the cell-surface activation of two mechanoreceptors: Notch and E-cadherin. By measuring cellular responses to a spectrum of spatial, chemical, temporal, and mechanical inputs at the single-molecule and single-cell levels, we reveal how spatial segregation and mechanical force cooperate to direct receptor activation dynamics. This generalizable technique can be used to control and understand diverse mechanosensitive processes in cell signaling. VIDEO ABSTRACT.
        Cover page: A Mechanogenetic Toolkit for Interrogating Cell Signaling in Space and Time
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