Inside Out: Visualizing chemical transformations and inter-cellular interactions with nanometer-scale resolution

In Pixar’s Inside Out, Joy proclaims, “Do you ever look at someone and wonder, what’s going on inside?” My group asks the same question about systems crucial to sustainable energy and health. This presentation will describe new techniques that enable dynamic, in situ visualization of chemical transformations and inter-cellular interactions with nanometer-scale resolution. We focus in particular on i) plasmon photocatalysis; ii) all-optical enantiomer separation; and iii) inter-cellular force sensing using unique electron, atomic, and optical microscopies. First, we explore nanomaterial phase transitions induced by solute intercalation, to understand and improve materials for optical energy conversion and storage.  As a model system, we investigate hydrogen intercalation in palladium nanocrystals. Using light-coupled environmental electron microscopy and spectroscopy, we monitor this reaction with sub-2-nm spatial resolution and millisecond time resolution. Particles of different sizes, shapes, and crystallinities exhibit distinct thermodynamic and kinetic properties, highlighting several important design principles for next-generation photocatalysis and energy storage. Then, we investigate optical tweezers that enable selective optical trapping of chiral molecules, with the ultimate goal of improving pharmaceutical and agrochemical efficacy. These tweezers are based on nanophotonic resonators that, when illuminated with circularly polarized light, result in distinct forces on enantiomers. In particular, one enantiomer is repelled from the tweezer while the other is attracted. Using atomic force microcopy, we map such chiral optical forces with pico-Newton force sensitivity and 2 nm lateral spatial resolution, showing distinct force distributions for each enantiomer. Finally, we present design of nanoparticles for efficient and force-sensitive upconversion. These optical force probes exhibit reversible changes in their emitted color with applied nano- to micro-Newton forces. We show how these nanoparticles provide a platform for understanding intra-cellular mechanical signaling in vivo, using C. elegans as a model organism.