Person:

Sun, Li

We image the chiroptical response of crossed nanowire junctions as a function of the vertical offset between the nanowires and the incident wavelength. These samples show chiroptical “hot spots” with strongly localized circular differential scattering at the nanowire crossing points. These chiroptical hot spots are not apparent in the spatially averaged spectra. The sign and magnitude of the chiroptical enhancement show a complex dependence on sample geometry, which we reproduce with a fully retarded analytical scattering model. These results suggest strategies for engineering devices with enhanced chiral light-matter interactions.

Adoptive Immunotherapy has long been explored as a possible cure for challenging diseases including cancer and HIV infection. The key step in such therapies is to identify and select disease-specific effector cells, which in the past have relied on well-plate based bulk manipulations. But as effector cells against a specific disease are often scarce, bulk studies are ineffective at identifying and selecting the rare effector cells with accuracy. It also takes weeks to prepare a desired population. Though recent advances such as genetically engineered T cell technology and the mutation selection technology have shown great promises, the former is limited by the difficulty in identifying the receptor and antigen, the latter is limited by the direct cell surface fluorescent tagging which could impairs the functional epitomes of surface activation marker and the ineffectiveness of the surface activation marker based selection. Thus I developed a microfluidic system to identify and select effector cells with unprecedented accuracy and speed, by probing the dynamic single cell immune response through co assessing single cell cytokine secretion and cytolysis in picoliter droplets.

Ultrasmooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle sizes of 200 nm or more. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances in small clusters. The high monodispersity of the particles we demonstrate should facilitate the self-assembly of nanoparticle clusters with uniform optical resonances, which could in turn be used to fabricate optical metafluids. Narrow size distributions are required to control not only the spectral features but also the morphology and yield of clusters in certain assembly schemes.