Hydrogel nanostructures for plasmonic and biosensor applications
Date of Issue2017
School of Chemical and Biomedical Engineering
Plasmonics is recently emerged nanophotonics research area that focuses at sub-wavelength confinement of light energy by its coupling to surface plasmons - collective oscillations in charge density and associated electromagnetic field at surfaces of metals. Hybrid responsive polymer-metallic nanostructures represent an attractive class of materials with actively tunable plasmonic properties. Such characteristics may enable new applications of plasmonics in analytics that utilize direct or optical spectroscopy-based detection of molecular analytes as well as in development of novel miniaturized plasmonic components. This thesis describes novel implementations ofthermo-responsive N-isopropylacrylamide (pNIPAAm) based hydrogel to metallic nanostructures that support surface plasmons. It reports means of structuring a photo-crosslinkable pNIPAAm layer with features exhibiting size as small as lOOnm by nano-imprint lithography and laser interference lithography. A new technique for in situ observation of swelling characteristics of such nanoscopic soft matter objects that are arranged in a period array was developed based on optical waveguide mode-enhanced diffraction measurements. pNIPAAm periodic structures highly swell in water (swelling ratio up to 10) and they can be prepared on around 1 cm2 area on a gold surface. A structure that acts as a tunable plasmonic crystal was prepared and by its reversible swelling and collapsing a plasmonic bandgap can be open and closed. In addition, responsive pNIPAAm material was employed as a "glue" in plasmonic structures. Firstly, it was employed to serve as a responsive cushion that tethers a thin metallic film with arrays of nanoholes to a solid glass surface. The swelling and collapsing of the cushion is demonstrated to mediate the extraordinary transmission and potentially offer a new means of the implementation of nanohole arrays surface plasmon resonance biosensor with flow-through architecture. Lastly, pNIPMm was used as a glue in order to form a composite film with high density of nanoparticles that were imprinted with a low molecular weight organic molecule. The composite film exhibited highly open architecture through which the target analyte L-Boc-phenylalanine-anilide (L-BFA) can freely diffuse and become affinity capture. Direct detection of affinity binding at concentrations around uM was carried by optical waveguide spectroscopy as the composite film can serve at the same time as large capacity affinity binding matrix and an optical waveguide.