Self-assembly of polymer/nanoparticle films for fabrication of fiber-optic sensors based on SPR

Surface Plasmon Resonance (SPR) is an optical phenomenon which can be used for the sensitive detection of macromolecular interactions at a sensor surface by detecting small changes in refractive index resulting from adsorbed species. Previous work toward fiber-optic SPR sensors has employed metal films sputtered or evaporated onto waveguides. In this work, a novel nanofabrication approach using a combination of self-assembled monolayers (SAMs) and electrostatic layer-by-layer (LbL) self assembly was investigated toward precise deposition of metal nanomaterials onto fibers, which could enable excellent control over surface properties as well as provide an enhanced plasmon signal due to the roughened metal surfaces. Furthermore, nanoassembly allows production of nanocomposite materials that may possess attractive optical properties. To study this possibility, ultrathin films with architecture {Au/polymer}n (n = 1-10) were deposited on flat silica substrates, then on optical fibers. Physical measurements of deposited mass were performed with quartz crystal microbalance (QCM). The influence of particle size, number of layers, and,distance from surface on the magnitude of optical signals was investigated by measuring the absorption spectrum for each configuration. In addition, sequential and simultaneous bimetallic (Au/Ag) film layering and testing was also completed to assess the effect of nanocomposite metal films on SPR signals. Fluorescent anti-Immunoglobulin G (IgG) antibody was deposited on the outside surface, which was then exposed to IgG for observation of shifting resonance peak due to target binding. The results show that nanoassembly is a promising approach to precise yet cost-effective fabrication of optical biosensors.