(Digital Presentation) Fabricating SERS-Active Nanofibers Covered with Au Nanoparticles for SERS Optophysiology

Abstract

Nanofibers as biosensors have attracted great attention due to its facile removal from the biosystem after a period of intra- or extracellular measurements and site-specific measurement among others. The application of nanofibers covered with Au nanoparticles as SERS sensor circumvents the aggregation and accumulation of Au nanoparticles in vitro or in vivo, in addition to the greater Raman enhancement of signal than on planar surface. We report here on a strategy using block copolymer brush-layer templating and ligand exchange for fabricating highly reproducible and stable SERS-active nanofibers with tip diameters down to 60 nm and covered with well-dispersed and uniformly distributed branched AuNPs, which have intrinsic hotspots favoring inherently high plasmonic sensitivity. In addition, AuNPs with tunable morphology and adjacent spacing on the nanofibers can be adjusted using an in situ growth technique, thereby enhanced SERS sensitivity was obtained due to the asymmetric structure and coupling between the adjacent AuNPs. Tunable AuNP morphologies and hence the optical characteristics of the AuNPs on the nanofibers can be easily controlled by choice of experimental parameters, particularly the growth time. Besides, finite difference time domain (FDTD) simulations were performed to gain more insight into the electric-field enhancement of AuNPs on the high-curvature substrates. Furthermore, SERS application of these nanosensors in pH sensing and Hg2+ detection is demonstrated here, offering appealing and promising candidates for real time monitoring of extra/intra-cellular species in vitro or in vivo. In addition to SERS sensing, these highly uniform nanosensors have other far-reaching implications, including medical diagnostics, therapeutics and so on.