Free-Standing Single Ag Nanowires for Multifunctional Optical Probes

Miniaturized and manipulable optical probes are the foundation for developing in situ characterization devices in confined space. We developed two methods for fabricating free-standing single Ag nanowires (AgNWs) directly at the tip of a glass capillary either by chemical or electrochemical reduction. The electrochemical nature of both methods resulted in a rapid growth rate of AgNWs up to 1.38 μm/s and a controllable length from 5 to 450 μm. The AgNWs with a unique anisotropic structure allow localized surface plasmon resonance and surface plasmon waveguides in the radial direction and axial direction, respectively. We verified the possibility of using single AgNWs as an optical dispersion device and waveguide probe. By controlling the experimental conditions, rough-surface AgNWs with high surface-enhanced Raman scattering (SERS) activity were also fabricated. These SERS-active probes also exhibited advantages in acquiring molecular information from a single living cell.