Photothermal Behaviors of Flowing Media Caused by Localized Surface Plasmon Resonance of Au Nanorings

Based on the scanning of photothermal optical coherence tomography (PT-OCT), the photothermal behavior of a flowing medium generated by the enhanced absorption of localized surface plasmon resonance of incorporated Au nanorings (NRIs) is observed. In particular, the effects of air bubble generation and thermally induced bubble size oscillation in a flowing medium through the incorporation of Au NRIs and modulated laser illumination are demonstrated. The size oscillation of the air bubble produces the vibration of the flowing medium, which is synchronized with the laser modulation, for generating PT-OCT signal. At the resonance frequency of flowing-medium vibration, the PT-OCT signal reaches the maximum level. The resonance frequency is related to the mass density and viscosity of the flowing medium and is independent of the flow speed of the medium in a vessel. Such a relation can be used for in situ monitoring the mass density and viscosity of a flowing medium.