Resonant Microbubble as a Microfluidic Stage for All-Optical Photoacoustic Sensing

All-optical photoacoustic sensing is emerging as a sensitive technique for inspecting small volumes of fluids, for applications such as liquid biopsies, drug discovery, development of contrast agents for photoacoustic imaging, and analysis of gases. The authors implement a whispering-gallery-mode microbubble resonator as a multifunctional component for all-optical photoacoustic sensing. A laser pulse triggers photoacoustic activation of a sample in the cavity of the resonator, and the transient deformation of the cavity wall as a resonant oscillation is monitored. This configuration promises high sensitivity to optical absorbance, and removes the need for impedance-matched media.