All-optical photoacoustic sensing with hollow microresonators

We developed an all-optical photoacoustic (PA) sensing platform based on whispering gallery mode (WGM) hollow resonators able to detect plasmonic nanoparticles in microfluidics. A silica microbubble resonator (MBR) made on a capillary and exhibiting high optical and mechanical Q factors acts as a unique ultrasound transducer for photoacoustic characterization of metallic nanoparticles. The system was tested with gold nanorods (GNR) placed inside the MBR and acoustic detection was achieved by monitoring the enhanced modulation of the optical resonances at the microbubble mechanical eigenfrequencies.