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

We implement a whispering-gallery-mode microbubble resonator (MBR) as a multifunctional component for all-optical photoacoustic inspection of materials in a platform combining microfluidic design and high sensitivity to spectral absorbance. In our setup, the MBR acts both as the acoustic transducer and as the vial for a sample causing the photoacoustic event, thus dictating its operational frequency and removing any need for impedance-matching media. We challenge our setup in the assessment of the photostability of gold nanorods to demonstrate its validity. We develop a numerical model to qualitatively interpret the experimental signal as a transient shift of the resonance condition of the MBR. Possible implementations of the MBR in photoacoustic sensors are discussed.