Microbubble whispering gallery mode resonator as an all-optical platform for the characterisation of photoacoustics contrast agents

This article presents a microbubble resonator (MBR) as an all-optical ultrasound transducer specialized for the characterisation of photoacoustics (PA) contrast agents. In the presented proof-of-concept experiment, a well-known contrast agent (gold nanorods, GNRs) was placed within the MBR and acoustic detection was achieved by monitoring an MBR optical resonance, exploiting the MBR mechanical resonances to enhance the transduction mechanism. The read-out signal from the MBR was validated through a numerical simulation and through the reconstruction of the GNRs photostability trend, proving the feasibility of the characterisation. This work sets the stage for the application of the MBR system to a specific task, taking advantage of its promising features: sensitive PA detection, extremely small volume, ease of integration in a microfluidic circuit, absence of acoustic matching material and scalability