Isometrically Resolved Photoacoustic Microscopy Based on Broadband Surface Plasmon Resonance Ultrasound Sensing

Photoacoustic microscopy (PAM) can measure optical absorption-based molecular specificities within tissues. Despite the diffraction-limited lateral resolution in optical-resolution photoacoustic microscopy (OR-PAM), the ongoing challenge is poor axial resolution because of an insufficient ultrasound detection bandwidth, which hampers PAM volumetric imaging. We propose polarization-differential surface plasmon resonance (SPR) sensing for broadband and high sensitivity photoacoustic (PA) detection, allowing OR-PAM with comparable resolution along lateral and axial directions. This sensor possesses an estimated noise-equivalent-pressure sensitivity of similar to 477 Pa over an approximately linear pressure response up to 107 kPa. Moreover, an improved PA detection bandwidth of similar to 173 MHz permits an axial resolution (similar to 7.6 mu m) that approaches the lateral resolution (similar to 4.5 mu m) of our OR-PAM system. The capability in spatially isometric micrometer-scale resolution enables in vivo volumetric label-free imaging of the microvasculature of a mouse ear. The SPR sensing technology promises broader applications of PAM in biomedical studies such as microcirculation.