Optical-scanning evanescent sensor for high-speed broadband photoacoustic microscopy.

Photoacoustic microscopy with high spatial resolution and fast imaging acquisition allows observing dynamic processes of optical absorption-based microanatomic structures in three dimensions. An evanescent sensor accesses ultrasonic detection with high sensitivity and broad bandwidth while suffering from limited field of view (FOV), thus compromising the photoacoustic imaging acquisition rate. Here, we develop an optical-scanning evanescent sensor by fast deflection of the interrogation light along the interface of prism and water using a one-dimensional galvanometer, demonstrating excellent detection sensitivity of ∼132 Pa with a broadband frequency response of >140-MHz at an enlarged FOV of ∼2.90 × 0.19 mm2. Incorporating the optical-scanning evanescent sensor in photoacoustic microscopy, a volumetric image (∼3.0 × 0.25 × 1.0 mm3) with micrometer-scale spatial resolution is acquired within ∼2.5 s by synergistically scanning both photoacoustic illumination laser and sensor's interrogation light. High-speed imaging of flowing microparticles within a capillary tube offers the visualizations of the traveling processes in three dimensions. Potentially, the optical-scanning evanescent sensor allows photoacoustic microscopy accommodating to dynamic imaging at cellular level such as in vivo flow cytometry of circulating tumor cells. [ABSTRACT FROM AUTHOR]