Shear-Force Photoacoustic Microscopy: Toward Super-resolution Near-Field Imaging

Abstract

© 2022 Wiley-VCH GmbH.Optical-resolution photoacoustic microscopy (OR-PAM) enables both high-resolution and high-contrast imaging of optical chromophores ranging from biological tissues to inorganic samples. The lateral spatial resolution of OR-PAM depends on its optical configuration and is primarily determined by the numerical aperture of the objective lens. This study demonstrates a novel, lens-free, shear-force photoacoustic microscopy system using a tapered fiber, serving as a proof-of-concept toward the implementation of super-resolution, near-field scanning photoacoustic microscopy. An uncoated tapered fiber is attached to a quartz tuning fork, thereby maintaining the near-field distance between the fiber and sample surface via a shear-force detection mechanism. Light-field simulation confirms an evanescent wave at the end of the uncoated, tapered fiber. Based on the photoacoustic simulation and 2D photoacoustic scanning experimental results, targets are imaged with high-lateral resolutions of the order of 1.0 ± 0.3 µm. These results demonstrate the existence of near-field photoacoustic signals and the potential for future development of super-resolution, near-field, scanning photoacoustic microscopy.