Shear‐Force Photoacoustic Microscopy: Toward Super‐Resolution Near‐Field Imaging

Abstract

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.

Functional photoacoustic imaging: from nano- and micro- to macro-scale

“…DP-pAFM, dual-pulse photoactivated atomic force microscopy; NSPM, near-field scanning photoacoustic microscopy; PA, photoacoustic. The images are reproduced with permission from [ 24 , 27 , 28 ] …”

“…However, because pAFM or AFM-IR indirectly measures the PA effect in the sample through a cantilever tip, errors can be introduced by probe defects. Our group has presented a solution to the probe defect issue in a study on near-field scanning photoacoustic microscopy (NSPM) [ 27 ]. NSPM directly acquires PA signals by bringing a tapered optical fiber to within a few nm of the sample surface, without the use of a lens (Fig.…”

High-resolution label-free ultraviolet photoacoustic microscopy via an ultraviolet-transparent ultrasound transducer

“…Photoacoustic (PA) imaging, relying on the PA effect from light absorption by contrast agents or molecules within tissue, offers non-invasive insights into biological specimens. [1][2][3][4][5][6][7][8] Ultraviolet photoacoustic microscopy (UV-PAM) stands out among PA imaging systems, presenting label-free, histology-like images, particularly highlighting cell nuclei due to their UV light absorption. 9 UV-PAM is gaining attention as an alternative to conventional histopathology, with significant potential for streamlined intraoperative frozen section (FS) diagnosis.…”

An Ultraviolet‐Transparent Ultrasound Transducer Enables High‐Resolution Label‐Free Photoacoustic Histopathology

“…[1] The specific PA excitation is highly dependent on the wavelength of the light. Among the various PA DOI: 10.1002/lpor.202300652 imaging systems, [2][3][4][5][6][7][8][9] ultraviolet photoacoustic microscopy (UV-PAM) stands out as a label-free imaging modality capable of producing histology-like images of biological specimens. Because nucleic acids in cell nuclei exhibit strong light absorption at UV wavelengths, the UV-PAM highlights cell nuclei without requiring additional labeling, [10,11] providing a contrast comparable to that achieved by the hematoxylin and eosin (H&E) staining widely used in conventional histology.…”