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

Ultraviolet photoacoustic microscopy (UV-PAM), based on the high intrinsic optical absorption of DNA/RNA, holds great promise for intraoperative label-free histopathological imaging modalities. Although clinical histopathology requires high-resolution images to observe individual cell structures, conventional UV-PAM suffers from relatively low resolution compared to the clinical histological modalities. Notably, opto-ultrasound beam combiners or ring-shaped ultrasound transducers, which have been used as geometrically coaxial methods of conventional reflection-mode UV-PAMs, restrict the numerical apertures (NA) due to their long working distances and/or hollow structures. Here, an ultraviolet-transparent ultrasound transducer (UV-TUT) is demonstrated that enables high-resolution reflection-mode UV-PAM by improving the NA (0.38) and consequent spatial resolution (0.47 ± 0.03 µm). The study has successfully demonstrated its superior performance with mouse brain tissue and performed photoacoustic histopathology with cancerous animal tissues. This work proposes the ultimate form of a label-free reflection-mode UV-PAM system with the potential to boost the practical use of intraoperative photoacoustic histopathology.