Subwavelength-resolution label-free photoacoustic microscopy of optical absorption in vivo

TLDR

Optical absorption provides essential biological information, yet conventional optical microscopy cannot detect it directly and relies on fluorescence or scattering that often require labeling. The study develops in vivo subwavelength‑resolution photoacoustic microscopy (SW‑PAM) to achieve high optical‑absorption contrast without labeling. SW‑PAM attains subwavelength resolution by detecting acoustic signals generated from the optical absorption of endogenous pigments. SW‑PAM reaches diffraction‑limited resolution, resolves subcellular organelles, images vasculature and early‑stage melanoma with 12:1 and 17:1 contrast ratios without labeling, and its ability to span micro‑ to macro‑scales may accelerate clinical translation.

Abstract

Optical absorption provides essential biological functional information but cannot be sensed by mainstream optical microscopy technologies directly, which detect fluorescence or scattering and may require undesirable labeling. Here we developed in vivo subwavelength-resolution photoacoustic microscopy (SW-PAM) that provides exquisitely high optical-absorption contrast due to nonfluorescent, or fluorescent, endogenous pigments. Having approached the ultimate diffraction-limited optical resolution, SW-PAM can resolve subcellular organelles. Vasculature and early-stage melanoma were imaged with 12:1 and 17:1 contrasts, respectively, without labeling. SW-PAM along with the scaled-up macroscopy, as the only technology that measures the same contrast origin over such a wide length scale, can potentially accelerate translation from microscopic research to clinical practice.