Oblique white light (OWL) microscopy for rapid, slide-free histology of fresh tissue

Oblique White Light (OWL) microscopy is a low-cost, slide-free imaging technique that enables real-time, H&E-like visualization of thick, unsectioned tissue. Using oblique white-light epi-illumination and an RGB camera, OWL captures high-resolution color images without requiring fixation, slicing, or complex optics. The system retrofits standard inverted microscopes for ~$50, making it accessible for widespread adaptations and low-resource settings. Validated across multiple mouse organs, OWL images closely resemble traditional FFPE histology in contrast and morphology. Optimal staining protocols achieve nuclear density and stain infiltration similar to FFPE slides. OWL supports imaging from 2.5X to 40X, enabling both widefield and cellular-level views. The approach is non-destructive and compatible with standard histology stains, allowing downstream FFPE or molecular analyses. With its speed (