Parallel multilayer photoacoustic microscopy of slide-free histology using a droplet-shaped UV beam.

Label-free and slide-free histological imaging of surgical tissues is vital for guiding surgical decisions during tumor resection. UV photoacoustic microscopy can be employed to discern atypical cytologic characteristics without using exogenous contrast agents, but the narrow depth of field limits image quality and delays histological visualization when scanning unprocessed tissue specimens with large thicknesses and irregular surfaces. Here, we develop a liquid crystal-based metalens for precise wavefront engineering of the incident UV light to create a droplet-shaped photoacoustic excitation beam. An axially extended depth of field with subcellular lateral resolution is achieved using multiple optical foci during photoacoustic microscopy, enabling parallel discrete multilayer imaging of slide-free specimens. Fast and accurate observations of microarchitectural details offer label-free high-throughput histology insights of unprocessed human glioma specimens without sectioning and staining, demonstrating the feasibility of rapid multilayer histological imaging in thick tissues and supporting the future development of intraoperative pathological assessment techniques.