A Reversible Clearing Strategy Enables Robust Label‐Free Phase Imaging of Thick Tissues

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ABSTRACT Thick biological specimens impose strong scattering and attenuation that severely degrade transmission quantitative phase imaging (QPI) and limit label‐free in vitro tissue slices assessment. We introduce a simple, room‐temperature, reversible optical clearing strategy based on a glycerol‐tartrazine solution (GTS; 60% glycerol, 10% tartrazine) to mitigate these scattering‐driven failure modes and improve phase‐map structural visibility in optically thick samples. As a demanding proof‐of‐concept, we apply GTS to 50–80 µm murine liver‐and‐kidney sections, highly heterogeneous tissues that are particularly challenging for transmission QPI, and show rapid transparency enhancement while preserving morphology. We demonstrate improved high‐throughput examination and reduced phase artifacts after GTS immersion compared with phosphate‐buffered saline (PBS) and a reference clearing protocol using complementary histopathological QPI implementations, Fourier ptychographic microscopy and lensless digital holographic microscopy with pixel‐super‐resolution. Improvements are confirmed quantitatively by a significant increase in the one‐pixel‐lag autocorrelation of phase‐gradient values. GTS is stable for months at room‐temperature; the clearing effect strengthens with immersion time, and its clearing is reversible within ∼15 min by PBS washing, enabling subsequent staining or other multimodal analyses on the same section. Overall, this reversible clearing strategy advances biophotonics, enabling low‐cost, scalable, label‐free quantitative histology and high‐throughput computational tissue imaging in strongly scattering thick specimens.