Bidirectional quantitative scattering microscopy

Quantitative phase microscopy (QPM) and interferometric scattering (iSCAT) microscopy are powerful label-free imaging techniques that are widely used in biomedical applications. Each method, however, possesses distinct limitations: QPM, which measures forward scattering (FS), excels at imaging microscale structures but struggles with rapidly moving nanoscale objects, whereas iSCAT, based on backward scattering (BS), is highly sensitive to nanoscale dynamics but lacks the ability to comprehensively image microscale structures. Here, we introduce bidirectional quantitative scattering microscopy (BiQSM), an approach that integrates FS and BS detection using off-axis digital holography with bidirectional illumination and spatial-frequency multiplexing. BiQSM achieves spatiotemporal consistency and a dynamic range 14 times wider than QPM, enabling simultaneous imaging of nanoscale and microscale cellular components. We demonstrate BiQSM's ability to reveal spatiotemporal behaviors of intracellular structures and small particles using FS and BS images. Time-lapse imaging of dying cells further highlights BiQSM's potential as a label-free tool for monitoring cellular vital states through structural and motion-related changes. By bridging the strengths of QPM and iSCAT, BiQSM advances quantitative cellular imaging, opening avenues for studying dynamic biological processes.