Zhang's lab develops two core optical technologies: spectroscopic single-molecule localization microscopy (sSMLM), which multiplexes emission-spectrum measurement with single-molecule localization to reach ~5 nm spatial resolution, and visible-light optical coherence tomography (vis-OCT), which exploits higher tissue contrast at visible wavelengths for micron-scale retinal and tumor-vasculature imaging in patients. Applications span cancer nanopathology and ophthalmology, including in-vivo human retinal oximetry.