Characterizing UV-induced photodamage to improve long-term, dynamic live cell imaging with UV microscopy

Ultraviolet (UV) microscopy of live cells has been challenging due to phototoxicity, with UV radiation affecting cellular components leading to irreversible cell death. Despite this challenge, recent advances in UV light sources and detectors have renewed interest in UV microscopy due to its high resolution and label-free molecular imaging capabilities. Indeed, UV microscopy has been recently demonstrated for a wide variety of cellular imaging applications, including multispectral imaging of cancer tissue sections, cells at varying time scales, and hematological analysis of whole blood cells. While these studies have leveraged UV microscopy to image static samples and cellular dynamics over short periods of time, UV phototoxicity remains a problem during live cell imaging sessions lasting over several hours and longitudinal imaging of a single sample. In this work, we characterize UV-induced photodamage by quantifying the flux required for cell death at notable wavelengths in the deep-UV region. We demonstrate how this flux can vary with cell adherence type using adherent and non-adherent cell lines. We then present fractionation studies conducted over time scales ranging from several hours to days and discuss the ability of cell populations to recover in each case. Finally, we provide viable live-cell imaging frameworks for UV microscopy applications ranging from single multispectral imaging sessions to long-term observation of samples.