Label-free visualization and quantitative analysis of Far UV-C skin safety with dynamic optical coherence tomography with subcellular resolution

The recent COVID-19 pandemic sparked interest in interventional public health measures like ultraviolet germicidal irradiation (UVGI) of occupied spaces with the development of Far UV-C (200-230 nm) emitting sources promising similar antimicrobial properties as conventional (254 nm) disinfecting lamps without adverse effects on human skin. When investigating the impact of different UV irradiation parameters, the visualization of cellular damage, like apoptosis and formation of photoproducts, currently requires immunohistochemical tissue processing and is of an invasive nature. Dynamic-microscopic optical coherence tomography (dmOCT) is a non-invasive technique that generates label-free images based on the dynamic scattering properties of cells. In this study, we expose an in-vitro human skin model to either UV-A/B or Far UV-C to demonstrate the ability of dmOCT to visualize cell death, followed by UV-induced photodamage, and perform immunohistochemical analysis. Our results clearly show a change in dynamic contrast within the viable epidermis and changes in the morphology of keratinocyte nuclei after UV-A/B exposure with 250 mJ/cm², which were observable in the histology as well. In contrast, exposure to 2000 mJ/cm² of Far UV-C did not have an effect on keratinocytes within the epidermis in either the dmOCT imaging or the immunohistochemistry experiment. In addition to demonstrating Far UV-C skin safety, these findings highlight the potential of dmOCT to assess tissue damage and viability non-invasively.