ABSTRACT
The inactivation of pathogens through the irradiation of ultraviolet light depends on how light propagates within the medium where the microorganism is immersed. A simple geometrical optics analysis, and a fluence evaluation reveal some reservoirs where the pathogen may hide and be weakly exposed to the incoming radiation. This geometrical hide-outs also generate a tail in the plot of the total inactivation plot vs. the incoming fluence. We have analyzed these facts using geometrical optics principles and illumination engineering computational packages. The results obtained from previous biomedical measurements involving SARS-CoV-2 have been used to evaluate the inactivation degree for an spherical geometry applicable to airborne pathogens, and for an spherical cap geometry similar to that used in biomedical experiments. The case presented here can be seen as the worst-case scenario applicable under collimated illumination.
ABSTRACT
The optical absorption coefficient of culture media is critical for the survival analysis of pathogens under optical irradiation. The quality of the results obtained from experiments relies on the optical analysis of the spatial distribution of fluence which also depends on the geometry of the sample. In this contribution, we consider both the geometrical shape and the culture medium's absorption coefficient to evaluate how the spatial distribution of optical radiation affects pathogens/viruses. In this work, we exposed SARS-CoV-2 to UV-C radiation ([Formula: see text] = 254 nm) and we calculated-considering the influence of the optical absorption of the culture medium-a characteristic inactivation fluence of [Formula: see text] = 4.7 J/m2, or an equivalent 10% survival (D90 dose) of 10.8 J/m2. Experimentally, we diluted the virus into sessile drops of Dulbecco's Modified Eagle Medium to evaluate pathogen activity after controlled doses of UV irradiation. To validate the optical absorption mode, we carried out an additional experiment where we varied droplet size. Our model-including optical absorption and geometrical considerations-provides robust results among a variety of experimental situations, and represents our experimental conditions more accurately. These results will help to evaluate the capability of UV disinfecting strategies applied to a variety of everyday situations, including the case of micro-droplets generated by respiratory functions.