Biological auto(chemi)luminescence imaging of oxidative processes in human skin

Oxidative processes in all types of organisms cause the chemical formation of electronically excited species, with subsequent ultra-weak photon emission termed biological auto(chemi)luminescence (BAL). Imaging of this luminescence phenomenon using ultra-sensitive devices could potentially enable monitoring of oxidative stress in optically accessible areas of the human body, such as skin. Although oxidative stress induced by UV light has been explored, for chemically induced stress, there is no in vivo quantified imaging of oxidative processes in human skin using BAL under the controlled extent of oxidative stress conditions. Furthermore, the mechanisms and dynamics of BAL from skin have not been fully explored. Here, we demonstrate that different degrees of oxidative stress on the skin can be spatially resolved quantitatively through non-invasive label-free BAL imaging. Additionally, to gain insight into the underlying mechanisms, a minimal chemical model of skin based on a mixture of lipid, melanin, and water was developed and used to show that it can be used to reproduce essential features of the response of real skin to oxidative stress. Our results contribute to novel, noninvasive photonic label-free methods for quantitative sensing of oxidative processes and oxidative stress.