Highly sensitive imaging for ultra-weak photon emission from living organisms

•The history of imaging technology in the field of ultra-weak photon emission (UPE) analysis is reviewed.•A variety of spontaneous UPEs from living organisms has been studied, however it has still been under fundamental research.•Historical aspect of UPE imaging is helpful for further progress of the application of UPE for diagnosis.

Spontaneous ultra-weak photon emissions (UPEs) are from living organisms. Often designated as biophoton emissions, they are associated with reactive oxygen species production. They have long been explored for use in the extraction of pathophysiological information of living bodies. Because of its potential non-invasiveness and because it is completely passive, it has been anticipated for application to human diagnosis. However, because of the weakness of its signal and the complexity of the mechanisms, practical applications of UPE and efforts have remained restricted.Imaging of UPE is a powerful tool for the practical application of UPE. Furthermore, efforts to develop imaging technique have been made from the early period of UPE study. This report explains the history of UPE study, particularly describing the development of imaging technology and its application covering agriculture and medicine are reviewed. Furthermore, the issue of what was achieved and what is necessary for the additional advancement of UPE will be discussed for practical application.