All living things, including humans, constantly emit a ghostly glow 鈥� and it appears to vanish almost as soon as we die. Monitoring this signal could one day help track forest health or even detect diseases in people.
The existence of this barely perceptible glow has been controversial, but it is thought to be the result of a process called ultraweak photon emission. Mitochondria and other energy-producing machinery in our cells involve molecules gaining and losing energy, in turn emitting the equivalent of a few photons a second per square centimetre of skin tissue. However, these 鈥渂iophotons鈥� are extremely difficult to detect and disentangle from other biological processes or light sources, such as the radiation produced by any warm object.
Now, at the University of Calgary in Canada and his colleagues have isolated what happens to these biophotons when an animal dies, imaging ultraweak photon emission across an entire mouse before and after its death. 鈥淭he fact that ultraweak photon emission is a real thing is undeniable at this point,鈥� says Oblak. 鈥淭his really shows that this is not just an imperfection or caused by other biological processes. It鈥檚 really something that comes from all living things.鈥�
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Oblak and his team used digital cameras that could detect single photons to produce two hour-long exposure images of four hairless mice, one before and one after death. The animals were kept at the same temperature to exclude heat as a factor and in a dark box to avoid light pollution. They found that biophoton emission significantly decreased after death across the whole mouse.
They also took pictures of umbrella tree (Heptapleurum arboricola) leaves they had cut, and found that the plant鈥檚 injury repair mechanism increased biophoton emission, while various drugs applied to the plant surface, such as the numbing drug benzocaine, also appeared to do the same.
It isn鈥檛 surprising that biophotons stop being emitted when you die because they are a byproduct of metabolic cellular processes that cease after death, says at the Central Laser Facility in Oxford, UK, and previous research has shown this for individual cells and smaller body parts. However, it hasn鈥檛 been done for a whole animal before, and because Oblak and his team have been careful to exclude other potential light sources, we can be confident that we are really seeing biophotons, says Mackenzie.
at the Czech Academy of Sciences in Prague says the absence of biophotons after death is mainly due to the lack of blood flow around the body, because oxygen-rich blood is one of the key drivers of metabolism, which produces biophotons. If the blood had been kept artificially circulating, then they would still observe the same biophoton emission, he says. 鈥淚t鈥檚 not related to the systemic liveliness, it鈥檚 related to the liveliness of the optically accessible tissue.鈥�
The technology could one day be used to monitor living tissue without performing invasive tests, or monitoring forest health from afar at night, says Oblak. 鈥淭he nice thing about ultraweak photon emission is it鈥檚 a complete passive monitoring process.鈥�
The Journal of Physical Chemistry Letters
