Biophoton

Biophotons are tiny particles of light produced by biological systems. The name comes from the Greek words "bios," meaning life, and "phos," meaning light. These photons exist in the ultraviolet and visible light ranges. While they are a type of bioluminescence, they are much weaker than typical bioluminescence. Most bioluminescent systems, like those using luciferin and luciferase, are bright enough to see with the naked eye. In contrast, biophotons are non-thermal and extremely faint. Scientists often call this phenomenon ultraweak photon emission, or UPE.

To understand how biophotons are created, we must look at chemical reactions inside cells. A common process is chemi-excitation caused by oxidative stress. This involves reactive oxygen species, which are highly reactive molecules. These species can cause reactions through enzyme catalysis using peroxidase or lipoxygenase. These chemical events can create triplet excited species. When these species return to a lower energy level, they release photons. This mechanism is very similar to phosphorescence, where an object glows after absorbing light.

Researchers can observe these emissions using highly sensitive equipment. Because the light is so faint, standard cameras cannot see it. Scientists use photomultiplier tubes to measure emissions from fish eggs, animals, and humans. They also use ultra low noise CCD cameras to create images. For example, imaging plant materials might require an exposure time of 15 minutes. Some specialized Electron Multiplying CCD cameras, or EM-CCDs, are used to detect light from yeast cells as they begin to grow.

The study of biophotons has a long history. In the 1920s, the Russian embryologist Alexander Gurwitsch discovered ultraweak photon emissions in the ultraviolet range. He called them "mitogenetic rays." He believed these rays helped stimulate cell division. For this discovery, Gurwitsch was awarded the Stalin Prize in 1941. Later, in the 1970s, Fritz-Albert Popp studied these emissions at the University of Marburg in Germany. He found that the light spans a wide spectral distribution from 200 to 750 nm. However, his claims regarding the coherence of the light were criticized for lacking scientific rigor.

Biophotons provide significant data regarding the health of living organisms. In plants, imaging biophotons from leaves helps scientists assay R gene responses. These genes and their proteins help plants recognize pathogens. This triggers a defense signaling network known as the hypersensitive response. This response involves the generation of reactive oxygen species. Biophotons have also been seen in the roots of stressed plants. For instance, a rapid rise in temperature can induce biophoton emission due to oxidative stress.

Measuring these emissions has important scientific and medical value. One emerging technique is photoencephalography. This method tracks ultraweak biophoton emissions originating from the human brain. It offers a non-invasive way to study neural activity. Additionally, monitoring UPE provides a low-cost, label-free way to track drug therapies. This is especially useful for studying pharmacological interventions in diseases involving a reactive oxygen species response.

There is an ongoing debate about whether biophotons help cells communicate. Some hypothesize that injured cells release light as a "distress signal" due to high oxidative stress. However, this mechanism has not been fully demonstrated. Some scientists criticize the communication theory because the signals are much weaker than natural background illumination. It is very difficult to separate these tiny signals from the many other chemical interactions happening between cells. Therefore, the idea that biophotons facilitate cellular communication remains under investigation.