How Does 405nm Lighting Destroy Bacteria?

How Does 405nm Light Destroy Bacteria?

The mechanism of bacterial inactivation is thought to be by photo-stimulation of endogenous intracellular porphyrins, which leads to the generation of reactive oxygen species (ROS). This is illustrated in the diagrams in the figure below. Numerous studies have been done to better understand and verify this mechanism for how 405 nm light can deactivate bacteria.

Step 1: A porphyrin is exposed to 405nm light

Step 2: Reactive Oxygen Species (ROS) are then formed that can attack the cell

A porphyrin is a large ring molecule consisting of four pyrroles, which are smaller rings made from four carbons and single nitrogen. These pyrrole molecules are connected together through a series of single and double bonds which forms the molecule into a large ring. Porphyrins are capable of absorbing certain wavelengths of light, especially when associated with different ions. Porphyrins cause both the red color of blood and the green color of plants. Porphyrin molecules serve a number of purposes in animals, plants, and even bacteria. For this reason, porphyrin is considered an evolutionarily conserved molecule. This means that because of its usefulness, countless lines of organisms have used and modified porphyrins to fit their needs.

A porphyrin molecule is an organic molecule that must be created and destroyed by specific proteins. Because proteins are programmed by the DNA, any mutations in the DNA can cause malfunctions in the protein which processes porphyrin molecules. While usually extremely helpful, a porphyrin which hasn't formed properly or cannot be broken down poses a serious threat to the body. Porphyrin molecules are highly interactive. They can disrupt the cell membrane, and because they hold an iron molecule with the potential to act as an electron sink, they encourage the formation of free radicals.

Laboratory studies have shown that a range of light wavelengths in the region of 400-425nm can be used for bacterial inactivation, but optimal antimicrobial activity has been found at 405 nm. This peak in activity correlates with the absorption maximum of porphyrin molecules which react with oxygen or cell components when exposed to light at this wavelength causing oxidative damage to the cell membrane and microbial cell death. Bacteria use porphyrins in a similar way to animal cells, although the final molecules they use may look very different from those in animals. Certain bacteria also have the ability to photosynthesize, and like plants, they use porphyrins to capture the energy of the sun.

Among the ROS,·OH is the most potent damaging radical which can react with all biological macromolecules (lipids, proteins, nucleic acids and carbohydrates). It is highly reactive and can lead to the formation of DNA-protein cross-links, single- and double-strand breaks, base damage, lipid peroxidation and protein fragmentation. Bacteria are more susceptible to this oxidative stress than human tissue due to fewer antioxidants and less efficient repair mechanisms.

Research published in 2018 has shown that airborne cells are 3-4 times more susceptible to 405 nm light than samples in liquids or on surfaces.11 Results demonstrated successful aerosol inactivation, with a 99.1% reduction achieved with a 30 minute exposure to an irradiance of 22 mWcm2.