Why is ultraviolet light used to kill bacteria?

For decades, bacteria-killing UV light has been used to disinfect various objects and surfaces, but how does it work and why does it kill bacteria? bacteria, first of all we also learn some knowledge about UV rays.

What is a UV lamp?

Light is a small part of the electronic spectrum and it covers all types of electronic radiation. However, not all of these radiations are visible to the naked eye. The colors we see make up the visible light portion of the spectrum, which is organized based on the energies, wavelengths, and frequencies of each type of radiation.

Electromagnetic spectrum

Ultraviolet rays are light with wavelengths shorter than visible light but longer than X-rays. UV light has a wavelength range between 200-400 nm and is classified into UVA, UVB, and UVC. In which UVC has the shortest wavelength (200-280 nm), followed by UVB (280-320 nm) and then UVA (320-400 nm). One factor that makes UV light different from regular visible light is its ionizing power, which means it can charge or "ionize" the molecules it comes in contact with. Also, another point to note is that the energy is inversely proportional to the wavelength, the shorter the wavelength, the more energy the light has, which means UVC rays have the most energy but the potential to harm The living organism is also the largest.

Surely you've also heard that UV rays say they're harmful and that's why we need to wear sunscreen when going out in the sun. In fact, although UVB causes sunburn, moderate exposure to UVB rays helps the body synthesize vitamin D, which also explains why doctors often recommend that we should be exposed to sunlight. certain levels of sunlight to enhance or maintain vitamin D levels.

The sun is our biggest source of light.

The sun produces many types of light, of which there are 3 types of UV rays, of which UVC rays are the most harmful and some UVB rays are reflected by the ozone layer of the Earth's atmosphere. Most of the UV rays that reach the surface of the planet have up to 95% of UVA rays, it is the least harmful to us. As for UVC light, its high energy characteristics make for the most impressive microbiological killing.

How to kill bacteria by UV rays

DNA and some proteins inside the bacteria can absorb these ionizing UVC rays, causing structural damage. DNA is made of nitrogenous bases called purines and pyrimidines; adenine (A), thymine (T), guanine (G) and cytosine (C). A and G are purines, while C and T are pyrimidines. These bases work in pairs, where A complements or opposes the T on the DNA molecule, as opposed to G and C. Billions of bases bond together in all possible combinations to make up the bases. DNA sequence.

DNA structure

When absorbing UVC rays, the most affected fractions are where adjacent pyrimidines reside, which would cause two adjacent hymines to bind together and isomerize, rather than bind to the opposite element. . Other bases are also affected but the TT dimer is most commonly formed, creating collisions in the DNA strands that conflict with natural DNA replication processes.

UVC rays form the dimer thymine

In the case of non-replicating DNA, the bacteria cannot replicate and will eventually die, to be more precise, exposure to UVC rays will cause DNA mutations. As bacterial cells develop more and more mutations in their DNA, they signal themselves to undergo apoptosis - the process of programmed cell death. At this time, the cells will not multiply and the DNA replication is also hindered, as a result, they kill themselves. UVC rays can cause cell mutations in just a few minutes, while UVA and UVB rays can also damage DNA but are not as effective as UVC rays.

UV rays cause DNA damage

How effective is UVC sterilization?

Whether UV sterilization is effective or not depends on the exposure time and the material of the subject. UVB and UVC rays will be shielded so if we are protected with glasses, we will not get sunburned. But UVA rays can pass through because their wavelength is similar to normal light, so if you shine UVC rays through a glass window, there is no effect.

UV rays are most effective at disinfecting hard and flat surfaces, so if you want to disinfect thoroughly, UVC rays need to reach all surface areas that need to kill bacteria. Rough surfaces or objects with grooves and ridges are not accessible to UV rays, which means bacteria in those areas still exist.

In addition, another important factor is the time of exposure to UV rays, it is necessary to expose the surfaces to be disinfected to UV rays for a few minutes, if only the direction of the UV rays for about 5-10 seconds will not be able to remove them. effectively duplicate.

Pocket UV lamp

Current household UV devices, although advertised by manufacturers as effective, are not in reality. Researchers have found that it is not always possible to kill 99.9% of bacteria in just a few seconds. These inefficient devices usually only kill 50% of bacteria. To maximize the effect, you need to increase the UV exposure time to at least 10-15 minutes.