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UV Disinfecting Robots

By the end of the year, Singapore will have more than 200 locally made autonomous (self-controlling) UV mobile robots in shopping malls, healthcare, and transportation sectors to help fight against Covid-19. But how do these UV robots actually work?

UV-C bots in hospitals.

Normally UV radiation from the Sun consists of UV-A, UV-B, and UV-C, which are classified as such according to their wavelengths. UV-A has the longest wavelength of 315 to 400 nanometers and accounts for approximately 95% of the ultraviolet radiation that reaches the Earth’s surface. It can penetrate to deep layers of the skin and is responsible for immediate tanning, and contributes to skin aging and wrinkling. UV-B has a medium wavelength range of 280 to 315 nanometers and can be responsible for delayed tanning and burning as well as promotes the development of skin cancer. However, most UV-B rays are filtered out by the ozone. Lastly, UV-C rays have the shortest wavelength ranging from 200 to 280 nanometers and are the most damaging type of UV. However, it is completely filtered out by the ozone layer and therefore does not reach the Earth’s surface.

UV-C rays position in the electromagnetic spectrum.

These robots emit UV-C rays as they are the most biologically damaging. This is due to their short wavelengths as it means that these rays have high frequencies (as the wavelength is inversely proportional to frequency) and therefore are the most energetic.

Because of its high frequency and energy, these rays are good at genetically modifying the genetic material of both viruses and humans. This is due to the fact that wavelengths of 200 to 300 nanometers are strongly absorbed by nucleic acids, particularly pyrimidine nucleic acids: cytosine, thymine, and uracil (RNA). The absorbed energy can then result in defects in the genome including a defect called pyrimidine dimers. These dimers can prevent DNA or RNA replication or can prevent the expression of certain essential proteins which leads to the death of the organism.

UV radiation changes the structure of the DNA of the microorganism through its base-pairs. This change in structure inhibits replication as well as the production of essential proteins which leads to the death of microorganisms.

But what exactly is a dimer? A dimer is when two monomers (single molecule) that are joined together. So pyrimidine dimers are molecular lesions (damage to the structure of biological molecules such as DNA) formed from thymine and cytosine bases in DNA though photochemical reactions (chemical reaction caused by light). The photons in the UV-C rays encourages the formation of a covalent bond between consecutive nucleotides on one strand, which destroys the normal base-pairing in the double-stranded DNA in that structure. It also does the same thing to a particular type of RNA, called dsRNA (double-stranded RNA) by targeting the pyrimidine bases uracil and cytosine. Up to 50 to 100 of such reactions per second can occur during exposure to UV-C rays. This alters the base-pairing and therefore the structure of the DNA or RNA. If uncorrected, these lesions or places of altered base-pairing can inhibit polymerase (an enzyme that synthesizes long chains of nucleic acid using the principle of the base pairs during DNA replication), cause misreading during transcription (first step of gene expression/ to make a protein) or replication, or can even stop DNA or RNA replication. By inhibiting replication as well as the production of essential proteins, the virus cannot replicate itself and therefore is destroyed.

Pyrimidine Dimers caused by UV-C rays. Consecutive pyrimidine bases (thymine, cytosine, and for RNA, uracil) on a single strand form covalent bonds with each other which disrupts the normal base-pairing structure of the double-stranded DNA or RNA.

In short, UV-C can inactivate the virus and destroy it by genetically modifying and manipulating the virus’s DNA or RNA. UV-C rays kill around 99% of the bacteria and have been clinically proven to kill viruses, and therefore it helps decontaminate the environment more efficiently than manual cleaning, protecting the frontline cleaning staff. Usually, complex molecules such as bacteria can often repair the minor breakages within seconds by a reaction called nucleotide excision repair - which is a DNA repair mechanism - or photolyase (DNA repair enzyme) reactivation. However, since viruses are such simple microorganisms, they don’t have these enzymes or those DNA or RNA repair mechanisms. This makes them unable to correct these lesions and therefore cannot repair the damage to their genetic material. This eventually leads to their inactivation and their deaths.

However, these UV-C rays are also dangerous to humans as they can penetrate through the skin and genetically modify human DNA. Pymiramdine dimers caused by these rays can lead to melanoma, a type of skin cancer. Luckily, most of us are unlikely to come upon UV-C rays, as they are filtered out by the ozone layer in the atmosphere long before the radiation encounters our skin.

The atmosphere filters out most of the UV radiation from the Sun. UV-C rays are filtered out before they reach the Earth's surface, preventing any organisms on Earth from encountering this radiation.

These robots will move around autonomously and are guided by light detection and ranging sensors. These sensors are important in so when people are too near to the UV Bot, it can immediately shut off its lamp to prevent any danger. Also, the public will need to keep a 5m distance from the robot and generally won't be near the robot by different methods of separation such as setting up a temporary partition or closing the door to space where the bots are, etc.

"This is just the start. We are already making more robots to introduce to the line-up. PBA will have a family of robots for commercial spaces, on top of hospitals, transport, supermarkets, shopping malls. Eventually, we will be getting the robot into homes," the group's chief executive Derrick Yap told The Straits Times on Thursday, 23rd of April 2020.

How UV-C bots work in homes in Denmark.

Countries such as China, Denmark, and more have already started implementing the use of UV-C robots in their daily routine to decrease the virus from spreading. Hopefully, these UV-C robots will be proven effective in Singapore too, and in our fight globally towards the extermination of Covid-19.

Works Cited

The Strait Times, 23rd April 2020 - UV disinfecting robots to be deployed in fighting Covid-19

BBC Future, Zaria Gorvett, 24th April 2020 - Can you kill coronavirus with UV light?

WHO. “UV Radiation.” Ultraviolet Radiation and the INTERSUN Programme, World Health Organization, 9 Mar. 2016,

“Ultraviolet Germicidal Irradiation.” Wikipedia, Wikimedia Foundation, 18 June 2020,

“Pyrimidine Dimer.” Wikipedia, Wikimedia Foundation, 6 May 2020,

Images Used

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