Ultraviolet Light and Transilluminators

Ultraviolet Light

Ultraviolet (UV) light is non-ionizing radiation, emitted by the sun and some artificial sources. Some lasers, incandescent, halogen, fluorescent, and mercury vapor lamps serve as artificial sources of UV radiation. The light is classified into UVA, UVB, and UVC. The wavelength of UVA is 315-399 nm. The wavelength of UVB is 280-314 nm. Then, the wavelength of UVC is 100-279 nm. Around all of the UV radiation falling on the earth is UVA since UVB and UVC are mostly absorbed by ozone. Continuous exposure to UV light can cause premature aging, sunburn, skin cancer, eye diseases, melanoma, squamous cell cancer, and basal cell cancer.

UV Transilluminator

A UV transilluminator is a typical equipment present in biosciences laboratories for the visualization of target proteins and DNA. The transilluminator utilizes intense UV irradiation to make visible the fluorescent tags used in gels. Ethidium bromide is a commonly used fluorescent marker in the laboratory for visualization under UV transilluminator.

Specifications of UV Transilluminator

• Depending on the type and amount of sample, the UV transilluminator is operated in any of the three wavelength bands. 254, 312, and 365 nm are typical wavelengths. 312 nm are used for standard gel documentation in the gel doc system. This corresponds to ethidium bromide’s fluorescence excitation peak. 254 nm is used in crosslinking applications as it causes higher DNA damage. The intensity of illumination can be selected using high, medium, or low levels.
• High intensity provides imaging with a lower concentration of the sample. However, this mode is not recommended during longer exposure times. Medium intensity is good to view a single bank quickly. Lower intensity focuses on photography on multiple bands and is suggested for use during the availability of higher sample amounts. Also, it is used when the signal of the fluorescence is weaker.
• Extraordinary uniform intensity can produce high-quality images. Multiple gels can be placed on the surface with uniform illumination of each lane and gel. The coefficient of variance is less than 5% in uniformity for the full filter area.
• Low performance transilluminators have 8 watt bulbs, whereas high performance transilluminators can have more bulbs with each up to 25 watt. Background noise signal is the lowest in the case of high performance ones.
• Mini UV transilluminators are also there. It comes in handy during basic documentation and preparative tasks. It can also serve as a precursor visualization before the main experiment as unwanted parts of the gel can be cut after the visualization. The size and illumination area are also lesser. It is used to save bench space. In addition, it is easier to clean. Besides, they are tiltable and movable.
• To prevent the risk of exposure to UV radiation, UV-to-blue converter plates can be placed on top of a transilluminator for conversion of UV to blue light. In addition, an amber filter should also be attached for visualization. They serve as a cheaper counterpart to blue LED transilluminators. 
• Another is the UV-to-white converter plate, which converts UV to white light and is used in viewing colored dyes in table models. It is utilized to view colored samples like coomassie blue or silver stained gels. It serves as a cheaper alternative to white LED transilluminators.
• The size of the UV transilluminator may range from 8*8 cm to 25*25 cm. The base of the transilluminator is light-absorbing via painting. 

Use and Applications of UV Transilluminator

The main usage of a UV transilluminator is in the visualization of protein and DNA polyacrylamide and agarose gels after the process of electrophoresis. It is used for gel electrophoresis, protein fluorescence, and gel fluorescence. It is predominantly used when ethidium bromide is used as a fluorescent tag. It is used to find out the tumor and facilitate medical inspection. It provides researchers with the compact footprint of the gel. The gels are placed directly on the surface of the UV transilluminator. But the wavelength will change depending on the specific application. 

When a transilluminator is illuminated at the wavelength of 365 nm, there is no occurrence of photonicking, thus facilitating the usage of UV radiation for extended periods. This can be used for routine imaging in a gel documentation system. A wavelength of 302 nm is useful for fast observation of a single band.  Illumination at 245 nm can be used for the recording of gels. 

Transilluminators  are used for the below mentioned purposes:

• Chemiluminescence western blot
• Multiplex fluorescence,
• DNA gels 
• Protein gels 
• Plant imaging 
• Fluorescent dyes 
• Colorimetric imaging 
• Counting of colony
• Gel to gel comparison
• PCR product sizing
• Verification of integrity of RNA after extracting
• Purification of DNA fragments after digestion using restriction enzymes
• Quantification of DNA
• Plaques or colonies on agar petri plates

Choosing a UV Transilluminator for a Gel Imaging System

For different sizes of gels, the viewing surface area differs. Wavelength also differs as the concentration and purpose of gel imaging change. Some transilluminators have a single wavelength, while some have a facility for dual wavelengths. The dimensions of the benchtop unit also vary as some are very compact, while some are elongated. In addition, some models are stationary, whereas some are hand-held/portable. Some models have an option of variable intensity setting, whereas some are without the choice of intensity setting. Some models have options to choose high, medium, and low levels of intensity of irradiation. Some models have only a high level of setting. The switch on the transilluminator is called triple intensity or dual intensity switch or single intensity switch depending on the option of having wavelengths. Smaller size transilluminators can accommodate midi and mini-sized gels. For highly demanding experiments, stationary ones are chosen.

Protection while handing Transilluminator

Since intense UV light is used for visualization of fluorescent markers used in agarose gel electrophoresis, the radiation is perilous to both eyes and skin. Hence, a UV blocking cover is provided with each transilluminator. If the instrument is used without putting the cover or if there is no cover, then it is compulsory to protect the exposed eyes and skin of the operator. Users should be made aware not of the glass door in the transilluminator in cutting the gel.

Protection is done by wearing:

• A face shield
• Long laboratory coats and sleeves
• Heavy-duty laboratory gloves
• Smart glasses if given by the provider

Conclusion

From the above paragraphs, we come to know about the specifications and applications of UV transilluminators. This type of illuminator is cheaper compared to LED light transilluminators. But choosing an ethidium bromide fluorescent tag for UV light illumination compromise on disposal of gel and the safety of the operator.