This technote compares the bacterial disinfection efficacy of UV-LED lamps with that of UV discharge lamps, specifically mercury lamps.
UV discharge lamps have been widely used for disinfecting fruit, vegetables, processed food, and equipment surfaces. The UVC region of the spectrum (200-280 nm) is the most effective for killing bacteria, as the bacteria’s DNA has a peak absorption at 265 nm. The most commonly used UV discharge lamp is the Mercury Discharge Lamp, which has a high-intensity UVC radiation at 254 nm. Although the peak emission of a mercury lamp does not precisely coincide with the peak absorption of the bacteria's DNA, it is sufficiently close that it could inflict severe damage and destroy them. However, there are some limitations for the mercury lamp, which are listed as follows:
L'ampoule de la lampe au mercure est fragile et pourrait se briser en cas de choc. Dans ce cas, le mercure toxique serait libéré dans l'environnement.
· The mercury lamp does not emit well under cold temperature conditions, and therefore, the irradiance decreases at lower temperatures.
· There is a long warm-up time for the mercury lamp, and it does not immediately reach maximum power as soon as it is turned on.
· Tel que mentionné précédemment, la longueur d’onde d’émission est limitée à 254 nm, ce qui ne correspond pas au pic d’absorption de l’ADN des bactéries tel que déterminé par la courbe d’efficacité germicide.
A suitable alternative to a mercury discharge lamp for germicidal disinfection is a UV LED. The UV LED is a p-n junction device, and the recombination of electron-hole pairs at the junction emits photons. Depending on the p-n junction design, different wavelengths can be emitted. The UV LED will have the following advantages over the mercury discharge lamp:
Les DEL UV pourraient être conçues pour avoir un pic d'émission plus proche du pic d'absorption germicide. Elles seraient plus efficaces à des fins de désinfection.
· La puissance des DEL UV ne dépend pas de la température
· UV LEDs have tiny sizes and are not fragile.
· Les DEL UV ne contiennent pas de mercure toxique
· Les DEL UV émettent dès qu’elles s’allument et n’ont pas de temps de préchauffage.
· For equal power, the UV LED produces more irradiance at the same distance as compared to a Mercury lamp.
In one research study, three different types of bacteria, namely E. coli, Salmonella, and Listeria, were grown in agar media and were subjected to illumination by four UV LEDs at various wavelengths and one mercury discharge lamp at fluence levels of 0.1, 0.2, 0.5, and 0.7 mJ/cm2. The UV LED irradiance was 4.5 mW/cm2, so the intense mercury lamp needed to be attenuated using 52 polypropylene thin sheets by a factor of nearly 200 to bring its irradiance down to 4 mW/cm2. The three bacterial cultures, grown in petri dish agar media, were illuminated with these LEDs and the mercury lamp at four different fluences (as mentioned above), and the reduction in bacterial concentration was measured on a log scale.
E. coli and Salmonella both show an OD6 reduction at 0.7 mJ/cm2, and Listeria shows an OD5 reduction at the exact dosage, as observed in the graphs. The attenuated mercury lamp in each case has a much lower reduction. Both E. coli and Salmonella are gram-negative types of bacteria, whereas Listeria is a gram-positive bacterium. Studies have shown that gram-positive bacteria require a higher dosage to be killed than gram-negative bacteria, since they are more resistant to UV irradiation2. The main reason the mercury lamp is not showing the same level of efficacy in germicidal disinfection is the inverse-square law attenuation of the radiation, compared to the more directional nature and greater concentration on the target area of the UV LED.
Français Les mêmes travaux de recherche ont également été menés sur du fromage en tranches de dimensions 85 mm x 85 mm x 2 mm. Il a été constaté qu'à une dose de 3 mJ/cm², E. coli et Salmonella présentaient une réduction de 4 à 5 log, et Listeria une réduction de 3 à 4 log. Une comparaison a également été effectuée entre la DEL 266 nm et la DEL 279 nm et il a été constaté que pour les trois espèces de bactéries, la destruction logarithmique était légèrement supérieure pour la DEL UV 266 nm (E. coli : 4,88, Salmonella : 4,72, Listeria 3,52) que pour la LED 279 nm (E. coli : 4,04, Salmonella : 3,91, Listeria 3,24).
Allied Scientific Pro is on the quest to use photonics technology to battle the pandemic and offers various disinfection lamps on its product line.
Plusieurs longueurs d'onde de crête sont disponibles : 222 nm, 230 nm, 254 nm, 265 nm, 275 nm et 280 nm. Pour plus d'informations, consultez le lien suivant :
https://www.alliedscientificpro.com/shop/high-power-uv-led-365nm-uvee-portable-light-17575
Références :
1- Utilisation de diodes électroluminescentes UVC à des longueurs d'onde de 266 à 279 nanomètres pour inactiver les agents pathogènes d'origine alimentaire et pasteuriser le fromage en tranches, S.J.Kim et.al, Applied and Environmental Microbiology, Volume 82, Numéro 1, 2016.
2- Résistance du génome d'Escherichia coli et de Listeria monocytogenes à l'irradiation évaluée par l'induction de dimères de cyclo-butane pyrimidine et de photoproduits 6-4 à l'aide de rayonnements gamma et UVC, S Beauchamp et.al, Radiat Physics Chem 81 : 1193-1197, 2012