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Lasers Aid in Bacteria Destruction

Photonics Spectra
Feb 1998
Stephanie A. Weiss

GLASGOW, Scotland, UK -- Heating bacteria to high temperatures will kill them, but exposing them to Nd:YAG laser light does it better, according to research findings at the University of Glasgow.
Ian Watson, Duncan Stewart-Tull and co-workers at the university have been studying methods of improving food and medical decontamination. Heating bacteria to high temperatures kills most bacterial species, but the process can be time-consuming and can damage perishable substrates.
Results presented at the International Conference on Lasers and Electro-Optics in San Diego showed that when E. coli suspensions were heated in a waterbath to 50 °C and left for 20 minutes, bacteria viability dropped by one D-value (90 percent).
Exposure to light from a 100-W Nd:YAG laser raised the temperature to 50 °C in 25 seconds and dropped the E. coli viability by three D-values (99.9 percent).
Under the microscope the bacterial cells appeared blistered, and there was evidence of cell rupture, the researchers reported.

Concentration effects
Bacterial concentration affects the efficiency of laser light in killing bacteria: The optical characteristics of more concentrated suspensions are such that they reduce the penetration of light.
The researchers acknowledged that an effective UV lamp would be cheaper than a laser and could accomplish a similar goal; however, they are investigating synergistic effects that might occur when combining exposure of bacteria to UV and infrared laser light.

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