Comparative bactericidal activities of lasers operating at seven different wavelengths

Watson, I. A. , Ward, G. D., Wang, R. K., Sharp, J. H. , Budgett, D. M., Stewart-Tull, D. E., Wardlaw, A. and Chatwin, C. R. (1996) Comparative bactericidal activities of lasers operating at seven different wavelengths. Journal of Biomedical Optics, 1(4), pp. 466-472. (doi: 10.1117/12.250684)

Abstract

Seven laser instruments, delivering radiation at a selection of wavelengths in the range of 0.355 to 118 μm, were investigated for their ability to kill <i>Escherichia coli</i> as a lawn of the bacteria on nutrient agar culture plates. Easily the most effective was a 600-W CO₂ laser operating at 10.6 μm, which produced 1.2- cm² circular zones of sterilization at energy densities of around 8 J cm^-2 in a 30-msec exposure. Circular zones with an area of 0.7 cm² were achieved with 200 W from a Nd:YAG laser delivering 8-ms, 10-J pulses of 1.06 μm radiation at 20 Hz. The exposure time, however, was 16 s and the energy density (1940 J cm^-2) was more than 240 times higher than with the CO₂ laser. This difference is believed to be partly due to the much higher absorption of radiation at 10.6 μm than at 1.06 μm, by water in the bacterial cells and the surrounding medium (nutrient agar). Sterilization was observed after exposure to frequency-tripled Nd:YAG laser radiation at 355 nm (3.5 J cm^-2). Lasers that were totally ineffective in killing Escherichia coli (with their wavelength and maximum energy densities tested) were the far infrared laser (118 μm; 7.96 J cm^-2), the laser diode array (0.81 μm; 13,750 J cm^-2), and the argon ion laser (0.488 μm; 2210 J cm^-2). The speed at which laser sterilization can be achieved is particularly attractive to the medical and food industries. Glenn D. Ward,‡ Ruikang K. Wang,† James H. Sharp,† David M. Budgett,† Duncan E. Stewart-Tull,‡ Alastair C. Wardlaw,‡ and Chris R. Chatwin

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Watson, Dr Ian and Chatwin, Prof Christopher and Wardlaw, Prof Alastair and Stewart-Tull, Prof Duncan and Sharp, Dr James
• Authors: Watson, I. A., Ward, G. D., Wang, R. K., Sharp, J. H., Budgett, D. M., Stewart-Tull, D. E., Wardlaw, A., and Chatwin, C. R.
• College/School: College of Medical Veterinary and Life Sciences > School of Infection & Immunity; College of Science and Engineering > School of Engineering > Systems Power and Energy
• Journal Name: Journal of Biomedical Optics
• Publisher: Society of Photo-optical Instrumentation Engineers
• ISSN: 1083-3668
• ISSN (Online): 1560-2281