Date of Award

Spring 2003

Document Type

Restricted Thesis

Terms of Use

© 2003 Joanne C. Gaskell. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Amy Cheng Vollmer

Second Advisor

Andrea Stout


Laser tweezers are a powerful tool for manipulating microbiological objects. Laser tweezers, or optical traps, trap cells in the light gradient near the focal region of a laser beam; however, there is evidence to suggest that this trapping causes damage and can induce cellular stress responses. Previous studies have shown that damage is reduced under anaerobic conditions, implicating oxygen. 100uL samples of log phase E. coli containing a katG'::luxCDABE plasmid were exposed to the focal region of an infrared beam for 15 minutes. Bioluminescence measurements indicated that katG expression was increased by as much as 12% in cells exposed to the laser at 900 mW. At a power of 2W, the response of the exposed sample decreased by 0.7%, and those cells were less viable. A dose response curve suggests that extremely high powers may be lethal to cells and that oxidative damage increases in a power-dependent manner. Results support the hypothesis that tweezing causes oxidative damage in E. coli.