Trapping Bacteria

Initial Attempt At Trapping Bacteria (Vibrio Cholerae)

Observations

To begin using the optical tweezers to perform biological measurements, Vibrio Cholerae bacteria was obtained from the Biophysics department. Particulars about the bacteria are described in under the Vibrio Cholerae section.

Using the objective just to image the bacteria, there were three basic types of bacterial behavior observed. First there were single vibrio cells traversing the slide at very fast velocity, close to 50 microns per second. Next observed were slightly larger organisms, possibly multiple cells linked together, which moved around with considerable energy (wiggling and writhing) but with lower overall velocity across the slide. Finally there were large chains of bacteria that moved very sluggishly throughout the slide.

Trapping

Next using the IR laser to attempt optical trapping, the sample was scanned to see if any trapping was possible. The fastest level of bacteria never seemed affected by the optical trap. None of these samples were trapped. The medium speed bacteria also was generally too strong and also did not appear to be affected by the optical trap. This could mean that they can easily overpower the piconewton forces, or that they are swimming in a different plane then the focal point of the laser. One of the larger, more vigorous, bacteria was trapped but escaped before any force measurements could be recorded. Finally the large sluggish bacteria were trapped with ease. It was noticed that as time wore on more of these slow chains begin to occur, possibly from the lack diminishing supply of nutrient broth in the slide which led to more sluggish behavior. A success apart from the trapping was that the IR laser appeared to do no harm to the bacteria and they wriggled away after the trap had been sufficiently weakened.

Initial Escape Force Measurements