Optical Tweezers for Biology

Optical tweezers are used to finely capture and move microorganisms or anything microscopic. For this experiment, the focus was to capture biological specimens, and measure the amount of energy they have in their tails. It is a method in which they use to thrust themselves around in a solution. With that it can be determine how much energy is produced by the tail in order for them to escape a laser trap.

The first thing that was done was the set up capturing apparatus. To start this the first things that should be done is preparing the fiber optic laser that will be used. There should be equipment in the room to allow for practice before the real one should be done.

Following up with the apparatus set up is the laser set up. There should be instructions in the lab to help with the set up. A short simplified version of it would be as follows

1. Strip the plastic from the fiber optic wire

2. Set up two part polymer, with a ratio of 2:1, A to B. Mix very well and pour into a syringe

3. Using a head of a laser, slowly push the polymer into the tiny hole until it comes out the other end.

4. Push the now stripped fiber optic laser into the tiny hole. DO SO SLOWLY OR IT WILL BREAK

5. Once all the way through, let dry/ cook in the over for the allotted time.

6. Once out of the oven, cut the leftover off and dispose of it.

7. Now being sanding down the tip and polishing it as follows. It should be done in figure 8 motions as follows in the book provided.

8. Once polishing is complete and it has passed all the benchmarks, the apparatus can then be set up.

After the fiber optic is set up to be a laser, finish setting up the apparatus. Our apparatus consisted of a laser which bounced off of a mirror into a one way mirror. This is then further reflected up to the lens of the microscope. At side of it we have a stand which moves the glass slide in all 3 different vectors. The x,y and z plane.

For the Winter, another addition was added to the apparatus. That was an machine that would oscillate the mount slowly in sin function in order to produce a small movement of the beads. This method was to be used to measure the drag force produced. Since the beads don't move. This is a excellent option to take to measure their movements.

This now leads to the set up of the slides. There are instructions located with the lab. Here is a shortened version of the process.

1. Using methanol which is flammable, carefully clean the slide with it and lens cleaning tissue provided by Thor labs. 2. Using the same method clean the coverslip with methanol and lens cleaning tissue. 3. Using a microcentrifuge

There is a solution known as methyl cellulose. It has the ability to hinder and slow the movement of any microorganism as well as other microscopic mass present. This is the way that we bypassed the problem of the microscopic masses moving pass our field of view. They move extremely quickly and any twitch to focus or lock on to the target would shake it around making it even harder to capture.

The first thing to try to capture are glass beads. The glass beads are good practice as they have a clear path and direction that they are traveling in. They don't have a tail and will therefore move in a easily predictable path. There are two types of beads to pick from. There is a vial that had PEG and one that does not contain PEG. PEG is a short name for Polyethylene glycol. It is meant to prevent the beads from being trapped against the glass surface of the coverslip or the slide. The PEG is better for starting to practice and capture the beads. The ones without the PEG is great for fine tuning the apparatus to focus in more on the beads.

Once you have become good enough at capturing beads, the next step is to catch biological organism. This follows the same process as the beads.