Lab 1 Report -- Nathan S Lachenmyer

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Goals

  • Familiarize myself with optical trapping system
  • Learn culture e coli, trap them!

Calibration

All calibrations and experiments done at 20 mW.

Position Calibration

  • Learned to make microfluidic devices out of double-stick tape and a slide -- this was really neat!
  • Made two samples with 1 um microspheres
    • One sample with free-floating spheres (in H2O)
    • Another one with 'stuck' spheres in NaCl (I cheated :( )
  • Took a position calibration on the optical trap setup, seen below

1um cal.png

calibration: 502463 Volts / m = 1.99 um / volt

Trap Stiffness Calibration

  • Did all three versions of the trap calibration, resulting in the following trap spring constants:
Method Trap Stiffness (pN / nm)
Stokes 2.26e-5 pN/nm
Equipartition Theorem 1.23e-5 pN/nm
PSD *Need Bandwidth of DAQ*

Experiments

E Coli

  • Learned to culture E Coli (sort of)
  • Examined the various cultures to determine which ones had the fastest spinners / spinners in the appropriate direction with Steve
  • E Coli weren't spinning very well -- swapped out the blue LED for a Red LED to determine if the wavelength made a difference
    • As far as we could tell, the LED color made no difference
    • We also couldn't figure out why the E Coli were spinning so slowly
  • Worked with Steve to cut the flagella of E Coli by drawing them in and out of a pipette multiple times
    • This improved the spinning frequency of the E Coli!

Ecoli.png

Doing an FFT analysis of the QPD spectrum, I find that the low-frequency components are pretty noisy (unfortunately). However, there is a small peak at approximately 6 Hz -- according to the appleyard paper, the e coli flagellar motor spin frequency is approximately 4-10 Hz, so this is in good agreement.

Are the units on your time plot actually seconds? It doesn't seem to jive with your frequency plot or my experience. 
If the 100s is actually 1s, then I agree with the roughly 6Hz spin frequency.

DNA Tethers

  • Learned to make the DNA tethers
  • Was able to trap a microsphere tethered to the slide via DNA

Dna raw.png

Results from this plot: -From the plot we can determine the length of the DNA (where the QPD signal is zero as a result of the trapped microsphere being trapped in the optical gradient) and the extension length of the DNA (where the force begins to increase as the stage moves further away; at this point the glass slide is moving while the microsphere is trapped, stretching out the DNA tether).

Tether Length: 0.97 microns Extension Length: 1.77 microns

this suggests that the DNA can extend to almost twice its length!