Limits of Detection:Report Requirements

• Before you go to the lab, read the optical trapping lab manual and the the Atomic Force Microscopy lab manual
• Attend an optical trap lab session during the week of 11/28-12/3.
• Attend an AFM lab session during the week of 12/5-12/9.
• The mini-lab report will be due at midnight on 12/13.
• The report should be answer-book style, like a problem set.
• Your report should be in PDF format, submitted to Stellar prior to the deadline. Include your last name in the filename.
• Submit all the computer code (.m files) that you used in your analysis as a single, separate zip file to Stellar.

You will gather data as a group; however, reports must be individually authored. Everything in your report, including computer code, must be entirely your own work.

Answer the following questions:

1. Optical trap calibration
   1. What is the responsivity of the QPD in microns per Volt?
   2. What is your estimate of the trap stiffness as a function of power as determined by the three different calibration methods (equipartition, PSD roll-off, and Stokes drag)? Plot your results.
   3. Which method is superior? Explain why.
   4. What is the minimum detectable force as a function of power and bandwidth?
2. AFM
   1. What is the stiffness of the cantilever you measured?
   2. How does the stiffness compare to the value computed from the cantilever's material properties and from the Sader method?
   3. What is the smallest force you could measure using that cantiliver?
   4. How could you modify the cantilever design to measure smaller forces? What is the smallest force that could practically be detected using a silicon nitride cantilever?
   5. How does the minimum detectable force compare to typical forces in biological systems (e.g. antibody/antigen binding, DNA hybridization, interdomain forces in proteins, etc.)?