Assignment 5, Part 1: viscosity and diffusivity in glycerol-water mixtures
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This is Part 1 of Assignment 5.
Estimating the diffusion coefficient by tracking suspended microspheres
1. Track some 0.84μm Nile Red Spherotech polystyrene beads in water-glycerin mixtures (Samples A and B contain 30% and 50% glycerin, respectively).
- Notes: Fluorescent microspheres have been mixed for you by the instructors into water-glycerin solutions A and B. (a) Vortex the stock Falcon tube, and then (b) transfer the bead suspension into its imaging chamber (consisting of a microscope slide, double-sided tape delimiting a 2-mm channel, and a 22mm x 40mm No. 1.5 coverslip, and sealed at both ends nail polish).
- Tip 1: Do not choose to monitor particles that remain stably in focus: these are likely to be 'sitting on the coverslip' and their motion will not be representative of diffusion in the viscous water-glycerol fluid.
- Tip 2: Limit the ROI to a region with only 3 or 4 particles. Long movies with the whole field of view is a sure way to make MATLAB complain.
2. Record movies of beads diffusing in the two glycerol solutions and use your newly developed code to estimate the diffusion coefficient of each sample.
- Consider how many particles you should track and for how long. What is the uncertainty in your estimate?
- Calculate the viscosity of the solution and estimate the glycerin/water weight ratio of each solution. (Hint: what is the relationship between diffusion coefficient and viscosity? You may find that this chart is a useful reference.)
Turn in for the viscosity part:
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- Overview
- Part 1: MSD difference tracking and microscope stability
- Part 2: Live cell particle tracking of endocytosed beads
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