Design and Documentation (BMC)

This experiment focuses on particle tracking, a key task in contemporary biophysics necessary to characterize the motion of cells, intracellular structures, and molecular machines. Tracking is accomplished by collecting the photons emitted by a point source with a CCD camera on a microscope, and subsequently fitting the intensity distribution (the point spread function) on each frame. The center of the 2-D PSF yields an estimate of the point source’s location, which can be correlated frame-to-frame to generate a track for the particle. The statistical pattern of a particle's trajectory can be fit to Einstein's model of random motion due to thermal energy to determine the relative importance of diffusive and bulk flow mechanisms to the particle's motion. In this experiment, students first study brownian motion of nanoparticles in suspension, investigating the relative effects of particle size, fluid viscosity, and solute molecular weight on particle motion. Students then observe intracellular transport of cytoplasmic structures within living onion cells. Skills developed in this lab include brightfield and darkfield microscopy, pipetting, experimental design, graphical interpretation of diffusion coefficient, and data analysis in MatLab. Students have the option of doing some programming in C# or Matlab and trying different algorithms for identifying and tracking particles.