In practice this research amounts to measuring the tiny forces acting between single biological molecules or tiny probe particles floating in some sort of complex gooey material. To do this, we infer the forces by watching how the probe particles move, and then applying physical models to deduce the driving force. The main tools we employ are optical and fluorescence microscopies, novel optical tweezer setups, and lots of image processing to follow the motion of the probes or molecules.
If you'd like more details as to how we can track hundreds of bacteria-sized
particles to better than a few nanometers, my colleague Eric Weeks has
set up a nice page here.
Preprint(s):"Two-Point Microrheology of Inhomogeneous Soft Materials"
Crocker JC, Valentine MT, Weeks ER, Gisler T, Kaplan PD, Yodh AG, Weitz DA, Download PDF
Selected papers:"Three-dimensional direct imaging of structural relaxation near the colloidal glass transition" Weeks ER, Crocker JC, Levitt AC, Schofield A, Weitz DA Science 287 627-631 (2000). Download PDF
"Attractions between hard colloidal spheres in semiflexible polymer
"Entropic colloidal interactions in concentrated DNA solutions"
"Entropic attraction and repulsion in binary colloids probed with
a line optical tweezer"
"When like charges attract: The effects of geometrical confinement
on long-range colloidal interactions" Crocker JC, Grier DG, Phys
Rev Lett 77 1897-1900 (1996).
"Microscopic Measurement of the Pair Interaction Potential of Charge
Stabilized Colloid" Crocker JC, Grier DG, Phys Rev Lett
73 352-355 (1994).
"Comment on `Monte Carlo study of structural ordering in charged colloids using a long-range attractive interaction'" Grier DG, Crocker JC, Phys Rev E 61 980-982 (2000). Download PDF
"Measurement of the hydrodynamic corrections to the Brownian motion
of two colloidal spheres" Crocker JC, J. Chem Phys 106
"Origin of stratification in creaming emulsions"
"Methods of digital video microscopy for colloidal studies"