Light Scattering Topic 3 Part 2 Biophysics

Single Particle Rough Treatment Sample - dipole Light Source k 0  The scattering angle, , is defined w/r transmitted light in the scattering plane. The scattering plane is defined by the vectors k and k 0. Go over description of light in terms of exponential function (board).

Single Particle Rough Treatment Bottom line Light can be described by electric field For Horizontally polarized light intensity the |E| 2 given by For vertically polarized light For unpolarized light Why is there angular dependence for one but not the other? Why does the sky usually appear blue?

Dilute gas of small particles Use Classius-Mosotti relation to express polarizability  in terms of index of refraction, n. Scattered light per unit volume goes as molecular weight

Macromolecules in solution R  = KcM, with With small interaction get Kc/ R  = 1/M + 2Bc where B = 2 nd virial coefficient – fudge factor.

Large macromolecules Mostly Forward Scattering Get molecular weight and size Zimm plot

Nephelometer

Raw Data Why plot as Log(sin(angle)? Why buffer give more noise? What do you notice about angular dependence?

Data from Chen et al BJ 2004