Dynamic Light Scattering Of Biopolymers And Biocolloid

Of the physical techniques available for the study of biopolymers and other macromolecular and colloidal systems, dynamic light scattering is, perhaps, the most fascinating. The very idea of extracting useful dynamical and structural information from random fluctuations in the intensity of light scattered from otherwise unperturbed equilibrium solutions1-3 seems, at first glance, almost too good to be true. Indeed, for fragile preparations that are prone to suffer undesirable fates at the slightest change in solution conditions, dynamic light scattering may be the perfect technique. It is nondestructive, relatively rapid, and typically requires only modest amounts of material. In routine applications, even on unfamiliar samples, the dust-removal procedure (either gravity flow Millipore ® filtration or low-speed centrifugation) requires 10 to 20 min, and determination of the translational diffusion coefficient to an accuracy of a few percent, or less, requires 5 min. Verification that the dynamical motions, in fact, obey the diffusion equation requires an additional 5 to 20 min. The amounts of solution required are typically a few milliliters, although similar experiments have been run on volumes as small as 15 μl.4 The concentrations needed, which depend on salt concentration and refractive index increment, and inversely on molecular weight, generally lie in the range 0.5 to 2.0 mg/ml for polypeptides with Mr ∼ 100, 000.