In the realm of biophysics and biochemistry, light scattering is used extensively to evaluate the molecular weight and size of macromolecules and particles in suspension. Bacteria scatter strongly but are too large for the conventional procedures. By extending the wavelength lambda of the incident radiation into the infrared, we show that the effective size of the bacteria (relative to lambda ) is reduced, and the usual Zimm plot measurements and procedure can be applied to evaluate the molecular weight and size. Details of the apparatus, its alignment, calibration and use are given along with data for aqueous suspensions of three species.
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