Figure 2.

Illustration of the principle of contrast variation SAXS. In CV-SAXS, the electron density of the solvent is increased until it matches one of the components of a multicomponent system. In this figure, the electron density is represented as color. In the top panel (no contrast agent), we model a protein-nucleic acid complex in regular aqueous solvent. In the bottom panel, the electron density of the solvent is increased (schematically shown as color change from white to red to black) by the addition of sucrose until it matches the electron density of the protein (red). Under this contrast matched condition any scattering signal that contains a contribution from the protein component blends into the background e.g. disappears. Only the scattering from the more electron dense nucleic acid is detected.