The amount (volume and concentration) of sample that you need will vary by method and by the Kd (equilibrium dissociation constant) of the interaction. For guidelines see the CMI technology comparison table. Binding assays will typically have one binding partner at a fixed concentration (or immobilized on a surface) and one binding partner at a variable concentration. The high concentration for the variable analyte will typically be 10-100X Kd, depending on the method.
