In biochemistry or chemistry, filter binding assay is a simple way to quickly study many samples.
This information reveals the affinity between the two molecules and allows prediction of the amount bound given any set of initial conditions.
The DNA is "labeled" by the addition of radioactive phosphate derived from adenosine triphosphate.
After equilibration, an equal volume from each tube is squirted onto small, round, nitrocellulose filters which are arranged on a vacuum plate (a flat surface that has a vacuum applied from below to suck fluid downward).
This assay is no longer used widely, but it is rapid and simple, and can give a lot of information.