In biological systems, a double layer is the surface where two different phases of matter are in contact.
Biological double layers are much like their interfacial counterparts, but with several notable distinctions.
The surface of biological cells carry many different types of chemical groups, each with a different dissociation constant, causing them to have varying electric charges at a physiological pH.
This biospecific feature is typical for all biosurfaces, including proteins, macromolecules and biological cells.
This does not apply; instead, the cell surface is a finite thickness polyelectrolyte layer with a volume charge.