Investigating forces between charged particles in the presence of oppositely charged polyelectrolytes with the multi-particle colloidal probe technique

► Novel multi-particle colloidal probe technique based on the atomic force microscope is discussed. ► Forces between charged particles in the presence of polyelectrolytes are studied. ► Repulsive electrostatic double-layer forces are dominant away from the isoelectric point (IEP). ► Close to the IEP attractive van der Waals and patch-charge forces are important.