Nanoparticle haloing has been utilized as a method to stabilize colloidal systems for a number of years. However, the real interaction forces responsible for this mechanism have not been elucidated by experimental force measurements though some aspects have been investigated through simulation and theoretical calculation. The Atomic Force Microscopy (AFM) Colloidal Probe technique has been utilized to directly measure the interaction forces between silica surfaces in a variety of nanoparticle suspensions. The spring constant of the AFM probe was calibrated by a DLVO force fitting method for accurate force measurement. Force curves between silica surfaces were investigated in different nanoparticle dispersions by varying both the size and the type of nanoparticle and the volume fraction and the pH of the nanoparticle suspensions. The different contributions of the van der Waals force, electrostatic force, and depletion force and the transition between them will be discussed.