ANALYSIS OF STERIC REPULSION FORCES IN ATOMIC-FORCE MICROSCOPE WITH POLYETHYLENE OXIDE IN AQUEOUS-MEDIA

We present a theoretical analysis for the use of long-range intermolec ular steric repulsion forces for imaging by atomic force microscope (A FM). Polyethylene oxide (PEO) is assumed to be terminally attaching to a spherical AFM tip in aqueous media. Only two long-range intermolecu lar forces (van der Waals attraction and steric repulsion) are conside red. All calculated forces are near 10(-11) N, which should not produc e deformation of the soft protein surface. Calculations are presented as a function of surface density and chain length of terminally attach ed PEO, and other variables. Longer chain length and maximal surface d ensity of terminally attached PEO to a smaller sized spherical AFM tip (modified AFM system) is appropriate to obtain optimum images of prot eins on the surface.