ATOMIC-FORCE MICROSCOPY OF HUMAN SERUM-ALBUMIN (HSA) ON POLY(STYRENE ACROLEIN) MICROSPHERES/

Atomic Force Microscopy (AFM) in the tapping mode was used for the obs ervation of bare poly (styrene/acrolein) P(SA) microspheres and micros pheres with attached HSA. Prior to the AFM observations the P(SA) micr ospheres were immobilized covalently on the surface of quartz slides m odified with gamma-amino-propyltriethoxysilane. Atomic Force Microscop y pictures were registered for the dry samples. The partial coalescenc e of the P(SA) microspheres connected to the quartz surface with amino groups has been observed. The AFM pictures of the single P(SA) micros pheres revealed that the surface of these particles is smooth and that any irregularities, if present, do not exceed 1 nm. The surface of mi crospheres with attached HSA has very clearly different morphology wit h regular pattern of HSA macromolecules. Cracks on the surfaces of som e microspheres with HSA revealed that protein macromolecules are attac hed to these particles in several layers. In the case of some other mi crospheres the defects in protein attachment allowed the observation o f the border between the bare surface of the P(SA) microspheres and th e surface covered with protein macromolecules. Comparison of the thick ness of the HSA layers on the P(SA) microspheres with the dimensions o f HSA macromolecules, determined earlier from the x-ray studies, sugge sts that the first layer, 3.0 +/- 0.2 nm thick, is formed of the HSA m acromolecules arranged flatly on the surface whereas protein macromole cules in the subsequent layers, each 8.6 +/- 1 nm thick, are adsorbed protruding from the surface.