The discrimination of IgM and IgG type antibodies and Fab' and F(ab)2 antibody fragments on an industrial substrate using scanning force microscopy.

We have previously employed scanning force microscopy (SFM) to study antibody-antigen molecular interactions on microtiter wells used for enzyme linked immunosorbant assays (ELISA). Here we demonstrate the ability of SFM to image and discriminate different types of antibody and antibody fragments bound to an ELISA well surface. The samples studied include a type IgG antibody with a proportion of bound IgM and two-dimensional films of whole IgG antibody, and Fab' and F(ab)2 antibody fragments. Molecular resolution is achieved in each case despite the size of substrate features exceeding most of the molecular dimensions observed. Analysis of the data shows that the SFM overestimates molecular dimensions by an approximately constant amount, which is proposed to principally result from the effects of a finite probe size and not from deformation of the molecular species due to the imaging forces employed.