Scanning electron microscopy studies of protein-functionalized atomic force microscopy cantilever tips

Protein-functionalized atomic force microscopy (AFM) tips have been used to investigate the interaction of individual ligand-receptor complexes. Herei n we present results from scanning electron microscopy (SEM) studies of pro tein-functionalized AFM cantilever tips. The goals of this study were (1) t o examine the surface morphology of protein-coated AFM tips and (2) to dete rmine the stability of the coated tips. Based on SEM images. we found that bovine serum albumin (BSA) in solution spontaneously adsorbed onto the surf ace of silicon nitride cantilevers, forming a uniform protein layer over th e surface. Additional protein layers deposited over the initial BSA-coated surface did not significantly alter the surface morphology. However, we fou nd that avidin-functionalized rips were contaminated with debris after a se ries of force measurements with biotinylated agarose beads. The bound debri s presumably originated from the transfer of material from the agarose bead . This observation is consistent with the observed deterioration of functio nal activity as measured in ligand-receptor binding force experiments.