Example III (cont.): In situ  Tapping Mode AFM Observations of A beta in Contact with a Model Hydrophobic Surface (Highly Oriented Pyrolotic Graphite)
Dt = 256 s
In situ Tapping Mode AFM Observations of Ab in Contact with Graphite  
T.Kowalewski, D.M. Holtzman PNAS (1999)
Our approach:
•We are interested in the role of surface interactions in Ab aggregation.  This question is especially relevant, given that the intra- and extra-cellular environments are highly congested and heterogeneous.
•We are studying this problem through direct in situ tapping mode AFM observations of various model surfaces remaining in contact with physiological solutions of Ab.
Shown here is the course of Ab aggregation in contact with the hydrophobic surface of highly oriented pyrolitic graphite (HOPG).  HOPG can be viewed as an analog of biologically hydrophobic environments such as interior of lipid bilayers or lipoprotein particles.
In contact with HOPG surface, Ab  forms elongated, flat sheets which form raft-like assemblies.  Interestingly, all sheets and rafts tend to be oriented along three preferential directions.