Weak precursor state binding of protein molecules to size-selected gold nanoclusters on surfaces

We have employed liquid phase atomic force microscopy (AFM) to explore the immobilization of green fluorescent protein (GFP) molecules on films of size-selected gold clusters pinned on the surface of graphite. Previous studies indicated covalent binding between such clusters and a variety of proteins. For GFP, strong binding does not occur, but tapping mode AFM shows evidence of weak interactions between protein and cluster. This also occurs if the clusters are functionalized via thiolate molecules which present amine or carboxyl groups. We identify this weak “precursor” binding as a route to prepare the system for chemisorption, e.g. by peptide bond activation.