Self-assembled monolayers for polymer and protein cationization with time-of-flight secondary ion mass spectrometry

Detection of cationized polymers and proteins with time-of-flight secondary ion mass spectrometry has been achieved using novel substrates consisting of carboxylic acid terminated self-assembled monolayers (SAMs) with silver ion substituted headgroups. However, other metal ions (Na, Cu, Tl, or Li) a s SAM headgroups can be used as well. Polymers were deposited on the metal ion derivatized SAMs by spin coating while proteins were adsorbed onto the substrates. Control experiments carried out on nonsubstituted and methyl-te rminated SAMs suggest that only metal ions in close proximity to the polyme r can cationize the molecules and their fragments. Both cationized fragment s and whole molecular species were observed for 1 kD polyethyleneoxide and low molecular weight proteins (<2 kD). (C) 2000 American Vacuum Society. [S0734-2101(00)15704-5].