I would like to bind BSA to a silver surface so that I can utilize plasmonic sensing to detect the BSA. There seems to be two methods of doing this: 1) to rely on electrostatic forces or 2) to form a covalent bond. The former seems to be the easier route, especially for someone like me who does not have a background in chemistry/biology.
So I found a paper (https://doi.org/10.1016/0021-9797(91)90121-N), which has been cited 54 times, that determined a silver (oxide) surface has an isoelectric point (iP) of ~10 pH. So this should mean that it has a positive charge when a neutral pH solution covers the surface. In other literature BSA has been shown to have an iP of pH 4-5, so it should become negatively charged in a neutral pH solution. So the BSA should bond to the silver surface in a neutral solution, correct?
The reason I ask is two-fold. First, I found a more recent paper (https://doi.org/10.1021/am400909g) that has a conflicting value for the iP of a silver film (~3 pH). Second, I found a paper (https://doi.org/10.1016/j.vibspec.2003.09.003) were the authors adsorbed BSA onto silver films, but with the intermediate step of applying 2-mercaptoethanesulphonate to the silver surface. Why the need for this if the silver should attract the BSA electrostatically?
In addition, if BSA bonding to silver were to work in this way, am I correct in thinking that a neutral solvent such as phosphate buffered saline would hinder the electrostatic bonding process because the positive and negative ions from the salt solution would bond to the respectively charged molecules and neutralize the charge?