Measurement of protein adsorption to gold surface by radioiodination methods: suppression of free iodide sorption

The adsorption of albumin and fibrinogen to gold metal using proteins radiolabeled with 125I is reported. Previous studies indicated that the interaction of the metal surface with free 125I− ion, present in trace amounts during protein adsorption experiments, resulted in substantial uptake, thus giving erroneously high estimates of adsorbed protein. Different approaches were investigated either to suppress the sorption of 125I− ion to gold or to differentiate between the sorption of labeled protein and 125I−. In the latter case an appropriate correction to the radioactivity on the surface should allow a valid estimate of protein adsorption. It was found that the addition of small amounts of nonradioactive iodide to the protein solution effectively suppresses the binding of 125I− ion (present in trace amounts relative to nonradioactive iodide) to the gold surface. An alternative approach involving pre-exposure to sodium iodide was not effective in suppressing the sorption of 125I− to gold. It was also found that treatment of gold surface with SDS is not 100% efficient in eluting adsorbed protein.