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 I-125 is reported. Previous studies indicated that the interaction of the metal surface with free I-125(-) 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 I-125(-) ion to gold or to differentiate between the sorption of labeled protein and I-125(-). 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 I-125(-) 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 I-125(-) to gold. It was also found that treatment of gold surface with SDS is not 100% efficient in eluting adsorbed protein. (C) 2000 Elsevier Science B.V. All rights reserved.