Measurement of protein adsorption to metals using radioiodination methods: a caveat

The adsorption of fibrinogen and albumin, measured by radiolabelling with 125I, from single protein solutions to four metal surfaces (gold, silver, titanium and copper) is reported. The measured amounts of adsorbed protein were found to be erroneously high due to interactions of residual free 125I-iodide ion, present in the protein solution, with the metal surfaces. The “apparent” adsorption was particularly high on gold and silver. Treatment of the protein-adsorbed metal surfaces with 2% aqueous sodium dodecyl sulfate (SDS) removed the protein, but left the iodide ion attached. Adsorbed amounts estimated from the radioactivity of the SDS-eluates were significantly lower than those estimated from total surface radioactivity. These results suggest that caution should be used when interpreting data on the adsorption of 125I-labelled proteins to metal surfaces, since artifacts can arise due to metal-iodide ion interactions.