Tuesday, November 9, 2010: 5:00 PM
250 A Room (Salt Palace Convention Center)
Removing adsorbed protein from metals has significant health and industrial consequences. Surgeons and ship owners desire clean metal surfaces to minimize transmission of disease via surgical instruments and surface fouling (to reduce friction and corrosion), respectively. A major finding of this work is that, besides protein-metal surface adhesion energy, adsorption of protein-associated water determines the access and hence ability to remove adsorbed proteins from metal surfaces with a strong alkaline-surfactant solution (NaOH and 5 mg/ml SDS in PBS at pH 11). This is demonstrated with 3-blood proteins (bovine serum albumin, immunoglobulin and fibrinogen) and 5 transition metal substrates (platinum, gold, tungsten, titanium and 316 grade stainless steel (SS)). Difference measurements between a quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance spectroscopy (SPR) provides a measure of the water content in protein-adsorbed layers. Hydrophobic adhesion forces, obtained with atomic force microscopy, between the proteins and the metals correlate with the amount of the adsorbed protein-water complex. Thus, the amount of protein adsorbed decreased with platinum, gold, tungsten, titanium and stainless steel, in this order. Neither sessile contact angle nor surface roughness of the metal substrates was useful here. All three globular proteins behaved similarly on addition of the alkaline-surfactant cleaning solution, in that platinum and gold exhibited an increase, while tungsten, titanium and stainless steel showed a decrease in weight. According to dissipation measurements, the adsorbed layer for platinum and gold was rigid, while that for the tungsten, titanium and stainless steel was much more flexible. Thus access to the metal surface by the NaOH/SDS was hindered and facilitated, respectively. This difference was also demonstrated with respect to water content comparing QCM-D and SPR measurements for the three blood proteins on gold. Hence both the amount of water associated with adsorbed protein and hydrophobic adhesion energy to a metal surface determine its removal efficiency by cleaning solutions.