Non-specific adherence of oxide particles as a means of quantifying protein adsorption on surfaces

This paper reports quantification of a method for measuring amounts of protein adsorbed to a surface; the method is especially useful for revealing macroscopic spatial patterns of adsorption. The experiments tested the effectiveness of iron oxide suspensions adsorbed onto the adsorbed protein to indicate, in separate trials, the amount of either human plasma fibrinogen or human serum albumin (HSA) present on glass slides. Corresponding trials, using radioactively labeled proteins, were performed to calibrate the amount of either albumin or fibrinogen adsorbed onto similar slides out of solutions of varying bulk concentrations. The oxide deposits were quantified using a scanner and an image analysis program. The isotherms produced from the collected data indicate a continuous, monotonic correlation between light absorbed by adherent oxide and surface concentration of protein. The same correlation applies to albumin and fibrinogen when surface concentrations are expressed in weight units. These results confirm that patterns of oxide deposition correspond to patterns of protein deposition and show clearly how qualitative observations, such as those previously reported, can be made quantitative with scanning and digital image analysis.