IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Biomaterials Wednesday Sessions
       Session BI+AS-WeA

Paper BI+AS-WeA4
Limits of Detection and Identification for Adsorbed Protein Films using XPS, ToF SIMS and Multivariate Analysis

Wednesday, October 31, 2001, 3:00 pm, Room 102

Session: Surface Characterization
Presenter: S.L. McArthur, University of Washington
Authors: S.L. McArthur, University of Washington
M.S. Wagner, University of Washington
M. Shen, University of Washington
T.A. Horbett, University of Washington
D.G. Castner, University of Washington
Correspondent: Click to Email
In the ongoing development of biomaterial surfaces capable of resisting protein adsorption, surface analytical means of accurately detecting and subsequently identifying sub monolayer amounts of protein are becoming critical. The surface and chemical sensitivity of ultrahigh vacuum techniques such as XPS and ToF-SIMS have been utilized for some time in the detection of adsorbed protein films. More recently, multivariate analysis techniques have enabled the identification of the adsorbed species from both single and binary solutions via ToF-SIMS. In the instances where protein adsorption is low factors such as surface chemistry, surface coverage and roughness can be expected to complicate data interpretation, strongly influencing the both the detection sensitivity and accuracy of the protein identification. In this study a number of different surfaces were incubated in protein solutions of varying concentrations from 0.1ng/ml to 100µg/ml. Protein adsorption was quantified using radiolabelling and each surface analyzed using both XPS and ToF-SIMS. The results of the study illustrated the significant role of surface chemistry on the detection limits for adsorbed proteins. Not surprisingly, the presence of nitrogen in the substrate hindered the detection of protein by XPS, although detection limits remained high (<10ng/cm@super2@) for ToF-SIMS. The most interesting finding was the poor detection limits on PTFE surfaces, where both XPS and ToF-SIMS were unable to detect proteins below 100ng/cm@super2@. The detection limit of ToF-SIMS for protein adsorbed onto mica was 0.1 attomole of protein, rivaling the sensitivity of liquid and gas phase MS. Multivariate classification methods were also implemented to identify the adsorbed protein at submonolayer surface coverages. These results were also highly dependent on the substrate chemistry and morphology. Both XPS and ToF-SIMS are useful tools for the characterization of low levels of adsorbed protein.