title: Limits of detection for time of flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS): detection of low amounts of adsorbed protein.
abstract: Characterization of biomaterial surfaces requires analytical techniques that are capable of detecting a wide concentration range of adsorbed protein. This range includes detection of low amounts of adsorbed protein (<10 ng/cm2) that may be present on non-fouling biomaterials. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) are surface sensitive techniques capable of detecting adsorbed proteins. We have investigated the lower limits of detection of both XPS and ToF-SIMS on four model substrates each presenting unique challenges for analysis by XPS and ToF-SIMS: mica, poly(tetrafluoroethylene), allyl amine plasma polymer and heptyl amine plasma polymer. The detection limit for XPS ranged from 10 ng/cm2 of fibrinogen (on mica) to 200 ng/cm2 (on allyl amine plasma polymers). The detection limit for ToF-SIMS ranged from 0.1 ng/cm2 of fibrinogen to 100 ng/cm2, depending on the substrate and data analysis. Optimal conditions provided detection limits between 0.1 ng/cm2 and 15 ng/cm2 on all of the substrates used in this study. While both techniques were shown to be effective in detecting protein, the sensitivity of both XPS and ToF-SIMS was shown to be dependent on substrate surface chemistry and the organization of the adsorbed protein film. This study specifically highlights the applicability of ToF-SIMS in the characterization of low level protein adsorption.
authors.affiliation: Department of Chemical Engineering, National ESCA and Surface Analysis Center for Biomedical Problems, University of Washington, Seattle 98195-1750, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Wagner
authors.forename: Sally L
authors.initials: SL
authors.lastname: McArthur
authors.forename: Mingchao
authors.initials: M
authors.lastname: Shen
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Horbett
authors.forename: David G
authors.initials: DG
authors.lastname: Castner
mesh_terms: D000327:Adsorption; D005340:Fibrinogen / Q000032:analysis / Q000378:metabolism; D006801:Humans; D011506:Proteins / Q000032:analysis* / Q000378:metabolism; D012680:Sensitivity and Specificity; D018629:Spectrometry, Mass, Secondary Ion / Q000592:standards*; D013057:Spectrum Analysis / Q000592:standards; D013499:Surface Properties; D014965:X-Rays
chemical_list: D011506:Proteins; D005340:Fibrinogen