AVS 47th International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI+MC-MoA

Paper BI+MC-MoA8
Detection of Intact Biomolecules with Matrix-Enhanced ToF-SIMS

Monday, October 2, 2000, 4:20 pm, Room 202

Session: Characterization of Biomaterial Interfaces
Presenter: D.G. Castner, University of Washington
Authors: D.G. Castner, University of Washington
P. Kingshott, University of Washington
J. Nesiba, University of Washington
S.L. Golledge, University of Washington
B.D. Ratner, University of Washington
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An improved understanding of the interfacial interactions between biomolecules and surfaces is important for the successful design of the next generation of biomaterials. This study combines the high surface sensitivity and chemical specificity of ToF-SIMS with the 'soft' ionization capabilities of MALDI. Model peptides with beta-sheet and alpha-helix structures were used in conjunction with MALDI matrix molecules [2,5-dihydroxybenzoic acid (DHB) and sinapinic acid (SA)] to facilitate generation of molecular ions with the SIMS Cs+ ion source. The positive ToF-SIMS spectra from the beta-sheet peptide incorporated into crystals of DHB show peaks representative of sodium-adduct ions of the peptide (M-H+Na+) (m/z 1096.7). The spectrum from the bulk beta-sheet contains only fragment ions and no molecular ions, suggesting that there is a synergistic effect in producing sodium adduct molecular ions when both Na and matrix molecules are present. When sodium is eliminated from the system, peaks that can be assigned to the M+ ion (m/z 1074.7) can still be detected. Molecular ions from the alpha-helix peptide were also detected when DHB was present. The use of SA as matrix failed to generate peptide molecular ions, suggesting the matrix-specific nature of this MALDI-SIMS technique. Imaging-SIMS indicated that the peptides are incorporated within the DHB matrix crystals, but are not fully incorporated into the SA crystals. This shows the importance of good mixing between the peptides and matrix molecules for detection of intact molecular ions.