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

Paper BI+MC-MoA6
Quantitative Chemical Mapping of Lipid-protein Langmuir-Blodgett Layers by Laser-SNMS

Monday, October 2, 2000, 3:40 pm, Room 202

Session: Characterization of Biomaterial Interfaces
Presenter: N. Bourdos, Westfälische Wilhelms-Universität, Germany
Authors: N. Bourdos, Westfälische Wilhelms-Universität, Germany
F. Kollmer, Westfälische Wilhelms-Universität, Germany
R. Kamischke, Westfälische Wilhelms-Universität, Germany
H.-J. Galla, Westfälische Wilhelms-Universität, Germany
A. Benninghoven, Westfälische Wilhelms-Universität, Germany
Correspondent: Click to Email
Quantitative molecular mapping of chemically modified or functionalized surfaces is still an important challenge in surface analysis. We demonstrate that analyzing sputtered neutrals may be a big step forward in the quantitative mapping of laterally structured overlayers of organic molecules or biomolecules, respectively. We studied samples consisting of phospholipids and a small 34-residue peptide, the surfactant protein C (SP-C). These overlayers are phase-separated into a fluid and condensed phase. They were prepared on Au substrates with the Langmuir-Blodgett (LB) technique and investigated using a combined SIMS/SNMS instrument equipped with a reflectron-type TOF analyzer, a 30 keV Ga+ primary ion source, and an excimer laser for resonantly enhanced multiphoton post-ionization of neutrals. Laser-SNMS was applied for the first time to study LB layers. The SP-C clearly engenders typical amino acid-specific neutral fragments, by which it can be identified and localized on a surface. Most of them result from the cleavage of the COOH group, e. g., CH@sub4@N, C@sub 4@H@sub 8@N or C@sub 5@H@sub 12@N. The small CN is not typical of a certain amino acid but the entire molecule. It is the most intense peptide-based secondary particle and therefore gives excellent maps of SP-C-rich domains formed in the overlayer. It is possible to calculate the protein content in a lipid layer by histogram evaluation. The yields and damage cross-sections calculated from TOF-SIMS measurents indicate that the lateral resolution may be far below instrument limitations (beam focus). A quantitative comparison of the secondary particle emission from SP-C-rich and SP-C-free domains (on the same substrate) allowed some insight into the process of secondary ion and neutral generation from the molecular overlayer as well as from the substrate.