AVS 51st International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoA

Paper AS-MoA1
Single Photon Ionization of a Derivatized Peptide Covalently Bound to a Surface

Monday, November 15, 2004, 2:00 pm, Room 210A

Session: SIMS II - Biological and Organic
Presenter: L. Hanley, University of Illinois at Chicago
Authors: P.D. Edirisinghe, University of Illinois at Chicago
S.S. Lateef, University of Illinois at Chicago
C.A. Crot, University of Illinois at Chicago
L. Hanley, University of Illinois at Chicago
J.F. Moore, Argonne National Laboratory
W.F. Calaway, Argonne National Laboratory
M.J. Pellin, Argonne National Laboratory
Correspondent: Click to Email
Covalently bound peptides, proteins, and other biomolecules are widely used for microarrays, microfluidic channels, cell growth surfaces, and biosensors. Detection of these surface bound species by matrix assisted laser desorption ionization or secondary ion mass spectrometry (SIMS) is often complicated by low ionization yields and/or high fragmentation. Single photon ionization is one method that shows great promise for enhancing ionization yields with a minimum of fragmentation. The fluorine excimer laser is an intense laboratory source of vacuum ultraviolet radiation, but the 7.87 eV photons it generates are lower in energy than the ionization potential of many target species. A method is described here whereby derivatization of peptides with the Fmoc group allows efficient fluorine laser single photon ionization of the entire labeled peptide. Various Fmoc labeled peptides are covalently bound to oxidized Si(100) wafers via maleimide coupling to surface bound aminopropyltriethoxysilane. Physisorbed films of Fmoc labeled peptides, unlabelled peptides, and various amino acids are prepared by drying a solution thereof onto the silicon wafer. Both covalently bound and physisorbed peptides are analyzed by laser desorption photoionization (LDPI) mass spectrometry. Only the Fmoc labelled peptides form large ions identified as common peptide fragments bound to either Fmoc or the surface linker. Unlabelled peptides and amino acids do not form large representative ions. Electronic structure calculations performed with Gaussian 98 indicate the Fmoc label is behaving as an ionization tag for the entire peptide, lowering the ionization potential of the complex below the 7.87 eV photon energy. This method should allow detection of many molecular species covalently or electrostatically bound to surfaces.