Preparative Soft and Reactive Landing of Multiply Charged Protein Ions on a Plasma-Treated Metal Surface

Abstract

Soft landing on a plasma-treated metal surface of multiply protonated protein ions from the gas phase results in a substantial retention of protein function, as demonstrated for trypsin and streptavidin. The majority of trypsin ions soft-landed at hyperthermal kinetic energies are undamaged and retain 72-98% of enzymatic activity after being washed into solution. A small fraction of trypsin ions that were landed at nominal kinetic energies of 130-200 eV remain tethered to the surface and show approximately 50% enzymatic activity. The streptavidin tetramer is found to dissociate to monomer units upon multiple charging in electrospray. The majority of soft-landed monomers can be washed into solution where they show affinity to biotin. The layer of streptavidin monomer that is immobilized on the surface can be detected if fluorescence-tagged and retains the ability to reversibly bind biotin. A mechanism is proposed to explain nondestructive protein ion discharge on the surface that considers proton migration from the soft-landed cations to the metal oxide layer and metal ion reduction by electron transfer from the bulk metal.

Planar Functionalized Surfaces for Direct Immunoaffinity Desorption/Ionization Mass Spectrometry

“…The SEM images proved that antibody was deposited on the ITO surface and that washing with polar solvents removed only the uppermost layers, whereas the bottom layers, which interact with the surface directly, survived the washing. This finding explains why antibodymodified MALDI surfaces maintained immunoaffinity capabilities even after the washing, in accordance with the previous literature on protein and polysaccharide reactive landing on conductive and semiconductive surfaces (29,30 ).…”

Effect of the surface on charge reduction and desorption kinetics of soft landed peptide ions

“…SL is defined as intact capture of mass-selected polyatomic ions on substrates [6,7] and has already been successfully used to study charge retention by small closedshell ions [6 -9] and peptide and protein ions deposited onto self-assembled monolayer surfaces (SAMs) [10 -13]. Retention of biological activity (but not charge) by proteins deposited on liquid [10,14] and on plasma treated metal surfaces [15] has also been demonstrated.Recently we reported the first detailed study of the kinetics of desorption and charge reduction following SL of doubly protonated Gramicidin S (GS) onto the FSAM surface [16]. We utilized an in-line 8 keV Cs ϩ ion gun that allowed us to interrogate the surface in situ and in real time using secondary ion mass spectrometry (SIMS).…”

“…SL is defined as intact capture of mass-selected polyatomic ions on substrates [6,7] and has already been successfully used to study charge retention by small closedshell ions [6 -9] and peptide and protein ions deposited onto self-assembled monolayer surfaces (SAMs) [10 -13]. Retention of biological activity (but not charge) by proteins deposited on liquid [10,14] and on plasma treated metal surfaces [15] has also been demonstrated.…”

Reactions of Organic Ions at Ambient Surfaces in a Solvent-Free Environment

“…Electrospray ionization (ESI) [17] offers a simple way to generate organic ions/aerosols in ambient air and subse-quently study their reactivity under vacuum using mass spectrometry (MS) [18][19][20] These vacuum-based experiments can employ either ion/molecule [21] or ion/surface reactions [22,23]. The instrumentation used in the ion/ surface reactions is similar to that used in the ion soft landing technique [24][25][26] except that the mass-selected polyatomic ions are given enough energy to react selectively with particular functional groups present at the surface.…”