Paper AS-MoA3
Soft Cluster-Induced Desorption and Ionization of Biomolecules – Influence of Surface Load and Sample Morphology on Desorption Efficiency

Monday, October 31, 2011, 2:40 pm, Room 102

Neutral cluster-induced desorption and ionization is a very soft method for transferring surface-adsorbed biomolecules into the gas phase [1]. Using neutral SO₂ clusters seeded in a He beam, the method makes use of the dipole moment of the cluster's constituents which allows both for solvation and charge transfer processes in the cluster [2]. Thus the cluster provides not only the energy for the desorption process but also serves as a transient matrix. As a consequence, desorption and ionization of oligopeptides and proteins is observed at low energies of the impacting clusters and without any fragmentation of the biomolecules.

Here we show that cluster-induced desorption and ionization of biomolecules can be efficiently applied for a wide range of surface concentrations and configurations, i.e. from µm-thick films down to surfaces prepared with submonolayer surface concentration of biomolecules. Highest signal intensity in the respective mass spectra was observed from thick films, indicating an efficient desorption mechanism from bulk-like material. In the submonolayer regime, the ion signal of the desorbed biomolecules was found to depend nonlinearly on surface concentration of the wet-chemically applied biomolecules. The behavior is traced back to the formation of multilayered islands of biomolecules on the surface, as observed by means of SEM and AFM, and a dominant contribution to the ion signal from these islands even at low coverage. With the current set-up and preparation scheme, the lower detection limit was shown to be 10^-13 mol.

[1] C. R. Gebhardt, A. Tomsic, H. Schröder, M. Dürr, and K.L. Kompa, Angew. Chem. Int. Ed. 48, 2009, 4162.

[2] C. R. Gebhardt, H. Schröder, K. L. Kompa, Nature 400, 1999, 544.