Electronic Sputtering of Biomolecules

Abstract

The erosion of surfaces under particle bombardment is called sputtering. For metallic targets, sputtering by elastic collisions between screened nuclei (nuclear sputtering) is the dominating mechanism. This effect is most important at low velocities, i.e. below the Bohr velocity, where nuclear stopping is the main energy loss mode. In insulators, where lifetimes of excited electronic states may be long enough to allow excitation energy to be transferred to atomic motion, sputtering due to electronic processes can occur as well. Sputtering of biomolecules by fast ions i.e. ions with a velocity larger than the Bohr velocity, has been shown to be related to electronic stopping [1,2] and may therefore be called electronic sputtering. Most of the ejected particles in sputtering processes are neutral. As recently shown at Uppsala by Salehpour et.al. [3] that is also the case for electronic sputtering of biomolecules.as will be discussed in some detail below. The analytical application of electronic sputtering of biomolecules is the method invented by Macfarlane and coworkers [4] called ²⁵²Cf-Plasma Desorption Mass Spectrometry (PDMS). As fission fragments are fast ions, this method may be described as fast ion-solid sample — SIMS with the time-of-flight technique. One of the most promising developments in the field of PDMS involves the use of samples consisting of adsorbed monolayers or submonolayers of biomolecules on polymer backings [5,6]. In this report. sample application by adsorbing proteins on nitrocellulose is discussed.