Scanning electron-stimulated desorption microscopy of model-biological surfaces

Abstract

Electron-stimulated desorption (ESD) of ions and neutrals from surfaces has been used to study chemisorption in many simple gas–solid systems^1,2, but there has been much less effort devoted to ESD studies with significant spatial resolution^3–7. ESD contrasts with scanning electron microscopy because ESD signals depend sensitively on the coverage and binding of an adsorbed species¹. Applying scanning ESD to biological surfaces permits the surface chemical variations to be mapped using simple low mass adsorbates⁸ in comparison with conventional electron microscopy of biological matters which relies on heavy-metal stain technology⁹. We show here how scanning ESD can complement scanning Auger electron microscopy in mapping the surface chemistry of biological substrates. A model biological substrate constructed from a deposited synthetic polypeptide monolayer (polymethyl-glutamate) is used as the controlled sample surface. Micrographs display a spatial variation in H⁺ desorption with a resolution of 10⁻⁴ cm. We also discuss limitations to resolution as dictated by signal-to-noise considerations. The contrast mechanism would be useful for studying the important biological surface problems such as membrane morphology, cell-interfacial composition, and cell-to-cell adhesion.