Surface characterisation of Escherichia coli under various conditions by near‐ambient pressure XPS

Abstract

Bacteria are inherently in a hydrated state and therefore not compatible to ultra‐high vacuum techniques such as XPS without prior sample preparation involving freeze drying or fast freezing. This has changed with the development of near‐ambient pressure (NAP)‐XPS, which makes it possible to characterise the bacterial surface with minimal sample preparation. This paper presents NAP‐XPS measurements of Escherichia coli under various NAP conditions: at 11 mbar in a humid environment, at 2 mbar after drying in the chamber, pre‐dried at 4 mbar, and at 1 mbar after overnight pumping at 10−4 mbar. The high‐resolution spectra of carbon, nitrogen, and oxygen are presented and found to be in general agreement with XPS measurements from freeze‐dried and fast‐frozen bacteria. However, it was found that the amount of carbon components associated with polysaccharides increases relative to aliphatic carbon during drying and increases further after overnight pumping. This implies that drying has an impact on the bacterial surface.