Cryo‐XPS: probing intact interfaces in nature and life

Experimental studies of solid–aqueous solution interfaces are of great importance for reaching a better chemical understanding of interfacial phenomena at the molecular level. This perspective article presents a recently developed approach for investigation of intact interfaces, based on fast freezing of centrifuged wet pastes followed by traditional XPS measurements at liquid nitrogen temperatures. Sample preparation and handling protocols, applicable to any suspension or gel, are discussed in detail. For mineral suspensions, cryogenic XPS is an important complement to traditional analyses of supernatant solutions and dry solids that is capable of revealing novel insights of the electrical double layer in terms of structure and composition. It can be used to study changes in the biochemistry of bacterial cell walls as influenced by external stimuli, and interfacial features related to biocompatibility of implant materials. Herein we review how the technique has been applied to minerals in electrolyte solutions, intact bacterial surfaces, and biomaterial interfaces in biologically relevant media, and highlight some future requirements for development of interface analysis methodologies. Copyright © 2016 John Wiley & Sons, Ltd.