  The understanding of protein structure, folding, and interaction with other
proteins remains one of the grand challenges of modern biology. Tremendous
progress has been made thanks to X-ray- or electron-based techniques that have
provided atomic configurations of proteins, and their solvation shell. These
techniques though require a large number of similar molecules to provide an
average view, and lack detailed compositional information that might play a
major role in the biochemical activity of these macromolecules. Based on its
intrinsic performance and recent impact in materials science, atom probe
tomography (APT) has been touted as a potential novel tool to analyse
biological materials, including proteins. However, analysis of biomolecules in
their native, hydrated state by APT have not yet been routinely achieved, and
the technique's true capabilities remain to be demonstrated. Here, we present
and discuss systematic analyses of individual amino-acids in frozen aqueous
solutions on two different nanoporous metal supports across a wide range of
analysis conditions. Using a ratio of the molecular ions of water as a
descriptor for the conditions of electrostatic field, we study the
fragmentation and behavior of those amino acids. We discuss the importance
sample support, specimen preparation route, acquisition conditions and data
analysis, to pave the way towards establishing guidelines for cryo-APT analysis
of biomolecules.
