Atom probe tomography of hydrated biomacromolecules: preliminary results

TL;DR

This study explores the potential of atom probe tomography (APT) for analyzing hydrated biomacromolecules, demonstrating preliminary feasibility and highlighting challenges like sample damage due to ice crystal formation.

Contribution

It presents a novel workflow for preparing and analyzing hydrated biological samples with APT, including cryogenic techniques and initial proof-of-concept results.

Findings

Elements from ferritin core and shell detected

Sample damage due to ice crystal formation observed

Preliminary data shows potential for analyzing intact biomolecules

Abstract

The folding and structure of biomacromolecules depend on the 3D distributions of their constituents, which ultimately controls their functionalities and interactions with other biomacromolecules. Atom probe tomography (APT) with its unparalleled compositional sensitivity at nanoscale spatial resolution, could provide complementary information to cryo-electron microscopy, yet routine APT analysis of biomacromolecules in their native state remains challenging. Here, a ferritin solution was used as a model system. Following plunge freezing in liquid nitrogen, cryogenic lift-out and cryo-APT analysis were performed. Elements from the ferritin core and shell are detected yet particles seem destroyed. We hence demonstrate the feasibility of preparing and analyzing bulk hydrated biological samples using APT, however, the cooling was too slow to vitrify the solution. This caused irrecoverable damage to the protein shell surrounding the ferritin particles due to ice crystal formation. We report on preliminary data from high-pressure frozen (HPF) deionized (DI) water, demonstrating a proof-ofprinciple experiments that intact biomacromolecules could be analyzed through a similar workflow in the future. We report on many trials (and errors) on the use of different materials for substrates and different substrate geometries, and provide a perspective on the challenges we faced to facilitate future studies across the community.