3D sub-nanometer analysis of glucose in an aqueous solution by cryo-atom probe tomography

T M Schwarz,B Gault,G Schmitz,J Kästner,H Solodenko,E Hadjixenophontos,R Lawitzki,P Stender,E M Weikum,C A Dietrich,J Ott

doi:10.1038/s41598-021-90862-8

Abstract

Atom Probe Tomography (APT) is currently a well-established technique to analyse the composition of solid materials including metals, semiconductors and ceramics with up to near-atomic resolution. Using an aqueous glucose solution, we now extended the technique to frozen solutions. While the mass signals of the common glucose fragments CxHy and CxOyHz overlap with (H2O)nH from water, we achieved stoichiometrically correct values via signal deconvolution. Density functional theory (DFT) calculations were performed to investigate the stability of the detected pyranose fragments. This paper demonstrates APT’s capabilities to achieve sub-nanometre resolution in tracing whole glucose molecules in a frozen solution by using cryogenic workflows. We use a solution of defined concentration to investigate the chemical resolution capabilities as a step toward the measurement of biological molecules. Due to the evaporation of nearly intact glucose molecules, their position within the measured 3D volume of the solution can be determined with sub-nanometre resolution. Our analyses take analytical techniques to a new level, since chemical characterization methods for cryogenically-frozen solutions or biological materials are limited.

Highlights

To create a saturated glucose solution, glucose was added to water until the solubility limit was reached and a sediment formed on the bottom of the test glass
For the Lift-Out process, tungsten wires were first etched in 2 mol NaOH solution by applying an AC voltage
The shuttle is attached to the high vacuum-coater (Leica EM ACE600), to carry out a freeze-etching process to remove ice crystals that were formed by the contact of the sample with air

Summary

Introduction

The shuttle is attached to the high vacuum-coater (Leica EM ACE600), to carry out a freeze-etching process to remove ice crystals that were formed by the contact of the sample with air. Leica EM ACE600 high vacuum coater is useful to improve the vacuum condition inside the shuttle ( 10−4 mbar), which is necessary to enable the transfer of the sample into the Focused-Ion-Beam (FIB) Microscope. In order to prepare cryogenic samples in the FIB (FEI Scios) into nano-shaped tips with an apex radius less than 100 nm, which is required for the APT method, the FIB has to be equipped with a custom made cryo-stage, which is cooled down to a temperature of − 150 °C using copper bands connected to a N2 Dewar attached to the microscope.

Results

Conclusion