Freezing instead of freeze-drying before spectroscopy preserves sample surface structure
Freezing instead of freeze-drying before spectroscopy preserves sample surface structure lead image
X-ray photoelectron spectroscopy (XPS) examines the surface chemistry of materials. XPS is not typically used to investigate biological samples because the vacuum inside the spectrometer requires that they must be dehydrated, which can rearrange surface structures.
However, Ramstedt and Shchukarev used cryogenic XPS to study the surface chemistry of a species of bacteria known as Pseudomonas fluorescens. This method enables a sample to be analyzed while frozen instead of dehydrated, preserving its original surface structure.
With cryogenic XPS, the authors obtained spectra corresponding to the bacterial cell surface. Previously, the team used cryogenic XPS to study the surfaces of microorganisms beyond bacteria, including algae, fungi, and viruses. Understanding surface chemistry is important because the surface of a cell dictates how it interacts with other cells and particles.
“Cryogenic XPS is not new, but it’s quite unusual that it’s used on biological specimens,” author Madeleine Ramstedt said. “This work illustrates that you can use cryogenic XPS to acquire spectra of an intact biological sample, while circumventing the whole need of freeze-drying.”
This method could also be used on non-biological, soft materials that need to stay hydrated.
In addition to presenting their reference spectra set, the researchers described their methodology in detail, demonstrating how to apply cryogenic XPS to biological samples. For those who want to compare this cryogenic XPS data with other measurements, they offer a link to near ambient pressure XPS data for the same species of bacteria.
Next, the authors will use cryogenic XPS to study communities of microorganisms, such as those in microbial biofilms.
Source: “Cryo-XPS spectra from bacterial reference strain Pseudomonas fluorescens DSM50090,” by Madeleine Ramstedt and Andrey Shchukarev, Surface Science Spectra (2022). The article can be accessed at https://doi.org/10.1116/6.0001575 .
