Researchers at the Institute of Electron Microscopy and Nanoanalytics at the Graz University of Technology have demonstrated ordinary espresso as an effective contrast agent for biological samples under the electron microscope. The images achieve a comparable or in some cases better quality than with the highly toxic and radioactive standard agent uranyl acetate.

Uranyl acetate is traditionally used to visualize tissue structures in ultra-thin sample sections. Due to its toxicity and radioactivity, the substance is banned in some laboratories for safety reasons. The team led by Claudia Mayrhofer, Ilse Letofsky-Papst and Robert Zandonella was looking for an alternative.

The idea came from observing dried coffee stains in cups. Initial tests showed that coffee stains biological samples and enhances contrasts. In systematic comparative experiments, the researchers treated ultra-thin sections of mitochondria under identical conditions with espresso and uranyl acetate. Image analysis software evaluated the microscope images. Espresso achieved very good contrast values, in some cases even higher than uranyl acetate.

The team sees coffee as a serious, environmentally friendly alternative. However, for widespread use in biological electron microscopy, further tests on different tissue types are required.

Original Paper:

Coffee – a ubiquitous substitute for uranyl acetate in staining of biological ultrathin sections for electron microscopy studies
Authors: Claudia Mayrhofer, Robert Zandonella, Willi Salvenmoser, Ilse Letofsky-Papst.
In: Methods (2025)

DOI: 10.1016/j.ymeth.2025.08.009

Editor: X-Press Journalistenbüro GbR

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