Chemistry Researchers discover the benefits of espresso for microscopy
The highly toxic and radioactive uranyl acetate is used when examining biological samples with an electron microscope. Researchers from Austria have looked for and found a harmless and inexpensive alternative: ordinary espresso.
08.01.2026, 12:17
SDA
The Graz University of Technology (TU Graz) announced on Thursday that images of the samples examined with this method were of equally good quality, in some cases even better. The researchers have published their findings in the journal "Methods".
Coffee is not only an invigorating drink, it also leaves colorful traces - in coffee cups and pots, on teeth and in ultra-thin sections of biological tissue. Claudia Mayrhofer from the Institute of Electron Microscopy and Nanoanalytics at Graz University of Technology (FELMI-ZFE) has become aware of the latter. In her latest study, she investigated the effect of coffee as a staining agent for contrast enhancement in transmission electron microscopy.
"I got the idea of using espresso as a contrast agent from the circular dried stains in forgotten coffee cups," explained Mayrhofer.
Environmentally friendly alternatives
Contrasting the ultra-thin tissue samples, which inherently exhibit only low contrast within the cell structures, is the last step before examination under an electron microscope.
One of the most commonly used staining agents for decades is uranyl acetate, but it is toxic and radioactive. Researchers have therefore been looking for alternatives that are as environmentally friendly as possible for some time.
Together with her team leader Ilse Letofsky-Papst, Mayrhofer has investigated the coloring properties of coffee in initial experiments with ultra-thin tissue sections of zebrafish. She concentrated on the mitochondrial membranes. For these initial experiments, a ten percent solution of fresh coffee grounds was prepared and boiled for 30 minutes. The staining ability of coffee compared to commercially available staining agents and uranyl acetate was evaluated based on the interference contrast between membranes and their surroundings.
"Espresso provided very good contrast values in comparison, in some cases they were even better than with uranyl acetate," reported Mayrhofer. However, further studies on different types of tissue are still required for broad application in biological electron microscopy.
