Researchers at Graz University of Technology (TU Graz) have demonstrated that espresso can serve as an environmentally friendly substitute for uranyl acetate in electron microscopy staining. Uranyl acetate, the standard agent used to make tissue structures visible under an electron microscope, is both highly toxic and radioactive, which restricts its use in some laboratories due to safety concerns.
The team from the Institute of Electron Microscopy and Nanoanalysis (FELMI-ZFE) at TU Graz compared the effectiveness of espresso with uranyl acetate for staining biological samples. Their results, published in the journal Methods, indicate that images obtained using espresso were of comparable quality to those prepared with uranyl acetate.
Claudia Mayrhofer, who oversees ultramicrotomy at the institute, described how she developed the idea: "I got the idea of using espresso as a staining agent from the circular dried stains in used coffee cups." She explained her process: "Initial tests have shown that coffee stains biological samples and enhances contrasts."
Mayrhofer collaborated with team leader Ilse Letofsky-Papst and graduate student Robert Zandonella to test various staining agents on ultra-thin sections of mitochondria. They evaluated image quality using specialized software. According to Mayrhofer, "Espresso provided comparatively very good contrast values, in some cases they were even better than with uranyl acetate."
Ilse Letofsky-Papst summarized their findings: "Our results show that coffee is a serious alternative to uranyl acetate. However, further investigations on different types of tissues are still required to enable a broad application in life science electron microscopy."
