Oolong tea extract as a substitute for uranyl acetate in staining of ultrathin sections

In conventional transmission electron microscopy, uranyl acetate staining is used to enhance the cellular components. However, uranyl acetate is considered a radioactive material that is very toxic if ingested or inhaled and subject to restrictions in many countries. In an attempt to introduce a substitute for uranyl acetate, we evaluated oolong tea extract (OTE) for staining of ultrathin sections. Tissue sections from normal rat liver representing an ideal model organ were processed according to a routine electron microscopic fixation and embedding procedure. Serial ultrathin sections were cut and processed with either routine double electron staining or 0.2% OTE staining for 30–40 min at room temperature followed by lead citrate staining (OTE staining method). Transmission electron microscopy observations revealed that all sub‐cellular structures in hepatocytes were clearly visible with OTE staining and the quality of staining was highly compatible with those of routine double staining methods. It is suggested that OTE could be used as a non‐radioactive and hazard‐free substitute for uranyl acetate in transmission electron microscopy staining.