UAR-EMS Stain is a new negative and positive stain which may be used as an alternative to uranyl acetate.


The UAR Stain is supplied as a concentrate. Please use the following dilutions:

  • For most very small particulate specimens like most viruses, dilute by 4x with distilled water.
  • If you are working with bacteria, then a dilution of 15-40x is needed.

Use similar dilutions for positive and negative staining. Positive staining will take place in 30 minutes at room temperature. For increased contrast of the stain, simply adjust the staining time.

Reference Article

Nakakoshi, Masamichi, Hideo Nishioka and Eisaku Katayama, 2011. New versatile reagents for biological transmission electron microscopy that substitute for uranyl acetate. Journal of Electron Microscopy, 60(6): 401-407.


Aqueous uranyl acetate has been extensively used as a superb staining reagent for transmission electron microscopy of biological materials. However, recent regulation of nuclear fuel material severely restricts its use even for purely scientific purposes. Since uranyl salts are hazardous due to biological toxicity and remaining radioactivity, development of safe and non-radioactive substitutes is greatly anticipated. We examined two lanthanide salts, samarium triacetate and gadolinium triacetate, and found that 1-10% solution of these reagents was safe but still possess excellent capability for staining thin sections of plastic-embedded materials of animal and plant origin. Although post-fixation with osmium tetroxide was essential for high-contrast staining, post-staining with lead citrate could be eliminated if a slow-scan CCD camera is available for observation. These lanthanide salts can also be utilised as good negative-staining reagents to study supra-molecular architecture of biological macro-molecules. They were not as effective as a fixative of protein assembly, reflecting the non-hazardous nature of the reagents.