What is the osmium metalorganic probe and why is it used?

The osmium metalorganic probe is a proprietary chemical compound developed and patented by Yenos Analytical (and Dr. Kanavarioti's earlier work at UCSC) that reacts with specific nucleobases in RNA molecules. Osmium tetroxide (OsO₄) is known to react with pyrimidine bases (uracil and thymine) in nucleic acids. The Yenos osmium metalorganic probe is a modified, stabilized form designed to specifically and efficiently tag miRNA molecules without degrading them. The bulky osmium group attached to the miRNA serves two purposes: it slows the molecule's transit through the nanopore (increasing signal detection time) and it creates a distinctive, reproducible current blockage pattern that identifies the molecule and distinguishes it from other RNA species in the sample.