How does an electrical signal become a miRNA count?

The MinION records the current through each nanopore channel many thousands of times per second. Software monitors these current traces for 'events' — characteristic transient reductions in current (dips below the 180 pA baseline) that indicate a molecule has entered the pore. For an osmium-tagged miRNA, the current dip has a specific depth (how far it drops), duration (how long the molecule stays in the pore), and shape (the current trace profile during translocation). The Yenos bioinformatics pipeline filters raw events to identify those matching the signature of each specific osmium-tagged miRNA. The number of valid events per unit time is the count of miRNA molecules, which is converted to a concentration and then expressed as an HL multiple.