What is a picoampere and why does 180 pA matter?

A picoampere (pA) is 10⁻¹² amperes — one trillionth of an ampere. 180 pA is the baseline ionic current through a single nanopore in the MinION/Yenos system under operating conditions. This baseline current is established by the flow of potassium and chloride ions through the nanopore in the presence of the salt buffer solution. When an osmium-tagged miRNA molecule enters the nanopore, it partially blocks the ion flow and reduces the current — often to 70–90% of baseline — for the duration that the molecule is inside the pore (typically microseconds to milliseconds). The magnitude and duration of this current blockage event is the measurement signal. The 180 pA baseline provides a highly stable reference against which these small blockage events are measured with precision.