Figure 1
K. Mathwig et al., Phys. Rev. Lett. (2012)

Cross currents. As fluid flows through the nanochannel, electrochemically active molecules (red) generate an electric current by shuttling electrons from the bottom electrode to the top one. When there’s an occasional random increase in the number of molecules, the slightly boosted current shows up at the second pair of electrodes slightly later than at the first pair, and the delay gives the flow rate.