Controlling the droplet cell environment in scanning electrochemical cell microscopy (SECCM) via migration and electroosmotic flow

, ferrocene derivatives and Ruthenium(III) hexamine) were filled in separate channels, where their limiting currents at the substrate electrode were used to distinguish the contribution of migration and EOF. Furthermore, EOF was visualized by fluorescence imaging. Finite element models were developed to further validate the experimental results quantitively. We showed that migration is affected by the charge number of the redox molecule. Meanwhile, EOF is affected by the surface charge on the wall of the nanopipette and the location of the slipping plane inside the electrical double layer, which can be tuned by the solution pH and the ionic strength of the electrolyte, respectively. The experimentally validated model can guide the precise modulation of droplet cell environment in SECCM, potentially enabling new scanning modes in SECCM.