Quantitative Visualization of Molecular Delivery and Uptake at Living Cells with Self-Referencing Scanning Ion Conductance Microscopy-Scanning Electrochemical Microscopy.

A multifunctional dual-channel scanning probe nanopipet that enables simultaneous scanning ion conductance microscopy (SICM) and scanning electrochemical microscopy (SECM) measurements is demonstrated to have powerful new capabilities for spatially mapping the uptake of molecules of interest at living cells. One barrel of the probe is filled with electrolyte and the molecules of interest and is open to the bulk solution for both topographical feedback and local delivery to a target interface, while a solid carbon electrode in the other barrel measures the local concentration and flux of the delivered molecules. This setup allows differentiation in molecular uptake rate across several regions of single cells with individual measurements at nanoscale resolution. Further, operating in a "hopping mode", where the probe is translated toward the interface (cell) at each point allows self-referencing to be employed, in which the carbon electrode response is calibrated at each and every pixel in bulk for comparison to the measurement near the surface. This is particularly important for measurements in living systems where an electrode response may change over time. Finite element method (FEM) modeling places the technique on a quantitative footing to allow the response of the carbon electrode and local delivery rates to be quantified. The technique is extremely versatile, with the local delivery of molecules highly tunable via control of the SICM bias to promote or restrict migration from the pipet orifice. It is expected to have a myriad of applications from drug delivery to screening catalysts.