Light-Addressable Ion Sensing for Real-Time Monitoring of Extracellular Potassium

We report here on a light addressable potassium (K⁺ ) sensor where light illumination of a semiconducting silicon electrode substrate results in a localized activation of the faradaic electrochemistry at the illuminated spot. This allows one, by electrochemical control, to oxidize surface bound ferrocene moieties that in turn trigger K⁺ transfer from the overlaid K⁺ -selective film to the solution phase. The resulting voltammetric response is shown to be K⁺ -selective, where peak position is a direct function of K⁺ activity at the surface of electrode. This concept was used to measure extracellular K⁺ concentration changes by stimulating living breast cancer cells. The associated decrease of intracellular K⁺ level was confirmed with a fluorescent K⁺ indicator. In contrast to light addressable potentiometry, the approach introduced here relies on dynamic electrochemistry and may be performed in tandem with other electrochemical analysis when studying biological events on the electrode.