Detection of the Spontaneous Action Potentials of HEK 293 Cells by Prussian Blue thin Films

The gold standard for investigating neuronal electrical activities has been electrodes. Modern electrophysiology methods boast high sensitivity and temporal resolution with the ability to measure single ion channels and networks of neurons. However, the spatial resolution and robustness are limited by the size and geometry of the electrode. In this era, optical methods have picked up momentum as powerful tools to measure the electrical activities of neurons by using an optical probe that transduces the electrical signal into an optical signal.Prussian blue (PB) is a mixed-valence inorganic material composed of alternating ferric and ferrous ions in a cubic, cyano-bridged lattice with open sites for alkaline metal intercalation. This material is known for its biocompatibility, insolubility in water, activities toward alkaline metal ions and electrochromicity. It is the latter property that makes Prussian blue an excellent candidate to measure the electrical potentials of excitable membranes. The color of this material depends on the applied electrical potential which in turn controls the redox state of the irons. Its blue color is turned to colorless by reduction and is recovered by oxidation. We hypothesize that the electrical potential of excitable membranes will modulate the spectral properties of the material which will be detected through a differential photodiode detector.A PB thin film was electrodeposited onto an ITO-coated glass slide and its optical properties were characterized. As a model for electrophysiology measurements, a clone line of modified HEK 293 cells that stably express Nav 1.3 and KIR 2.1 and generate spontaneous electrical action potentials were used. Herein, we demonstrate the ability to detect the extracellular action potentials of HEK 293 cells and evaluate the film's potential for imaging networks of neuronal cells.