Light Stimulation of Neurons on Organic Photocapacitors Induces Action Potentials with Millisecond Precision

Abstract

Nongenetic optical control of neurons is a powerful technique to study and manipulate the function of the nervous system. This research has benchmarked the performance of organic electrolytic photocapacitor (OEPC) optoelectronic stimulators at the level of single mammalian cells: human embryonic kidney (HEK) cells with heterologously expressed voltage‐gated K+ channels and hippocampal primary neurons. OEPCs act as extracellular stimulation electrodes driven by deep red light. The electrophysiological recordings show that millisecond light stimulation of OEPC shifts conductance‐voltage plots of voltage‐gated K+ channels by ≈30 mV. Models are described both for understanding the experimental findings at the level of K+ channel kinetics in HEK cells, as well as elucidating interpretation of membrane electrophysiology obtained during stimulation with an electrically floating extracellular photoelectrode. A time‐dependent increase in voltage‐gated channel conductivity in response to OEPC stimulation is demonstrated. These findings are then carried on to cultured primary hippocampal neurons. It is found that millisecond time‐scale optical stimuli trigger repetitive action potentials in these neurons. The findings demonstrate that OEPC devices enable the manipulation of neuronal signaling activities with millisecond precision. OEPCs can therefore be integrated into novel in vitro electrophysiology protocols, and the findings can inspire in vivo applications.

Electrical stimulation methods and protocols for the treatment of traumatic brain injury: a critical review of preclinical research

“…It is also possible to implant passive components in the brain that convert an external impulse from a source outside the skull into an electrical stimulus. An example for this would be photocapacitors [147][148][149], which charge up when they are irradiated by light pulses, creating an electric field at their surface, leading to the depolarization of adjacent neural cells. These photocapacitive devices can also be used in combination with temporal interference stimulation protocols [150].…”

Semiconducting electrodes for neural interfacing: a review

“…277,278 These devices have been used successfully used in in vitro and in vivo neurostimulation. 275,279 However, as mentioned, these are essentially photovoltaic or photocapacitive devices generating the charge with the PEDOT:PSS acting as the electrode layer. This is in contrast with semiconducting electrodes providing neuronal interfacing.…”

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“…∼80% biocompatibility indicates that it is generally well-tolerated by cells and has a relatively low level of adverse effects. Such biocompatibility levels are appropriate to grow primary neurons on the device for photostimulation [1]. …”