Photostimulation for In Vitro Optogenetics with High-Power Blue Organic Light-Emitting Diodes

Optogenetics, photostimulation of neural tissues rendered sensitive to light, is widely used in neuroscience to modulate the electrical excitability of neurons. For effective optical excitation of neurons, light wavelength and power density must fit with the expression levels and biophysical properties of the genetically encoded light-sensitive ion channels used to confer light sensitivity on cells-most commonly, channelrhodopsins (ChRs). As light sources, organic light-emitting diodes (OLEDs) offer attractive properties for miniaturized implantable devices for in vivo optical stimulation, but they do not yet operate routinely at the optical powers required for optogenetics. Here, OLEDs with doped charge transport layers are demonstrated that deliver blue light with good stability over millions of pulses, at powers sufficient to activate the ChR, CheRiff when expressed in cultured primary neurons, allowing live cell imaging of neural activity with the red genetically encoded calcium indicator, jRCaMP1a. Intracellular calcium responses scale with the radiant flux of OLED emission, when varied through changes in the current density, number of pulses, frequency, and pulse width delivered to the devices. The reported optimization and characterization of high-power OLEDs are foundational for the development of miniaturized OLEDs with thin-layer encapsulation on bioimplantable devices to allow single-cell activation in vivo.