Ultra-Flexible Organic Light Emitting Diode for Optical Stimulation

Applications of organic electronic devices are rapidly extending from consumer devices, such as display and lighting, to wearable and biomedical applications. A variety of organic electronic devices can be fabricated on polymer films under room-temperature solution processes, and this has led to the realization of lightweight, thin, flexible, and large-area devices. The flexibility of organic light-emitting diodes (OLEDs) is considerable advantages in potential applications, particularly in optogenetics, as OLEDs have a high affinity for the target tissue. However, for such applications, the OLED should be improved to achieve an emission intensity sufficient for activating light-gated ion channels.<br/>In this study, we developed an ultra-flexible OLED for optogenetics, and stimulated the brain and peripheral motor and sensory neurons of the W-TChR2V4 transgenic rat which expresses channelrhodopsin-2 (ChR2), one of light-gated cation channels, in these neurons. The total thickness of the devices, including the substrate and encapsulation layer, is only three micrometers, which is one order of magnitude thinner than the epidermal layer of the human skin. Due to the very thin substrate and neutral position, our device shows the highly flexibility and conformability. The OLEDs are directly laminated on the surface of skin. The maximum light power density of 0.48 mW/mm² was enough high to drive the OLED over the animal’s relatively low threshold of approximately 0.3 mW/mm² for nerve excitation. Using the OLED device, we stimulated motor and sensory neurons by virtue of stable and conformal contact to the body.