An ongoing effort in many neuroscience laboratories is to perform chronic optical imaging and multiplexed electrophysiological recordings in awake behaving mice. We have adapted the use of conformal thin parylene C in conjunction with conductive polymer PEDOT:PSS coating on the electrode sites to realize wearable microelectrode array devices with sufficient optical transparency to allow simultaneous multiphoton imaging and optogenetic manipulation. These devices replace the current cranial glass windows providing broadband measurements of the extracellular potential as well as a see-through optical access. We have developed a mechanical solution for installation, connectorization and protection of the device and circuit board aiming for lifetime of several months while worn by a mouse. Our design allows access for high numerical aperture microscope objectives and does not obstruct the mouse face and whiskers enabling meaningful behaviors.
Electrocorticography (ECoG) is a powerful tool for direct mapping of local field potentials from the brain surface. Progress in development of high-fidelity materials such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on thin conformal substrates such as parylene C enabled intimate contact with cortical surfaces and higher quality recordings from small volumes of neurons. Meanwhile, stimulation of neuronal activity is conventionally accomplished with electrical microstimulation and transcranial magnetic stimulation that can be combined with ECoG to form the basis of bidirectional neural interface. However, these stimulation mechanisms are less controlled and primitively understood on the local and cellular levels. With the advent of optogenetics, the localization and specificity of neuronal stimulation and inhibition is possible. Therefore, the development of integrated devices that can merge the sensitivity of ECoG or depth recording with optogenetic tools can lead to newer frontiers in understanding the neuronal activity.
Herein, we introduce a hybrid device comprising flexible inorganic LED arrays integrated PEDOT:PSS/parylene C microelectrode arrays for high resolution bidirectional neuronal interfaces. The flexible inorganic LEDs have been developed by the metal-organic vapor phase epitaxy of position-controlled GaN microLEDs on ZnO nanostructured templates pre-grown at precise locations on a graphene layer. By transferring it onto the microelectrode arrays, it can provides the individual electrical addressability by light stimulation patterns. We will present experimental and simulation results on the optoelectronic characteristics and light activation capability of flexible microLEDs and their evaluation in vivo.
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