MnO₂ Nanoflower Integrated Optoelectronic Biointerfaces for Photostimulation of Neurons

Optoelectronic biointerfaces have gained significant interest for wireless and electrical control of neurons. Three-dimentional (3D) pseudocapacitive nanomaterials with large surface areas and interconnected porous structures have great potential for optoelectronic biointerfaces that can fulfill the requirement of high electrode-electrolyte capacitance to effectively transduce light into stimulating ionic currents. In this study, the integration of 3D manganese dioxide (MnO₂ ) nanoflowers into flexible optoelectronic biointerfaces for safe and efficient photostimulation of neurons is demonstrated. MnO₂ nanoflowers are grown via chemical bath deposition on the return electrode, which has a MnO₂ seed layer deposited via cyclic voltammetry. They facilitate a high interfacial capacitance (larger than 10 mF cm^-2 ) and photogenerated charge density (over 20 µC cm^-2 ) under low light intensity (1 mW mm^-2 ). MnO₂ nanoflowers induce safe capacitive currents with reversible Faradaic reactions and do not cause any toxicity on hippocampal neurons in vitro, making them a promising material for biointerfacing with electrogenic cells. Patch-clamp electrophysiology is recorded in the whole-cell configuration of hippocampal neurons, and the optoelectronic biointerfaces trigger repetitive and rapid firing of action potentials in response to light pulse trains. This study points out the potential of electrochemically-deposited 3D pseudocapacitive nanomaterials as a robust building block for optoelectronic control of neurons.