Biointerfacing with AgBiS₂ Quantum Dots for Pseudocapacitive Photostimulation

Abstract Optoelectronic biointerfaces have emerged as a promising platform for controlling the nervous system at the cellular, tissue, and organ levels with potential clinical applications via transduction of light energy to ionic currents. To improve charge injection, supercapacitor materials like IrO x , TiN, and PEDOT have been incorporated as an additional layer on the photodiodes at electrode–electrolyte interfaces. Here, a bioelectronic design is demonstrated where AgBiS 2 quantum dots (QDs) serve as the photoabsorption material, hole transport medium, and pseudocapacitive electrode–electrolyte interface. The power‐law behavior of the anodic and cathodic peaks suggests that diffusion‐controlled and capacitive processes contribute to the charge storage mechanism. Furthermore, 3D Bode capacitance maps and phase angle responses indicate a high capacitance of 3.3 mF cm⁻ 2 at the half‐wave potential (0.044 V vs Ag/AgCl) in artificial cerebrospinal fluid (aCSF). For efficient transduction of light to electrical stimulation, AgBiS 2 QDs are embedded onto ZnO nanowires (NWs) in a photovoltaic device architecture, which produces twice the photocurrent (1.9 ± 0.3 mA cm⁻ 2 ) and nearly three times the charge injection (29 ± 2.3 µC cm⁻ 2 ) compared to the planar devices without NWs. Moreover, photostimulation of hippocampal neurons is demonstrated on the device without inducing significant oxidative stress. This study demonstrates an unconventional and efficient bioelectronic device via pseudocapacitive optoelectronic nanocrystals.