Hydrogel Patterning with Catechol Enables Networked Electron Flow

Reduction–oxidation (redox) reactions provide a distinct modality for biological communication that is fundamentally different from the more-familiar ion-based electrical modality. Biology uses these two modalities for communication through different systems (immune versus nervous), and uses different mechanisms to control the flow of the charge carriers: the flow of soluble ions is controlled using structural barriers (i.e., membranes) and gates (e.g., membrane-spanning protein channels), while the flow of insoluble electrons is controlled using redox-reaction networks. Here, a simple electrochemical approach to pattern catechols onto a flexible polysaccharide hydrogel is reported and it is demonstrated that the patterned catechol regions serve as nodes for the mediated flow of electrons through redox reactions. Electron flow through this node involves the switching of binary redox states (oxidized and reduced) and this node's redox state can be detected (i.e., “read”) by passively observing its optical absorbance, or actively switching its redox-state electrochemically. Further, this catechol node can be switched through biological mechanisms, and this enables the fabricated catechol node to be embedded within biochemical redox reaction networks to facilitate the spanning of bio-electronic communication. Thus, it is envisioned that catechols can emerge as a molecular equivalent to a transistor for miniaturize-able, deployable and sustainable redox-linked bioelectronics.