System-Level Network Analysis of a Catechol Component for Redox Bioelectronics

Abstract

Redox is a ubiquitous biological signaling modality that is providing opportunities for bioelectronics. Various experimental studies have demonstrated that catechols offer unique molecular electronic properties for redox-based bioelectronics because catechols can confer redox activity without conductivity. Here, we fabricated a catechol-containing hydrogel film at an electrode surface and characterized this film using dynamic spectroelectrochemical measurements and physics-based modeling (i.e., reaction–diffusion modeling). We show that (i) the flow of electrons through the catechol film involves a redox reaction network; (ii) the redox-state switching of the catechol node is gated by diffusible electron carriers (i.e., mediators) and synchronized to electron transfer at the electrode; and (iii) a physics-based reaction–diffusion model can be abstracted into readily measurable metrics that can be used to characterize the response characteristics of more complex experimental systems (i.e., systems that cannot be described from first principles). Finally, we performed a simple perturbation analysis to illustrate how theory can guide the selection of metrics capable of detecting interactions between the catechol-coated electrode and bio-relevant nodes of a redox interactome (i.e., metrics that are sensitive to redox network topology). Overall, this work provides a unifying framework to understand catechol-based electrode coatings and suggests how theory can guide the selection of metrics for data-driven analysis in emerging applications in redox bioelectronics.

Characterizing Electron Flow through Catechol‐Graphene Composite Hydrogels

“…These molecular electronic properties (i.e., the amplification, rectification, and gating of currents) have been previously reported for redox‐active but non‐conducting films in bioelectronics applications. [ 11,60,62,86 ]…”

“…The third output in Figure 3b is the optical absorbance (480 nm) associated with the redox state of the grafted catechol moieties. [6,11] The Cat-Gr-Chit hydrogel shows an oscillating absorbance output (ΔA Cat.Gr.Chit ; 0.019 ± 0.002), while the control Gr-Chit hydrogel shows no oscillations in the absorbance output (ΔA Gr.Chit ; ≈0). This oscillating output absorbance provides direct evidence that the redox state of some catechol moieties (i.e., the "conducting catechols") are being repeatedly switched between their reduced (catechol) and oxidized (quinone) states by electron transfer through the graphene network (note: Figure S3a, Supporting Information, shows the output absorbance does not oscillate for a Cat-Chit film that lacks Gr).…”

“…To facilitate interpretation, it is common to display time series data as phase plane plots of output versus input potential. [11,12] The first phase plane plot of Figure 3c shows the electrical current and optical absorbance output responses as a function of imposed potential. When the potential was swept into the oxidative region (approximately +0.3 V versus Ag/ AgCl), the optical absorbance was observed to increase which is consistent with the switching of the catechol to the oxidized quinone.…”

“…These molecular electronic properties (i.e., the amplification, rectification, and gating of currents) have been previously reported for redox-active but non-conducting films in bioelectronics applications. [11,60,62,86] To estimate the relative contributions of three electron transfer mechanisms, Figure 5b shows that we integrated the time series current plots. Specifically, probing of the Gr-Chit hydrogel allows an estimate of double layer charge conferred by graphene ( .…”

“…[10] In aqueous systems, electron-transfer is constrained by the solvent and typically occurs through at least two distinctly different mechanisms each of which favors different types of materials. [11][12][13] One electron-transfer mechanism is a metal-like conductivity. [14,15] Carbon-based nanomaterials have been especially important for conferring such conductivity [14,16] with benefits that include enhanced double layer charge storage for energy applications [17][18][19][20][21] and electrocatalytic properties for sensing applications.…”