Catechol‐Based Molecular Memory Film for Redox Linked Bioelectronics

Abstract

Recent biological research has demonstrated that redox is an independent biological-signaling modality. [1-8] This redox signaling modality is best understood in host-pathogen immune interactions where an oxidative burst generates a set of reactive species (e.g., reactive oxygen species) that can sometimes be transduced into second messengers (i.e., reactive electrophiles) [4] and ultimately alters biological function through post-translational protein modification (e.g., conversion of protein cysteine residues into disulfide crosslinks). [6] The functions and the coding of information in this redox signaling modality [1] are distinctly different from the information coded in genes or in the action potentials of the ionic electrical modality. Since this redox modality involves the "flow" of electrons through oxidation-reduction reactions, it is accessible to appropriate electrochemical measurement, and this provides new opportunities for biodevice communication. [9-13] Redox has similarities to the ionic electrical modality, however electrons are the charged species moving in the redox modality. Interestingly, while water is a conductor of ionic currents, it can be considered an "insulator" for the flow of electrons since free electrons do not normally exist in aqueous

Hydrogel Patterning with Catechol Enables Networked Electron Flow

“…Previous studies have assigned this peak to the oxidized quinone (Q) moieties. [ 26 ] The rightmost plot in Figure 3a shows the change in absorbance measured at 480 nm (Δ| A 480 |) decreased with time, and this change was larger for films written with a larger number of electrode writing strokes. These results indicate that: i) ascorbate can donate electrons to the film to convert the oxidized quinone moieties (Q‐state) into reduced catechol moieties (QH 2 ‐state); ii) the film's capacity to accept electrons can be adjusted by the extent of catechol modification; and iii) electron transfer to the film can be “passively” observed (i.e., without changing the state) by measuring optical absorbance.…”

“…In addition to detecting the pattern of the catechol that was irreversibly written into the film (Figure 2), it is also possible to detect the reversible switching of this catechol's redox state. To demonstrate optical detection of the redox‐state of the patterned catechol regions, [ 26 ] we started with a Chit 0 /agarose hydrogel that was patterned with two circular dots with the same extent of modification ( Q fab = 5 mC), and locally set the redox state of these dots to an oxidized (Q) state or a reduced (QH 2 ) state through mediated electrochemistry as illustrated in Figure a. Experimentally, the catechol‐patterned Chit 0 /agarose hydrogel film was immersed in Fc/Ru 3+ mediator solutions (0.1 m m each), a standard gold electrode was placed above each dot, and the imposed voltage was controlled to set the redox state.…”

“…[ 23–25 ] Third, the catechol and quinone redox states are distinguishable due to differences in their optical absorbance. [ 26–28 ] Finally, kinetic barriers for electron exchange with catechol‐quinone redox couples are often low which allows the oxidized quinone to accept electrons from a wide range of reductants, and allows the reduced catechol to donate electrons to a range of oxidants. [ 29 ]…”

Sensing the future of bio-informational engineering

“…Cellular redox in particular has proven to be a valuable source of cellular information that is easily accessible to human and device readable outputs. For example, detection and memory of redox state was achieved using a chatecol-chitosan-agarose matrix with optical or electrical output 59 . The ubiquitous nature of biological redox has made it possible to electronically interact with skin pigments such as melanin, control biological patterning and gene expression, and integrate two-way communication via redox stress signals 60 .…”

Redox Electrochemistry to Interrogate and Control Biomolecular Communication

“…Interestingly, redox-inactive materials can be conjugated with redox mediators such as catechols and quinones, and these are easily fabricated at discrete locations ( Liu et al., 2010 ). We have suggested that these materials can serve as a form of bioelectronic memory to locally address where specific communication events happen within a spatial domain, such as within the spatial resolution of an electrode array or gel ( Wu et al., 2020 ). That is, in these storage devices, a non-conducting material, such as catechol-modified chitosan, serves as a redox sink to sequester electrons away from the electrode.…”