Controlling electrocatalytic, photoelectrocatalytic, and load release processes using soft material-modified electrodes

Abstract

• Hemin/G-quadruplex hydrogel-modified electrode reveals triggered stiffness and switchable electrocatalysis. • Enzyme-loaded pH-responsive hydrogel-modified electrode show electroswitchable stiffness and load release functions. • An integrated photosystem I/glucose oxidase-modified electrode act as photoelectrochemical cell. Soft materials, such as hydrogels, polymers or biomaterials associated with electrodes provide interfaces revealing electrocatalytic, photoelectrocatalytic and controlled release of loads functions. These will be addressed by three examples demonstrated by our laboratory, including: (i) The assembly of a stimuli-responsive nucleic acid-based hydrogel on an electrode support, consisting of a hydrogel matrix crosslinked by duplex nucleic acid bridges and K + -ion-stabilized G-quadruplex bridges. By cyclic and reversible formation and dissociation of the G-quadruplexes by K + -ions and crown ether (CE), the switchable stiffness properties of the hydrogel are demonstrated. The integration of hemin into the G-quadruplex bridging units on electrocatalytic interface for the electrocatalyzed reduction of H 2 O 2 is introduced. In the presence of K + -ions/crown ether the switchable electrocatalytic functions of the electrode are demonstrated. (ii) A pH-responsive nucleic acid-based hydrogel matrix is immobilized on an electrode surface. The hydrogel interface is crosslinked by permanent nucleic acid bridges and pH-responsive crosslinking units. At acidic pH values, the pH responsive bridges are unlocked via generating i-motif structures, leading to an hydrogel interface of lower stiffness. Immobilization of ferrocene-modified glucose oxidase (GOx) in the hydrogel yields an electrically contacted enzyme electrode that stimulates the bioelectrocatalyzed oxidation of glucose and the acidification of the hydrogel. By incorporating a load into the hydrogel, the electrocatalyzed oxidation of glucose and the accompanying acidification of the hydrogel lead to a hydrogel of lower stiffness, allowing the controlled release of the load. (iii) A supramolecular, electrochemically contacted, photoresponsive matrix consisting of native photosystem I (PS I) interlinked to glucose oxidase (GOx) by an electrically contacting redox polymer consisting of polyvinyl imidazole Os 2+/3+ (bipyridine) 2 Cl complex is introduced. The organized assembly acts as a photobioelectrochemical fuel cell where photoinduced electron transfer from PS I to the electrode stimulates the bioelectrocatalyzed oxidation of glucose. The system demonstrates the light-induced oxidation of the glucose-fuel and the concomitant generation of electrical power.