Light Activated Electrochemistry: Light Intensity and pH Dependence on Electrochemical Performance of Anthraquinone Derivatized Silicon

Abstract

We seek to understand how the thermodynamics and kinetics of anthraquinone-containing self-assembled monolayer on silicon electrodes are affected by two key experimental variables: the intensity of the light assisting the anthraquinone/anthrahydroquinone redox process and the local solution environment. The substrates are chemically passivated poorly doped p-type silicon electrodes. The study presents a strategy for the selective modulation of either the anodic or the cathodic process occurring at the interface. Cyclic voltammetry studies showed that unlike for a proton-coupled electron transfer process performed at metallic electrodes, for the redox reaction of the anthraquinone unit on a silicon electrode it becomes possible to (i) selectively facilitate only the oxidation process by increasing the electrolyte pH or (ii) at a given pH value to increase the illumination intensity to anodically shift the onset of the reduction step only but leave the oxidation process thermodynamic unchanged. A model concerning the proton coupled electron transfer mechanism was proposed, where the electron transfer is the rate-determining step for the anthraquinone reduction while a deprotonation step is the rate-determining event for the anthrahydroquinone oxidation on poorly doped illuminated p-type silicon.

Light‐Addressable Ion Sensing for Real‐Time Monitoring of Extracellular Potassium

“…According to previous studies,t he light intensity change over silicon substrate will alter the space charge layer depth, minor carrier concentration, and the band bending level, as aresult, there will be an anodic/cathodic shift in the cyclic voltammetry for the redox species attached on p/n-type silicon with the increase of the illumination intensity. [6,20] Fort his reason, as eparate calibration curve was obtained by using the laser beam light source in the cell culture medium with increasing [K + ]( Figure S6A). Asimilar Nernst response was found while the overall redox peaks moved to more negative values due to light intensity increase.…”

“…[18] Va linomycin, which is ac yclic peptide-like molecule that binds K + ,m ay result in leakage of K + from the cells,was applied to stimulate the cells. [6,20] Fort his reason, as eparate calibration curve was obtained by using the laser beam light source in the cell culture medium with increasing [K + ]( Figure S6A). Accordingly,c yclic voltammetry was recorded before and after adding valinomycin in the illuminated region close to cells ( Figure S5C).…”

Light-addressable Electrodes for Dynamic and Flexible Addressing of Biological Systems and Electrochemical Reactions

“…In contrast to low-doped Si, for cyclic voltammograms without illumination, no redox peaks are observed for low-doped n-(8-12 Ωcm) and p-doped (1-10 Ωcm, Figure 8b, solid black line) Si. In contrast, with illumination, the ferrocene-terminated n-type Si has an E 1/2 (half-wave potential) = −140 mV vs. V Ag/AgCl and an E 1/2 = −370 mV vs. V Ag/AgCl for the p-type Si (Figure 8b The effects of the pH value of the electrolyte and light intensity on anthraquinone deposited on low-doped p-type Si (10-20 Ωcm) were further evaluated in Reference [95]. It was shown from cyclic voltammograms that E 1/2 for modified highly p-doped Si shifts with a slope of −58.5 mV pH −1 and therefore behaves similar to a conventional metal electrode (anthraquinone monolayer on gold electrode; shift E 1/2 = −59.2 mV pH −1 ), while for low-doped p-type Si , where illumination is needed for charge carrier generation, a slope of −44.0 mV pH −1 was obtained.…”

Applications of Monolayer‐Functionalized H‐Terminated Silicon Surfaces: A Review

“…Extensive literature is available on the coupling of electroactive moieties onto oxide‐free silicon substrates, as reviewed recently . Such moieties can have two stable redox states, such as ferrocene and quinones, or more than two redox states, such as metal‐complexed porphyrins,[41a,43] tetrathiafulvalene (TTF), and fullerene (C 60 ) . These systems are commonly used as model systems to investigate the charge transfer at surfaces, for example to study the influence of the linker length .…”