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Eumelanin is a natural pigment found in many organisms that provides photoprotection from harmful UV radiation. As a redox‐active biopolymer, the structure of eumelanin is thought to contain different redox states of quinone, including catechol subunits. To further explore the excited state properties of eumelanin, we have investigated the catechol/o‐quinone redox couple by spectroelectrochemical means, in a pH 7.4 aqueous buffered solution, and using a boron doped diamond mesh electrode. At pH 7.4, the two proton, two electron oxidation of catechol is promoted, which facilitates continuous formation of the unstable o‐quinone product in solution. Ultrafast transient absorption (femtosecond to nanosecond) measurements of o‐quinone species involve initial formation of an excited singlet state followed by triplet state formation within 24 ps. In contrast, catechol in aqueous buffer leads to formation of the semiquinone radical Δt>500 ps. Our results demonstrate the rich photochemistry of the catechol/o‐quinone redox couple and provides further insight into the excited state processes of these key building blocks of eumelanin. [ABSTRACT FROM AUTHOR]

A systematic examination of the microscopic factors affecting the aqueous solvent (electrolyte) window of polycrystalline (p) boron‐doped diamond (BDD) electrodes in chloride‐containing salt solutions is undertaken by using scanning electrochemical cell microscopy (SECCM) in conjunction with electron backscatter diffraction (EBSD) and Raman microscopy. A major focus is to determine the effect of the local boron doping level, within the same orientation grains, on the solvent window response. EBSD is used to select the predominant (110) orientated areas of the surface with different boron‐doped facets, thereby eliminating crystallographic effects from the electrochemical response. Voltammetric SECCM is employed, whereby a cyclic voltammogram is recorded at each pixel mapped by the meniscus‐contact SECCM cell. The data obtained can be played as an electrochemical movie of potential‐resolved current maps of the surface to reveal spatial variations of electroactivity, over a wide potential range, including the solvent (electrolyte) window. Local heterogeneities are observed, indicating that the solvent window is mainly linked to local dopant levels, with lower dopant levels leading to a wider window, that is, slower electrode kinetics for solvent/electrolyte electrolysis. Furthermore, the effects of O‐ and H‐surface termination of the BDD surface are investigated for the same electrode (in the same area). The surface termination is a particularly important factor: the solvent window of an H‐terminated surface is wider than for O‐termination for similar boron dopant levels. Furthermore, the anodic potential window of the O‐terminated surface is greatly diminished due to chloride electro‐oxidation. These studies provide new perspectives on the local electrochemical properties of BDD and highlight the importance of probing the electrochemistry of BDD at the level of a single crystalline grain (facet) to unravel the factors that control the solvent (aqueous) window of these complex heterogeneous electrodes. Factors affecting solvent window: The boron doping level and surface termination are important for changing the solvent window of boron‐doped diamond (BDD), as illustrated by correlative electrochemical microscopy (see picture). [ABSTRACT FROM AUTHOR]

We demonstrate, for the first time, the use of electrochemical imaging to identify defect and defect free areas in single crystal boron doped diamond (BDD) electrodes. Specifically, we show that defects contain different boron dopant concentrations than the surrounding single crystal matrix and that these variations can be visualized using intermittent contact−scanning electrochemical microscopy (IC-SECM). The measured IC-SECM tip currents provide quantitative information on the rates of electron transfer across the single crystal BDD electrodes, which correlate with variations in boron doping levels. In some instances, IC-SECM outperforms alternative methods such as Raman microscopy and cathodoluminescence imaging, due to its intrinsic surface-sensitivity, expanding the application and impact of electrochemical microscopy for materials characterization. The results obtained, and procedure outlined, are particularly valuable for the assessment and screening of single crystal BDD electrodes. [ABSTRACT FROM AUTHOR]

Detection of the genotoxic impurity hydrazine (HZ) in the presence of active pharmaceutical ingredients (APIs) represents a significant challenge to the pharmaceutical industry. Here we show how the use of electrochemical strategies in conjunction with metal nanoparticle (NP) functionalised polycrystalline boron-doped diamond (BDD) electrodes enables detection of HZ in the presence of two different electrochemically active APIs. By simply changing the chemical identity of the metal NP, which shifts the detection potential for HZ, it is possible to selectively screen out the API signature from the HZ current - voltage response. HZ detection limits of 11.1 µM (Au NP BDD) and 3.3 µM (Pt NP BDD) in the presence of excess acetaminophen and promazine respectively, were determined using differential pulse voltammetry in quiescent solution. [ABSTRACT FROM AUTHOR]