| Spectroelectrochemistry combines two very different techniques—spectroscopy and electrochemistry—providing more information about the redox mechanism of an electroactive analyte than can be acquired using traditional electrochemical methods alone. The oxidation state of an analyte is changed electrochemically by adding or removing electrons at an optically transparent electrode (OTE) while the spectroscopic response of the species in solution is simultaneously measured. Spectroelectrochemistry is useful for obtaining spectra and redox potentials for electrogenerated species as well as important information in the investigation of electrode reaction mechanisms, in electroanalytical applications, and, as demonstrated herein, in elucidating structural information about redox-active protein active sites.; The use of electrically conductive diamond as an OTE is a new area of research. Boron-doped diamond (BDD) possesses attractive qualities as both an electrode and an optically transparent material, making it an obvious choice for utilization as an OTE in transmission spectroelectrochemical measurements. Diamond OTEs offer several advantages over other materials including: (i) the possibility of optical measurements from the near-UV into the far-IR (0.25–100 μm), (ii) a low background current, (iii) a wide working potential window, (iv) stability in aqueous and nonaqueous solution environments during both cathodic and anodic polarization, and (v) resistance to fouling.; An added advantage of BDD OTEs is the versatility of fabrication, as BDD thin-films can be grown on a variety of substrates (e.g., quartz, undoped Si, and white diamond grown by chemical vapor deposition), and can also exist as freestanding disks. Each type of OTE possesses characteristics that can be exploited for a specific application. This work is a product of our long-term goal to develop BDD as an OTE for electroanalytical applications and the study of biological electron transfer mechanisms. Development of the OTE comprised the design and testing of thin-layer spectroelectrochemical cells and the electrochemical and spectroelectrochemical characterization of two systems: (i) a small molecule, ferrocene, in nonaqueous solvent/electrolyte systems, and (ii) a redox-active protein, cytochrome c. Besides the basic electrochemical and spectroelectrochemical characterizations of these systems, this work focused on determining the deposition conditions that produce an optimized balance between electrical conductivity and optical transparency in this material. |
