An sp² Patterned Boron Doped Diamond Electrode for the Simultaneous Detection of Dissolved Oxygen and pH

Abstract

A hybrid sp 2 -sp 3 electrochemical sensor comprising patterned regions of nondiamond-carbon (sp 2 ) in a boron doped diamond (sp 3 ) matrix is described for the simultaneous voltammetric detection of dissolved oxygen (DO) and pH in buffered aqueous solutions. Using a laser micropatterning process it is possible to write mechanically robust regions of sp 2 carbon into a BDD electrode. These regions both promote the electrocatalytic reduction of oxygen and facilitate the proton coupled electron transfer of quinone groups, integrated into the surface of the sp 2 carbon. In this way, in one voltammetric sweep (time of measurement ∼4 s) it is possible to determine both the DO concentration and solution pH. By varying the sp 2 pattern the response can be optimized toward both analytes. Using a closely spaced sp 2 microspot array, a linear response toward DO, across the range 0.0 to 8.0 mg L −1 (0.0 to 0.25 mM; sensitivity = −8.77 × 10 −8 A L mg −1 , R 2 = 0.9991) and pH range 4−10 (sensitivity = 59.7 mV pH −1 , R 2 = 0.9983) is demonstrated. The electrode is also capable of measuring both DO concentration and pH in the more complex buffered environment of blood. Finally, we show how the peak position for ORR is independent of pH, and thus via measurement of the difference in ORR and pH peak position, internal referencing is possible. Such electrodes show great promise for use in applications ranging from biomedical sensing to water analysis.

Assessment of acid and thermal oxidation treatments for removing sp2 bonded carbon from the surface of boron doped diamond

“…Briefly, ESI3 shows that the graphite clusters remain on the BDD surface, supporting the electrochemical data. Whilst the robustness of this remaining layer towards complete removal by acid oxidation is somewhat surprising, it is also extremely useful for electrochemical applications which make use of this hybrid sp 2 -sp 3 bonded material, [13,33,35] especially in the more challenging solution environments. [38] Thermal oxidation of laser ablated BDD Thermal oxidation was next investigated as a means for sp 2 removal from the ns-laser micromachined BDD surface.…”

“…one ns-pulse per 0.01 s, with a fluence of 15 J cm -2 , at a speed of 0.3 mm s -1 ; parameters typical of those used in the laser micromachining of BDD electrodes. [33,35] For electrochemical tests, the pits were machined in quintuplicate (×5), and spaced such that they were individually addressable. For electrochemical studies it was necessary to produce a reliable titanium carbide ohmic contact to the BDD.…”

“…This has been shown particularly for BDD, with regard to specific electrochemical applications. sp 2 bonded carbon improves the electrocatalytic activity of a BDD electrode towards important reactions such as oxygen reduction [33] and advanced oxidation processes. [34] sp 2 bonded carbon also possesses a wider range of surface functional groups, compared to diamond, some of which, e.g.…”

“…This contrasts with ns-laser micromachining where sp 2 bonded carbon structures can be written in the surface with a spatial resolution limited only by the laser optics, typically on the micron scale. For example, ns-laser techniques have been used to create arrays of micro-spots of sp 2 bonded carbon on a BDD electrode in order to increase the electrochemical sensitivity of the electrode towards pH, [13,35] dissolved oxygen [33] and hypochlorite [38]. sp 2 bonded carbon creation is also possible using ion implantation via the creation of defects in diamond, which when appropriately annealed, graphitise.…”

Polychlorinated Biphenyl Electrochemical Aptasensor Based on a Diamond–Gold Nanocomposite to Realize a Sub-Femtomolar Detection Limit

“… 25 Boron-doped diamond (BDD) is an excellent carbon material for electrochemical examinations 26 because of its chemical inertness, wide potential window, low background current, and good electrochemical stability. 27 − 29 …”