Surface patterning of polyacrylamide gel using scanning electrochemical cell microscopy (SECCM)

Scanning electrochemical cell microscopy is introduced as a new tool for the synthesis and deposition of polymers on SAM-functionalised Au surfaces. The deposition of poly(N-hydroxyethyl acrylamide) is shown to be enhanced through the electrochemical generation of activating Cu(I)Cl/Me6TREN catalyst. Initiation of the polymerisation reaction is most likely due to in situ generation of reactive oxygen species following oxygen reduction

Exploiting the properties of boron doped diamond for electrochemical sensing applications

This thesis explores utilising the advantageous electrochemical properties of polycrystalline boron doped diamond (BDD), including low background currents and a wide potential window, for a range of different electroanalytical applications. The newly developed technique Electrochemical X-ray Fluorescence is employed for the quantitative detection of palladium (Pd2+) in the presence of electroactive species relevant to the pharmaceutical industry. Significant improvements on analysis times are achieved by EC-XRF parameter optimisation and consideration of the detection limits required for the end application. Given that the quality of BDD utilised (the amount of sp2 content present) can directly impact on the electrochemical response observed, a new BDD characterisation technique is developed. This involves the electrochemical determination of the surface coverage of quinone groups only present on sp2 carbon. This technique is then applied for the characterisation of diamond films grown via chemical vapour deposition under low pressure conditions, identifying regions across BDD wafers with distinctly different electrochemical properties. A Nernstian BDD pH sensor is also successfully fabricated, capable of operating in both buffered and unbuffered solutions. This is achieved by controllably laser micromachining the BDD surface introducing pH sensitive quinone groups. The resulting sensor is found to be stable in a variety of extreme environments

Quantitative analysis of trace palladium contamination in solution using electrochemical X-ray fluorescence (EC-XRF)

The application of electrochemical X-ray fluorescence (EC-XRF), for the detection of palladium (Pd) contamination in a range of solutions containing electrochemically active compounds, present in excess and relevant to the pharmaceutical and food industries, is reported. In EC-XRF, EC is used to electrochemically pre-concentrate metal on an electrode under forced convection conditions, whilst XRF is employed to spectroscopically quantify the amount of metal deposited, which quantitatively correlates with the original metal concentration in solution. Boron doped diamond is used as the electrode due to its very wide cathodic window and the fact that B and C are non-interfering elements for XRF analysis. The effect of several parameters on the Pd XRF signal intensity are explored including: deposition potential (Edep), deposition time (tdep) and Pd2+ concentration, [Pd2+]. Under high deposition potentials (Edep = −1.5 V), the Pd XRF peak intensity varies linearly with both tdep and [Pd2+]. Quantification of [Pd2+] is demonstrated in the presence of excess acetaminophen (ACM), L-ascorbic acid, caffeine and riboflavin. We show the same Pd XRF signal intensity (for [Pd2+] = 1.1 μM and tdep = 325 s) is observed, i.e. same amount of Pd is deposited on the electrode surface, irrespective of whether these redox active molecules are present or absent. For tdep = 900 s we report a limit of detection for [Pd2+] of 3.6 ppb (34 nM). Even lower LODs are possible by increasing tdep or by optimising the X-ray source specifically for Pd. The work presented for Pd detection in the presence of ACM, achieves the required detection sensitivity stipulated by international pharmacopeia guidelines

Quinone electrochemistry for the comparative assessment of sp2 surface content of boron doped diamond electrodes

Surface coverage measurements of electroactive quinone groups present on sp2 carbon sites, are used to inform on the sp2 surface content of boron doped diamond (BDD) electrodes. Laser micromachining of an electrode surface is used to systematically increase the amount of sp2 carbon present by increasing the area machined. A linear relationship between quinone surface coverage and surface area lasered is determined (R2 = 0.9999). This approach can also be used for comparative assessment of electrodes containing different amounts of surface sp2 carbon. Keywords: Boron doped diamond, Quinone electrochemistry, sp2 carbon, Laser micromachining, Raman microscopy, Surface characterisatio

Deconvoluting surface-bound quinone proton coupled electron transfer in unbuffered solutions : toward a universal voltammetric pH electrode

While quinone proton coupled electron transfer (PCET) under buffered conditions is well understood, the situation is more complicated in unbuffered aqueous solutions. With a view to producing a quinone-based voltammetric pH electrode that can function universally in both buffered and unbuffered solutions by following a two-electron (2e–)/two-proton (2H+) Nernstian pathway over a wide pH range, the voltammetric response of strongly electronically coupled surface-bound quinones, directly integrated into a boron-doped diamond (BDD) electrode, is investigated. A laser ablation process enables integration of quinones into the BDD electrode surface with a high pKa1 (first protonation state) and with controllable, very low surface coverages (as low as 2 orders of magnitude below monolayer coverage). Under buffered conditions, one wave results for all pH values, and the 2e–/2H+ pathway is followed across the entire pH range. The measured ET rate constant values, from Laviron analysis, are also high, indicative of fast ET pathways. Under unbuffered conditions, one wave is again observed for all pH values; however, deviations from the buffered 2e–/2H+ behavior are seen in the neutral region (pH 6–8). While 2e–/2H+ transfer is maintained at all times, we attribute the observed deviation to local pH changes caused by the consumption and generation of protons at the electrode surface during the redox electrochemistry of the quinone. The associated proton fluxes generated at such sparse surface coverages are thought to be sufficiently high enough to prevent ET from occurring exclusively via a proton-independent route. By reducing surface coverage (down to ∼4 × 10–12 mol cm–2; the limit of our laser ablation process) local pH changes can be reduced but are not eradicated completely. By moving to a pulsed voltammetric technique, where for each potential step protons consumed at the electrode are immediately replaced, it is possible, provided the surface coverage is low enough, to obtain a Nernstian 2e–/2H+ response across a wide pH range in unbuffered solution

Controlled sp2 functionalization of boron doped diamond as a route for the fabrication of robust and nernstian pH electrodes

The development of a voltammetric boron doped diamond (BDD) pH sensor is described. To obtain pH sensitivity, laser micromachining (ablation) is utilized to introduce controlled regions of sp2 carbon into a high quality polycrystalline BDD electrode. The resulting sp2 carbon is activated to produce electrochemically reducible quinone groups using a high temperature acid treatment, followed by anodic polarization. Once activated, no further treatment is required. The quinone groups show a linear (R2 = 0.999) and Nernstian (59 mV/(pH unit)) pH-dependent reductive current–voltage response over a large analyzable pH range, from pH 2 to pH 12. Using the laser approach, it is possible to optimize sp2 coverage on the BDD surface, such that a measurable pH response is recorded, while minimizing background currents arising from oxygen reduction reactions on sp2 carbon in the potential region of interest. This enables the sensor to be used in aerated solutions, boding well for in situ analysis. The voltammetric response of the electrode is not compromised by the presence of excess metal ions such as Pb2+, Cd2+, Cu2+, and Zn2+. Furthermore, the pH sensor is stable over a 3 month period (the current time period of testing), can be stored in air between measurements, requires no reactivation of the surface between measurements, and can be reproducibly fabricated using the proposed approach. The efficacy of this pH sensor in a real-world sample is demonstrated with pH measurements in U.K. seawater

The impact of research culture on mental health & diversity in STEM

The onset of COVID-19, coupled with the finer lens placed on systemic racial disparities within our society, has resulted in increased discussions around mental health. Despite this, mental health struggles in research are still often viewed as individual weaknesses and not the result of a larger dysfunctional research culture. Mental health interventions in the science, technology, engineering, and mathematics (STEM) academic community often focus on what individuals can do to improve their mental health instead of focusing on improving the research environment. In this paper, we present four aspects of research that may heavily impact mental health based on our experiences as research scientists: bullying and harassment; precarity of contracts; diversity, inclusion, and accessibility; and the competitive research landscape. Based on these aspects, we propose systemic changes that institutions must adopt to ensure their research culture is supportive and allows everyone to thrive

Impact of chemical vapour deposition plasma inhomogeneity on the spatial variation of sp 2 carbon in boron doped diamond electrodes

The impact of plasma inhomogeneity on the sp2 content of thin film (∼micron) boron doped diamond (BDD) electrodes, grown using microwave chemical vapour deposition (MW-CVD) under different methane (CH4) concentrations (1% and 5%), is investigated. The sp2surface content (critical for interpreting electrochemical data) is comparatively assessed using a variety of electrochemical measurements: capacitance; solvent window analysis and quinone surface coverage. For all growths, distinctive regions containing appreciably differing amounts of sp2 carbon are identified, across the wafer. For example, on the 1% CH4 wafer, some areas exhibit electrochemical signatures indicative of high quality, minimal sp2 content BDD, whereas others show regions comprising significant sp2 carbon. Note Raman microscopy was unable to identify these variations. On the 5% CH4 wafer, no region was found to contain minimal levels of sp2 carbon. Changes in sp2 content across the BDD films indicates spatial variations in parameters such as temperature, methane and atomic hydrogen concentrations during growth, in this case linked directly to the use of a commonly employed multi-moded (overmoded) chamber for MW-CVD BDD synthesis. Varying sp2 levels can have significant impact on the resulting electrochemical behaviour of the BDD

Electrochemical x-ray fluorescence spectroscopy for trace heavy metal analysis : enhancing x-ray fluorescence detection capabilities by four orders of magnitude

The development of a novel analytical technique, electrochemical X-ray fluorescence (EC-XRF), is described and applied to the quantitative detection of heavy metals in solution, achieving sub-ppb limits of detection (LOD). In EC-XRF, electrochemical preconcentration of a species of interest onto the target electrode is achieved here by cathodic electrodeposition. Unambiguous elemental identification and quantification of metal concentration is then made using XRF. This simple electrochemical preconcentration step improves the LOD of energy dispersive XRF by over 4 orders of magnitude (for similar sample preparation time scales). Large area free-standing boron doped diamond grown using microwave plasma chemical vapor deposition techniques is found to be ideal as the electrode material for both electrodeposition and XRF due to its wide solvent window, transparency to the XRF beam, and ability to be produced in mechanically robust freestanding thin film form. During electrodeposition it is possible to vary both the deposition potential (Edep) and deposition time (tdep). For the metals Cu2+ and Pb2+ the highest detection sensitivities were found for Edep = −1.75 V and tdep = 4000 s with LODs of 0.05 and 0.04 ppb achieved, respectively. In mixed Cu2+/Pb2+ solutions, EC-XRF shows that Cu2+ deposition is unimpeded by Pb2+, across a broad concentration range, but this is only true for Pb2+ when both metals are present at low concentrations (10 nM), boding well for trace level measurements. In a dual mixed metal solution, EC-XRF can also be employed to either selectively deposit the metal which has the most positive formal reduction potential, E0, or exhaustively deplete it from solution, enabling uninhibited detection of the metal with the more negative E0