Edward P. Randviir

Electrochemical impedance spectroscopy: an overview of bioanalytical applications

The application of electrochemical impedance spectroscopy (EIS) has increased dramatically in the past few years due to its ability to elucidate a plethora of physical and electronic properties of electrochemical systems such as diffusion coefficients, electron transfer rate constants, adsorption mechanisms, charge transfer resistances, capacitances and pore sizes. This review provides a short introduction to the fundamental principles of EIS before exploring the many exciting and pertinent analytical applications regarding the numerous methods in biosensing, the application of EIS with graphene based materials and last, the use of EIS with screen printed electrodes.

Electrochemical measurement of the DNA bases adenine and guanine at surfactant-free graphene modified electrodes

The electrochemical oxidation of adenine and guanine is studied in aqueous media using commercially available, high purity graphene which is free from surfactants and has not been chemically modified in any way, and is contrasted with edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and graphite modified electrodes. In terms of graphene modified electrodes towards the electrochemical oxidation of adenine, the observed voltammetric response is reduced, in terms of the peak height with the electrochemical oxidation potential occurring at higher oxidation potentials than the underlying BPPG electrode. In comparison, control experiments utilising graphite modified electrodes display an improvement in the voltammetric signal and reduced oxidation potentials are observed compared to the bare BPPG underlying electrode. Such a response in addition to that observed at EPPG and BPPG confirms that the density of edge plane sites are critical, which is in strong agreement with current literature reports. The reduced response at the graphene modified electrode is thus due to graphene having a low density of electroactive (edge plane) sites, given its unique structure. In the case of the electrochemical oxidation of guanine, graphene modified electrodes interestingly exhibit a lower voltammetric response in terms of peak height compared to the underlying electrode, but interestingly exhibit a reduction in the oxidation potential compared to the underlying BPPG electrode. Such a response is a consequence of the unique structure of graphene since it has a large basal plane composition for the adsorption of guanine which, according to literature reports, adsorbs readily on basal plane sites. However, graphene unfortunately has a low density of edge plane sites which accounts for the reduced voltammetric response. Additionally, pH dependence studies performed on both adenine and guanine utilising graphene modified BPPG electrodes reveal an equal number of protons and electrons transferred, suggesting graphene does not change the electrochemical mechanism prior to the chemically irreversible step compared to that observed at graphitic electrodes. Critically, the electrode surface modification with graphene is found to be analytically unacceptable; this coupled with the reduction in the overall electrode kinetics from graphenes low density of edge plane sites questions its future use in the reliable sensing of DNA bases.

A new approach for the improved interpretation of capacitance measurements for materials utilised in energy storage

A simple galvanostatic circuit methodology is reported allowing the capacitance of an electrochemical electrolytic capacitor to be accurately measured, without recourse to expensive instrumentation. The method avoids problems found in current electrochemical impedance spectroscopy analysis, which give rise to profiles that may result in false or inaccurate derivation of the electrolytic capacitance. The advantages of this approach are that the circuit is easy and cheap to fabricate. The system is linear, regardless of the texture of the electrode and the type of electrolyte, and the measurement is direct so that no presumable equivalent circuit model is required. Such work is highly important for those developing new materials in energy storage, as it allows the reliable measurement of capacitance to be achieved without the need for expensive or complex instrumentation. This paper also highlights that users are more informed through checking capacitances using a variety of techniques, though such a circuit could in theory eliminate the need for affirmation of values utilising other electrochemical methods/techniques.

Electrode substrate innovation for electrochemical detection in microchip electrophoresis

Microchip electrophoresis (MCE) represents the next generation of miniaturised electrophoretic devices and carry benefits such as significant improvement in analysis times, lower consumption of reagents and samples, flexibility and procedural simplicity. The devices provide a separation method for complex sample matrices and an on‐board detection method for the analytical determination of a target compound. The detection part of MCE is increasingly leaning towards electrochemical methods, thus the selectivity and sensitivity of detection in MCE is dependent upon the chosen working electrode composition in addition to operating conditions of the chip such as separation voltage. Given the current plethora of electrode materials that are available, there exists a possibility to creatively integrate electrodes into MCE. This review will overview the application of several electrode materials, from the old through to the new. A particular recent focus has been the selectivity element of MCEs overcome with the use of enzymes, carbon composites and screen‐printed technologies.

Twittering About Research: A Case Study of the World's First Twitter Poster Competition.

The Royal Society of Chemistry held, to our knowledge, the world’s first Twitter conference at 9am on February 5 th, 2015. The conference was a Twitter-only conference, allowing researchers to upload academic posters as tweets, replacing a physical meeting. This paper reports the details of the event and discusses the outcomes, such as the potential for the use of social media to enhance scientific communication at conferences. In particular, the present work argues that social media outlets such as Twitter broaden audiences, speed up communication, and force clearer and more concise descriptions of a researcher’s work. The benefits of poster presentations are also discussed in terms of potential knowledge exchange and networking. This paper serves as a proof-of-concept approach for improving both the public opinion of the poster, and the enhancement of the poster through an innovative online format that some may feel more comfortable with, compared to face-to-face communication.

Graphene-Based Electrochemical Sensors

Since graphene was isolated and characterised in 2004 and 2005, its applications have been researched intensively for a broad range of applications, none more so than the field of electrochemical sensors, which aim to exploit the unique charge carrier mobility associated with graphene structures. This chapter explores graphene and its incorporation into electrochemical sensors. The chapter discusses graphene structure and the electrochemical responses arising from such structures on a macro-scale and examines production methods of graphene and how these affect the observed currents in electrochemical reactions as a result of such methods. The chapter subsequently explores sensors designed from a range of different graphenes, including surfactant-exfoliated graphene, surfactant-free graphene, chemical vapour deposition graphene, and reduced graphene oxide. The chapter finds that reduced graphene oxide is the most commonly employed route for graphene-based electrochemical sensors, owing to the scale of production being large, and its relatively cheap and straightforward production.

Incorporating Graphene into Fuel Cell Design

Since the fabrication and subsequent physical characterisation of graphene in 2004 and 2005, a host of potential uses have been suggested and researched. To date, some have had some success, while others are significantly lacking in critical research due to unforeseen problems with the electrochemical properties of graphene. Of the many applications, fuel cells were predicted to gain benefit from graphene; the focus of this book chapter is to assess whether graphene has a place in fuel cells, and disseminate the current state of research across the globe for this purpose. It is evident that the applicability of graphene as a fuel cell anode, cathode, or proton exchange membrane, is dramatically dependent upon the type of graphene used in the fuel cell design. Pristine graphenes lack the necessary active sites for low energy electrochemical reactions required in fuel cells, and therefore their use as anodes or cathodes is seemingly limited. However pristine graphene may permit protons across atomic scale defects in its lattice and prove to be a good material for a proton exchange membrane when coupled with its tensile strength. Laser-induced graphene is a relatively new technique for the fabrication of graphene but offers a potential route towards manufacture of 3D graphene architectures that could be useful for cathodic reactions such as oxygen reduction. Reduced graphene oxides in their many guises could also be useful, provided that a replicable standard can be formulated for fuel cell anode and cathodes. Graphene oxides also have potential for proton exchange membranes but may suffer from longevity issues as a result of the decreased hydrophobicity allowing swelling of the material when in an aqueous environment. Nitrogen-doped graphenes are also potential candidates for the future of fuel cell research for both anodic and cathodic reactions. The future of graphene as a fuel cell material is predicted to be several years away because the research in this area has not solved issues of longevity, reproducibility, and temperature tolerance, while maintaining a good cell voltage and current density.