Dimitrios K. Kampouris

Electrochemistry of graphene: not such a beneficial electrode material?

We critically evaluate the reported electro-catalysis of graphene using inner-sphere and outer-sphere electrochemical redox probes, namely potassium ferrocyanide (II) and hexaammine-ruthenium(III) chloride, in addition to L-ascorbic acid and β-nicotinamide adenine dinucleotide. Well characterised commercially available graphene is utilised which has not been chemically treated, is free from surfactants, and as a result of its fabrication has an extremely low oxygen content allowing the electronic properties to be properly de-convoluted. Surprisingly we observe that graphene exhibits slow electron transfer towards the electrochemical probes studied, effectively blocking underlying electron transfer of the supporting electrode substrate likely due to its large basal and low edge plane content. Such observations, never reported before, suggest that graphene may not be such a beneficial electrode material as widely reported in the literature. Density Functional Theory is conducted on symmetric graphene flakes of varying sizes indicating that the HOMO and LUMO energies are concentrated around the edge of the graphene sheet, at the edge plane sites, rather than the central basal plane region, consistent with experimental observations. We define differentiating coverage-based working regions for the electrochemical utilisation of graphene: ‘Zone I’, where graphene additions do not result in complete coverage of the underlying electrode and thus increasing basal contribution from graphene modification leads to increasingly reduced electron transfer and electrochemical activity; ‘Zone II’, once complete single-layer coverage is achieved, layered graphenevizgraphite materialises with increased edge plane content and thus an increase in heterogeneous electron transfer is observed with increased layering. We offer insight into the electrochemical properties of these carbon materials, invaluable where electrode design for electrochemical sensing applications is sought.

Next generation screen printed electrochemical platforms: Non-enzymatic sensing of carbohydrates using copper(II) oxide screen printed electrodes

The first example of a copper(ii) oxide screen printed electrode is reported which is characterised with microscopy and explored towards the electrochemical sensing of glucose, maltose, sucrose and fructose. It is shown that the non-enzymatic electrochemical sensing of glucose with cyclic voltammetry and amperometry is possible with low micro-molar up to milli-molar glucose readily detectable which compares competitively with nano-catalyst modified electrodes. The sensing of glucose shows a modest selectivity over maltose and sucrose while fructose is not detectable. An additional benefit of this approach is that metal oxides with known oxidation states can be incorporated into the screen printed electrodes allowing one to identify exactly the origin of the observed electro-catalytic response which is difficult when utilising metal oxide modified electrodes formed via electro-deposition techniques which result in a mixture of metal oxides/oxidation states. These next generation screen printed electrochemical sensing platforms provide a simplification over previous copper oxide systems offering a novel fabrication route for the mass production of electro-catalytic sensors for analytical and forensic applications.

Facile synthetic fabrication of iron oxide particles and novel hydrogen superoxide supercapacitors

A facile approach for the synthetic fabrication of iron oxide (Fe3O4) particles is presented and their potential application towards energy storage (as an electrode material within a supercapacitor) is explored. The Fe3O4 asymmetric supercapacitor is found to deliver a maximum specific capacitance of ∼120 F g−1 at a current density of 0.1 A g−1 in an aqueous electrolyte solution (3M KOH) retaining 93.70% of its initial capacity over 1000 cycles. Additionally, an iron based hydrogen superoxide [FeO(OH)] supercapacitor is readily fabricated and is found to exhibit a maximum specific capacitance of ∼400 F g−1 at a discharge current of 0.1 A g−1 in a 3M KOH solution.

In situ bismuth film modified screen printed electrodes for the bio-monitoring of cadmium in oral (saliva) fluid

We demonstrate that in situ bismuth film modified screen printed electrodes may be used for the bio-monitoring of cadmium(II) in artificial and diluted human oral (saliva) fluid at the low µg L−1 range. The analytical protocol is based on anodic stripping voltammetry where the bismuth film provides enhanced sensitivity for the electroanalytical deposition of cadmium(II) coupled with a simple change in pH of the oral (saliva) fluid sample permitting quantitative measurements in an electrochemically challenging media.

Screen printed electrochemical platforms for pH sensing

We explore the possible use of screen printing technology for fabricating disposable electrochemical platforms for the sensing of pH. These screen printed pH sensors incorporate the pH sensitive phenanthraquinone moiety which undergoes a Nernstian potential shift with pH, and the pH insensitive dimethylferrocene which acts as an internal reference. This generic approach offers a calibration-less and reproducible approach for portable pH measurements with the possibility of miniaturisation allowing incorporation into existing sensing devices. The advantages, limitations and future prospects of this fabrication approach for producing electrochemical platforms for pH sensing are also discussed.

Rapid and portable electrochemical quantification of phosphorus.

Phosphorus is one of the key indicators of eutrophication levels in natural waters where it exists mainly as dissolved phosphorus. Various analytical protocols exist to provide an offsite analysis, and a point of site analysis is required. The current standard method recommended by the Environmental Protection Agency (EPA) for the detection of total phosphorus is colorimetric and based upon the color of a phosphomolybdate complex formed as a result of the reaction between orthophosphates and molybdates ions where ascorbic acid and antimony potassium tartrate are added and serve as reducing agents. Prior to the measurements, all forms of phosphorus are converted into orthophosphates via sample digestion (heating and acidifying). The work presented here details an electrochemical adaptation of this EPA recommended colorimetric approach for the measurement of dissolved phosphorus in water samples using screen-printed graphite macroelectrodes for the first time. This novel indirect electrochemical sensing protocol allows the determination of orthophosphates over the range from 0.5 to 20 μg L(-1) in ideal pH 1 solutions utilizing cyclic voltammetry with a limit of detection (3σ) found to correspond to 0.3 μg L(-1) of phosphorus. The reaction time and influence of foreign ions (potential interferents) upon this electroanalytical protocol was also investigated, where it was found that a reaction time of 5 min, which is essential in the standard colorimetric approach, is not required in the new proposed electrochemically adapted protocol. The proposed electrochemical method was independently validated through the quantification of orthophosphates and total dissolved phosphorus in polluted water samples (canal water samples) with ion chromatography and ICP-OES, respectively. This novel electrochemical protocol exhibits advantages over the established EPA recommended colorimetric determination for total phosphorus with lower detection limits and shorter experimental times. Additionally this electrochemical adaptation allows the determination of dissolved phosphorus without the use of ascorbic acid and antimony potassium tartrate as reducing agents (as used in the colorimetric method). The potential portability of this protocol is demonstrated in the development of the PhosQuant electrochemical device and provides a portable device for the rapid electrochemical detection of dissolved phosphorus using screen-printed electrodes.

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.

Nickel oxide screen printed electrodes for the sensing of hydroxide ions in aqueous solutions

Nickel oxide bulk modified screen printed electrodes are developed for the first time and explored towards the electroanalytical sensing of hydroxide ions and shown to be analytically useful. The nickel oxide screen printed sensor allows the detection of hydroxide ions over the low micro-molar to milli-molar range with a detection limit of 23 µM. The sensor is simplified over existing analytical methodologies and given its disposable and economical nature holds promise for the sensing of hydroxide ions and consequently the measurement of pH in aqueous solutions.

Gold nanoparticle ensembles allow mechanistic insights into electrochemical processes.

Gold-nanoparticle-modified electrodes find wide and diverse applications in the area of electrochemistry. We demonstrate for the first time that gold-nanoparticle-modified electrodes can provide mechanistic information and we exemplify this with the electrochemical deposition of arsenic(III). Our approach of using nanoparticle ensembles is a facile and economical methodology that provides an alternative to using expensive gold single-crystal electrodes that require careful surface preparation before each measurement.

Fingerprinting breath: electrochemical monitoring of markers indicative of bacteria Mycobacterium tuberculosis infection

Recently it has been shown that chemical markers in exhaled air/breath can provide a methodology for the detection of tuberculosis infection. These markers consist of methyl phenylacetate, methyl p-anisate, methyl nicotinate and o-phenylanisole (2-methoxybiphenyl). Current approaches utilise gas chromatography-mass spectrometry (GCMS) which are useful for centralised testing of breath samples. The World Health Organization (WHO) require a portable, non-invasive diagnostic tool for the screening of tuberculosis infection. In order to meet this, we demonstrate proof-of-concept for the analytical sensing of the identified chemical markers in aqueous solutions using electrochemical based technology. We demonstrate that screen-printed electrochemical sensors can be used as the basis of a diagnostic tool for the electrochemical breathprinting of chemical markers (methyl nicotinate and 2-methoxybiphenyl) useful for the screening of tuberculosis infection. It is hoped that further development will facilitate the potential for a portable, hand-held, non-invasive breath diagnostic tool to be realised.