Jonathan P. Metters

Paper-based electroanalytical sensing platforms

We report the fabrication of paper-based graphite screen printed electroanalytical sensors. Consideration is taken as to determine the most suitable paper-based material enabling reproducible, robust and low cost effective sensor development, after which the paper-based sensor is electrochemically characterised and utilised for the sensing of the important model analytes NADH and nitrite. The analytical performance of the sensors are compared and contrasted to that of commercially available graphite based screen printed sensors fabricated upon traditional polyester substrates. It is found that the paper-based screen printed sensors offers competitive analytical performance when compared with traditional screen printed sensors and other graphite based electrodes offering limits of detection of 1.8 μM and 15.1 μM for NADH and nitrite respectively. As such, these screen printed paper-based analytical devices offer a innovative alternative to the well-established screen printing history of electrodes for use in electroanalytical sensing; the ability to fabricate screen printed electroanalytical sensors which are highly flexible provides the potential for a new class of point-of-care diagnostic devices that are ultra-low-cost, easy to use, and can be designed specifically for use in developing countries.

Cobalt Phthalocyanine Modified Electrodes Utilised in Electroanalysis: Nano-Structured Modified Electrodes vs. Bulk Modified Screen-Printed Electrodes

Cobalt phthalocyanine (CoPC) compounds have been reported to provide electrocatalytic performances towards a substantial number of analytes. In these configurations, electrodes are typically constructed via drop casting the CoPC onto a supporting electrode substrate, while in other cases the CoPC complex is incorporated within the ink of a screen-printed sensor, providing a one-shot economical and disposable electrode configuration. In this paper we critically compare CoPC modified electrodes prepared by drop casting CoPC nanoparticles (nano-CoPC) onto a range of carbon based electrode substrates with that of CoPC bulk modified screen-printed electrodes in the sensing of the model analytes l-ascorbic acid, oxygen and hydrazine. It is found that no “electrocatalysis” is observed towards l-ascorbic acid using either of these CoPC modified electrode configurations and that the bare underlying carbon electrode is the origin of the obtained voltammetric signal, which gives rise to useful electroanalytical signatures, providing new insights into literature reports where “electrocatalysis” has been reported with no clear control experiments undertaken. On the other hand true electrocatalysis is observed towards hydrazine, where no such voltammetric features are witnessed on the bare underlying electrode substrate.

Forensic electrochemistry: sensing the molecule of murder atropine

We present the electroanalytical sensing of atropine using disposable and economic screen printed graphite sensors. The electroanalytical determination of atropine is found to be possible over the concentration range of 5 μM to 50 μM with a detection limit of 3.9 μM (based on 3-sigma) found to be possible. We demonstrate proof-of-concept that this approach provides a rapid and inexpensive sensing strategy for determining the molecule of murder atropine in diet Coca-Cola samples.

Electroanalytical sensing of selenium(IV) utilising screen printed graphite macro electrodes

The electroanalytical determination of selenium(IV) via anodic stripping voltammetry is shown to be possible for the first time using screen printed graphite electrodes. The deposition potential and time was optimised allowing a linear range from 10 to 1000 μg L−1 in 0.1 mol L−1 HClO4 to be realised with a limit of detection (3σ) found to correspond to 4.9 μg L−1. Utilising these screen printed graphite electrodes, the detection of selenium(IV) in drinking (tap) water is shown to be feasible allowing a detection limit (3σ) of 19.2 μg L−1 to be realised which is below the levels set by the United States Environmental Protection Agency. Such an approach suggests the possibility of a disposable screening tool for selenium(IV) in drinking water samples.

Screen printed graphite electrochemical sensors for the voltammetric determination of antimony(III)

The electroanalytical determination of antimony(III) is explored using disposable and economical unmodified screen printed graphite macro-electrodes. These sensors are found to allow the sensing of antimony(III) via anodic stripping voltammetry over the range of 1 to 910 μg L−1 in pH 3.5 acetate buffer solutions with a limit of detection found to correspond to 0.58 μg L−1. The analytical protocol is applied to the sensing of antimony(III) in drinking water samples where a limit of detection was found to correspond to 1.2 μgL−1. The observed detection limits are well below those recommended by the US Environmental Agency and World Health Organisation for antimony(III) concentrations in drinking water. The effects of interferences on the electroanalytical protocol are also explored, where only copper(II) ions are found to be problematic due to the close proximity of the antimony and copper stripping peaks. Proof-of-concept is demonstrated that the interference from copper(II) ions can be eliminated through the application of a complexing agent.

Platinum screen printed electrodes for the electroanalytical sensing of hydrazine and hydrogen peroxide

We report the fabrication of platinum screen printed electrodes which are electrochemically characterised and evaluated as to their potential analytical application towards the sensing of hydrazine and hydrogen peroxide. In the case of hydrazine a linear range of 50 to 500 μM is possible with a limit of detection (3σ) of 0.15 μM achievable using cyclic voltammetry which can be reduced to 0.12 μM using chronoamperometry. The novelty of these platinum screen printed electrodes is highlighted in that the platinum on the screen printed electrode surface resides as an oxide, which is favourable for the electrochemical oxidation of hydrazine, which need to be formed via extensive potential cycling when using a traditional platinum electrode hence the platinum screen printed sensors alleviate these requirements. The electroanalytical reduction of hydrogen peroxide is shown to be feasible with a linear range over 100 and 1000 μM with a limit of detection (3σ) of 0.14 μM which is competitive with other reported analytical protocols.

Fabrication of co-planar screen printed microband electrodes.

We demonstrate the first example of the fabrication of co-planar 50 μm (width) screen printed graphite microbands (length: 20 mm), fabricated entirely via screen printing which are characterised both microscopically and electrochemically via cyclic voltammetry and evaluated towards the sensing of NADH offering a competitive limit of detection (3σ) of 0.24 μM. The fabricated electrodes are also shown to be extended to gold screen printed microbands which are evaluated towards the sensing of chromium(VI) offering a limit of detection (3σ) of 2.65 μM. These microbands are seen to be the first produced entirely through screen printed technology potentially allowing disposable, mass produced microbands to be realised.

Design of screen-printed bulk modified electrodes using anthraquinone–cysteamine functionalized gold nanoparticles and their application to the detection of dissolved oxygen

We investigated the electroanalytical determination of dissolved oxygen using low-cost disposable screen-printed bulk modified electrodes based on nanostructures. A nanostructure based on gold nanoparticles functionalized with an anthraquinone derivative and cysteamine was prepared. The nanostructured material was characterized morphologically using transmission electron microscopy and further physical characterization was carried out by energy-dispersive X-ray spectrometry. The prepared material was incorporated into a screen-printable graphite ink to develop the technology for the economic mass production of the next generation of field sensors. The electroanalytical determination of dissolved oxygen was possible in the range 0.2–6.1 mg L−1 with a detection limit of 0.131 mg L−1 (based on 3σ). We demonstrate proof-of-concept that this approach provides a rapid and inexpensive sensing strategy for the determination of dissolved oxygen in contaminated water samples.

Electroanalytical properties of screen printed shallow recessed electrodes

We report the fabrication of novel carbon based screen printed disc-shaped recessed electrodes (250 μm radius) which are electrochemically characterised and contrasted to other screen printed sensors previously reported upon within the literature. In these circumstances, the electrode is fabricated entirely through screen printing and the electrode geometry is defined by the dielectric (inert polymer) producing shallow recessed electrodes. In comparison to co-planar carbon screen printed electrodes, the shallow recessed screen printed electrodes exhibit a greater current density over the former. The potential electroanalytical applications of these carbon based disc-shaped shallow recessed electrodes are explored through the sensing of NADH and nitrite exhibiting analytically relevant limits of detection (3σ) of 5.2 and 7.28 μM respectively. Additionally, the electroanalytical sensing of nitrite is further trialled in a canal water sample demonstrating the robust nature of the sensors analytical performance. Furthermore we explore the potential improvement of the shallow recessed electrodes through the fabrication of pentagon-shaped carbon based shallow recessed electrodes, which are compared and contrasted with shallow recessed disc electrodes towards the electroanalytical sensing of manganese(II); we believe this to be the first example of such an electrode geometry. In comparison of the observed current density the disc-shaped shallow recessed electrode offers greater sensitivity over co-planar screen printed electrode, whilst in addition to this, a pentagon-shaped recessed electrode offers improved sensitivity over even that of the disc-shaped shallow recessed screen printed electrode. The ultra-low nM sensing of manganese(II) is shown to be possible at both the disc and pentagon shallow recessed electrodes exhibiting limits of detection (3σ) found to correspond to 63 and 36 nM respectively. Both the disc and pentagon-shaped shallow recessed screen printed electrodes are determined to offer greater analytical sensitivity as determined within this study and in comparison with previous literature using graphitic electrodes. The fabrication methodology of the shallow recessed electrodes is shown to be generic in nature such that the underlying carbon layer, which defines the composition of the shallow recessed working electrode, can be replaced with electrocatalytic surfaces. We demonstrate this with the fabrication of platinum disc-shaped shallow recessed screen printed electrodes, which are electrochemically characterised and explored towards the sensing of hydrazine and hydrogen peroxide displaying limits of detection (3σ) of 26.3 and 44.3 μM respectively, which are found to be analytically useful.

Development of a carbon nanotube paste electrode modified with zinc phosphate for captopril determination in pharmaceutical and biological samples

We report a novel electrode composite comprising zinc phosphate within a multiwalled carbon nanotube paste electrode matrix which is applied for the detection of trace amounts of captopril (CAP) via square-wave adsorptive anodic stripping voltammetry (SWAdASV); to the best of our knowledge this is the first report on such a composite electrode. Under optimum experimental conditions, the peak current of CAP was found to be linear over the concentration range from 3.7 to 67 μmol L−1 with a limit of detection of 0.1 μmol L−1. The proposed method was applied for the successful determination of CAP in commercial tablet excipients and biological samples using the electroanalytical protocol evaluated against the laboratory standard iodometric procedure. Excellent comparability between the two is found suggesting that the former can replace the latter within laboratory settings or can be applied to in-the-field applications.