Rashid O. Kadara

Printable thin film supercapacitors utilizing single crystal cobalt hydroxide nanosheets

Cobalt hydroxide (β-Co(OH)2) thin film supercapacitors are developed for the first time via screen printing and their potential application towards energy storage (as an electrode material within a supercapacitor) explored. The highly uniform, porous nanostructures were synthesized via a novel, hydrothermal, template-free approach. The nanostructures consist of amassing, arbitrarily layered, interconnecting nanosheets, resulting in a flower-like structure with many fissures. These nanostructures were fabricated into flexible thin film supercapacitors via screen printing for the first time. The β-Co(OH)2 asymmetric supercapacitor is found to deliver a maximum specific capacitance of ∼170 F g−1 at a current density of 0.5 μA in an aqueous electrolyte solution (3M KOH) retaining 99.69% of its maximum capacity over 600 cycles. Given the ability to mass produce such supercapacitors via screen printing, where readily, synthetically fabricated nanostructures can be incorporated, the application of this approach will likely be widely implemented.

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.

Electroanalytical sensing of nitrite at shallow recessed screen printed microelectrode arrays

We demonstrate that unmodified screen printed shallow recessed graphite microelectrode arrays can be used for the sensing of nitrite in aqueous solutions. The screen printed arrays comprise 6 microdiscs which have radii of 116 (±6) microns and are recessed by 4 microns and separated by 2500 microns from their nearest neighbour in a hexagonal arrangement. The screen printed arrays permit the low micromolar sensing of nitrite in aqueous solutions via cyclic voltammetry with the assessable linear range and detection limit further reduced through the application of amperometry. The protocol is shown to be feasible for the sensing of nitrite in river water samples at levels indicated by the World Health Organisation. The disposable nature and low cost of the sensor offer an economical and portable screening tool for nitrite.

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.

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.

Screen printed graphite macroelectrodes for the direct electron transfer of cytochrome c

We report the direct electrochemistry of cytochrome c at screen printed graphite electrodes which exhibits quasi-reversible voltammetric responses without the need for any chemical or electrochemical pre-treatment, use of mediators or nanomaterials. Through voltammetric studies and X-ray photoelectron spectroscopy (XPS) it is shown that carbonyl and carboxylic surface oxygenated species likely residing at edge plane like- sites/defects of the graphite comprising the screen printed electrodes are responsible for the favourable interaction of the cytochrome c with that of the screen printed electrochemical sensing platform.

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.

Exploring the electrochemical behavior of screen printed graphite electrodes in a room temperature ionic liquid

Screen printed graphite electrodes (SPGEs) have been characterized in the room temperature ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6] by studying pertinent electrochemical parameters of the electroactive species ferrocene (Fc), 1,4-benzoquinone (BQ), 1,4-diphenyl-9,10-anthraquinone (AQ), tetracyclone (TC) and benzophenone-3 (BZ-3). Diffusion coefficients and kinetics calculations together with Digisim simulations for comparison were performed. Additionally, the reductive cyclovoltammograms of organic carbonyl containing BQ, AQ, TC and BZ-3 derivatives provided valuable information and comparison of the electrochemical reduction of the CO functional group in model molecules of different size, solubility and π-aryl aromaticity. Finally, potentialities for the electroanalytical measurement of BZ-3 at SPGEs via the room temperature ionic liquid [C6MIM][PF6] have been evaluated.