Christopher W. Foster

Graphene‐Rich Wrapped Petal‐Like Rutile TiO2 tuned by Carbon Dots for High‐Performance Sodium Storage

Carbon dots inducing petal-like rutile TiO2 wrapped by ultrathin graphene-rich layers are proposed to fabricate superior anodes for sodium-ion batteries, featuring high-rate capabilities and long-term cyclelife, benefiting from promoted electron transport and a shortened Na+ diffusion length. High capacities of 144.4 mA h g-1 (at 837.5 mA g-1 ) after 1100 cycles and 74.6 mA h g-1 (at 3350 mA g-1 ) after 4000 cycles are delivered outstandingly.

Electrochemical lactate biosensor based upon chitosan/carbon nanotubes modified screen-printed graphite electrodes for the determination of lactate in embryonic cell cultures

l-lactate is an essential metabolite present in embryonic cell culture. Changes of this important metabolite during the growth of human embryo reflect the quality and viability of the embryo. In this study, we report a sensitive, stable, and easily manufactured electrochemical biosensor for the detection of lactate within embryonic cell cultures media. Screen-printed disposable electrodes are used as electrochemical sensing platforms for the miniaturization of the lactate biosensor. Chitosan/multi walled carbon nanotubes composite have been employed for the enzymatic immobilization of the lactate oxidase enzyme. This novel electrochemical lactate biosensor analytical efficacy is explored towards the sensing of lactate in model (buffer) solutions and is found to exhibit a linear response towards lactate over the concentration range of 30.4 and 243.9 µM in phosphate buffer solution, with a corresponding limit of detection (based on 3-sigma) of 22.6 µM and exhibits a sensitivity of 3417 ± 131 µAM(-1) according to the reproducibility study. These novel electrochemical lactate biosensors exhibit a high reproducibility, with a relative standard deviation of less than 3.8% and an enzymatic response over 82% after 5 months stored at 4 °C. Furthermore, high performance liquid chromatography technique has been utilized to independently validate the electrochemical lactate biosensor for the determination of lactate in a commercial embryonic cell culture medium providing excellent agreement between the two analytical protocols.

The electrochemical performance of graphene modified electrodes: An analytical perspective

We explore the use of graphene modified electrodes towards the electroanalytical sensing of various analytes, namely dopamine hydrochloride, uric acid, acetaminophen and p-benzoquinone via cyclic voltammetry. In line with literature methodologies and to investigate the full-implications of employing graphene in this electrochemical context, we modify electrode substrates that exhibit either fast or slow electron transfer kinetics (edge- or basal- plane pyrolytic graphite electrodes respectively) with well characterised commercially available graphene that has not been chemically treated, is free from surfactants and as a result of its fabrication has an extremely low oxygen content, allowing the true electroanalytical applicability of graphene to be properly de-convoluted and determined. In comparison to the unmodified underlying electrode substrates (constructed from graphite), we find that graphene exhibits a reduced analytical performance in terms of sensitivity, linearity and observed detection limits towards each of the various analytes studied within. Owing to graphenes structural composition, low proportion of edge plane sites and consequent slow heterogeneous electron transfer rates, there appears to be no advantages, for the analytes studied here, of employing graphene in this electroanalytical context.

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.

3D Printed Graphene Based Energy Storage Devices

3D printing technology provides a unique platform for rapid prototyping of numerous applications due to its ability to produce low cost 3D printed platforms. Herein, a graphene-based polylactic acid filament (graphene/PLA) has been 3D printed to fabricate a range of 3D disc electrode (3DE) configurations using a conventional RepRap fused deposition moulding (FDM) 3D printer, which requires no further modification/ex-situ curing step. To provide proof-of-concept, these 3D printed electrode architectures are characterised both electrochemically and physicochemically and are advantageously applied as freestanding anodes within Li-ion batteries and as solid-state supercapacitors. These freestanding anodes neglect the requirement for a current collector, thus offering a simplistic and cheaper alternative to traditional Li-ion based setups. Additionally, the ability of these devices’ to electrochemically produce hydrogen via the hydrogen evolution reaction (HER) as an alternative to currently utilised platinum based electrodes (with in electrolysers) is also performed. The 3DE demonstrates an unexpectedly high catalytic activity towards the HER (−0.46 V vs. SCE) upon the 1000th cycle, such potential is the closest observed to the desired value of platinum at (−0.25 V vs. SCE). We subsequently suggest that 3D printing of graphene-based conductive filaments allows for the simple fabrication of energy storage devices with bespoke and conceptual designs to be realised.

Exploring the electrical wiring of screen-printed configurations utilised in electroanalysis

In this technical note the often overlooked issue of electrically connecting screen-printed electrode sensors is considered. The electrical connection of screen-printed electrodes to the potentiostat/electronics can be a main issue when a true electrochemical response is trying to be obtained and if one does not have a stable electrical connection, the results that are obtained may lack reproducibility and therefore maybe discredited as “another failed electrochemical probe/analyte”. This paper considers the case of electrically connecting screen-printed with crocodile clips and compares that to the use of edge-connectors demonstrating the precise connection of an electrode setup when utilising crocodile clips can result in extremely reproducible electrochemical outputs when applied correctly.

Self-assembly of porous copper oxide hierarchical nanostructures for selective determinations of glucose and ascorbic acid

The simple design of CuO micro-/nanostructures has recently attracted tremendous interest particularly for the enzyme-less sensing of biological molecules due to their intrinsic electronic and catalytic properties. Consequently attention has been directed to the development of new CuO nanomaterials that have multi-interdisciplinary applications. Herein, we report for the first time the fabrication of hierarchical porous CuO micro-/nanostructures with flower- and hollow sphere-like morphology via a facile hydrothermal method. Our experimental findings clarify that the source of the copper-ions effectively control the assembly of CuO nano-building blocks via the one-step hydrolysis of [Cu(NH3)4(H2O)2]SO4 and [Cu(NH3)4(H2O)2]Cl2 precursors, which produce hollow sphere and flower-like morphologies for sensitive and selective determination of ascorbic acid and glucose, respectively. Moreover, such unique properties of macro-/mesoporous CuO with defined dimensions and topologies offer minimized diffusive resistance for the dispersion of active sites. The best performance of the glucose and ascorbic sensor can be obtained at +0.55 V in 0.1 M sodium hydroxide solution. The as-prepared CuO modified (drop-casted) screen-printed electrodes (SPE) exhibit a fast electroactive response with high sensitivity within a wide concentration range of glucose and ascorbic acid in real samples. Significantly, the anion-dependent approach might be used to control effectively the expansion and features of other metal oxide micro-/nanostructures.

Pencil drawn paper based supercapacitors

This is the first comprehensive analysis of paper-based supercapacitors, P-SCs, that are produced utilising commercially available pencils to draw an interdigitated design upon common household printing paper, developing cheap, green and reliable low profile electrical conductors and electrodes. The P-SCs are optimised in terms of the composition of pencil used, the number of layers and the analysis of single or double sided interdigitated electrode designs; such a comprehensive study is seldom explored in previous literature. A full analysis of the physical and electrochemical properties of the pencil drawn electrodes has been performed, including the application of a new capacitive testing/evaluation circuit applied to charge/discharge measurements/analysis, which provides a revolutionary and unambiguous analysis of the capacitance of the fabricated electrodes; an easy to use experiment guide is presented. The P-SCs are benchmarked using 0.1 M H2SO4 as the aqueous electrolyte. The P-SCs demonstrate a specific capacitance of ∼10.6 μF mg−1 at a charge current of 0.46 A g−1. The P-SCs are integrated into a novel pouch design, providing a flexible, cheap and easily manufactured supercapacitor, which demonstrates a capacitance of ∼101.4 μF, exhibiting a specific capacitance of ∼42.4 μF g−1 at a current density of 0.46 A g−1, exhibiting energy and power densities of ∼0.45 J mg−1 (0.125 mW h mg−1) and ∼0.03 W mg−1 respectively. The pouch cell, fabricated from P-SCs, utilises five parallel double-sided pencil drawn electrodes, with paper separators, and retains 82.2% of its maximum capacitance, after 5121 charge/discharge cycles at a current density of 0.09 A g−1. Last, a solid state P-SC is developed utilising a PVA–H2SO4 solid electrolyte, which demonstrates a specific capacitance of 141.8 μF g−1, at a charging current of 4.33 μA g−1.

Introducing Thermal Wave Transport Analysis (TWTA): A Thermal Technique for Dopamine Detection by Screen-Printed Electrodes Functionalized with Molecularly Imprinted Polymer (MIP) Particles

A novel procedure is developed for producing bulk modified Molecularly Imprinted Polymer (MIP) screen-printed electrodes (SPEs), which involves the direct mixing of the polymer particles within the screen-printed ink. This allowed reduction of the sample preparation time from 45 min to 1 min, and resulted in higher reproducibility of the electrodes. The samples are measured with a novel detection method, namely, thermal wave transport analysis (TWTA), relying on the analysis of thermal waves through a functional interface. As a first proof-of-principle, MIPs for dopamine are developed and successfully incorporated within a bulk modified MIP SPE. The detection limits of dopamine within buffer solutions for the MIP SPEs are determined via three independent techniques. With cyclic voltammetry this was determined to be 4.7 × 10−6 M, whereas by using the heat-transfer method (HTM) 0.35 × 10−6 M was obtained, and with the novel TWTA concept 0.26 × 10−6 M is possible. This TWTA technique is measured simultaneously with HTM and has the benefits of reducing measurement time to less than 5 min and increasing effect size by nearly a factor of two. The two thermal methods are able to enhance dopamine detection by one order of magnitude compared to the electrochemical method. In previous research, it was not possible to measure neurotransmitters in complex samples with HTM, but with the improved signal-to-noise of TWTA for the first time, spiked dopamine concentrations were determined in a relevant food sample. In summary, novel concepts are presented for both the sensor functionalization side by employing screen-printing technology, and on the sensing side, the novel TWTA thermal technique is reported. The developed bio-sensing platform is cost-effective and suitable for mass-production due to the nature of screen-printing technology, which makes it very interesting for neurotransmitter detection in clinical diagnostic applications.

Pencil It in: Exploring the Feasibility of Hand-Drawn Pencil Electrochemical Sensors and Their Direct Comparison to Screen-Printed Electrodes.

We explore the fabrication, physicochemical characterisation (SEM, Raman, EDX and XPS) and electrochemical application of hand-drawn pencil electrodes (PDEs) upon an ultra-flexible polyester substrate; investigating the number of draws (used for their fabrication), the pencil grade utilised (HB to 9B) and the electrochemical properties of an array of batches (i.e, pencil boxes). Electrochemical characterisation of the PDEs, using different batches of HB grade pencils, is undertaken using several inner- and outer-sphere redox probes and is critically compared to screen-printed electrodes (SPEs). Proof-of-concept is demonstrated for the electrochemical sensing of dopamine and acetaminophen using PDEs, which are found to exhibit competitive limits of detection (3σ) upon comparison to SPEs. Nonetheless, it is important to note that a clear lack of reproducibility was demonstrated when utilising these PDEs fabricated using the HB pencils from different batches. We also explore the suitability and feasibility of a pencil-drawn reference electrode compared to screen-printed alternatives, to see if one can draw the entire sensing platform. This article reports a critical assessment of these PDEs against that of its screen-printed competitors, questioning the overall feasibility of PDEs’ implementation as a sensing platform.