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 platfor

Electrochemical properties of CVD grown pristine graphene: monolayer- vs. quasi-graphene

We report the electrochemical properties of pristine monolayer, double layer and few-layer (termed quasi-) graphene grown via CVD and transferred using PMMA onto an insulating substrate (silicon dioxide wafers). Characterisation has been performed by Raman spectroscopy, optical spectroscopy, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy, revealing ‘true’ pristine single-layer graphene (O/C of 0.05) at the former and pristine quasi-graphene at the latter (O/C of 0.07); the term “quasi-graphene” is coined due to the surface comprising on average 4-graphene-layers. The graphene electrodes are electrochemically characterised using both inner-sphere and outer-sphere redox probes with electrochemical performances of the graphene electrodes compared to other available graphitic electrodes, namely that of basal- and edge- plane pyrolytic graphite electrodes constructed from Highly Ordered Pyrolytic Graphite (HOPG), with information on heterogeneous rate constants (ko) obtained. The electrochemical rate constants are predominantly influenced by the electronic properties of the graphene surfaces. Monolayer graphene is found to exhibit slow heterogeneous electron transfer (HET) kinetics towards the redox probes studied, with HET rates ca. 2 and 8 times faster at quasi-graphene and HOPG respectively, relative to that of the monolayer graphene electrode. Critically contrasting the performance of monolayer graphene to quasi-graphene and HOPG electrodes reveals that increasing the number of graphene layers results in improved electrochemical properties, where in terms of the electrochemical reversibility of the probes studied: monolayer-graphene < quasi-graphene < HOPG, as governed by the respective HET electrochemical rate constants. Given that edge plane sites are the predominant origin of fast electron transfer kinetics at graphitic materials, the slow HET rates at pristine single-layer graphene electrodes are likely due to graphene’s fundamental geometry, which comprises a small edge plane and large basal plane contribution. In the case of quasi-graphene and HOPG, they possess increasing global coverage of electrochemically reactive edge plane sites (respectively) and thus exhibit superior electrochemical performances over that of monolayer graphene. Last, the case of a double-layer graphene electrode is considered, which as a result of its fabrication possesses a large global coverage of edge plane like- sites/defects. In agreement with the former conclusions, the doublelayered defect-graphene electrode is found to exhibit fast/favourable electrochemical properties, which is attributed to its large edge plane content (i.e. defect abundant graphene) and thus is further evidence that the electrochemical response is dependent on the density of edge plane sites at graphene based electrodes (influenced by the coverage of graphene-defects and the number of graphene layers)

Surfactant exfoliated 2D hexagonal Boron Nitride (2D-hBN) explored as a potential electrochemical sensor for dopamine: surfactants significantly influence sensor capabilities.

Surfactant exfoliated 2D hexagonal Boron Nitride (2D-hBN) nanosheets are explored as a potential electrochemical sensing platform and evaluated towards the electroanalytical sensing of dopamine (DA) in the presence of the common interferents, ascorbic acid (AA) and uric acid (UA). Surfactant exfoliated 2D-hBN nanosheets (2-4 layers) fabricated using sodium cholate in aqueous media are electrically wired via a drop-casting modification process onto disposable screen-printed graphite electrodes (SPEs). We critically evaluate the performance of these 2D-hBN modified SPEs and demonstrate the effect of 'mass coverage' towards the detection of DA, AA and UA. Previous studies utilising surfactant-free (pristine) 2D-hBN modified SPEs have shown a beneficial effect towards the detection of DA, AA and UA when compared to the underlying/unmodified graphite-based electrode. We show that the fabrication route utilised to prepare 2D-hBN is a vital experimental consideration, such that the beneficial effect previously reported is considerably reduced when surfactant exfoliated 2D-hBN is utilised. We demonstrate for the first time, through implementation of control experiments in the form of surfactant modified graphite electrodes, that sodium cholate is a major contributing factor to the aforementioned detrimental behaviour. The significance here is not in the material per se, but the fundamental knowledge of the surfactant and surface coverage changing the electrochemical properties of the material under investigation. Given the wide variety of ionic and non-ionic surfactants that are utilised in the manufacture of novel 2D materials, the control experiments reported herein need to be performed in order to de-convolute the electrochemical response and effectively evaluate the 'underlying surface/surfactant/2D materials' electrocatalytic contribution

2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction

We explore the use of two-dimensional (2D) MoS2 nanosheets as an electro-catalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electro-catalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underling support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrodes individual electron transfer kinetics/properties. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER

The fabrication, characterisation and electrochemical investigation of screen-printed graphene electrodes

We report the fabrication, characterisation (SEM, Raman spectroscopy, XPS and ATR) and electrochemical implementation of novel screen-printed graphene electrodes. Electrochemical characterisation of the fabricated graphene electrodes is undertaken using an array of electroactive redox probes and biologically relevant analytes, namely: potassium ferrocyanide(II), hexaammine-ruthenium(III) chloride, N,N,N0 ,N0-tetramethyl-pphenylenediamine (TMPD), b-nicotinamide adenine dinucleotide (NADH), L-ascorbic acid (AA), uric acid (UA) and dopamine hydrochloride (DA). The electroanalytical capabilities of the fabricated electrodes are also considered towards the sensing of AA and DA. The electrochemical and (electro)analytical performances of the fabricated screen-printed graphene electrodes are considered with respect to the relative surface morphologies and material compositions (elucidated via SEM, Raman, XPS and ATR spectroscopy), the density of electronic states (% global coverage of edge-plane like sites/defects) and the specific fabrication conditions utilised. Comparisons are made between two screen-printed graphene electrodes and alternative graphite based screen-printed electrodes. The graphene electrodes are fabricated utilising two different commercially prepared ‘graphene’ inks, which have long screen ink lifetimes (43 hours), thus this is the first report of a true mass-reproducible screen-printable graphene ink. Through employment of appropriate controls/comparisons we are able to report a critical assessment of these screen-printed graphene electrodes. This work is of high importance and demonstrates a proof-of-concept approach to screen-printed graphene electrodes that are highly reproducible, paving the way for mass-producible graphene sensing platforms in the future

The fabrication, characterisation and electrochemical investigation of screen-printed graphene electrodes

We report the fabrication, characterisation (SEM, Raman spectroscopy, XPS and ATR) and electrochemical implementation of novel screen-printed graphene electrodes. Electrochemical characterisation of the fabricated graphene electrodes is undertaken using an array of electroactive redox probes and biologically relevant analytes, namely: potassium ferrocyanide(II), hexaammine-ruthenium(III) chloride, N,N,N0 ,N0-tetramethyl-pphenylenediamine (TMPD), b-nicotinamide adenine dinucleotide (NADH), L-ascorbic acid (AA), uric acid (UA) and dopamine hydrochloride (DA). The electroanalytical capabilities of the fabricated electrodes are also considered towards the sensing of AA and DA. The electrochemical and (electro)analytical performances of the fabricated screen-printed graphene electrodes are considered with respect to the relative surface morphologies and material compositions (elucidated via SEM, Raman, XPS and ATR spectroscopy), the density of electronic states (% global coverage of edge-plane like sites/defects) and the specific fabrication conditions utilised. Comparisons are made between two screen-printed graphene electrodes and alternative graphite based screen-printed electrodes. The graphene electrodes are fabricated utilising two different commercially prepared ‘graphene’ inks, which have long screen ink lifetimes (43 hours), thus this is the first report of a true mass-reproducible screen-printable graphene ink. Through employment of appropriate controls/comparisons we are able to report a critical assessment of these screen-printed graphene electrodes. This work is of high importance and demonstrates a proof-of-concept approach to screen-printed graphene electrodes that are highly reproducible, paving the way for mass-producible graphene sensing platforms in the future

Pencil it in: pencil drawn electrochemical sensing platforms.

Inspired by recent reports concerning the utilisation of hand drawn pencil macroelectrodes (PDEs), we report the fabrication, characterisation (physicochemical and electrochemical) and implementation (electrochemical sensing) of various PDEs drawn upon a flexible polyester substrate. Electrochemical characterisation reveals that there are no quantifiable electrochemical responses upon utilising these PDEs with an electroactive analyte that requires an electrochemical oxidation step first, therefore the PDEs have been examined towards the electroactive redox probes hexaammineruthenium(iii) chloride, potassium ferricyanide and ammonium iron(ii) sulfate. For the first time, characterisation of the number of drawn pencil layers and the grade of pencil are examined; these parameters are commonly overlooked when utilising PDEs. It is demonstrated that a PDE drawn ten times with a 6B pencil presented the most advantageous electrochemical platform, in terms of electrochemical reversibility and peak height/analytical signal. In consideration of the aforementioned limitation, analytes requiring an electrochemical reduction as the first process were solely analysed. We demonstrate the beneficial electroanalytical capabilities of these PDEs towards p-benzoquinone and the simultaneous detection of heavy metals, namely lead(ii) and cadmium(ii), all of which are explored for the first time utilising PDEs. Initially, the detection limits of this system were higher than desired for electroanalytical platforms, however upon implementation of the PDEs in a back-to-back configuration (in which two PDEs are placed back-to-back sharing a single connection to the potentiostat), the detection limits for lead(ii) and cadmium(ii) correspond to 10 μg L(-1) and 98 μg L(-1) respectively within model aqueous (0.1 M HCl) solutions

2D Molybdenum Disulphide (2D-MoS2) Modified Electrodes Explored Towards the Oxygen Reduction Reaction

Two-dimensional molybdenum disulphide nanosheets (2D-MoS2)have proven to be an effective lectro- catalyst, with particular attention being focused on their use towards increasing the efficiency of the reac-tions associated with hydrogen fuel cells. Whilst the majority of research has focused on the Hydrogen Evolution Reaction (HER), herein we explore the use of 2D-MoS2 as a potential electrocatalyst for the much less researched Oxygen Reduction Reaction (ORR). We stray from literature conventions and perform experiments in 0.1 M H2SO4 acidic electrolyte for the first time, evaluating the electrochemical performance of the ORR with 2D-MoS2 electrically wired/immobilised upon several carbon based elec-trodes (namely; Boron Doped Diamond (BDD), Edge Plane Pyrolytic Graphite (EPPG), Glassy Carbon (GC) and Screen-Printed Electrodes (SPE)) whilst exploring a range of 2D-MoS2 coverages/masses. Conse-quently, the findings of this study are highly applicable to real world fuel cell applications. We show that significant improvements in ORR activity can be achieved through the careful selection of the under-lying/supporting carbon materials that electrically wire the 2D-MoS2and utilisation of an optimal mass of 2D-MoS2. The ORR onset is observed to be reduced to ca.+0.10 V for EPPG, GC and SPEs at 2D-MoS2 (1524 ng cm−2 modification), which is far closer to Pt at +0.46 V compared to bare/unmodified EPPG, GC and SPE counterparts. This report is the first to demonstrate such beneficial electrochemical responses in acidic conditions using a 2D-MoS2 based electrocatalyst material on a carbon-based substrate (SPEs in this case). Investigation of the beneficial reaction mechanism reveals the ORR to occur via a 4 electron process in specific conditions; elsewhere a 2 electron process is observed. This work offers valuable insights for those wishing to design, fabricate and/or electrochemically test 2D-nanosheet materials towards the OR

Telephone based self-management support by 'lay health workers' and 'peer support workers' to prevent and manage vascular diseases: a systematic review and meta-analysis

Background: Improved prevention and management of vascular disease is a global priority. Non-health care professionals (such as, ‘lay health workers’ and ‘peer support workers’) are increasingly being used to offer telephone support alongside that offered by conventional services, to reach disadvantaged populations and to provide more efficient delivery of care. However, questions remain over the impact of such interventions, particularly on a wider range of vascular related conditions (such as, chronic kidney disease), and it is unclear how different types of telephone support impact on outcome. This study assessed the evidence on the effectiveness and cost-effectiveness of telephone self-management interventions led by ‘lay health workers’ and ‘peer support workers’ for patients with vascular disease and long-term conditions associated with vascular disease. Methods: Systematic review of randomised controlled trials. Three electronic databases were searched. Two authors independently extracted data according to the Cochrane risk of bias tool. Random effects meta-analysis was used to pool outcome measures. Results: Ten studies were included, primarily based in community settings in the United States; with participants who had diabetes; and used ‘peer support workers’ that shared characteristics with patients. The included studies were generally rated at risk of bias, as many methodological criteria were rated as ‘unclear’ because of a lack of information. Overall, peer telephone support was associated with small but significant improvements in self-management behaviour (SMD = 0.19, 95% CI 0.05 to 0.33, I2 = 20.4%) and significant reductions in HbA1c level (SMD = -0.26, 95% CI −0.41 to −0.11, I2 = 47.6%). There was no significant effect on mental health quality of life (SMD = 0.03, 95% CI −0.12 to 0.18, I2 = 0%). Data on health care utilisation were very limited and no studies reported cost effectiveness analyses. Conclusions: Positive effects were found for telephone self-management interventions via ‘lay workers’ and ‘peer support workers’ for patients on diabetes control and self-management outcomes, but the overall evidence base was limited in scope and quality. Well designed trials assessing non-healthcare professional delivered telephone support for the prevention and management of vascular disease are needed to identify the content of effective components on health outcomes, and to assess cost effectiveness, to determine if such interventions are potentially useful alternatives to professionally delivered care

Electroanalytical detection of pindolol: comparison of unmodified and reduced graphene oxide modified screen-printed graphite electrodes

Recent work has reported the first electroanalytical detection of pindolol using reduced graphene oxide (RGO) modified glassy carbon electrodes [S. Smarzewska and W. Ciesielski, Anal. Methods, 2014, 6, 5038] where it was reported that the use of RGO provided significant improvements in the electroanalytical signal in comparison to a bare (unmodified) glassy carbon electrode. We demonstrate, for the first time, that the electroanalytical quantification of pindolol is actually possible using bare (unmodified) screenprinted graphite electrodes (SPEs). This paper addresses the electroanalytical determination of pindolol utilising RGO modified SPEs. Surprisingly, it is found that bare (unmodified) SPEs provide superior electrochemical signatures over that of RGO modified SPEs. Consequently the electroanalytical sensing of pindolol is explored at bare unmodified SPEs where a linear range between 0.1 μM–10.0 μM is found to be possible whilst offering a limit of detection (3σ) corresponding to 0.097 μM. This provides a convenient yet analytically sensitive method for sensing pindolol. The optimised electroanalytical protocol using the unmodified SPEs, which requires no pre-treatment (electrode polishing) or electrode modification step (such as with the use of RGO), was then further applied to the determination of pindolol in urine samples. This work demonstrates that the use of RGO modified SPEs have no significant benefits when compared to the bare (unmodified) alternative and that the RGO free electrode surface can provide electro-analytically useful performances