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 fabricationthe pencil grade utilised HB to 9B and the electrochemical properties of an array of batches i. 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.
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. Among academia and industry, there is constant focus on the Hands drawn in pencil dating of low cost and efficient analytical techniques. In consideration of this, electrochemically-based analytical systems have been continually analysed and benchmarked. Indeed, the development of portable,
Hands drawn in pencil dating cost, and miniaturised analytical devices has promoted a true scientific revolution over the last decades [ 1 ].
An extremely attractive and effective technique to incorporate these electroactive materials is via the utilisation of screen-printing technology [ 2 ]. These screen-printed sensors have actually transformed the field due to their capability to bridge the gap between laboratory experiments with in-field implementation [ 34567 ]. This is exemplified by the billions of dollars per annum that the glucose sensing market has benefited from in its use of screen-printed electrodes, these handheld sensors allow individuals to measure their own blood glucose levels in the comfort of their home [ 89 ].
Such technology allows for the mass production of highly reproducible electrode configurations and, due to scales of economy, inexpensive sensing and disposable electrochemical platforms can be regularly fabricated [ 3 ].
However, as electrochemists, we are constantly searching for novel electrode configurations. Taking advantage of pencil-based approaches that have just begun [ 10 ], we now focus on the creation of readily available hand-drawn pencil graphitic electrodes PDEswhere one can potentially draw their own electrochemical system. The pencil-drawn approach offers an interesting method to develop sensing platforms, where devices can be fabricated in minutes using nothing more than readily available pencils.
The difference in blackness arises from the "Hands drawn in pencil dating" relative fractions of graphite in the composition between harder and softer pencil leads. Upon its application, it was observed that in the majority of cases, electrochemical oxidation of an array of analytes was not feasible using these PDEs, unless a prior electrochemical reduction step was first implemented.
Different pencil grades and their graphite deposition A ; fabrication of Pencil-drawn Electrodes B ; a typical final Pencil-drawn Electrode C and an image of a sheet of screen-printed electrodes fabricated via the screen-printing process D.
As mentioned previously, this is an area that has received increased interest over recent years, and Table 1 provides an overview of the current research into the electroanalytical application of PDEs.
For example, Dossi et al. Additional reports from this
Hands drawn in pencil dating have explored the electrochemical detection of analytes such as potassium ferrocyanide [ 12 ], 1,2-hydroxybenzene [ 14 ], dopamine, paracetamol [ 13 ] and ortho-diphenols in edible oil samples [ 19 ].
Also, these PDEs have been recently implemented in electrophoresis devices for an interesting contactless conductivity detection of inorganic cations in human tears [ 1 ]. Honeychurch has demonstrated that the electrochemical detection of lead II within real canal water samples can also be achieved via the use of hand-drawn PDEs on a polyvinylchloride substrate [ 18 ].
Furthermore, fully-drawn electroanalytical sensors in a different configuration have been reported by Li et al. Overview of current literature on pencil-drawn electrode systems, in order of publication date. In this paper, we critically analyse pencil-drawn electrodes PDEs that have been fabricated with a range of commercially available Derwent pencils.
We compare the electron transfer properties and electrochemical sensing capabilities for the detection of dopamine and acetaminophen of our hand-drawn electrodes to that of graphitic-based screen-printed electrodes. In addition, we analyse the effect of a pencil-drawn reference electrode and compare it to screen-printed alternatives, exploring the overall feasibility and suitability of these "Hands drawn in pencil dating" as a full electrode system.
All chemicals were purchased from Sigma-Aldrich at analytical grade and were used as received without any further purification.
The solutions were prepared with deionised water of resistivity not less than All experiments throughout this study were conducted using a three electrodes configuration utilising nickel coil and Saturated Hands drawn in pencil dating Electrodes SCE as a counter and reference, respectively. Survey spectra were acquired over the binding energy range —0 eV using a pass energy of 50 eV and high resolution scans were made over the C Hands drawn in pencil dating and O 1s lines using a pass energy of 20 eV.
In each case, the analysis was an area-average over a region approximately 1. The energy scale of the instrument is calibrated according to ISOand the intensity scale is calibrated using an in-house method traceable to the UK National Physical Laboratory [ 23 ].
Data were quantified using Scofield cross sections corrected for the energy dependencies of the electron attenuation lengths and the instrument transmission [ 24 ]. Data interpretation was carried out using CasaXPS software v2. Electrical resistance measurements were carried out using a 4-wire measurement method, usually used to measure small resistances in thin films.
The benefit of this system is that it prevents the resistance in the wires and connectors from being included in any measurements. After defining the surface area, a connecting strip from the top of the circle allows for a crocodile clip connection to be employed with the potentiostat [ 26 ]. It is noted that a prior report indicated that these polyester based electrodes do not suffer from capillary action as observed in the case of paper-based sensors, causing the solution to wick-up the electrode towards the electrical connections and resulting in electrical shorting, thus compromising the electrochemical measurement [ 27 ].
Screen-printed graphite macroelectrodes SPEs "Hands drawn in pencil dating" also used for comparative purposes.
A previously used carbon-graphite ink formulation product code: After curing again at the same conditions as before, the screen-printed electrodes were ready to be used. The k 0 values for the PDEs were deduced using the Nicholson equation for an electrochemically quasi -reversible process as described by Equation In this paper, we report the electrochemical and physiochemical characterisation of pencil-drawn electrodes PDEs fabricated on ultra-flexible polyester substrates.
We first optimise the amount of graphite deposited onto the polyester substrate by hand-drawing 15, 30, 60 and times see Figure 1 through comparison of its electrochemical performance using the outer-sphere redox probe hexaammineruthenium III chloride. As can be observed, a general increase of k 0 values is evident. However, upon utilising a PDE drawn times, there is no further significant improvement among the value for k 0.
Consequently, 60 times was chosen for further experiments. A plot of peak height vs. The PDE1s drawn 15 and 30 times have values that correspond to mV and mV respectively, indicating that an improvement within the reversibility is offered when utilising PDEs that have been drawn an increased number of times. The combination of these components in different proportions determines the grade of the pencil and gives rise to distinct properties. Higher grades are associated with an increasing amount of graphite within the pencils, making them softer and darker when drawn on a substrate.
In order to examine the influence of the different grades used for the fabrication of PDEs, the electrochemical response of various PDEs were evaluated using the outer-sphere redox probe hexaammineruthenium III chloride in 0. Unexpectedly, besides the PDE fabricated using pencil 7B, which reported a very resistive CV towards hexaammineruthenium III chloride redox probe, none of the other PDEs provided effective electrochemical responses, possibly due to the combination of graphite and clay within the pencil lead not creating an adequate conductive layer on the polyester substrate.
It "Hands drawn in pencil dating" important to note that the subsequent utilisation of higher pencil grades did not provide expected shades when drawn on the plastic substrate and all the pencil leads i. Raman spectroscopy Hands drawn in pencil dating SEM analysis of PDEs fabricated using pencil HB and 4B from Box 1 were carried out to investigate any correlation between the electrochemical behaviour of different grade PDEs and the morphology and characteristics of their surfaces.
Also evident is the slight protrusion shoulder present on the 2D peak in the case of the 4B supporting the former statement.
The latter point concerning the adhesive considerations of the pencil lead onto the substrate is also illustrated in Figure S2 B, with SEM images showing a dense and graphitic deposition upon using the HB pencil. The graphite deposit utilising the 4B is vastly contrasted to that of the HB and it is clear that less material and lower quality graphite has adhered to the surface in this case Figure S2 D.
Hands drawn in pencil dating Whatever the reason, this phenomenon is highly interesting and will require separate, more independently focused studies to fully understand
Hands drawn in pencil dating mechanism, which surpasses the intended scope of this paper. For the purpose of this work, we can conclude that the HB pencil performs more favourably than the 4B and other grades; thus, for further tests we focus solely on the use of this pencil type.
Next, our attention was turned to investigating the reproducibility of PDEs when employing the fabrication of five other batches of HB pencils belonging to the same commercial brand, as reported in the Experimental Section. Figure S3 shows a series of cyclic voltammograms recorded for each PDE assayed, including the pencil-drawn working electrode PDE1 previously studied for comparative purposes.
It is important to note that appropriate electrochemical measurements were only feasible when using PDE1, PDE3 and PDE5, even though very resistive voltammetric profiles and high peak-to-peak separation were observed for the aforementioned redox couples, particularly utilising PDE3 and PDE5.