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Voltammetric sensor using a symmetrical derivative of anthrone3 (1,7-diamino-3,9-dibutyl benzo[1,2,3-de:4,5,6-d’e’]diquinoline-2,8(3H,9H)-dione) (SPE-A) has been developed as a probe for Hg(II) ions. Performance of the probe as screen-printed electrode modified with the receptor (SPE-A) has been compared with anthrone3 in solution phase, using 1:1 water-acetonitrile solvent system. Anthrone3 displayed an electrochemically quasi-reversible nature in voltammograms with both the systems and is presented as a novel disposable voltammetric sensor for mercury ions. Upon interaction with cations, both the electrode systems showed sensitivity towards Hg2+ ions with a lower detection limit of 0.61 µM. The magnitude of the voltammetric current with the SPE-A exhibited three times the current obtained with a bare glassy carbon electrode (GC). Kinetic performance of the SPE-A electrode is better than the GC electrode. The morphological studies indicate reusability of the electrodes.

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.

Corrosion inhibitors are widely used in the water industry for steam condensate treatment. Due to their application into the food industry, the Food and Drug Administration (FDA) legislate that such inhibitors are not to exceed 10 mg L−1. Various analytical protocols exist to provide an offsite analysis and a point of site analysis is required. Consequently, the first example has been reported for the indirect electroanalytical determination of cyclohexylamine and morpholine, two important corrosion inhibitors using disposable and economical screen-printed graphite macroelectrodes. These two analytes have been demonstrated to have no measureable direct electrochemical signatures in aqueous solutions using carbon and noble metal based macroelectrodes and we propose, for the first time, an indirect electrochemical sensing protocol which utilises screen-printed graphite macroelectrodes. This indirect approach utilises an EC type-mechanism using the compounds, N,N′-(1,4-phenylene)dibenzenesulfonamide and N-(4-amino-2-methyl-phenyl)-benzenesulfonamide as mediators. In this approach the mediators are electrochemically oxidised which then chemically react with the target analytes, cyclohexylamine and morpholine; the products of these reactions are then electrochemically interrogated and provide an indirect electroanalytical signal with which to quantify cyclohexylamine and morpholine. The two mediators are required for the two analytes as one mediator cannot measure both analytes. It is demonstrated that this indirect sensing protocol allows the electroanalytical detection of cyclohexylamine and morpholine over the range 1 to 10 mg L−1 in pH 10 carbonate buffer utilising cyclic voltammetry. This indirect electroanalytical protocol is found to exhibit a limit of detection (3σ) of 0.9 and 1 mg L−1 for cyclohexylamine and morpholine respectively which are significantly below the FDA sanctioned levels. This indirect electroanalytical protocol utilising screen-printed sensors has the potential to be applied into-the-field enabling the measurement of these two neutralizing amines to ensure they do not exceed FDA guidelines.

We demonstrate that the electrochemical signa- tures of graphene screen-printed electrodes towards hy- drazine are not due to the reported benefits of graphene per se but rather it is the metallic impurities which can.

The electrochemical sensing of new psychoactive substance(s) (NPSs), synthetic cathinone derivatives also termed "legal highs", are explored with the use of metallic modified screen-printed electrochemical sensors (SPES). It is found that no significant electrochemical enhancement is evident with the use of either in situ bismuth or mercury film modified SPES compared to the bare underlying electrode substrate. In fact, the direct electrochemical reduction of the cathinone derivatives mephedrone (4-methylmethcathinone; 4-MMC) and 4'-methyl-N-ethylcathinone (4-methylethcathinone; 4-MEC) is found to be possible for the first time, without heavy metal catalysis, giving rise to useful voltammetric electroanalytical signatures in model aqueous buffer solutions. This novel electroanalytical methodology is validated toward the determination of cathinone derivatives (4-MMC and 4-MEC) in three seized street samples that are independently analyzed with high-performance liquid chromatography (HPLC) wherein excellent agreement between the two analytical protocols is found. Such an approach provides a validated laboratory tool for the quantification of synthetic cathinone derivatives and holds potential for the basis of a portable analytical sensor for the determination of synthetic cathinone derivatives in seized street samples.

The pursuit of ultraflexible sensors has arisen from the recent implementation of electrochemical sensors into wearable clothing where extensive mechanical stress upon the sensing platform is likely to occur. Such scenarios have witnessed screen-printed electrodes being incorporated into the waistband of undergarments for the determination of key analytes while others have reported incorporation into a neoprene wetsuit. In these conformations, the substrates which the sensors are printed upon need to be ultraflexible and capable of withstanding extensive individual mechanical stress. Therefore the composition, thickness and its combination of screen-printed ink require extensive consideration. A common short-coming within the field of screen-printed derived sensors is the lack of consideration towards the substrate material employed, and is rather in favour of the development of new electrode geometries and screen-printing inks. In this paper we explore the screen-printing of graphite based electroanalytical sensing platforms onto graphic paper commonly used in house-hold printers, and for the first time both tracing paper and ultraflexible polyester-based substrates are used. These sensors are electrochemically benchmarked with the redox probes hexaammine-ruthenium(III) chloride and potassium ferrocyanide(II). The effect of mechanical contortion upon two types of electrode substrates is also performed where it was found that these ultraflexible based polyester-based electrodes are superior to the previously reported ultraflexible paper electrodes since they can withstand extensive mechanical contortion, yet they still give rise to useful electrochemical performances. Most importantly the ultraflexible polyester 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 resulting in electrical shorting, therefore compromising the electrochemical measurement; as such this new substrate can be used as a replacement for paper-based substrates and yet still be resilient to extreme mechanical contortion. A new configuration is also explored using these electrode substrate supports where the working carbon electrode contains the electrocatalyst, cobalt(II) phthalocyanine (CoPC), and is benchmarked towards the electroanalytical sensing of the model analytes citric acid and hydrazine which demonstrate excellent sensing capabilities in comparison to previously reported screen-printed electrodes.

We report the fabrication of screen printed microelectrode arrays which are comprised of six working electrodes (50 μm radii) which are separated from their nearest neighbour by an average distance of 2272 (±0.3) μm and arranged in a circular configuration around a common counter and reference electrode. Due to their facile fabrication, different inks can be used to give rise to both graphite- and gold-based screen printed microelectrode arrays. Additionally due to their fabrication design, the microelectrodes comprising the array are sufficiently separated to ensure no diffusional overlap which is commonly encountered by microelectrode arrays reported within the literature. The electrochemical sensing characteristics of the graphite screen printed microelectrode arrays are evaluated using acetaminophen, dopamine and nitrite giving rise to limits of detection (3σ) of 4.29, 3.24 and 5.24 μM respectively. Further to this, the gold-based screen printed microelectrode arrays are explored towards the electroanalytical sensing of chromium (VI) yielding a limit of detection (3σ) of 8.28 μM. Proof-of-concept is further demonstrated through the determination of chromium (VI) within an environmental (canal water) sample. Due to the analytically useful responses observed at the graphite and gold screen printed microelectrode arrays, these disposable and economical electrodes hold promise for in-the-field sensing applications. Additionally the working electrode composition can be readily changed through the use of the desired screen printing ink (i.e. Pd, Pt, Cu, etc.) allowing the tailoring of the electrode surface enabling electrocatalytic microelectrode arrays to be readily derived.

We report the first known fabrication of palladium screen-printed macroelectrodes which are electrochemically characterised, and their potential usefulness in analytical applications explored towards the sensing of formaldehyde, hydrazine and protons with limits of detection (3σ) of 1.6 mM, 4.0 μM and 41.5 μM determined for each of the analytes, respectively. Proof of concept for the potential sensing of both hydrogen and methane gas is also explored. Such applications demonstrate the plethora of potential uses for screen-printed sensors, particularly those fabricated utilising palladium, giving rise to the niche market of sensors capable for the utilisation away from the laboratory and within the field.

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.

We report the fabrication of screen printed graphite microband electrodes which are electrochemically characterised and critically explored with the electroanalytical applications for the sensing of NADH and nitrite. The screen printed graphite band electrodes consist of graphite microbands printed upon a flexible plastic substrate which are 10 mm in length and 100 μm in width. The graphite microbands have a critical microscopic dimension imparting microelectrode behaviour whilst the length yields an increase in the current output. Electroanalytical characterisation with the electrochemical detection of NADH and nitrite reveal that experimental limits of detection (3 σ ) of 0.48 and 0.05 μM respectively are possible. The screen printed graphite band electrodes are benchmarked against screen printed graphite macroelectrodes as well as graphite ultramicrobands, where in terms of current density, the band electrodes exhibit a greater response over the former, but not the latter. However, in terms of analytical reproducibility, the band electrodes exhibit an improved response over that of the graphite ultra-microelectrodes. The mass production of disposable microband electrodes holds great promise in electrochemistry, particularly as a base transducer for utilisation in electroanalytical sensing where the benefits of the microscopic domain of the band electrode imparting improvements in the analytical performance can be realised.

We overview recent developments in the fabrication of the world’s smallest electrode, the carbon nanotube via chemical vapour deposition (CVD) and demonstrate how these electrodes are beneficially utilised and tailored towards the electrochemical sensing of target analytes. The use of carbon nanotubes arrays grown via CVD to beneficially tailor the arrays to their intended electro-analytical application is also highlighted.

Surfactants are routinely used in the production of graphene and additionally in their solubilisation with the aim of reducing the likelihood of coalescing. We demonstrate that surfactants, which are an inherent property of graphene, are a major contribution to the electrochemical performance. Using well characterised commercially available graphene we demonstrate that the surfactant may be detrimental in electrochemical processes, for example in the electrochemical oxidation of NADH, used prolifically as the basis of over 300 biosensors, and in the electrochemical oxidation of acetaminophen, an analgesic and antipyretic drug which requires routine monitoring in a plethora of areas. The use of control experiments in the form of surfactant modified carbon electrodes is particularly encouraged in de-convoluting the origin of the electrochemical response of graphene modified electrodes.

This chapter overviews the use of carbon nanomaterials in the field of electroanalysis and considers why carbon-based nanomaterials are widely utilized and explores the current diverse range that is available to the practising electrochemist, which spans from carbon nanotubes to carbon nanohorns through to the recent significant attention given to graphene.

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) screen-printed 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. Financial support for this research was supplied by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).

In this paper in situ bismuth, antimony, tin modified electrodes and combinations thereof are explored towards the model target analytes cadmium(II) and lead(II), chosen since they are the most widely studied, to explore the role of the underlying electrode substrate with respect to boron-doped diamond, glassy carbon, and screen-printed graphite electrodes. It is found that differing electrochemical responses are observed, dependent upon the underlying electrode substrate. The electrochemical response using the available range of metallic modifications is only ever observed when the underlying electrode substrate exhibits relatively slow electron transfer properties; in the case of fast electron transfer properties, no significant advantages are evident. Furthermore these bismuth modified systems which commonly employ a pH 4 acetate buffer, reported to ensure the bismuth(III) stability upon the electrode surface can create create a problem when sensing at low concentrations of heavy metals due to its high background current. It is demonstrated that a simple change of pH can allow the detection of the target analytes (cadmium(II) and lead(II)) at levels below that set by the World Health Organisation (WHO) using bare graphite screen-printed electrodes.

This chapter overviews the use of electrochemical sensors for the sensing of nitrogen compounds in respect of their potential use in gas sensing. The roles of electrode material, electrolyte, configurations and overall design of current electrochemical gas sensors for nitrogen compounds sensing are considered and critiqued. The use of electrochemical sensors in medical diagnosis for the measurement of compounds in breath is also briefly overviewed.

We introduce the concept of screen-printed back-to-back electroanalytical sensors where in this facile and generic approach, screen-printed electrodes are printed back-to-back with a common electrical connection to the two working electrodes with the counter and reference electrodes for each connected in the same manner as a normal “traditional” screen-printed sensor would be. This approach utilises the usually redundant back of the screen-printed sensor, converting this “dead-space” into a further electrochemical sensor which results in improvements in the analytical performance. In the use of the back-to-back design, the electrode area is consequently doubled with improvements in the analytical performance observed with the analytical sensitivity (gradient of a plot of peak height/analytical signal against concentration) doubling and the corresponding limit-of-detection being reduced. We also demonstrate that through intelligent electrode design, a quadruple in the observed analytical sensitivity can also be realised when double microband electrodes are used in the back-to-back configuration as long as they are placed sufficiently apart such that no diffusional interaction occurs. Such work is generic in nature and can be facilely applied to a plethora of screen-printed (and related) sensors utilising the commonly overlooked redundant back of the electrode providing facile improvements in the electroanalytical performance.

It has recently been demonstrated that 2-aminoacetophenone (2-AA) is a chemical indicator in exhaled air/breath of Pseudomonas aeruginosa infection associated with progressive life threatening decline of lung function in cystic fibrosis sufferers [Scott-Thomas et al., BMC Pulm. Med., 2010, 10, 56]. Currently the detection of 2-AA involves laboratory based instrumentation such as mass spectrometry and a hand-held point-of-care type breath device would be ideal in providing real-time results within seconds to accelerate patient care decision-making processes. To this end, we demonstrate proof-of-concept that the chemical marker 2-AA, indicative of Pseudomonas aeruginosa infection, can be measured using electrochemical based sensing strategies. A range of commercially available electrode substrates are explored demonstrating for the first time that 2-AA is electrochemically active within aqueous based solutions providing an (electro)analytical signal. Glassy carbon, boron-doped diamond and platinum electrodes have been explored towards the electrochemical oxidation of 2-AA. Electrode fouling is observed requiring pre-treatment in the form of mechanical polishing between voltammetric scans and measurements. To alleviate this, screen-printed graphite electrodes are shown to be a more viable option for implementation into breath sensing devices and overcome the fouling problem since due to their low cost and disposable nature, a new electrode can be used for each measurement. The analytical utility of the platinum, screen-printed and boron-doped diamond electrodes were found to correspond to 6.85, 7.66 and 4.86 mM respectively. The challenges associated with the electrochemical sensing of 2-AA in breath that need to be overcome are discussed. This generic approach where electrochemical based technology is used to provide measurements for chemical markers in exhaled air/breath for medical diagnostics termed electrochemical breathprints (ec-breathprints), has the potential to be developed into a hand-held point-of-care breath diagnostic tool for identifying Pseudomonas aeruginosa infection in exhaled air/breath.

A novel method is reported, whereby screen-printed electrodes (SPELs) are combined with dispersive liquid–liquid microextraction. In-situ ionic liquid (IL) formation was used as an extractant phase in the microextraction technique and proved to be a simple, fast and inexpensive analytical method. This approach uses miniaturized systems both in sample preparation and in the detection stage, helping to develop environmentally friendly analytical methods and portable devices to enable rapid and onsite measurement. The microextraction method is based on a simple metathesis reaction, in which a water-immiscible IL (1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [Hmim][NTf2]) is formed from a water-miscible IL (1-hexyl-3-methylimidazolium chloride, [Hmim][Cl]) and an ion-exchange reagent (lithium bis[(trifluoromethyl)sulfonyl]imide, LiNTf2) in sample solutions. The explosive 2,4,6-trinitrotoluene (TNT) was used as a model analyte to develop the method. The electrochemical behavior of TNT in [Hmim][NTf2] has been studied in SPELs. The extraction method was first optimized by use of a two-step multivariate optimization strategy, using Plackett–Burman and central composite designs. The method was then evaluated under optimum conditions and a good level of linearity was obtained, with a correlation coefficient of 0.9990. Limits of detection and quantification were 7 μg L−1 and 9 μg L−1, respectively. The repeatability of the proposed method was evaluated at two different spiking levels (20 and 50 μg L−1), and coefficients of variation of 7 % and 5 % (n = 5) were obtained. Tap water and industrial wastewater were selected as real-world water samples to assess the applicability of the method. The authors would like to thank the Spanish Ministry of Science and Innovation (project n. CTQ2011-23968), Generalitat Valenciana (Spain) (projects n. ACOMP/2013/072 and PROMETEO/2012/038) and Universidad de Alicante (Spain) (project n. GRE12-45) for the financial support. E.F. also thanks Generalitat Valenciana for her fellowship.

This chapter overviews the use of metallic nanoparticle modified electrodes for the electroanalytical sensing of trace metal ions. Consideration is first given to theoretical aspects of nanoparticle modified architectures followed by an overview of progress made towards the sensing of pertinent heavy metal ions using nanoparticle constructed electrochemical sensing platforms.

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,N′,N′-tetramethyl-p-phenylenediamine (TMPD), β-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 (>3 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.

Recently it has been shown that chemical markers in exhaled air/breath can provide a methodology for the detection of tuberculosis infection. These markers consist of methyl phenylacetate, methyl p-anisate, methyl nicotinate and o-phenylanisole (2-methoxybiphenyl). Current approaches utilise gas chromatography-mass spectrometry (GCMS) which are useful for centralised testing of breath samples. The World Health Organization (WHO) require a portable, non-invasive diagnostic tool for the screening of tuberculosis infection. In order to meet this, we demonstrate proof-of-concept for the analytical sensing of the identified chemical markers in aqueous solutions using electrochemical based technology. We demonstrate that screen-printed electrochemical sensors can be used as the basis of a diagnostic tool for the electrochemical breathprinting of chemical markers (methyl nicotinate and 2-methoxybiphenyl) useful for the screening of tuberculosis infection. It is hoped that further development will facilitate the potential for a portable, hand-held, non-invasive breath diagnostic tool to be realised.

The production and abuse of new psychoactive substances, known as "legal highs" which mimic traditional drugs of abuse is becoming a global epidemic. Traditional analytical methodologies exist which can provide confirmatory analysis but there is a requirement for an on-the-spot analytical screening tool that could be used to determine whether a substance, or sample matrix contains such legal, or formally "legal highs". In this paper the electrochemical sensing of (±)-methcathinone and related compounds at a range of commercially available electrode substrates is explored. We demonstrate for the first time that this class of "legal highs" are electrochemically active providing a novel sensing protocol based upon their electrochemical oxidation. Screen-printed graphite sensing platforms are favoured due to their proven ability to be mass-produced providing large numbers of reliable and reproducible electrode sensing platforms that preclude the requirement of surface pre-treatment such as mechanical polishing as is the case in the use of solid/re-usable electrode substrates. Additionally they hold potential to be used on-site potentially being the basis of an on-site legal high screening device. Consequently the electroanalytical sensing of (±)-methcathinone (3a), (±)-4′-methylmethcathinone [3b, 4-MMC, (±)-mephedrone] and (±)-4′-methyl-N-ethylcathinone (3c, 4-MEC) is explored using screen-printed sensing platforms with the effect of pH explored upon the analytical response with their analytical efficiency evaluated towards the target legal highs. Interesting at pH values below 6 the voltammetric response quantitatively changes from that of an electrochemically irreversible response to that of a quasi-reversible signature which can be used analytically. It is demonstrated for the first time that the electroanalytical sensing of (±)-methcathinone (3a), (±)-mephedrone (3b) and 4-MEC (3c) are possible with accessible linear ranges found to correspond to 16–200 μg mL(−1) for 3a (at pH 12) and 16–350 μg mL(−1) for both 3b and 3c in pH 2, with limits of detection (3σ) found to correspond to 44.5, 39.8 and 84.2 μg mL(−1) respectively. Additionally adulterants that are commonly incorporated into cathinone legal highs are electrochemically explored at both pH 2 and 12.

Faculty of Science and Engineering, School of Chemistry and the Environment, Division of Chemistry and Environmental Science,Manchester Metropolitan University, Chester Street, Manchester M15GD, Lancs, UKtel: ++(0)1612471196; fax: ++(0)1612476831Website: www.craigbanksresearch.com*e-mail: c.banks@mmu.ac.ukReceived: June 13, 2013Accepted: August 15, 2013Published online: September 18, 2013AbstractThe influence of mechanical contortion upon the electrochemical performance of screen-printed graphite paper-based electroanalytical sensing platforms is evaluated and contrasted with traditionally employed polymeric basedscreen-printed graphite sensors. Such a situation of implementation can be envisaged for the potential sensing of an-alytes on the skin where such sensors are based, for example in clothing where mechanical contortion, viz, bendingwill occur, and as such, its effect upon electrochemical sensors is of both fundamental and applied importance. Theeffect of mechanical contortion or stress upon electrochemical behaviour and performance is of screen printed sen-sors is explored. Comparisons are made between both paper- and polymeric- based sensing platforms that are evalu-ated towards the sensing of the well characterised electrochemical probes potassium ferrocyanide(II), hexaammine-ruthenium(III) chloride and nicotinamide adenine dinucleotide (NADH). It is determined that the paper-based sen-sors offer greater resilience in terms of electrochemical performance after mechanical stress. We gain insights intothe role played by both the effect of the time of mechanical contortion and additionally the potentially detrimentaleffects of repeated contortion are explored. These unique paper-based sensors hold promise for widespread applica-tions where flexible and ultra-low cost sensors are required such as applications into medical devices were ultra-lowcost sensors are a pre-requisite, but also for utilisation within applications which require the implementation ofultra-flexible electroanalytical sensing platforms such as in the case of wearable sensors, whilst maintaining usefulelectrochemical performances.Keywords: Ultra flexible substrates, Paper-based electrochemical sensors, Screen printing, Mechanical stress onelectrochemical sensorsDOI: 10.1002/elan.201300274Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/elan.201300274

The electroanalytical sensing of Rohypnol® (flunitrazepam) is reported for the first time utilising screen-printed graphite electrodes without the requirement for any additional pre-treatment or modification. The methodology is shown to be useful for quantifying low levels (μg mL(-1)) of Rohypnol® in not only buffered solutions but also two internationally favoured drinks: Coca Cola™ and the alcopop WKD™ without any sample pre-treatment. The current analytical approaches for the sensing of Rohypnol® are also summarised within this paper. The niche of this electroanalytical protocol is the lack of the requirement of any pre-treatment of the sample/beverage or electrode modification (cleaning, pre-treatment etc.) for the determination of Rohypnol® in beverages and offers a potential rapid, cost-effective, yet suitably sensitive and accurate screening solution to the problem posed by coloured drinks to products such as the colour changing 'Smart Cup'.

Improvements in analytical methods for the determination and quantification of methylcytosine in DNA are vital since it has the potential to be used as a biomarker to detect different diseases in the first stage such as in the case of carcinomas and sterility. In this work we utilized screen printed graphite electrodes (SPGE) for studying the electrochemical response of all free DNA bases, methylcytosine and short oligonucleotides by cyclic voltammetry (CV) and square wave voltammetry (SWV). CV and SWV responses of free DNA bases and methylcytosine have been investigated by using SPGE platforms and the feasibility of detecting and quantifying cytosine and methylcytosine as free DNA moieties has been evaluated as a function of pH, concentration and the presence of the other free DNA bases in solution simultaneously. Repeatability of using SWV has been performed for the electrochemical behavior of both 250 μM cytosine and 250 μM methylcytosine in the presence of 25 μM guanine, with coefficient of variations of 6.9% and 2.6% respectively based upon peak current (N = 5). Six-mer oligonucleotides with a sequence 5′-XXXCGC-3′, where the XXX motif corresponds to TTT, TTA, TAA and AAA have been performed using SWV in 0.1 M acetate buffer pH 5.0 to explore how the DNA base position effects the electrooxidation of guanine and cytosine into the oligonucleotide. Furthermore SWV comparisons of the electrooxidation of the oligonucleotides 5′-CGCGCG-3′ and its methylated 5′-mCGmCGmCG-3′ have been performed with concentrations in acetate buffer solutions, and the interaction of both oligonucleotides with the graphitic surface of the SPGE has been demonstrated by fitting well-known adsorption models such as Freundlich and Langmuir kinetics according to the SWV current response of guanine, cytosine and methylcytosine into the oligonucleotide.

Screen printed carbon nanotube electrodes (SPEs) are explored as electroanalytical sensing platforms for the detection of capsaicin in both synthetic capsaicin solutions and capsaicin extracted from chillies and chilli sauces utilising both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is found that the technique which is most applicable to the electroanalytical detection of capsaicin depends upon the analyte concentration: for the case of low capsaicin concentrations, CV is a more appropriate method as capsaicin exhibits characteristic voltammetric waves of peak heights relevant to the capsaicin concentration; but for the case of high capsaicin concentrations where the voltammetric waves merge and migrate out of the potential window, EIS is shown to be a more appropriate technique, owing to the observed linear increases in R(ct) with increasing concentration. Furthermore, we explore different types of screen printed carbon nanotube electrodes, namely single- and multi- walled carbon nanotubes, finding that they are technique-specific: for the case of low capsaicin concentrations, single-walled carbon nanotube SPEs are preferable (SW-SPE); yet for the case of EIS at high capsaicin concentrations, multi-walled carbon nanotube SPEs (MW-SPE) are preferred, based upon analytical responses. The analytical performance of CV and EIS is applied to the sensing of capsaicin in grown chillies and chilli sauces and is critically compared to 'gold standard' HPLC analysis.

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 single-walled carbon nanotube sensors are presented which are fabricated upon flexible polyester substrates and are benchmarked against standard screen printed graphite electrodes and additionally commercially available single- and multi-walled carbon nanotube electrodes. The screen printed single-walled carbon nanotube sensors (SW-SPE) are benchmarked using potassium ferrocyanide (II), dopamine, hydrazine and capsaicin and are found to be analytically useful, in particular towards the sensing of capsaicin down to low micromolar levels with a limit of detection (3σ) of 1.9 μM improving on those determined utilising commercially available single- and multi-walled carbon nanotube sensors. These electrodes hold potential for those who have developed electroanalytical methodologies in the laboratory and wish to translate this into the field as the sensors are potentially disposable, highly reproducible and easily mass produced.

Glucose sensing represents a billion dollar per annum global market which has its origins in screen printing and electrochemistry. Screen printing can produce economical one-shot disposable sensors which can be used for the rapid, sensitive, and portable analysis of many target analytes in a plethora of areas. However, for new sensors based on this process to be developed and implemented commercially, next generation screen printed electrodes need to be designed with the boundaries of screen printing pushed and their fundamental understanding needs consideration.

We report the fabrication of gold screen printed macro electrodes which are electrochemically characterised and contrasted to polycrystalline gold macroelectrodes with their potential analytical application towards the sensing of chromium(III) and (VI) critically explored. It is found that while these gold screen printed macro electrodes have electrode kinetics typically one order of magnitude lower than polycrystalline gold macroelectrodes as is measured via a standard redox probe, in terms of analytical sensing, these gold screen printed macro electrodes mimic polycrystalline gold in terms of their analytical performance towards the sensing of chromium(III) and (VI), whilst boasting additional advantages over the macro electrode due to their disposable one-shot nature and the ease of mass production. An additional advantage of these gold screen printed macro electrodes compared to polycrystalline gold is the alleviation of the requirement to potential cycle the latter to form the required gold oxide which aids in the simplification of the analytical protocol. We demonstrate that gold screen printed macro electrodes allow the low micro-molar sensing of chromium(VI) in aqueous solutions over the range 10 to 1600 μM with a limit of detection (3σ) of 4.4 μM. The feasibility of the analytical protocol is also tested through chromium(VI) detection in environmental samples.

Correction for ‘Quantification of corrosion inhibitors used in the water industry for steam condensate treatment: the indirect electroanalytical sensing of morpholine and cyclohexylamine’ by Athanasios V. Kolliopoulos et al., Environ. Sci.: Water Res. Technol., 2015, 1, 40–46.

Screen printing is widely used to fabricate disposable and economical electrochemical sensors and has helped us to establish the route from ‘lab-to-market’ for a plethora of sensors. We overview recent developments in the field where screen printed electrochemical sensors are utilised. Starting with their fundamental understanding, through to highlighting new developments in bulk metal and mediator modified electrodes, as well as novel advantageous electrode designs, we demonstrate the wide and diverse range of applications that sensors based on this fabrication approach have achieved.

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.

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.

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.

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.

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.

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.