A Capillary Electrophoresis End‐Column Amperometric Detection System Incorporating Disposable Copper‐Plated Screen‐Printed Carbon Electrodes

We report here the development of copper‐plated screen‐printed carbon electrodes (designated as Cu‐SPE) to employ as electrochemical detectors for the determination of sugars by capillary electrophoresis (CE). A simple end‐column amperometric detection system with easily exchangeable (or even disposable) electrode and capillary in CE is described in this study. A complex alignment procedure was not required in this system based on the end‐column electrode arrangement using an 85 cm length and 20 μm (i.d.) capillary. The optimized separation voltage and applied potential were 9 KV and 0.4 V (vs. Ag/AgCl), respectively, for the detection of sugars using the Cu‐SPE. Good resolution was obtained by this proposed system with migration times of 28.8, 29.5, 29.9, 30.7, 31.2, and 32.0 min for galactose, glucose, arabinose, fructose, xylose, and ribose, respectively.     

Determination of Lead(II) Using Screen‐Printed Bismuth‐Antimony Film Electrode

This work presents a disposable bismuth‐antimony film electrode fabricated on screen‐printed electrode (SPE) substrates for lead(II) determination. This bismuth‐antimony film screen‐printed electrode (Bi‐SbSPE) is simply prepared by simultaneously in situ depositing bismuth(III) and antimony(III) with analytes on the homemade SPE. The Bi‐SbSPE can provide an enhanced electrochemical stripping signal for lead(II) compared to bismuth film screen‐printed electrodes (BiSPE), antimony film screen‐printed electrodes (SbSPE) and bismuth‐antimony film glassy carbon electrodes (Bi‐SbGC). Under optimized conditions, the Bi‐SbSPE exhibits attractive linear responses towards lead(II) with a detection limit of 0.07 µg/L. The Bi‐SbSPE has been demonstrated successfully to detect lead in river water sample.     

Ultraflexible Screen‐Printed Graphitic Electroanalytical Sensing Platforms

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.     

Batch‐injection versus Flow‐injection Analysis Using Screen‐printed Electrodes: Determination of Ciprofloxacin in Pharmaceutical Formulations

This article highlights the potential use of multi‐walled carbon‐nanotube modified screen‐printed electrodes (SPEs) for the amperometric sensing of ciprofloxacin and compares the association of batch‐injection analysis (BIA) and flow‐injection analysis (FIA) with amperometric detection. Both analytical systems provided precise (RSD<5 %) and sensitive determination of ciprofloxacin (LOD<0.1 μmol L^?1) within wide linear range (up to 200 μmol L^?1). Accuracy of both methods was attested by recovery values (93–107 %) and comparison with capillary electrophoresis. The BIA system is completely portable (especially due to association with SPEs) and provided faster analyses (130 h^?1) and more sensitive detection than the FIA system due to the higher flow rates of injection.     

Detection of α‐Methylacyl‐CoA Racemase in Serum and Urine Using a Highly Sensitive Electrochemical Immunodetector

The detection of α‐methylacyl‐CoA racemase (AMACR), a novel biomarker for prostate cancer, is demonstrated in serum and urine using a novel immuno‐detection method. The detection system consists of a three‐electrode conventional electrochemical cell modified with a gating electrode for applying a gating voltage V_G to the immune complex immobilized on the working electrode to provide signal amplification. The detection system is realized by integrating gating electrodes with screen‐printed electrodes. This detection method does not require involved sample preparation procedures. The detection was demonstrated in serum and urine samples on the nanogram/mL level with V_G equal to 0.6 V. Detection in serum was also performed on the picogram/mL level with a limit of 100 picogram/mL with V_G=0.6 V being a necessary condition.     

Commercial Screen‐Printed Gold Electrodes for the Detection and Quantification of Aminothiols in Human Plasma by Liquid Chromatography with Electrochemical Detection

In order to show the possibilities of screen‐printed electrodes in HPLC detection, a method is presented for routine quantification of aminothiols in human plasma. It uses commercial gold screen‐printed electrodes and provides a rapid, simple and economical procedure with a disposable detector and without any additional electrode. By working at 98 : 2 (0.05 % trifluoroacetic acid: methanol) and 0.9 V, it allows us to determine cysteine (Cys), cysteinyl‐glycine (Cys‐Gly), and homocysteine (HCys) at μmol/L levels. The method was validated, and linearity range, detection and quantification limits, precision and accuracy were evaluated by external calibration and by using N‐acetylcysteine as internal standard, which exhibited better precision.     

Fabrication of Miniaturised Screen‐printed Glucose Biosensors,Using a Water‐based Ink,and the Evaluation of their Electrochemical Behaviour

This paper describes a simple, convenient approach to the fabrication of microband electrodes and microband biosensors based on screen printing technology. These devices were printed in a three‐electrode configuration on one strip; a silver/silver chloride electrode and carbon counter electrode served as reference and counter electrodes respectively. The working electrodes were fabricated by screen‐printing a water‐based carbon ink containing cobalt phthalocyanine for hydrogen peroxide detection. These were converted into a glucose microband biosensor by the addition of glucose oxidase into the carbon ink. In this paper, we discuss the fabrication and application of glucose microband electrodes for the determination of glucose in cell media. The dimensions (100–400 microns) of the microband electrodes result in radial diffusion, which results in steady state responses in the absence of stirring. The microband biosensors were investigated in cell media containing different concentrations of glucose using chronoamperometry. The device shows linearity for glucose determination in the range 0.5 mM to 2.5 mM in cell media. The screen‐printed microband biosensor design holds promise as a generic platform for future applications in cell toxicity studies.     

Batch‐injection Amperometric Analysis on Screen‐printed Electrodes: Analytical System for High‐throughput Determination of Pharmaceutical Molecules

This work presents a single analytical system able to perform high‐throughput determinations of different pharmaceutical molecules on screen‐printed electrodes (SPEs) assembled on a batch‐injection analysis (BIA) cell. Two types of SPEs, both containing a carbon conductive ink as working electrode, were selected for the determination of levamisole (LVM) in aqueous and sodium levothyroxine (NaLVT) in hydroethanolic media. The main analytical characteristics of the proposed system for both examples are high precision (RSD <3.8 %, n=10), low detection limits (submicromolar range), and high sample‐throughput (>150 h^?1) using a single SPE, demonstrating the extended lifetime of such sensors, which are adequate for routine pharmaceutical analysis. The proposed analytical system requires battery‐powered portable devices, including potentiostat and reader, electronic micropipette, BIA cell and SPEs, and can be applied for a wide range of pharmaceutical molecules. In case of analyte adsorption on electrode surface, fast electrode cleaning can be supplied by external stirring easily adapted to the cell, which is demonstrated in this work for NaLVT determination.     

Back‐to‐Back Screen‐Printed Electroanalytical Sensors: Extending the Potential Applications of the Simplistic Design

In our previous paper (Analyst, 2014 , 139, 5339) we introduced the concept of the back‐to‐back electrochemical design where the commonly overlooked back of screen‐printed electrodes are utilised to provide electroanalytical enhancements in screen‐printed electroanalytical sensors. In this configuration the overall sensor comprises of a flexible polyester substrate which has a total of two working, counter and reference electrodes present on the sensor, with a set of electrodes on each side of the substrate. The sensors are designed to allow for a commonly shared electrical connection to the potentiostat and do not require any specialised connections. In this paper we demonstrate proof‐of‐concept extending the electroanalytical utility of the back‐to‐back screen‐printed electrode sensors to bulk modified single‐walled carbon‐nanotubes and electrocatalytic cobalt phthalocyanine microband electrodes. The electroanalytical applications of these novel electrode configuration are exemplified towards the sensing of dopamine, capsaicin and hydrazine. This paper demonstrates the versatility of the back‐to‐back configuration where different surface modifications can be readily employed giving rise to enhancements in sensor performance.     

Screen‐Printed Electrochemical 96‐Well Plate: a High‐Throughput Platform for Multiple Analytical Applications

A new screen‐printed electrochemical array formed by 96 three‐electrode electrochemical cells with carbon‐based working electrodes (DRP‐96X110) was developed by DropSens. The electrochemical and electro(analytical) performance of this multiple‐analysis plate is herein presented. Different proofs of concept relying on reference benchmark redox compounds, streptavidin‐biotin high affinity interactions and magnetic‐based immunoassays were carried out. The results showed the electrochemical plate versatility and usefulness as an innovative high‐throughput transducer surface for multiple and decentralized applications.     

Screen‐Printed Contactless Conductivity Detector for Microchip Capillary Electrophoresis

A new method for mass fabrication of silver ink conductivity detector electrodes for poly(methylmethacrylate) (PMMA) microchip electrophoretic systems has been developed based on screen‐printing technology. Printing of silver conductivity electrodes was performed through a patterned stencil on thin PMMA sheets. Following the electrode fabrication, the PMMA sheets are cut into cover sheets, and are aligned and sealed to the channel plate thus establishing a complete microchip separation device. The effects of the electrode width and spacing on the response and resolution have been investigated and the optimized electrode performance was compared to commonly used aluminum electrodes in the determination of ammonium, methyl ammonium, and sodium. The utility of the screen‐printed contactless conductivity detector (SPCCD) electrodes is further demonstrated for the separation and detection of organic acids with excellent reproducibility (RSD values of 3.7% and 4.1% for oxalate and tartrate, respectively). The thick‐film fabrication of the electrode material demonstrates the ability to mass‐fabricate detection devices with total process of device fabrication requiring less than 4 h (including the fabrication of channel plate, cover sheet with the electrodes, and subsequent bonding). The fabrication method described here is convenient and does not compromise the detector performance, hence offers great promise for producing single use field deployable analytical microsystems.     

Voltammetric Determination of 5‐Aminoquinoline at Carbon Film Electrode and Carbon and Gold Screen Printed Electrodes – A Comparative Study

Aminoquinolines are widely used as antimalarial drugs and thus there is an ever increasing demand for their determination. In this paper, non‐traditional carbon film electrode developed in our laboratory (CFE) with easily replaceable carbon film was used for the determination of 5‐aminoquinoline (5‐AQ) and compared with well‐established commercially available carbon screen printed electrode (CSPE) and gold screen printed electrode (AuSPE). Electrochemical behavior of 5‐AQ was characterized by cyclic and differential pulse voltammetry. Differences in electrochemical behavior of 5‐AQ at different electrodes were evaluated. Determination of 5‐AQ was carried out by differential pulse, square wave, and direct current voltammetry. Practical applicability of the method was verified by direct determination of 5‐AQ in model samples of drinking and river water. Achieved limits of quantitation were in submicromolar concentrations. It was found out that novel CFE in terms of overall performance is in most aspects superior to routinely used commercially available CSPE and AuSPE.     

New Screen‐Printed Ion‐Selective Electrodes for Potentiometric Titration of Cetyltrimethylammonium Bromide in Different Civilic Media

The performance of home‐made printed carbon ink in the fabrication of a simple screen‐printed carbon paste electrodes (SPCPEs) was studied. Such electrodes are applied for the potentiometric titration and hence determination of cetyltrimethylammonium bromide (CTAB) in different pharmaceuticals and water samples. The performances of the new screen printed electrodes towards CTAB are compared with those for carbon paste, coated‐wire, coated graphite and polyvinyl chloride electrodes. SPCPEs have been successfully used for the potentiometric titration of CTAB in the analytical grad solutions, with a potential jump amounts to 1050 mV. The effect of plasticizer type, carbon content, binding materials, printing ink formulation, response time and printing process are optimized. The method is applied for pharmaceutical preparations with a percentage recovery of 99.20 % and RSD=0.45. The electrodes passes a near‐Nernstian cationic slope of 58.70±1.3 and 56.32±2.4 mV and lower detection limit of 6.8×10^?7 and 5.80×10^?7 M with a reproducibility of 0.145 and 3.25 % and response time of about 3 s and exhibit adequate shelf‐life of 6 and 2 months for SPCPE and CPE, respectively. The frequently used CTAB of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two phase titration method. The sensitivity of the proposed method is comparable with the official method indicating its possibility to be used in field measurements.     

Versatile Electrochemical Platform for the Determination of Phenol‐like Compounds Based on Laccases from Different Origins

Simple and fast methods for the monitoring of phenol‐like compounds are relevant in diverse fields ranging from waste management to neurosciences. Laccases are copper‐containing enzymes, which, depending on their origin, are able to oxidize different phenol compounds at different pH conditions. Through adequate laccase immobilization, disposable screen printed electrodes can be used as interphase to build amperometric phenol sensors. In this work three different laccases were studied for the determination of phenol‐like compounds, two of them are isoenzymes from Trametes trogii and the third one from Rhus vernicifera . Their immobilization on screen printed electrodes is presented for the construction of amperometric sensors. The electrode substrate is composed by graphite screen printed electrodes modified with carbon nanotubes and silica microspheres where, depending on the application, one of the three laccases is adsorbed. As each laccase shows an optimum working pH, they were conveniently selected to determine dopamine at physiological pH and catechol at acid pH. Determinations in the micromolar range were possible in both cases. Chronoamperometry shows to be an effective technique for their determinations, simpler than other electrochemical methods already presented in the literature.     

A new capillary electrophoresis end-column amperometric detection system without the need for capillary/electrode alignment

A self-aligning end-column amperometric detection system for capillary electrophoresis was constructed. In this system, the electrode and capillary were exchanged easily and the capillary/electrode alignment procedure is not required. Gold, gold/mercury amalgam, copper and carbon fiber could be used as the working electrode. The principle is in the use of two disk holders with the capillary and the electrode in the center, so that by inserting the disk holders into a groove in the working electrode port, the capillary and the electrode are automatically aligned and the distance between the capillary and the electrode is assured at 0.24 mm. The relative standard deviation obtained using five different gold/mercury amalgam microdisk electrodes for determination of cysteine was 1.5% for the migration time and 3.3% for the electrophoretic peak current. The simple and convenient system was attractive for the routine analysis by capillary electrophoresis with electrochemical detection. The system was applied to the determination of promethazine hydrochloride in human serum.     

DNA‐Modified Screen‐Printed Electrodes with Nanostructured Films of Multiwall Carbon Nanotubes,Hydroxyapatite and Montmorillonite

Nanostructured films were deposited at the surface of working electrode of the screen‐printed assembly and utilized for the surface modification with double‐stranded DNA. The basic electrochemical properties of the sensors were investigated using voltammetric methods. Modified electrodes were also characterized by scanning electron microscopy and electrochemical impedance measurements. It was found that the electrode modification with DNA and nanomodifier leads to an enhanced sensitivity of the DNA voltammetric detection. New potentialities of the utilization of the K₃[Fe(CN)₆] cyclic voltammetric signal and electrochemical impedance spectroscopy were found. The DNA‐based biosensors showed good repeability and necessary stability within several days.     

Adsorptive Stripping Voltammetric Determination of 4‐Hexylresorcinol in Pharmaceutical Products Using Multiwalled Carbon Nanotube Based Electrodes

A sensitive electroanalytical method is presented for the determination of 4‐hexylresorcinol using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT‐BPPGE). This method is also extended to the use of a MWCNT modified screen‐printed electrode (MWCNT‐SPE), thereby demonstrating that this approach can easily be incorporated into a facile and inexpensive electrochemical sensor.     

A New Infrared Spectroelectrochemical Cell for the Detection of Species Generated by Platinum and Screen‐Printed Carbon Electrodes

In this paper, we describe a simple and effective infrared (IR) spectroelectrochemical cell for detecting species generated from an electrochemical system featuring low‐IR‐reflectivity electrodes. The IR detection mode of attenuated total reflection (ATR) was employed to construct the spectroelectrochemical cell. Two kinds of electrodes, platinum (Pt) and screen‐printed carbon (SPC), were used to examine the performance of this new cell in detection of electroactive species generated by cyclic voltammetry. Because data generated from highly reflective electrodes are available in the literature, Pt electrode was used to characterize the performances of the developed spectroelectrochemical cell. Results indicated that species generated electrochemically can be observed readily and their responses were comparable to those described in the literature. The cell volume could be lower than 300 μL, which suggests that this approach may be very useful to obtain chemical information during electrochemistry for biological fluids with limited sample volumes. By examining the electrochemical behavior of several amino acids using both Pt and SPC electrodes, the redox behaviors can be readily observed indicating a new spectroelectrochemical cell was successfully developed for the purpose of using of SPC electrode.     

Textile‐based Electrochemical Sensing: Effect of Fabric Substrate and Detection of Nitroaromatic Explosives

This study examines the influence of textile substrates upon the behavior of wearable screen‐printed electrodes and demonstrates the attractive sensing properties of these sensors towards the detection of nitroaromatic explosives. Compared to electrodes printed on common cotton or polyester substrates, GORE‐TEX‐based electrochemical sensors display reproducible background cyclic voltammograms, reflecting the excellent water‐repellant properties of the GORE‐TEX fabric. The wetting properties of different printed textile electrodes are elucidated using contact angle measurements. The influence of laundry washing and mechanical stress is explored. The GORE‐TEX‐based printed electrodes exhibit favorable detection of 2,4‐dinitrotoluene (DNT) and 2,4,6‐trinitrotoluene (TNT) explosives, including rapid detection of DNT vapor.     

Microliter Volume Determination of Cosmetic Mercury with a Partially Crosslinked Poly(4‐vinylpyridine) Modified Screen‐Printed Three‐Electrode Portable Assembly

We successfully demonstrated microliter (μL) volume determination of Mercury (Hg) using an in‐built screen‐printed three electrodes containing partially crosslinked poly(4‐vinlylpyridine) (designated as pcPVP) modified carbon‐working, carbon‐counter, and Ag⁺‐quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 μL‐droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag⁺ quasi‐reference system shifted the Hg‐SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100–1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N=3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin‐lightening agents in parallel with ICP‐OES measurements.