Screen-printed Platinum Electrodes Research Articles

Temperature-Sensitive Sensors Modified with Poly(N-isopropylacrylamide): Enhancing Performance through Tailored Thermoresponsiveness.

The development of temperature-sensitive sensors upgraded by poly(N-isopropylacrylamide) (PNIPAM) represents a significant stride in enhancing performance and tailoring thermoresponsiveness. In this study, an array of temperature-responsive electrochemical sensors modified with different PNIPAM-based copolymer films were fabricated via a "coating and grafting" two-step film-forming technique on screen-printed platinum electrodes (SPPEs). Chemical composition, grafting density, equilibrium swelling, surface wettability, surface morphology, amperometric response, cyclic voltammograms, and other properties were evaluated for the modified SPPEs, successively. The modified SPPEs exhibited significant changes in their properties depending on the preparation concentrations, but all the resulting sensors showed excellent stability and repeatability. The modified sensors demonstrated favorable sensitivity to hydrogen peroxide and L-ascorbic acid. Furthermore, notable temperature-induced variations in electrical signals were observed as the electrodes were subjected to temperature fluctuations above and below the lower critical solution temperature (LCST). The ability to reversibly respond to temperature variations, coupled with the tunability of PNIPAM's thermoresponsive properties, opens up new possibilities for the design of sensors that can adapt to changing environments and optimize their performance accordingly.

A new electrochemical sensor based on a screen-printed electrode modified with an ion-imprinted PEDOT for the detection and the quantification of Cd(II)

In this study, an electrochemical sensor was developed using an ion imprinting technique to create a film, facilitating rapid, sensitive, cost-effective and multiplexed determination of cadmium ions in nature. Indeed, pollution by this substance is of great concern due to its toxic health risks and its cumulative and persistent nature in living organisms. The sensor was functionalized with cyclic voltammetry by directly electropolymerizing ethylenedioxythiophene (EDOT) in the presence of Cd(II) as a template on screen-printed platinum electrodes. After electropolymerization, the structure and the morphology of the sensor ion imprinted polyethylendioxythiophene (IIP-PEDOT/SPPtE) were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and scanning electron microscopy (SEM/EDX). The electrochemical properties of the sensor were studied by cyclic voltammetry and electrochemical impedance spectroscopy. All experimental parameters were optimized by square wave voltammetry. IIP-PEDOT/SPPtE exhibited a linear concentration range of 0.5 to 75 µg/L, a detection limit of 0.07 µg/L and a quantification limit of 0.21 µg/L. Furthermore, the proposed sensor revealed good reproducibility, high stability and high selectivity for cadmium over several potential interferents. The developed device was successfully applied to the Cd(II) detection in industrial water samples via the standard addition method. The results were compared to analyzes of the same samples by ICP-MS. A high recovery rate of around 90–102.2 % and an RSD equal to 5.8 % and 2.5 % were observed.

Parallel Amperometric and Potentiometric Multianalyte Detection in a Microfluidic System

The adoption of microfluidic technologies in electrochemical biosensor development has enabled quantitative biomarker monitoring that use significantly lower volumes of reagents and samples, miniaturized electrodes, and inexpensive fabrication techniques, while presenting opportunities for multianalyte detection. We describe the fabrication of amperometric and potentiometric biosensors on a multichannel, platinum screen-printed electrode (SPE) and demonstrate their operation in parallel on a microfluidic multianalyte electrochemical sensor array (µMESA) platform.Working electrodes (WEs) of an SPE were were modified with either enzymes or ion selective membranes (ISMs) for amperometric or potentiometric measurements respectively. Oxidase enzymes were dissolved in an osmium (II) bis(2,2'-bipyridine)chloride-poly(vinylimidazole-allylamine) redox polymer and immobilized on four WEs. The use of this osmium-based electron transfer mediator has been previously reported to lower the oxidation potential of analytes and to improve overall sensor performance. The remaining four WEs were modified by electrodeposition of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), an intrinsically conductive polymer. Solid contact ISMs were prepared by combining ionophores, lipophilic ion exchangers, and a fluorosilicone polymer, and drop casting the mixtures on PEDOT:PSS-coated WEs. Plasticizer-free ISMs improve sensor lifetime by lowering the glass transition temperature and eliminating leaching of plasticizers from the ISM. By utilizing these strategies, we fabricated amperometric sensors for glucose and lactate, and potentiometric sensors for K+ and Ca2+ ions. Glucose is a primary substrate for energy metabolism while lactate is a major metabolite and signaling molecule. K+ ions maintain cell membrane physiology and homeostasis whereas Ca2+ ions serve as messengers during muscle activity and neurotransmission.Sensor characteristics like sensitivity, selectivity, linear range, and operational longevity for each biosensor were assessed using chronoamperometry or chronopotentiometry techniques on a potentiostat/potentiometer instrument. The results indicate that the sensor fabrication strategies described, in combination with our µMESA platform, can be used to measure changes in metabolite concentrations under laminar flow. Ultimately, this versatile technology may provide novel insights into complex physiological and pathological processes in biological systems.

Reliable and inexpensive dissolved oxygen sensing materials

Bare, non-pretreated platinum wires and screen-printed platinum electrodes were used as both working and counter electrodes in the measurement of dissolved oxygen using a chronoamperometric method. The oxygen reduction current response in the diffusion state was used for a linear determination of air saturation. We evaluated the two different materials in general for their sensing performance such as conditioning time, accuracy, resolution and stability over 13 h of continuous mid-term measurement. A good performance was found for the wire electrodes in terms of accuracy with a current slope of 1.0–1.6 µA (% as)-1 and a resolution of 10–15 nA (Lowest Level of Detection = 0.1% as), but with an unstable current response result over the course of the measurement. The screen-printed electrodes have a resolution of 10–18 nA (Lowest Level of Detection = 0.6–0.8% as) and an accuracy of 620–660 nA (% as)-1 but they showed promising reproducibility and stability. Both materials require several hours of conditioning in the chronoamperometric method before a stable current response is achieved. For biotechnological applications, the platinum screen printed electrodes were evaluated in typical parameter settings (pH 4.0 and 7.4, salinity 0.1 to 10x phosphate buffered saline and temperature 12 to 42 °C) and showed correlations between the response time and stability and the temperature. No correlations were found between salinity, pH and the current response. In this paper, we present inexpensive electrode materials and a simple to implement chronoamperometric method for reliable direct measurement of dissolved oxygen in aqueous media.Graphical abstract

Self-cleaning sensors based on thermoresponsive polymeric film modified screen-printed platinum electrodes

Self-cleaning sensors based on thermoresponsive polymeric film modified screen-printed platinum electrodes

Electroactive molecularly imprinted polymer nanoparticles for selective glyphosate determination

Redox-active molecularly imprinted polymer nanoparticles selective for glyphosate, MIP-Gly NPs, were devised, synthesized, and subsequently integrated onto platinum screen-printed electrodes (Pt-SPEs) to fabricate a chemosensor for selective determination of glyphosate (Gly) without the need for redox probe in the test solution. That was because, ferrocenylmethyl methacrylate was added to the polymerization mixtures during the NPs synthesis so that the resulting MIP-Gly NPs contained covalently immobilized ferrocenyl moieties as the reporting redox ingredient, conferring these NPs with electroactive properties. MIP-Gly NPs of four different compositions were evaluated. The herein described approach represents a simple and effective way to endow MIP NPs with electrochemical reporting capabilities with neither the need to functionalize them post-synthesis nor to use electrochemical mediators present in the tested solution during the analyte determinations. MIP-Gly NPs synthesized using allylamine and squaramide-based monomers appeared most selective to Gly. The Pt-SPEs modified with MIP-Gly NPs were characterized with differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Changes in the DPV peak originating from the oxidation of the ferrocenyl moieties in these MIP-Gly NPs served as the analytical signal. The DPV limit of detection and the linear dynamic concentration range for Gly were 3.7 pM and 25 pM–500 pM, respectively. Moreover, the selectivity of the fabricated chemosensors was sufficiently high to determine Gly successfully in spiked river water samples.

Chemosensor Based on Molecularly Imprinted Nanoparticles for Selective Determination of Glyphosate

Glyphosate is a commonly used herbicide that can kill some weeds and grasses. Unfortunately, exposure to glyphosate is considered potentially harmful to humans. It may cause liver and kidney damage as well as can affect the endocrine system.1 Furthermore, the International Agency for Research on Cancer considers glyphosate as a probable carcinogen.2 Glyphosate determination often requires additional steps allowing quantification by commonly employed chromatographic techniques. Therefore, low-cost, rapid, and reliable ways to determine this pesticide are essential.We devised and fabricated an electrochemical chemosensor for the selective determination of the target toxin, glyphosate. As a recognition unit in this sensor, electroactive molecularly imprinted nanoparticles (nanoMIPs) with an internal redox probe were used.3 The MIP nanoparticles were synthesized using a solid-phase synthesis protocol.4 The nanoMIPs were characterized by several methods, including dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The obtained nanoparticles were covalently immobilized on screen-printed platinum electrodes and successfully used for electrochemical determination of glyphosate in the absence of any external redox probe. Chemosensor fabricated that way demonstrated high sensitivity and selectivity with respect to structural analogs of glyphosate and other phosphate-containing analytes. The practical application of this self-reporting MIP-based chemosensor for detecting pesticide was further verified in river water samples with satisfying results. These results prove that our sensor's detectability is sufficient for the on-site detection of glyphosate pesticide.

New Materials for Extreme Environment Solid-State Electrochemical Sensors

Sensing technology for extreme temperatures and environmental conditions is becoming increasingly important for applications in space travel and hypersonic technology. Solid state electrochemical systems based on yttria-stabilized zirconia (YSZ), utilizing Pt or perovskite-oxide electrodes are candidates for ultra-harsh environment sensing. Little is known on the stability or sensitivity of these materials around their sintering temperatures (1200-1500°C). In this work, sensors consisting of 8 mol% YSZ with either sputtered or screen-printed platinum electrodes were characterized in-situ with electrochemical impedance spectroscopy over temperatures from 800-1400°C with oxygen concentrations ranging from 0.04 to 0.30 atm. Sensor degradation was present both during a single test and with subsequent testing. The source of the degradation can be found both in the electrolyte and the electrode. For the electrode, morphological, chemical, or diffusion-based reactions with the electrolyte could be the source. The degradation of the electrical conductivity of commonly used 8 mol% YSZ with time at temperatures above 1000°C is likely caused by nano-microstructural changes to the defect structure of the crystal. This leads to the need for new materials for high temperature sensors. These can be split into electrode materials and electrolyte materials. This work focuses on determining the high temperature stability of these new materials. For example, higher doping levels of YSZ have shown negligible conduction loss with time. Degradation testing has also revealed inconsistent electrical stability between single and poly crystalline YSZ electrolytes. Electrode materials will focus on oxide-perovskites like lanthanum-strontium-manganite and platinum alloys or composites aimed to prolong electrode stability/usefulness. Through this investigation, the chemical, thermal, and electrical stability of these materials alone and with respect to each other are explored using electrochemical impedance spectroscopy and electron microscopy. The work will guide future research in this topic with respect to material selection for extreme environment sensors.

Graphene-Based Gas Sensor Loaded with Lead-Free Perovskite Nanocrystals

Introduction Semiconducting devices based on graphene show outstanding potential due to their mechanical, electronic and chemical properties. However, the development of commercial graphene-based gas sensors is still challenging due to significant drawbacks that should be overcome. For instance, pristine graphene shows poor sensitivity and selectivity towards gas molecules, which makes necessary its modification/functionalisation. Sensing performance can be improved using different strategies such as the decoration of graphene with metal oxide nanoparticles. However, the use of metal oxides generally involves operating the sensor well above room temperature, thus increasing power consumption and reducing the lifetime of the sensor due to aging.Therefore, new research efforts have been focused towards the development of graphene loaded with alternative nanomaterials. Recently, perovskite nanocrystals have been identified as a promising option due to their superior sensitivity and selectivity, combined with their capability to work under room temperature conditions. However, the use of perovskites in gas sensing has been limited due to their degradation when exposed to ambient moisture, hindering its potential application under real conditions. Nevertheless, we demonstrated for the first time a stable gas sensor (over 6 months) based on graphene loaded with a lead halide perovskite (MAPbBr3), even when operated under atmospheres with a significant level of moisture [1]. The reason is that the hydrophobic character of the graphene protects the perovskite nanocrystals against their degradation in humid environments.More recently, we studied the role of the anions and cations in the gas sensing mechanism towards volatile organic compounds (VOCs) [2]. Considering the perovskite formula (ABX3), we synthesized several nanocrystals by changing the cation A (MA, FA and Cs) and the anion X (Br, I and Cl). However, the use of lead in these perovskites induces potential risks to human health and the environment. For that reason, graphene loaded with lead-free perovskites has been developed here to reduce the potential risks associated with the manipulation of lead and to assess the new sensing properties by replacing the cation B. Method Lead-free perovskite nanocrystals (Cs3Cu2Br5) have been synthesized through a hot injection method. Afterwards, the graphene nanoflakes have been loaded with Cs3Cu2Br5 via impregnation technique. Once a homogeneous perovskite distribution was achieved, the nanocomposite was deposited via spray pyrolysis onto alumina substrates with platinum screen-printed electrodes. The gas sensors were placed in an airtight testing chamber connected to an automated gas mixture and delivery system. The gas sensing properties were studied under dry and humid conditions. Characterization Several characterisation techniques were employed to analyse the nanomaterials synthesised. The crystalline structure of lead-free perovskite was evaluated through X-Ray Diffraction (XRD), while X-Ray Photoelectron Microscopy (XPS) was performed to graphene nanoflakes to analyse the carbon configuration (sp2 and sp3 ratio) and to study the presence of different oxygen functional groups. High-Resolution Transmission Electron Microscopy (HR-TEM) was used to assess size and interplanar distances in perovskite nanocrystals. Additionally, the spatial distribution of perovskites over the graphene nanoflakes was evaluated via a Field Emission Scanning Electron Microscope (FESEM). Finally, the sensing properties of the sensitive hybrid film have been assessed. Results and Conclusions The as-synthesized Cs3Cu2Br5 perovskite nanocrystals show high crystallinity and an average size of a few nanometres. Furthermore, NO2 detection at room temperature has been demonstrated to be sensitive and reproducible (Figure 1). Preliminary measurements using this lead-free perovskite show responses to NO2 about 3-fold higher than those registered for graphene loaded with MAPbBr3 nanocrystals reported in [1]. This nanomaterial has been demonstrated as a feasible option to work at room temperature. Room temperature operation translates into low-power consumption and enhanced sensor lifetime, since high operating temperatures usually involve non-reversible changes in the crystalline structure of nanomaterials. Besides, the well-known instability of perovskites in the presence of relative humidity is overcome thanks to the protective character of graphene-based due to its high hydrophobicity. The combination of these two nanomaterials in the same composite allows taking advantage of the outstanding properties of both, graphene nanoflakes and perovskite nanocrystals. Therefore, gases can be detected at trace levels in a few minutes by using low-cost and low-power sensors.However, the use and manipulation of lead presents additional dangerousness, e.g. at the synthesis of perovskites or at disposal of sensors, which might put at risk human health and the environment. For that reason, the development of a graphene-based gas sensor loaded with lead-free perovskites constitutes a step forward to achieve more sustainable chemoresistors, linked to the concept of green chemistry. Furthermore, once the effect of the cation A and the anion X was assessed, this novel approach will provide a deep understanding about the role of cation B in the sensing mechanisms.

Design and fabrication of a smart sensor using in silico epitope mapping and electro-responsive imprinted polymer nanoparticles for determination of insulin levels in human plasma

A robust and highly specific sensor based on electroactive molecularly imprinted polymer nanoparticles (nanoMIP) was developed. The nanoMIP tagged with a redox probe, combines both recognition and reporting capabilities. The developed nanoMIP replaces enzyme-mediator pairs used in traditional biosensors thus, offering enhanced molecular recognition for insulin, improving performance in complex biological samples, and yielding high stability. Also, most of existing sensors show poor performance after storage. To improve costs of the logistics and avoid the need of cold storage in the chain supply, we developed an alternative to biorecognition system that relies on nanoMIP. NanoMIP were computationally designed using “in-silico” insulin epitope mapping and synthesized by solid phase polymerisation. The characterisation of the polymer nanoparticles was performed by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform Infrared (FT-IR) and surface plasmon resonance (SPR). The electrochemical sensor was developed by chemical immobilisation of the nanoMIP on screen printed platinum electrodes. The insulin sensor displayed satisfactory performances and reproducible results (RSD = 4.2%; n = 30) using differential pulse voltammetry (DPV) in the clinically relevant concentration range from 50 to 2000 pM. The developed nanoMIP offers the advantage of large number of specific recognition sites with tailored geometry, as the resultant, the sensor showed high sensitivity and selectivity to insulin with a limit of detection (LOD) of 26 and 81 fM in buffer and human plasma, respectively, confirming the practical application for point of care monitoring. Moreover, the nanoMIP showed adequate storage stability of 168 days, demonstrating the robustness of sensor for several rounds of insulin analysis.

Development of a highly nanoporous platinum screen-printed electrode and its application in glucose sensing

The non-enzymatic detection of glucose has many advantages, but for practical applications the selectivity of these sensors must be improved. In this study a glucose sensor was fabricated by cyclic electrodeposition of a nanoporous platinum film onto screen-printed carbon electrodes from chloroplatinic acid/copper sulphate solutions. With successive electrodeposition cycles from 1.4 to −0.6 V vs. Ag/AgCl, the electrochemical surface area of the electrode increased with a maximum roughness factor of 3680 being obtained for an electrode subjected to 350 cycles. Scanning electron microscopy was used to characterise the surface morphology of the modified electrode. The electrocatalytic ability of the electrode towards glucose was investigated by amperometry in phosphate buffer (pH 7.4) at 0.4 V vs Ag/AgCl. The sensor exhibited excellent stability, a linear range up to 13 mM, and a fast response time of <5 s. Enlargement of the electrochemical surface area, resulted in excellent selectivity towards glucose, while signals for common interferents decreased. The sensor was successfully applied to the quantification of glucose in real blood plasma samples, where results achieved were in close agreement with those obtained using a commercial glucometer.

Sensor based on electrosynthesised imprinted polymeric film for rapid and trace detection of copper(II) ions

Herein we report the fabrication, characterisation and application of a novel voltammetric sensor based on an electrosynthesised ion imprinted polymer (IIP) film for the determination of copper(II) in water samples. This sensitive and highly selective sensor was prepared by electropolymerisation of p-phenylenediamine in the presence of Cu2+ as template, combined with the screen-printed technology for the transducer element. Electrochemical methods were used to control the electropolymerisation process, the template removal and the subsequent rebinding. The electrosynthesised film on the surface of screen-printed platinum electrodes was characterised by cyclic voltammetry (CV), scanning electron microscopy (SEM), and FTIR-ATR analysis. The incubation of the IIP-modified electrode with Cu2+ resulted in an increase of the redox properties of the obtained polymer. The performance of the proposed sensor was observed in acetate buffer (50 mM, pH = 5) over the Cu2+ concentration range 0.95–244 nM, with a limit of detection of 2.7 nM. The multivariate approach was employed in order to evaluate the influence of four variables on the sensitivities of the imprinted sensor towards the template. The IIP sensor showed high affinity to copper in comparison with the non-imprinted polymer (NIP). The reproducibility of the sensor was evaluated on five different sensors and it was estimated as 7.75 % (RSD). Selectivity studies were performed against several potential interferents, such as Ni2+, Mn2+, Ag+, Hg2+, Zn2+, Co2+, Pb2+ and Cd2+ ions. The application of the proposed sensor in spiked drinking water revealed a good recovery (95–105 %).

Stable Electrochemical Measurements of Platinum Screen-Printed Electrodes Modified with Vertical ZnO Nanorods for Bacterial Detection

The study is aimed at investigating the stability of electrochemical and biosensing properties of ZnO nanorod-based platinum screen-printed electrodes (SPEs) applied for detection of bacterial pathogens. The platinum SPEs were designed and patterned according to standard photolithography and lift-off process on a silicon wafer. ZnO nanorods (NRs) were grown on the platinum working electrode by the hydrothermal method, whereas Salmonella polyclonal antibodies were selected and immobilized onto ZnO NR surface via a crosslinking process. Morphological and structural characteristics of ZnO NRs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the ZnO NRs were grown vertically on platinum electrodes with a diameter around 20-200 nm and a length of 5-7 μm. These modified electrodes were applied for detection of Salmonella enteritidis at a concentration of 103 cfu/mL by electrochemical measurements including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The ZnO NR-modified platinum electrodes could detect Salmonella bacteria well with stable measurements, and the signal to noise ratio was much higher than that of 3 : 1. This study indicated that ZnO NR-modified platinum SPEs could be potential for the development of biochips for electrochemical detection of bacterial pathogens.

Development of a selective chloride sensing platform using a screen-printed platinum electrode

A new and selective voltammetric method for chloride determination is proposed, based on platinum and chloride interactions. A screen-printed platinum electrode (SPPtE) functions as a sensing platform, which promotes the formation of chloro-adsorbed species on the electrode surface, acting as an effective means of anion-determination in several matrices. The pretreatment of the SPPtE and careful control of the cathodic stripping voltammetric parameters yielded a well-defined electrochemical signal. This cathodic peak was due to the adsorption of chlorine, which had previously been oxidized from chloride anions in the initial anodic deposition step. It offers a simple, low-cost, fast, reproducible (RSD < 6%) and precise method for selective chloride determination, with limit of detection of 0.76 mM, and a sensitivity of − 24.147 µA mM −1 for a broad determination range of up to 150 mM. Chloride determination was correctly performed with single drops of environmental, pharmaceutical and food samples. In addition, the sensor was successfully adapted as a flexible screen-printed platinum electrode sensor using Gore-Tex® as support for printing.

Highly activated screen-printed carbon electrodes by electrochemical treatment with hydrogen peroxide

An easy effective method for the activation of commercial screen-printed carbon electrodes (SPCEs) using H2O2 is presented to enhance sensing performances of carbon ink. Electrochemical activation consists of 25 repetitive voltammetric cycles at 10 mV s−1 using 10 mM H2O2 in phosphate buffer (pH 7). This treatment allowed us to reach a sensitivity of 0.24 ± 0.01 μA μM−1 cm−2 for the electroanalysis of H2O2, which is 140-fold higher than that of untreated SPCEs and 6-fold more than screen-printed platinum electrodes (SPPtEs). Electrode surface properties were characterized by SEM, EIS and XPS. The results revealed atomic level changes at the electrode surface, with the introduction of new carbon‑oxygen groups being responsible for improved electro-transfer properties and sensitivity. Our method was compared with other previously described ones. The methodology is promising for the activation of commercial carbon inks-based electrodes for sensor applications.

Recycling Metals from Spent Screen-Printed Electrodes While Learning the Fundamentals of Electrochemical Sensing

A laboratory experiment in which students recycle silver and platinum selectively from spent screen-printed platinum electrodes is described. The recovered silver in solution is used to show its spontaneous redox reaction with a copper sheet. The recovered platinum is electrodeposited onto a screen-printed carbon electrode to develop a sensor for hydrogen peroxide quantification in a commercially available hair lightener. The experiment is designed for a 3 h laboratory period and can be adapted for upper-division undergraduate education, graduate education, or even research students in electrochemistry, environmental chemistry, analytical chemistry, materials science, chemical engineering, or physical chemistry laboratories. It allows students to train in adequately handling strong acids, working in fume hoods, and neutralizing acid gases. It also allows one to teach the basics of metal recycling and enables students to learn the fundamentals of electrochemical sensing. The experiment also helps to raise student awareness of waste disposal problems and how recycling can help to reduce the amount of waste that we create.

Study of electropolymerized PEDOT:PSS transducers for application as electrochemical sensors in aqueous media

Electropolymerized poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) onto screen-printed platinum electrodes was tested for stable charge/discharge cycle using cyclic voltammetry (CV) in aqueous media and its adhesion to the electrode surface was also examined. Electropolymerized PEDOT:PSS maintained most of its initial CV behavior after water-flow test (flow rate=1ml/s), whereas drop-cast PEDOT:PSS did not, indicating better adhesion and retention of the polymer's mechanical and electrical properties. Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) suggest that film structure influence the stability of the redox current measurements. These results prove that careful electropolymerization techniques for synthesizing the PEDOT:PSS transducer are worth pursuing in developing robust electrochemical sensors suitable for continuous use in aqueous media. Developing such transducers is important for developing electrochemical sensors for biomedical and/or environmental monitoring where aqueous flow usually occurs on electrode surfaces.

Platinum electrode regeneration and quality control method for chronopotentiometric and chronoamperometric determination of antioxidant activity of biological fluids

The state of the indicator electrode surface, its quality control and regeneration methods play a major role in electroanalysis results. It is especially important in in the analysis of biological fluids and tissue, because the adsorption of biological matrix components may distort analytical signals and results of the analysis. This article describes an integrated approach to resolving the problem, which includes the selection of regeneration and quality control methods evaluation of availability of platinum screen-printed electrodes for chronopotentiometric and chronoamperometric analysis, as well as their use for determining antioxidant activity of blood serum and ejaculate. The electrodes are treated with solvents (acetone or ethanol) or subjected to annealing. Sources of information about the availability of electrodes for measurements are chronopotentiograms, chronoamperograms and cyclic voltammograms. For chronopotentiometric and chronoamperometric analyses, the most effective regeneration method is annealing at 750°C for 1h. Satisfactory regenerated platinum screen-printed electrodes are used as indicator electrodes for evaluating antioxidant activity of blood serum and ejaculate with the use of chronopotentiometry and chronoamperometry. The role of indifferent electrolyte in analytical signal formation is considered. Composition of solution used for different biological fluids (blood serum/plasma, ejaculate) was optimized and unified. The obtained results demonstrate a strong correlation: r=0.91 for blood serum and r=0.80 for the ejaculate.

Recurrent potential pulse technique for improvement of glucose sensing ability of 3D polypyrrole

In this work, a new approach for using a 3D polypyrrole (PPy) conducting polymer as a sensing material for glucose detection is proposed. Polypyrrole is electrochemically polymerized on a platinum screen-printed electrode in an aqueous solution of lithium perchlorate and pyrrole. PPy exhibits a high electroactive surface area and high electrochemical stability, which results in it having excellent electrocatalytic properties. The studies show that using the recurrent potential pulse technique results in an increase in PPy sensing stability, compared to the amperometric approach. This is due to the fact that the technique, under certain parameters, allows the PPy redox properties to be fully utilized, whilst preventing its anodic degradation. Because of this, the 3D PPy presented here has become a very good candidate as a sensing material for glucose detection, and can work without any additional dopants, mediators or enzymes.

Amperometric L-arginine biosensor based on a novel recombinant arginine deiminase

The authors describe an amperometric biosensor for the amino acid L-arginine (L-Arg). It is based on the use of a Nafion/Polyaniline (PANi) composite on a platinum screen-printed electrode (Pt-SPE) using a novel recombinant arginine deiminase isolated from Mycoplasma hominis. The protein was over-expressed, purified and employed as a biorecognition element of the sensor. Enzymatic hydrolysis of L-Arg leads to the formation of ammonium ions which diffuse into the Nafion/PANi layer and induce the electroreduction of PANi at a potential of −0.35 V (vs Ag/AgCl). L-Arg sensitivity is 684 ± 32 A·M−1·m−2, and the apparent Michaelis-Menten constant (KM app) is 0.31 ± 0.05 mM. The calibration plot is linear over the range 3–200 μM L-Arg, the limit of detection is 1 μM, and the response time (for 90% of the total signal change to occur) is 15 s. The sensor is selective and exhibits good storage stability (> 1 month without loss in signal). The biosensor was applied to the analysis of L-Arg in pharmaceutical samples and of ammonium and L-Arg in spiked human plasma obtained from blood of healthy volunteers and those with a hepatic disorder. Data generated were found to be in good agreement with a reference fluorometric enzymatic assay.