Paper-Based Screen-Printed Electrodes: A New Generation of Low-Cost Electroanalytical Platforms.

Screen-printed technology has helped considerably to the development of portable electrochemical sensors since it provides miniaturized but robust and user-friendly electrodes. Moreover, this technology allows to obtain very versatile transducers, not only regarding their design, but also their ease of modification. Therefore, in the last decades, the use of screen-printed electrodes (SPEs) has exponentially increased, with ceramic as the main substrate. However, with the growing interest in the use of cheap and widely available materials as the basis of analytical devices, paper or other low-cost flat materials have become common substrates for SPEs. Thus, in this revision, a comprehensive overview on paper-based SPEs used for analytical proposes is provided. A great variety of designs is reported, together with several examples to illustrate the main applications.

A low-cost smartphone controlled portable system with accurately confined on-chip 3D electrodes for flow-through cell electroporation.

Microscale flow-through electroporation at DC voltage has advantages in delivering small molecules. Yet, electroporation based on constant voltage are liable to generate electrolysis products which limits the voltage-operating window. Parallel on-chip 3D electrodes with close and uniform spacing are required to cut down voltage as well as provide enough electric field for electroporation. Here we present a simple electrode fabrication method based on capillary restriction valves in Z-axis to achieve parallel 3D electrodes with controllable electrode spacing in PDMS chips. With electrodes accurately placed in close range, a low voltage of only 1.5 V can generate enough electric field (>400 V/cm) to make cell membrane permeable. Squeeze flow is introduced to produce higher electric field (>800 V/cm) at a fixed voltage for more efficient electroporation. Benefit from the electrode fabrication method and application of squeeze flow, we develop a smartphone controlled microfluidic electroporation system which integrate functions of sample injection, pressure regulating, real-time observation and constant DC power supply. The system is used to electroporate two cell lines, showing a permeabilization percentage of 63% for HEK-293 cells and 58% for CHO-K1 cells with optimal parameters. Thus, the portable microfluidic system provides a cost-effective and user-friendly flow-through cell electroporation platform.

Low-cost, thin-film, mass-manufacturable carbon electrodes for detection of the neurotransmitter dopamine.

A flexible, thin-film carbon electrode is reported for detection of the key neurotransmitter dopamine using standard electroanalytical techniques of cyclic voltammetry, differential pulse voltammetry and square wave voltammetry. The thin-film electrode has been explored as a possible low-cost solution to detect low concentrations of dopamine and its performance has been compared with a commercially available screen printed carbon electrode. It was found that the thin-film electrode is more sensitive than the screen printed electrode, and can faithfully detect dopamine between 50 pM and 1 mM concentrations. The electrode provides a limit of detection of ~50 pM, displays good selectivity between dopamine and ascorbic acid, and is able to show a level of differentiation between the two compounds in terms of peak currents as well as oxidative potentials at physiologically relevant concentrations. This is in contrast to the screen printed electrode which is unable to discriminate between dopamine and ascorbic acid at the same concentrations. The key advantages of the presented electrode system are its low-cost, flexible substrate, and the ability to achieve very low levels of dopamine detection without requiring any electrode surface modification steps, a key factor in reducing fabrication costs and overall device complexity.

Inkjet-printed PEDOT:PSS multi-electrode arrays for low-cost in vitro electrophysiology.

Multi-electrode arrays (MEAs) have become a key element in the study of cellular phenomena in vitro. Common modern MEAs are still based on costly microfabrication techniques, making them expensive tools that researchers are pushed to reuse, compromising the reproducibility and the quality of the acquired data. There is a need to develop novel fabrication strategies, able to produce disposable devices that incorporate advanced technologies beyond the standard metal electrodes on rigid substrates. Here we present an innovative fabrication process for the production of polymer-based flexible MEAs. The device fabrication exploited inkjet printing, as this low-cost manufacturing method allows for an easy and reliable patterning of conducting polymers. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was used as the sole conductive element of the MEAs. The physical structure and the electrical properties of the plastic/printed MEAs (pMEAs) were characterised, showing a low impedance that is maintained also in the long term. The biocompatibility of the devices was demonstrated, and their capability to successfully establish a tight coupling with cells was proved. Furthermore, the pMEAs were used to monitor the extracellular potentials from cardiac cell cultures and to record high quality electrophysiological signals from them. Our results validate the use of pMEAs as in vitro electrophysiology platforms, pushing for the adoption of innovative fabrication techniques and the use of new materials for the production of MEAs.

Ball-milled biochar for alternative carbon electrode.

Ball-milled biochars (BM-biochars) were produced through ball milling of pristine biochars derived from different biomass at three pyrolysis temperatures (300, 450, and 600 °C). The results of scanning electron microscopic (SEM), surface area, hydrodynamic diameter test, and Fourier transform infrared spectroscopy (FTIR) revealed that BM-biochars had smaller particle size (140-250 nm compared to 0.5-1 mm for unmilled biochar), greater stability, and more oxygen-containing functional groups (2.2-4.4 mmol/g compared to 0.8-2.9 for unmilled biochar) than the pristine biochars. With these changes, all the BM-biochar-modified glassy carbon electrodes (BM-biochar/GCEs) exhibited prominent electrochemical properties (e.g., ΔEp of 119-254 mV compared to 850 mV for bare GCE). Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) show that ball-milled 600 °C biochar/GCE (BMBB600/GCE and BMBG600/GCE) had the smallest peak-to-peak separation (ΔEp = 119 and 132 mV, respectively), series resistance (RS = 88.7 and 89.5 Ω, respectively), and charge transfer resistance (RCT = 1224 and 1382 Ω, respectively), implying its best electrocatalytic activity for the reduction of Fe(CN)63-. It is supposed that the special structure (i.e., internal surface area, pore volume, oxygen-containing functional groups, and graphitic structure) facilitates the electron transfer and reduces interface resistance. Economic cost of BM-biochar/GCE was 1.97 × 10-7 USD/cm2, much lower than that of a "low-cost platinum electrode" (0.03 USD/cm2). The results indicate potential application of the novel BM-biochar for low cost and high efficient electrodes. Graphical abstract.

Xerogel based catalyst for improved cathode performance in microbial fuel cells.

In a microbial fuel cell (MFC) the reduction reaction at cathode has been a limiting factor in achieving maximum power density, and numerous strategies have been implemented in an attempt to overcome this. Herein, we demonstrate that carbon xerogel (CX) doped with iron (Fe) and nitrogen (N) followed by modification with graphene oxide (GO) is an efficient catalyst for MFCs. The CXFeNGO catalyst was characterized using a scanning electron microscope, and X-ray diffraction, and the catalytic activity was confirmed using cyclic voltammetry studies. At the anode, colonization of bacterial cells on the electrode surface, forming a biofilm, was observed. When the CXFeNGO-modified electrode was used at the cathode in the MFC, a maximum power density of 176.5 ± 6 mW m-2 was obtained, compared to that of plain graphite electrode, which produced 139.1 ± 4 mW m-2. The power density of the modified electrode is thus 26.8% higher. The power density further increased to 48.6% when the pH of the catholyte was increased to 12, producing a power density of 207 ± 4 mW m-2.

Development of a low-cost electrochemical sensor based on babassu mesocarp (Orbignya phalerata) immobilized on a flexible gold electrode for applications in sensors for 5-fluorouracil chemotherapeutics.

There are increasing concerns regarding the risks arising from the contamination of manipulators of antineoplastic drugs promoted by occupational exposure or even in the dosage of drugs. The present work proposes the use of an electrochemical sensor based on a biopolymer extracted from the babassu coconut (Orbignya phalerata) for the determination of an antineoplastic 5-fluorouracil (5-FU) drug as an alternative for the monitoring of these drugs. In order to reduce the cost of this sensor, a flexible gold electrode (FEAu) is proposed. The surface modification of FEAu was performed with the deposition of a casting film of the biopolymer extracted from the babassu mesocarp (BM) and modified with phthalic anhydride (BMPA). The electrochemical activity of the modified electrode was characterized by cyclic voltammetry (CV), and its morphology was observed by atomic force microscopy (AFM). The FEAu/BMPA showed a high sensitivity (8.8 µA/µmol/L) and low limit of detection (0.34 µmol/L) for the 5-FU drug in an acid medium. Electrochemical sensors developed from the babassu mesocarp may be a viable alternative for the monitoring of the 5-FU antineoplastic in pharmaceutical formulations, because in addition to being sensitive to this drug, they are constructed of a natural polymer, renewable, and abundant in nature. Graphical abstract ᅟ.

Low-cost nanowired α-MnO2/C as an ORR catalyst in air-cathode microbial fuel cell.

In this work, low cost α-MnO2 nanowires and α-MnO2 nanowires supported on carbon Vulcan (α-MnO2/C) have been synthesized via a simple and facile hydrothermal method for application in microbial fuel cells. The prepared samples have been characterized by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). Electrocatalytic activities of the samples have been evaluated by means of cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in a neutral phosphate buffer solution. EIS was performed at different potentials to gain further insight into the kinetic properties of α-MnO2/C. Both catalysts were used in air cathode microbial fuel cells to achieve power densities of 180 and 111 mWm-2 for α-MnO2/C and pristine α-MnO2 nanowires, respectively. α-MnO2/C functions as a good and economical alternative for Pt free catalysts in practical MFC applications, as shown by the findings of stability test and voltage generation cycles in long-term operation of MFC.

Textile band electrodes as an alternative to spot Ag/AgCl electrodes for calf bioimpedance measurements.

OBJECTIVE: To evaluate the performance of five different types of textiles as band electrodes for calf bioimpedance measurements in comparison with conventional spot Ag/AgCl electrodes. APPROACH: Calf bioimpedance measurements were performed in 10 healthy volunteers with five different textile materials cut into bands and Ag/AgCl spot electrodes as a baseline. Collected bioimpedance data were analyzed in terms of precision, fit error and presence of measurement artifacts. Each textile material was also evaluated for participant comfort. MAIN RESULTS: Bioimpedance values for spot electrodes were higher at low frequencies as compared with band electrodes but not at high frequencies. This suggests that spot electrodes have frequency dependent current distributions that adversely impact their use for volume measurements and band electrodes are preferable. The SMP130T-B fabric had the highest precision and the lowest best fit error to the Cole model of the tested textile materials. However, it was the least comfortable textile and most expensive. The Stretch material performed slightly worse than the SMP130T-B fabric, but was half the cost and the most comfortable. SIGNIFICANCE: These results suggest that there are suitable textile materials for use as dry, band electrodes for calf bioimpedance measurements and that these band electrodes enable greater current uniformity. These textiles could be integrated into a compression sock for remote monitoring of diseases such as Congestive Heart Failure.

Bread-derived 3D macroporous carbon foams as high performance free-standing anode in microbial fuel cells.

Microbial fuel cells (MFCs) are a promising clean energy source to directly convert waste chemicals to available electric power. However, the practical application of MFCs needs the increased power density, enhanced energy conversion efficiency and reduced electrode material cost. In this study, three-dimensional (3D) macroporous N, P and S co-doped carbon foams (NPS-CFs) were prepared by direct pyrolysis of the commercial bread and employed as free-standing anodes in MFCs. As-obtained NPS-CFs have a large specific surface area (295.07 m2 g-1), high N, P and S doping level, and excellent electrical conductivity. A maximum areal power density of 3134 mW m-2 and current density of 7.56 A m-2 are generated by the MFCs equipped with as-obtained NPS-CF anodes, which is 2.57- and 2.63-fold that of the plain carbon cloth anodes (areal power density of 1218 mW m-2 and current density of 2.87 A m-2), respectively. Such improvement is explored to mainly originate from two respects: the good biocompatibility of NPS-CFs favors the bacterial adhesion and enrichment of electroactive Geobacter species on the electrode surface, while the high conductivity and improved bacteria-electrode interaction efficiently promote the extracellular electron transfer (EET) between the bacteria and the anode. This study provides a low-cost and sustainable way to fabricate high power MFCs for practical applications.

Cost-Effectiveness of POC Coagulation Testing Using Multiple Electrode Aggregometry.

BACKGROUND: The economic effects of Point-of-Care (POC) coagulation testing including Multiple Electrode Aggregometry (MEA) with the Multiplate device have not been examined. METHODS: A health economic model with associated clinical endpoints was developed to calculate the effectiveness and estimated costs of coagulation analyses based on standard laboratory testing (SLT) or POC testing offering the possibility to assess platelet dysfunction using aggregometric measures. Cost estimates included pre- and perioperative costs of hemotherapy, intra- and post-operative coagulation testing costs, and hospitalization costs, including the costs of transfusion-related complications. RESULTS: Our model calculation using a simulated true-to-life cohort of 10,000 cardiac surgery patients assigned to each testing alternative demonstrated that there were 950 fewer patients in the POC branch who required any transfusion of red blood cells. The subsequent numbers of massive transfusions and patients with transfusion-related complications were reduced with the POC testing by 284 and 126, respectively. The average expected total cost in the POC branch was 288 Euro lower for every treated patient than that in the SLT branch. CONCLUSIONS: Incorporating aggregometric analyses using MEA into hemotherapy algorithms improved medical outcomes in cardiac surgery patients in the presented health economic model. There was an overall better economic outcome associated with POC testing compared with SLT testing despite the higher costs of testing.

A novel biosensor for p-nitrophenol based on an aerobic anode microbial fuel cell.

P-nitrophenol is one of the most common contaminants in chemical industrial wastewater, and in situ real-time monitoring of PNP cannot be achieved by conventional analytical techniques. Here, a two-chamber microbial fuel cell with an aerobic anode chamber was tested as a biosensor for in situ real-time monitoring of PNP. Pseudomonas monteilii LZU-3, which was used as the biological recognition element, can form a biofilm on the anode electrode using PNP as a sole substrate. The optimal operation parameters of the biosensor were as follows: external resistance 1000Ω, pH 7.8, temperature 30°C, and maximum PNP concentration 50mgL(-1). Under these conditions, the maximum voltages showed a linear relationship with PNP concentrations ranging from 15±5 to 44±4.5mgL(-1). Furthermore, we developed a novel portable device for in situ real-time monitoring of PNP. When the device was applied to measure PNP in wastewater containing various additional aromatic compounds and metal ions, the performance of the biosensor was not affected and the correlation between the maximum voltages and the PNP concentrations ranging from 9±4mgL(-1) to 36 ± 5mgL(-1) was conserved. The results demonstrated that the MFC biosensor provides a rapid and cost-efficient analytical method for real-time monitoring of toxic and recalcitrant pollutants in environmental samples.

Molybdenum Carbide Nanoparticles on Carbon Nanotubes and Carbon Xerogel: Low-Cost Cathodes for Hydrogen Production by Alkaline Water Electrolysis.

Low-cost molybdenum carbide (Mo2 C) nanoparticles supported on carbon nanotubes (CNTs) and on carbon xerogel (CXG) were prepared and their activity for the hydrogen evolution reaction (HER) was evaluated in 8 m KOH aqueous electrolyte at 25-85 °C. Measurements of the HER by linear scan voltammetry allowed us to determine Tafel slopes of 71 and 74 mV dec(-1) at 25 °C for Mo2 C/CNT and Mo2 C/CXG, respectively. Stability tests were also performed, which showed the steady performance of the two electrocatalysts. Moreover, the HER kinetics at Mo2 C/CNT was enhanced significantly after the long-term stability tests. The specific activity of both materials was high, and a higher stability was obtained for the activated Mo2 C/CNT (40 A g(-1) at -0.40 V vs. the reversible hydrogen electrode).

A new soft material based in-the-ear EEG recording technique.

Long-term electroencephalogram (EEG) is important for seizure detection, sleep monitoring and etc. In-the- ear EEG device makes such recording robust to noise and privacy protected (invisible to other people). However, the state-of-art techniques suffer from various drawbacks such as customization for specific users, manufacturing difficulties and short life cycle. To address these issues, we proposed silvered glass silicone based in-the-ear electrode which can be manufactured using conventional compression moulding. The material and in-the-ear EEG are evaluated separately, showing that the proposed method is durable, low-cost and easy-to-make.

Microchip-based electrochemical detection using a 3-D printed wall-jet electrode device.

Three dimensional (3-D) printing technology has evolved dramatically in the last few years, offering the capability of printing objects with a variety of materials. Printing microfluidic devices using this technology offers various advantages such as ease and uniformity of fabrication, file sharing between laboratories, and increased device-to-device reproducibility. One unique aspect of this technology, when used with electrochemical detection, is the ability to produce a microfluidic device as one unit while also allowing the reuse of the device and electrode for multiple analyses. Here we present an alternate electrode configuration for microfluidic devices, a wall-jet electrode (WJE) approach, created by 3-D printing. Using microchip-based flow injection analysis, we compared the WJE design with the conventionally used thin-layer electrode (TLE) design. It was found that the optimized WJE system enhances analytical performance (as compared to the TLE design), with improvements in sensitivity and the limit of detection. Experiments were conducted using two working electrodes - 500 µm platinum and 1 mm glassy carbon. Using the 500 µm platinum electrode the calibration sensitivity was 16 times higher for the WJE device (as compared to the TLE design). In addition, use of the 1 mm glassy carbon electrode led to limit of detection of 500 nM for catechol, as compared to 6 µM for the TLE device. Finally, to demonstrate the versatility and applicability of the 3-D printed WJE approach, the device was used as an inexpensive electrochemical detector for HPLC. The number of theoretical plates was comparable to the use of commercially available UV and MS detectors, with the WJE device being inexpensive to utilize. These results show that 3-D-printing can be a powerful tool to fabricate reusable and integrated microfluidic detectors in configurations that are not easily achieved with more traditional lithographic methods.

Post-treatment of molasses wastewater by electrocoagulation and process optimization through response surface analysis.

Molasses wastewater is a high strength effluent of food industry such as distilleries, sugar and yeast production plants etc. It is characterized by a dark brown color and exhibits a high content in substances of recalcitrant nature such as melanoidins. In this study, electrocoagulation (EC) was studied as a post treatment step for biologically treated molasses wastewater with high nitrogen content obtained from a baker's yeast industry. Iron and copper electrodes were used in various forms; the influence and interaction of current density, molasses wastewater dilution, and reaction time, on COD, color, ammonium and nitrate removal rates and operating cost were studied and optimized through Box Behnken's response surface analysis. Reaction time varied from 0.5 to 4 h, current density varied from 5 to 40 mA/cm(2) and dilution from 0 to 90% (v/v expressed as water concentration). pH, conductivity and temperature measurements were also carried out during each experiment. From preliminary experiments, it was concluded that the application of aeration and sample dilution, considerably influenced the kinetics of the process. The obtained results showed that COD removal varied between 10 and 54%, corresponding to an operation cost ranging from 0.2 to 33 euro/kg COD removed. Significant removal rates were obtained for nitrogen as nitrate and ammonium (i.e. 70% ammonium removal). A linear relation of COD and ammonium to the design parameters was observed, while operation cost and nitrate removal responded in a curvilinear function. A low ratio of electrode surface to treated volume was used, associated to a low investment cost; in addition, iron wastes could be utilized as low cost electrodes i.e. iron fillings from lathes, aiming to a low operation cost due to electrodes replacement. In general, electrocoagulation proved to be an effective and low cost process for biologically treated molasses-wastewater treatment for additional removal of COD and nitrogen content and color reduction. Treated effluent samples with good quality were produced by EC, with COD, NH4-N and NO3-N concentrations of 180, 52 and 2 mg/l respectively. Response surface analysis revealed that optimized conditions could be established under moderate molasses wastewater dilution, (e.g. 45%), at 3.5 h treatment time and 33 mA/cm(2) current density.

Development of a Novel, Low-Cost, Disposable Wooden Pencil Graphite Electrode for Use in the Determination of Antioxidants and Other Biological Compounds.

The development of portable sensors that can be used outside the lab is an active area of research in the electroanalytical field. A major focus of such research is the development of low-cost electrodes for use in these sensors. Current electrodes, such as glassy-carbon electrodes (GCEs), are costly and require time-consuming preparation. Alternatives have been proposed, including mechanical pencil-lead electrodes (MPEs). However, MPEs themselves possess numerous drawbacks, particularly structural fragility. In this paper, we present a novel pencil-graphite electrode (PGE) fabricated from a regular HB#2 pencil. This PGE is a simple, disposable, extremely low-cost alternative to GCEs ($0.30 per PGE, vs. $190 + per GCE), and possesses the structural stability that MPEs lack. PGEs were characterized by square-wave voltammetry of ferricyanide, gallic acid, uric acid, dopamine, and several foodstuffs. In all cases, PGEs demonstrated sensitivities comparable or superior to those of the GCE and MPE (LOD = 5.62 × 10(-4) M PGE, 4.80 × 10(-4) M GCE, 2.93 × 10(-4) M MPE). Signal areas and peak heights were typically four to ten times larger for the PGE relative to the GCE.

Biosensor Regeneration: A Review of Common Techniques and Outcomes.

Biosensors are ideally portable, low-cost tools for the rapid detection of pathogens, proteins, and other analytes. The global biosensor market is currently worth over 10 billion dollars annually and is a burgeoning field of interdisciplinary research that is hailed as a potential revolution in consumer, healthcare, and industrial testing. A key barrier to the widespread adoption of biosensors, however, is their cost. Although many systems have been validated in the laboratory setting and biosensors for a range of analytes are proven at the concept level, many have yet to make a strong commercial case for their acceptance. Though it is true with the development of cheaper electrodes, circuits, and components that there is a downward pressure on costs, there is also an emerging trend toward the development of multianalyte biosensors that is pushing in the other direction. One way to reduce the cost that is suitable for certain systems is to enable their reuse, thus reducing the cost per test. Regenerating biosensors is a technique that can often be used in conjunction with existing systems in order to reduce costs and accelerate the commercialization process. This article discusses the merits and drawbacks of regeneration schemes that have been proven in various biosensor systems and indicates parameters for successful regeneration based on a systematic review of the literature. It also outlines some of the difficulties encountered when considering the role of regeneration at the point of use. A brief meta-analysis has been included in this review to develop a working definition for biosensor regeneration, and using this analysis only ∼60% of the reported studies analyzed were deemed a success. This highlights the variation within the field and the need to normalize regeneration as a standard process across the field by establishing a consensus term.

A method for optimizing EEG electrode number and configuration for signal acquisition in P300 speller systems.

OBJECTIVE: The P300 speller is intended to restore communication to patients with advanced neuromuscular disorders, but clinical implementation may be hindered by several factors, including system setup, burden, and cost. Our goal was to develop a method that can overcome these barriers by optimizing EEG electrode number and placement for P300 studies within a population of subjects. METHODS: A Gibbs sampling method was developed to find the optimal electrode configuration given a set of P300 speller data. The method was tested on a set of data from 15 healthy subjects using an established 32-electrode pattern. Resulting electrode configurations were then validated using online prospective testing with a naïve Bayes classifier in 15 additional healthy subjects. RESULTS: The method yielded a set of four posterior electrodes (PO8, PO7, POZ, CPZ), which produced results that are likely sufficient to be clinically effective. In online prospective validation testing, no significant difference was found between subjects' performances using the reduced and the full electrode configurations. CONCLUSIONS: The proposed method can find reduced sets of electrodes within a subject population without reducing performance. SIGNIFICANCE: Reducing the number of channels may reduce costs, set-up time, signal bandwidth, and computation requirements for practical online P300 speller implementation.