Electrochemical Paper-based Analytical Device Research Articles

Electrochemical paper-based analytical devices containing magnetite nanoparticles for the determination of vitamins B2 and B6

Disposable electrochemical paper-based analytical devices were developed from a conductive ink using graphite powder, automotive varnish and magnetite nanoparticles. The addition of magnetite nanoparticles in the conductive ink improved the sensitivity of the analytical devices. The devices were applied in the quantification of vitamins B2 (VB2) and B6 (VB6) in commercial dietary supplements. The characterization of the analytical devices was carried out by microscopy and electrochemical techniques. Square wave voltammetry (SWV) was used to study the electrochemical behavior of the vitamins and the experimental parameters were optimized (pH, supporting electrolyte and SWV parameters). The calibration plot for VB2 (−484 mV vs. graphite) was obtained in Britton-Robinson buffer (pH 2.0) in the range of 2.0 to 20.0 μmol L−1 with a detection limit of 0.25 µmol L−1. Similarly, for the VB6 (+675 mV vs. graphite), the calibration plot was obtained in McIlvaine buffer (pH 4.0) in the range of 0.2 to 2.0 mmol L−1 with a detection limit of 29.5 µmol L−1. The analytical devices were employed to determine VB2 and VB6 levels in B-complex supplements (capsules and sublingual liquid) and the results were compared with those provided by fluorescence spectrometry. The statistical analysis showed no considerable difference in terms of the precision and accuracy of the data obtained by both methods.

Nanocoral-like Polyaniline-Modified Graphene-Based Electrochemical Paper-Based Analytical Device for a Portable Electrochemical Sensor for Xylazine Detection

A portable electrochemical device for xylazine detection is presented for the first time. An electrochemical paper-based analytical device (ePAD) was integrated with a smartphone. The fabrication of the ePAD involved wax printing, low-tack transfer tape, and cutting and screen-printing techniques. Graphene ink was coated on the substrate and modified with nanocoral-like polyaniline, providing an electron transfer medium with a larger effective surface area that promoted charge transfer. The conductive ink on the ePAD presented a thickness of 25.0 ± 0.9 μm for an effective surface area of 0.374 cm2. This sensor was then tested directly on xylazine using differential pulse voltammetry. Two linear responses were obtained: from 0.2 to 5 μg mL–1 and from 5 to 100 μg mL–1. The detection limit was 0.06 μg mL–1. Reproducibility was tested on 10 preparations. The relative standard deviation was less than 5%. The applicability of the sensor was evaluated with beverage samples spiked with trace xylazine. Recoveries ranged from 84 ± 4 to 105 ± 2%. The developed sensor demonstrated excellent accuracy in the detection of trace xylazine. It would be possible to develop the portable system to detect various illicit drugs to aid forensic investigations.

Rapid urinary albumin detection using a simple redox cycling process coupled with a paper-based device

• An electrochemical-chemical (EC) redox cycling process using a mixture of potassium ferricyanide and methylene blue was proposed for sensitive and rapid detection of urinary albumin in 1 min. • A disposable electrochemical paper-based analytical device (ePAD) was proposed as a new detection platform and easily get rid of waste. • The highly sensitive and selective albumin detection was obtained without creatinine correction. • The main features are the use of low-cost devices, rapid detection, and simple procedures. A novel electrochemical-chemical (EC) redox cycling process was proposed for the sensitive, simple, and rapid detection of urinary albumin. This system employs a unique detection scheme based on the combination of ferricyanide ([Fe(CN) 6 ] 3− ) and methylene blue (MB) for signal amplification without the need for any electrode surface modifications. Measurements of bovine serum albumin (BSA) were performed as proof of concept using disposable electrochemical paper-based analytical devices (ePADs) as detection platforms. The quantification of albumin is accomplished by using an indirect detection strategy. In the absence of BSA, electron transfer via EC redox cycling process occurs readily between the redox species and the electrode surface, resulting in a large electrochemical signal. The redox species solution containing BSA, on the other hand, provides a low signal current due to the hindrance of BSA on the electrode surface, which impedes the electron transfer of the proposed redox probe. Under the optimized conditions, the linear range was 1–500 mg dL −1 with a detection limit of 0.072 mg dL −1 . This finding leads to the development of a powerful method for the direct detection of albumin at a low concentration and no requirement for correction by creatinine. The proposed devices were successfully used to detect albumin in real urine samples with satisfactory results, demonstrating good agreement with the standard method and the reliability. Aside from the ease and rapidity, the proposed method is inexpensive, sensitive, and a promising tool for clinical diagnosis of chronic kidney disease and suitable for point-of-care testing in developing countries.

The recent development of nanomaterials enhanced paper-based electrochemical analytical devices

• This manuscript reviews the history and new developments of ePADs from 2016 to 2021. • This review focuses on construction and representative applications of ePADs. • The limiting factors and future development of ePADs have been discussed. Integration of electrochemical detection methods into paper-based analytical devices (PADs) provides a powerful tool for the area of point-of-care testing (POCT) because the electrochemical PADs (termed as ePADs) enable to rapidly determine a broad spectrum of analytes from ions to living cells in a miniaturized, cost-effective and user-friendly manner. Recently, nanomaterials and their composites were extensively introduced in ePADs for improvement of their detection performance. This review attempts to provide a comprehensive information on the ePADs including a general aspect of ePADs and recent development of ePADs by highlighting selected publication. We mainly focus on the fabrication of ePADs, enhancement strategies of nanomaterials and potential applications of ePADs in the fields of environmental monitoring, food safety management and disease diagnosis. Based on the limitations and challenges associated with the development of ePADs, the future perspectives of this research field are proposed.

Fully drawn electrochemical paper-based glucose biosensors fabricated by a high-throughput dual-step pen-on-paper approach with commercial writing stationery

This work reports the fabrication of fully drawn fluidic electrochemical paper-based analytical devices (ePADs) using a low-cost and rapid dual-step pen-on-paper plotting approach for the enzymatic assay of glucose. The desired fluidic patterns were formed on the paper substrate using an inexpensive computer-controlled x-y plotter and a commercial hydrophobic marker pen. Electrodes were further deposited on the devices using a second x-y plotting step with a commercial writing pencil. Enzymatic paper-based biosensors were prepared by immobilizing glucose oxidase and potassium ferricyanide (as a mediator) at the test area of the ePADs; the cost of each biosensor was < 0.05 € in terms of materials. A simple, low-cost and rapid method was further developed for the amperometric enzymatic determination of glucose using the biosensing ePADS. The limit of quantification was 0.08 mmol L−1, the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 12% and the assay time was 120 s. The ePADs were applied to the determination of glucose in food samples with recoveries in the range 94–106%.

Paper-Based Electrodes Conjugated with Tungsten Disulfide Nanostructure and Aptamer for Impedimetric Detection of Listeria monocytogenes.

In this study, we report on a novel aptasensor based on an electrochemical paper-based analytical device (ePAD) that employs a tungsten disulfide (WS2)/aptamer hybrid for the detection of Listeria monocytogenes. Listeria is a well-known causative pathogen for foodborne diseases. The proposed aptasensor signifies many lucrative features which include simple, cost-effective, reliable, and disposable. Furthermore, the use of an aptamer added more advantageous features in the biosensor. The morphological, optical, elemental composition, and phase properties of the synthesized tungsten disulfide (WS2) nanostructures were characterized by field-emission scanning electron microscopy (FESEM), RAMAN spectroscopy, photoluminescence (PL), and X-ray diffraction (XRD), while electrochemical impedance spectroscopy was performed to corroborate the immobilization of aptamer and to assess the L. monocytogenes sensing performance. The limit of detection (LoD) and limit of quantification (LoQ) of the aptasensor was found to be 10 and 4.5 CFU/mL, respectively, within a linear range of 101–108 CFU/mL. The proposed sensor was found to be selective solely towards Listeria monocytogenes in the presence of various bacterial species such as Escherichia coli and Bacillus subtilis. Validation of the aptasensor operation was also evaluated in real samples by spiking them with fixed concentrations (101, 103, and 105) of Listeria monocytogenes, thereby, paving the way for its potential in a point-of-care scenario.

Low-cost electrochemical paper-based device for exosome detection.

Exosomes are vesicles released by healthy and cancer cells into the extracellular matrix and bodily fluid. Cancer cell-derived exosomes have attracted much attention in early-stage detection and prognostication of treatment response. Thus, detecting exosomes is of great interest to biology and medicine. However, many conventional detection methods require high-cost equipment and centralized laboratory facilities, making diagnostics inaccessible in limited-resource settings. This study reports a proof-of-concept low-cost electrochemical paper-based analytical device to quantify both the total bulk and cancer cell-derived exosomes in cell culture media. The device employs a sandwich immune assay design, where exosomes are initially captured using the electrode-bound generic antibodies (i.e. CD9) and subsequently detected via ovarian cancer-specific CA125 antibodies. Our proposed device quantifies the total bulk exosome concentration with a detection limit of 9.3 × 107 exosomes per mL and ovarian cancer cell-derived exosomes with a detection limit of 7.1 × 108 exosomes per mL, with a relative standard deviation of <10% (n = 3). We suggest that this low-cost and simple electrochemical paper-based device could be an alternative tool for detecting disease-specific exosomes in biological samples with the potential to be further developed for point-of-care diagnosis.

Smart sensor for assessment of oxidative/nitrative stress biomarkers using a dual-imprinted electrochemical paper-based analytical device

We present a novel dual-imprinted electrochemical paper-based analytical device (Di-ePAD) to simultaneously determine 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 3-nitrotyrosine (3-NT) and assess oxidative and nitrative biomarkers in urine and plasma samples. The Di-ePAD was designed with hydrophobic barrier layers formed on filter paper to provide three-dimensional circular reservoirs and assembled electrodes. The molecularly imprinted polymer (MIP) was synthesized using a silica nanosphere decorated with silver nanoparticles (SiO2@AgNPs) as a core covered with dual-analyte imprinted sites on the polymer to recognize selectively and bind the target biomarkers. This strategy drives monodispersity and enhances the conductivity of the resulting MIP core-shell products. 3-NT-MIP and 8-OHdG-MIP were synthesized by successively coating the surface of SiO2@AgNPs with l-Cysteine via the thiol group, then terminating with MIP shells. The dual imprinted core-shell composites possess attractive properties for the target biomarkers' sensing, including catalytic activity, selectivity, and good conductivity. The Di-ePAD revealed excellent linear dynamic ranges of 0.01–500 μM for 3-NT and 0.05–500 μM for 8-OHdG, with detection limits of 0.0027 μM for 3-NT and 0.0138 μM for 8-OHdG. This newly developed method based on the synergistic effects of SiO2@AgNPs combined with promising properties of MIP offers outstanding selectivity, sensitivity, reproducibility, simplicity, and low cost for quantitative analysis of 3-NT and 8-OHdG. The proposed Di-ePAD showed good accuracy and precision when applied to actual samples, including urine and serum samples validated by a conventional HPLC method.

An Enzymatic Multiplexed Impedimetric Sensor Based on α-MnO2/GQD Nano-Composite for the Detection of Diabetes and Diabetic Foot Ulcer Using Micro-Fluidic Platform

Diabetes is widely considered as a silent killer which affects the internal organs and ultimately has drastic impacts on our day-to-day activities. One of the fatal outcomes of diabetes is diabetic foot ulcer (DFU); which, when becomes chronic, may lead to amputation. The incorporation of nanotechnology in developing bio-sensors enables the detection of desired biomarkers, which in our study are glucose and L-tyrosine; which gets elevated in patients suffering from diabetes and DFUs, respectively. Herein, we report the development of an enzymatic impedimetric sensor for the multi-detection of these biomarkers using an electrochemical paper-based analytical device (µ-EPADs). The structure consists of two working electrodes and a counter electrode. One working electrode is modified with α-MnO2-GQD/tyrosinase hybrid to aid L-tyrosine detection, while the other electrode is coated with α-MnO2-GQD/glucose oxidase hybrid for glucose monitoring. Electrochemical impedance spectroscopy has been employed for the quantification of glucose and L-tyrosine, within a concentration range of 50–800 mg/dL and 1–500 µmol/L, respectively, using a sample volume of approximately 200 µL. The impedance response exhibited a linear relationship over the analyte concentration range with detection limits of ~58 mg/dL and ~0.3 µmol/L for glucose and tyrosine respectively, with shelf life ~1 month. The sensing strategy was also translated to Arduino-based device applications by interfacing the µ-EPADs with miniaturized electronics.

Single-Use Fluidic Electrochemical Paper-Based Analytical Devices Fabricated by Pen Plotting and Screen-Printing for On-Site Rapid Voltammetric Monitoring of Pb(II) and Cd(II).

This work reports the fabrication of integrated electrochemical fluidic paper-based analytical devices (ePADs) using a marker pen drawing and screen-printing. Electrodes were deposited on paper using screen-printing with conductive carbon ink. Then, the desired fluidic patterns were formed on the paper substrate by drawing with a commercial hydrophobic marker pen using an inexpensive computer-controlled x-y plotter. The working electrode was characterized by cyclic voltammetry and scanning electron microscopy. The analytical utility of the electrochemical PADs is demonstrated through electrochemical determination of Pb(II) and Cd(II) by anodic stripping voltammetry. For this purpose, the sample was mixed with a buffer solution and a Bi(III) solution, applied to the test zone of the PAD, the metals were preconcentrated as a bismuth alloy on the electrode surface and oxidized by applying an anodic potential scan. The proposed manufacturing approach enables the large-scale fabrication of fit-for-purpose disposable PADs at low cost which can be used for rapid on-site environmental monitoring.

An automated fast-flow/delayed paper-based platform for the simultaneous electrochemical detection of hepatitis B virus and hepatitis C virus core antigen

Electrochemical paper-based analytical devices (ePADs) are useful analytical devices that serve as point-of-care testing (POCT) devices for various clinical biomarkers in view of their simplicity, portability, and low-cost format. However, multistep reagent manipulation usually restricts the performance of the device for end users. Herein, we developed a sequential ePAD for sequential immunosensing fluid delivery by integrating dual flow behaviors (fast-flow/delayed) within a single paper platform for the simultaneous detection of hepatitis B surface antigen (HBsAg) and hepatitis C core antigen (HCVcAg). In the present work, a fast-flow channel was used for the automated washing of unbound antigens, while a delayed channel was created to store a redox reagent for further electrochemical analysis with a single buffer loading (the analysis time can be completed within 500 s). Hence, the undesirable complex procedure of multi-step reagent manipulation is scarcely needed by the user. The detection limit of the proposed ePAD was as low as 18.2 pg mL−1 for HBsAg and 1.19 pg mL−1 for HCVcAg. In addition, this proposed ePAD was also proven to be effective in real clinical sera from patients to verify its biological applicability. The ePAD sensor shows high promise as an easy-to-use, portable, and extendable sensor for other multiplex biological assays.

Sandpaper-based electrochemical devices assembled on a reusable 3D-printed holder to detect date rape drug in beverages

This study describes the development of a new electrochemical paper-based analytical device (ePAD) on alumina sandpaper substrate through a pencil-drawing process for square wave voltammetry measurements of midazolam maleate used as a “date rape drug” in beverages. The proposed ePAD was assembled on a reusable 3D printed holder to delimit its geometric area and ensure better robustness. The ePAD was characterized by scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and Raman spectroscopy. The direct drawing of ePADs on sandpaper platforms through a graphite pencil has offered suitable repeatability (RSD = 1.0%) and reproducibility (RSD = 4.0%) using [Fe(CN)6]4– as redox probe. The proposed ePAD provided linear behaviour in the midazolam maleate concentration range between 2.5 and 150 mg L−1 and a limit of detection of 2.0 mg L−1. The feasibility of the ePAD for forensic application was successfully demonstrated through the detection of midazolam in different beverages (water, beer, liquor, and vodka). The intended application revealed low interference of other compounds present in beverages. Based on the achieved results, the proposed ePAD has offered great accuracy with no statistical difference at 95% confidence level from the data recorded by high performance liquid chromatography. The operational simplicity and the robustness ensured by the assembling on a reusable 3D printed holder make the ePAD drawn on sandpaper platform a powerful and promising analytical tool for the analysis of “date rape drugs” opening new possibilities for on-site forensic investigations.

An All-in-One Solid State Thin-Layer Potentiometric Sensor and Biosensor Based on Three-Dimensional Origami Paper Microfluidics.

An origami three-dimensional design of a paper-based potentiometric sensor is described. In its simplest form, this electrochemical paper-based analytical device (ePAD) is made from three small parts of the paper. Paper layers are folded on each other for the integration of a solid contact ion selective electrode (here a carbon-paste composite electrode) and a solid-state pseudo-reference electrode (here writing pencil 6B on the paper), which are in contact with a hydrophilic channel fabricated on the middle part (third part) of the paper. In this case, the pseudo-reference and working electrodes are connected to the two sides of the hydrophilic channel and hence the distance between them is as low as the width of paper. The unmodified carbon paste electrode (UCPE) and modification with the crown ether benzo15-crown-5 (B15C5) represented a very high sensitivity to Cu (II) and Cd2+ ions, respectively. The sensor responded to H2O2 using MnO2-doped carbon paste electrode (CPE). Furthermore, a biosensor was achieved by the addition of glucose oxidase to the MnO2-doped CPE and hence made it selective to glucose with ultra-sensitivity. In addition to very high sensitivity, our device benefits from consuming a very low volume of sample (10.0 µL) and automatic sampling without need for sampling devices.

Multiwalled Carbon Nanotube (MWCNT) Based Electrochemical Paper-Based Analytical Device (ePAD) for the Determination of Catechol in Wastewater

A novel platform for the phenolics in wastewater based on an electrochemical multiwalled carbon nanotube paper-based analytical device (MWCNT-ePAD) has been developed. Phenolics such as catechol are widely used in industrial processes. Catechol has a strong aroma and is a possible human carcinogen. Therefore, this work focused on the determination of catechol in wastewater. The ePAD was fabricated on chromatography paper. Graphite ink was used as the working electrode and counter electrode, while Ag/AgCl ink was employed as a pseudo reference electrode. The sensitivity of the MWCNT-ePAD biosensor toward phenolics was improved using a multiwall carbon nanotube modified working electrode. The determination of phenolics as the enzyme-catalyzed reaction product using laccase was performed by chronoamperometry. The MWCNT-ePAD biosensor was used for the determination of catechol from 0.8 to 3.0 mg/L with a detection limit of 0.25 mg/L. The reproducibility of the MWCNT-ePAD biosensor was less than 4.95%, and the lifetime of the device was more than 30 days. Additionally, the developed biosensor was applied to determine catechol in wastewater with consistent results compared to a Folin-Ciocalteu assay. The MWCNT-ePAD biosensor was rapid (15 s), cost-effective (0.7 $), and required low reagent consumption (15 µL) with accurate phenolic determination in wastewater by the combination of a paper-based device, an electrochemical biosensor, and a nanomaterial technology.

Impedimetric Paper-Based Enzymatic Biosensor Using Electrospun Cellulose Acetate Nanofiber and Reduced Graphene Oxide for Detection of Glucose From Whole Blood

The excellent characteristics of nanocellulose fiber-based papers have made them one of the most attractive and innovative materials for the development of electrochemical paper-based analytical devices (ePADs). Here, the authors describe a new ePAD based on cellulose nanofibers (CNs) for the determination of glucose concentration from whole blood samples. Cellulose acetate (CA) nanofibers were prepared by the electrospinning method. Then, the paper layer regenerated to cellulose by deacetylation in alkaline solution. To obtain a smooth and continuous CNs layer, it was treated with trimethyl chitosan (TMC). The formation of CA layer, its alkaline regeneration and TMC modification was confirmed by atomic force microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and energy dispersiveX-ray. Screen-printed three electrodes (SPEs) were fabricated by sputtering a thick layer of gold (Au) on the TMC/CNs substrate. Subsequently, reduced graphene oxide (rGO) was used to modify the surface of the working electrode. The fabrication steps of rGO-Au-SPE were characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscop. The results showed that design, construction and modification process was well achieved. Next, glucose oxidase is successfully immobilized onto the regenerated CNs layer which has been previously located in the sensing area of the rGO-Au-SPEs. The ePAD glucose assay exhibited high sensitivity of $9.9\times 10^{-4}~\text{K}\Omega ^{-1} \cdot \text{mM} ^{-1}$ to glucose in the range 3.3 – 27.7 mM ( $\text{R}^{2} =0.99$ ) with a detection limit of 0.1 mM, high reproducibility (RSD = 0.57-1.59%) and outstanding selectivity as well as stability. This biosensing motif represents a general platform for the analysis of other biomarkers.

Enhanced performance of pencil-drawn paper-based electrodes by laser-scribing treatment.

Electrochemical Paper-based Analytical Devices (ePADs) are an alternative to traditional portable analytical techniques due to features such as low-cost, easy surface modification with different materials, and high sensitivity. A fast and simple method to fabricate enhanced ePADs using pencil-drawing which involves the CO2 laser treatment of the carbon surface deposited on paper is described. The electrochemical performances of the devices were evaluated using cyclic voltammetry (CV) with different redox probes and electrochemical impedance spectroscopy (EIS). The electrochemical results show that a treated surface presents a lower resistance to charge transfer and changes the approach of the probe and the overlap of its orbitals with the electrode. To investigate the effects of the laser treatment process, chemical and structural characteristics were evaluated using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results indicated that laser treatment promoted the restoration of carbon–carbon double bonds and removed a thin layer of nanodebris present in commercial pencils, resulting in an improvement of the electrochemical kinetics. As a proof-of-concept, the Pencil-Drawing Electrode (PDE) was used for the detection and quantification of furosemide (FUR) in a sample of synthetic urine, exhibiting a limit of detection (LOD) of 2.4 × 10−7 mol L−1. The percentages of recovery of the FUR added to the samples A and B were 95% and 110%, respectively. The analysis using CO2 laser-treated PDE resulted in a fast, simple, and reliable method for this doping agent.

Electrochemical paper-based analytical device for multiplexed, point-of-care detection of cardiovascular disease biomarkers

• The multiplexed ePADs for simultaneous three important CVDs biomarkers was created. • ePADs provide low detection limits and wide linear range for CVDs biomarker detections. • Good selectivity and high sensitivity were achieved. • The sensor was successfully applied to detect CVDs biomarkers in serum sample. Cardiovascular diseases (CVDs) are the number one cause of death globally. Therefore, a sensitive and affordable point-of-care sensing device is needed for the diagnosis and monitoring of diseases. Herein, we demonstrated an electrochemical paper-based analytical device (ePAD) coupled with a label-free immunoassay for simultaneous determination of three important CVDs biomarkers including C-reactive protein (CRP), troponin I (cTnI), and procalcitonin (PCT). The ePAD was created by stacking a wax-patterned paper and a transparency film using laser-cut double-sided adhesive to define the sample inlet, three separate detection zones for each analyte, and fluidic channels that connect the inlet and detection zones. Antibodies to the target biomarkers were immobilized on graphene oxide (GO)-modified carbon electrodes stencil-printed on the ePAD. Concentrations of the CVDs biomarkers were determined by square wave voltammetry (SWV). A significant decrease in current response in a concentration-dependent manner was observed in the presence of the cardiac biomarkers while there was no observable change in current response in the absence of the biomarkers. Good linearity (R 2 > 0.99), low detection limits (0.38 ng mL −1 , 0.16 pg mL −1 , and 0.27 pg mL −1 for CRP, cTnI, and PCT, respectively), and good reproducibility (RSD < 5 %) were achieved for the quantifications. Furthermore, the immunosensor has been applied to simultaneously detect the three biomarkers in serum samples with satisfactory results. The proposed immunosensor can be a great alternative for the early detection of cardiovascular diseases at the point-of-care.

Insights into electrochemical behavior in laser-scribed electrochemical paper-based analytical devices

Laser-scribed electrochemical paper-based devices (LS-ePADs) are emerging as a greener alternative to conventional carbon electrochemical sensors since their fabrication does not involve the use of chemicals and the resulting devices show good reproducibility, scalability, and interesting electrochemical properties. This work evaluates the electrochemical properties of LS-ePADs using techniques such as cyclic voltammetry and electrochemical impedance spectroscopy (EIS), together with surface characterization by Raman spectroscopy and scanning electron microscopy. The voltammetric behavior of the porous electrode can be described as diffusional to the top electrode layer. Since the porous structure could affect the mass transport, EIS was used to prove that transport resistance is not limiting the charge transfer process in the electrode response. The graphene-based material that forms the electrode surface, identified by Raman spectroscopy, allows a considerably fast electron transfer between the LS-ePADs and the ferri/ferrocyanide molecules.

Electrochemical analysis of anionic analytes in weakly supported media using electron transfer promotion effect: a case study on nitrite

In this study, a simple technique was developed for the electrochemical detection of anionic analytes in weakly supported media. This was conducted by the use of electrochemical paper-based analytical devices (ePADs). A sensing platform was modified with nereistoxin and used to determine nitrite as a case study. The electrochemical response was improved due to the accelerated electron transfer between the sensing platform and the nitrite through the electrostatic interaction of the amino group of nereistoxin and the nitrite. The electrocatalytic current of the nitrite in the presence of nereistoxin was enhanced in the weakly supported media. By using nereistoxin as a signal enhancer, 97% of the electrochemical signal was obtained at the low ionic strength of the electrolyte, while less than 35% of this signal was obtained in the absence of nereistoxin. The limit of detection was as low as 20 nM using an ePAD. Generally, the proposed ePAD serves as a promising, efficient and low-cost device for sensing applications in weakly supported media.

Paper-Based Electrochemical Devices for the Pharmaceutical Field: State of the Art and Perspectives.

The current international pharmaceutical scenario encompasses several steps in drug production, with complex and extremely long procedures. In the last few decades, scientific research has been trying to offer valid and reliable solutions to replace or support conventional techniques, in order to facilitate drug development procedures. These innovative approaches may have extremely positive effects in the production chain, supplying fast, and cost-effective quality as well as safety tests on active pharmaceutical ingredients (APIs) and their excipients. In this context, the exploitation of electrochemical paper-based analytical devices (ePADs) is still in its infancy, but is particularly promising in the detection of APIs and excipients in tablets, capsules, suppositories, and injections, as well as for pharmacokinetic bioanalysis in real samples.