Commercial Screen-printed Carbon Electrodes Research Articles

A novel enzymeless electrochemical sensor based on Ni(OH)2–NiO(OH) nanoelectrocatalyst for sensitive and selective detection of uric acid in PBS simulated body fluid

Neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and Huntington's disease are increasing worldwide. Therefore, the development of a low-cost, highly stable, and portable device for rapid and accurate risk assessment of relevant biomarkers, especially uric acid (UA), by electrochemical detection is currently attracting much attention. Herein, an electrochemical enzymeless UA sensor based on highly active Ni(OH)2–NiO(OH) nanoelectrocatalyst decorated on polyaniline–carbon nanotubes (PANI-CNTs) nanocomposite film, which was modified on a commercial screen-printed carbon electrode (SPCE) by electrodeposition method for sensitive and selective detection of UA. The sensing behavior of the modified electrode (named Ni(OH)2–NiO(OH)/PANI-CNTs/SPCE) is examined in a simulated body fluid (phosphate buffer solution-PBS, 0.01 M, pH 7.4) using differential pulse voltammetry (DPV) technique. The obtained results showed that the Ni(OH)2–NiO(OH)/PANI-CNTs/SPCE electrode exhibited outstanding electrocatalytic performance for the detection of UA at low potential (0.33 V vs. Ag/AgCl) without exhibiting interfering signals of dopamine (DA), glucose (Glu), ascorbic acid (AA) and urea. The sensor exhibited extra high sensitivity (386.8 μA mM−1 cm−2), high selectivity, good reproducibility, and durable stability with the ability to detect UA at both low (5–100 μM) and high (100–800 μM) levels with a very low detection limit down to 0.11 μM (individual detection of UA) and 0.29 μM (detection of UA in presence of DA) in a simulated body fluid. The recovery test using the proposed electrochemical sensor showed a high recovery percentage (>99.81 %), making it a viable option for practical applications.

Waste DVD polycarbonate substrate for screen-printed carbon electrode modified with PVP-stabilized AuNPs for continuous free chlorine detection

An electrochemical free chlorine sensor was developed by modifying a lab-made screen-printed carbon electrode (SPCE) with gold nanoparticles synthesized with polyvinylpyrrolidone (AuNPs-PVP). The electrode was made by screen printing carbon ink on a waste digital versatile disc (SPC-wDVD). PVP was used to stabilize AuNPs. Scanning electron microscopy showed that AuNPs aggregated without the stabilizer. The electrochemical behavior of the SPC-wDVD was evaluated by comparison with commercial SPCEs from two companies. Electrochemical characterization involved cyclic voltammetry and electrochemical impedance spectroscopy. The detection of free chlorine in water samples was continuous, facilitated by a flow-injection system. In the best condition, the developed sensor exhibited linearity from 0.25 to 3.0 and 3.0 to 500 mg L−1. The limit of detection was 0.1 mg L−1. The stability of the sensor enabled the detection of free chlorine at least 475 times with an RSD of 3.2 %. The AuNPs-PVP/SPC-wDVD was able to detect free chlorine in drinking water, tap water and swimming pool water. The agreement between the results obtained with the proposed method and the standard spectrophotometric method confirmed the precision of the developed sensor.

A Novel Approach Using Reduced Graphene Oxide for the Detection of ALP and RUNX2 Osteogenic Biomarkers.

In this work, we propose a new technique involving the modification of commercial screen-printed carbon electrodes with electrochemically reduced graphene oxide to serve as the starting point of a future electrochemical biosensor for the detection of two osteogenic biomarkers: alkaline phosphatase (ALP) and Runt-related transcription factor 2 (RUNX2). The electrodes were characterized after each modification by cyclic voltammetry and electrochemical impedance spectroscopy, showing the appropriate electrochemical characteristics for each modification type. The results obtained from scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements are well correlated with each other, demonstrating the successful modification of the electrodes with graphene oxide and its subsequent reduction. The bioreceptors were immobilized on the electrodes by physical adsorption, which was confirmed by electrochemical methods, structural characterization, and contact angle measurements. Finally, the functionalized electrodes were incubated with the specific target analytes and the detection relied on monitoring the electrochemical changes occurring after the hybridization process. Our results indicated that the pilot platform has the ability to detect the two biomarkers up to 1 nM, with increased sensitivity observed for RUNX2, suggesting that after further optimizations, it has a high potential to be employed as a future biosensor.

Electrochemical Determination of Fentanyl Using Carbon Nanofiber-Modified Electrodes.

In this work, we report the direct electrochemical oxidation of fentanyl using commercial screen-printed carbon electrodes (SPCEs) modified with carboxyl-functionalized carbon nanofibers (fCNFs). CNFs have surface chemistry and reactivity similar to carbon nanotubes (CNTs), yet they are easier to produce and are of a lower cost than CNTs. By monitoring the current produced during the electrochemical oxidation of fentanyl, variables such as fCNF loading, fentanyl accumulation time, electrolyte pH, and differential pulse voltammetry parameters were optimized. Under an optimized set of conditions, the fCNF/SPCEs responded linearly to fentanyl in the concentration range of 0.125-10 μM, with a limit of detection of 75 nM. The fCNF/SPCEs also demonstrated excellent selectivity against common cutting agents found in illicit drugs (e.g., glucose, sucrose, caffeine, acetaminophen, and theophylline) and interferents found in biological samples (e.g., ascorbic acid, NaCl, urea, creatinine, and uric acid). The performance of the sensor was also successfully tested using fentanyl spiked into an artificial urine sample. The straightforward electrode assembly process, low cost, ease of use, and rapid response make the fCNF/SPCEs prime candidates for the detection of fentanyl in both physiological samples and street drugs.

FAST MICROWAVE ASSISTED FUNCTIONALIZATION OF CARBON NANOFIBERS: A PROMISING ELECTROCHEMICAL SENSING PLATFORM FOR ELECTROACTIVE ANALYTES

This research introduces a novel approach for swiftly enhancing the electrochemical sensing capabilities of commercial screen-printed carbon electrodes through a rapid acid microwave-assisted functionalization of carbon nanofibers (f-CNFMW). A comparative analysis with the conventional refluxed system functionalization method (f-CNFRefluxed) was conducted to assess the electrochemical performance of the newly developed f-CNFMW. The voltametric study showed that f-CNF-MW significantly enhanced the electron transfer rate when testing common phenolic compounds such as hydroquinone, paracetamol, and caffeic acid. Moreover, the anodic oxidation potential for the majority of irreversible analytes was negatively shifted, indicating the high electro-catalytic activity of f-CNF-MW gained after this treatment, making it analytically useful for the electro-oxidation of some molecules that require high overpotential, mainly for purine bases and nitrite. Additionally, the developed f-CNF-MW exhibited remarkable resistance to fouling phenomena when exposed to bisphenol A and tryptophan, underscoring its potential for real-world applications. To sum up, this study highlights the potential of rapid microwave treatment in producing f-CNF-MW as a promising electrochemical nanomaterial, resulting in substantial improvements in electro-analytical capabilities compared to conventional methodologies.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables.

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

Electrochemical Sensing of Vitamin D3: A Comparative Use of Glassy Carbon and Unmodified Screen-Printed Carbon Electrodes

This work presents the electrochemical determination of cholecalciferol (Vitamin D3) in water-organic mixtures using a glassy carbon electrode (GCE) and commercial screen-printed carbon electrodes (SPCEs). The electrocatalytic behavior of Vitamin D3 on the surface of the working electrode produced a well-defined oxidation peak at +0.95 V (vs. Ag|AgCl, 3.0 mol L−1) and +0.7 V (vs. Ag-SPCE pseudo-reference electrode) for the GCE and SPCE, respectively, in 0.1 M LiClO4 prepared in 50% ethanol. The nature of the organic solvent needed for the solubilization of Vitamin D3 was evaluated, together with the concentration of the supporting electrolyte, the ratio of the water-organic mixture, the voltametric parameters for the cyclic voltammetry (CV), and square-wave voltammetry (SWV) analyses. Under the optimized conditions, a linear correlation between the anodic peak current and the concentration of Vitamin D3 was obtained over the range of 0.47 to 123 µmol L−1 and 59.4 to 1651 µmol L−1 for the GCE and SPCE, respectively. The determined limits of detection (LOD) were 0.17 (GCE) and 19.4 µmol L−1 (SPCE). The methodology was successfully applied to commercial supplement tablets of Vitamin D3. Additionally, this work shows the possibility of using non-modified GCE and SPCE for routine analysis of Vitamin D3.

A molecularly imprinted screen-printed carbon electrode for electrochemical epinephrine, lactate, and cortisol metabolites detection in human sweat

This study presents a novel approach to the detection of epinephrine, lactate, and cortisol biomarkers in human sweat using molecularly-imprinted polymers (MIP) embedded screen printed carbon electrode (SPCE) sensors. The epinephrine and lactate MIP SPCE sensors were fabricated by epinephrine or lactate-imprinted polyaniline co-polymerized with 3-aminophenylboronic acid and gold nanoparticles (PANI-co-PBA/AuNP) selective membrane on a commercial SPCE. The cortisol sensor was comprised of a cortisol-imprinted poly(glycidyl methacryate-co-ethylene glycol dimethacrylate) (poly (GMA-co-EGDMA)@AuNP selective membrane deposited on a SPCE. Both cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used as modes of analysis for the MIP SPCE sensors. All sensors exhibited a rapid (∼1 min) and selective response to the epinephrine, lactate, and cortisol target analytes, with excellent precision between scans for both CV and DPV analysis modes. For CV, the LOD for epinephrine, lactate, and cortisol was 8.2 nM, 13 mM, and 0.042 μM, respectively. The LOD for DPV were 0.60 nM, 2.2 mM, and 0.025 μM for epinephrine, lactate, and cortisol, respectively. The MIP SPCE sensor platforms were further validated through the successful quantification of epinephrine, lactate, and cortisol in human sweat.

Voltammetric determination of sulfamethoxazole using commercial screen-printed carbon electrodes

A differential pulse voltammetric (DPV) method using commercial screen-printed carbon electrodes (SPCE) is developed for a fast and cost-effective determination of the antibiotic sulfamethoxazole (SMX). Optimal measurements are carried out at pH 5.5 in acetate buffer and yield a detection limit of 15 µg/L and a linearity range of 50 – 600 µg/L with good repeatability (1.1%) and reproducibility (2.5%). The method is successfully applied to the analysis of a spiked tap water sample with very high reproducibility (0.4%) and good trueness (Recovery 95.2%).Additional considerations are made about the irreversible electrochemical oxidation of SMX, which is notoriously pH-dependent according to a process involving 2e- and 2H+, in agreement with several reported mechanisms in the literature. Besides, the analysis of other sulfonamide antibiotics is discussed, showing the key role of the free terminal amino group in oxidation, which makes almost undistinguishable voltammetric signals from different molecules sharing this moiety. In contrast, the acetylation of the mentioned group (e.g., in sulfonamide metabolites) drastically reduces the sensitivity of voltammetric measurements.

Differential Pulse Voltammetric Tuning of the Screen-Printed Carbon Electrode Surface to Enhance the Electrochemical Performance and Multiplex Detection

Screen-Printed Carbon Electrode (SPCE) has shown tremendous scope for the miniaturization and commercialization of low-cost electrochemical sensors and biosensors devices. But the commercial SPCEs have a narrow potential window (PW) that limits their versatile applications for various analytes owing to the presence of some inherent redox peaks in the wider PW. In this work, we have explored the most effective and innovative electrochemical tuning of the SPCE surface using DPV (differential pulse voltammetry) for the removal of those inherent redox peaks that are responsible for narrowing the working PW. After that, the electrochemical performance of the tuned SPCE electrode was evaluated in terms of a range of electrochemical parameters including reproducibility by CV (Cyclic Voltammetry), DPV and EIS (electrochemical impedance spectroscopy) measurements using [Fe(CN)6]3−/4− as a model redox analyte. In addition, the suitability of the tuned electrode for multiple analytes detection was tested in presence of a mixture of Cd2+ (cadmium), Cu2+ (copper) and Hg2+ (Mercury) ions using CV and DPV techniques. The electrochemical analysis data show that after electrochemical DPV treatment, the SPCE surface exhibits excellent reproducibility and electrochemical performance within a wider PW minimizing their inherent drawback creating a wide scope of their precise applications in various fields.

Imunocapture Magnetic Beads Enhanced and Ultrasensitive CRISPR-Cas13a-Assisted Electrochemical Biosensor for Rapid Detection of SARS-CoV-2.

The rapid and ongoing spread of the coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emphasizes the urgent need for an easy and sensitive virus detection method. Here, we describe an immunocapture magnetic bead-enhanced electrochemical biosensor for ultrasensitive SARS-CoV-2 detection based on clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) proteins, collectively known as CRISPR-Cas13a technology. At the core of the detection process, low-cast and immobilization-free commercial screen-printed carbon electrodes are used to measure the electrochemical signal, while streptavidin-coated immunocapture magnetic beads are used to reduce the background noise signal and enhance detection ability by separating the excessive report RNA, and a combination of isothermal amplification methods in the CRISPR-Cas13a system is used for nucleic acid detection. The results showed that the sensitivity of the biosensor increased by two orders of magnitude when the magnetic beads were used. The proposed biosensor required approximately 1 h of overall processing time and demonstrated an ultrasensitive ability to detect SARS-CoV-2, which could be as low as 1.66 aM. Furthermore, owing to the programmability of the CRISPR-Cas13a system, the biosensor can be flexibly applied to other viruses, providing a new approach for powerful clinical diagnostics.

Incorporation of ZIF-67 derived Co-N/C core-shell nanoparticles on functionalized MWCNT as a highly efficient electrocatalyst for nonenzymatic H2O2 sensor

This work focuses on the fabrication of zero-dimensional (0D) and one-dimensional (1D) based nanocomposite materials for hydrogen peroxide (H2O2) sensing applications. We demonstrate an environmentally friendly synthesis approach for ZIF-67 growth on CTAB functionalized MWCNT using deionized water as a solvent medium (ZIF-67@CT-MWCNT). The pyrolysis treatment effectively formed a 0D/1D composite structure consisting of core-shell Co/N dual-doped carbon nanospheres and a CT-MWCNT network (referred to as Co-N/C@CT-MWCNT). The characteristic properties of composite materials were clearly investigated by SEM, TEM, XRD, micro-Raman, and XPS analysis. The electrocatalytic properties of Co-N/C@CT-MWCNT toward H2O2 reduction are also examined by cyclic voltammetry and amperometry techniques. The results indicated that the Co-N/C@CT-MWCNT modified electrode shows fast electron transfer kinetics for reduction of H2O2 in pH 7 electrolyte compared to other control electrodes. It mainly depends on the high catalytic activity of Co-Nx active species and the high electron conductive carbon network in the composite structure. Amperometry determination of H2O2 reduction on Co-N/C@CT-MWCNT electrode was performed at − 0.4 V (vs. Ag/AgCl), which shows rapid H2O2 sensing response time within 2 s, resulting in a wide linear range (0.5 μM - 25.74 mM) with the detection limit of 0.18 μM. The Co-N/C@CT-MWCNT sensor also showed excellent sensitivity (868.88 μA mM−1 cm−2), operational stability, and selectivity to H2O2 sensing. Thus, our proposed hybrid electrocatalyst material could be able to fabricate with commercial screen-printed carbon electrodes for the real-time H2O2 sensing application.

Three-dimensional highway-like graphite flakes/carbon fiber hybrid electrode for electrochemical biosensor

Carbon-based electrodes are promising candidates for developing cheap, miniaturized, and disposable biosensors for effective, point-of-care disease management. However, their sensitivity is usually lower than gold electrodes due to polymer binders used during the procedure of ink formulating. Although surface pretreatment with reactive chemicals and addition of nanomaterials are available to enhance their sensor performance, both approaches may suffer from the use of hazardous substances and processing complexity. Here, we report an inexpensive, non-nanomaterials approach by making a graphite/carbon fiber (G/CF) hybrid electrode for biosensor applications. The hybrid electrode is formed by embedding a homemade graphite ink in the CF matrix of a commercially available carbon paper. This design resembles a super-efficient 3D highway network where ample expressways (CF) run through numerous small factories (locally distributed graphite flakes) for rapid goods pick-up and transportation (electron transfer). Featuring high conductivity, low impedance and large active surface area surpassing commercial screen-printed carbon electrodes, the G/CF hybrid electrodes show superior sensor performance for glucose detection as compared to counterparts prepared on electrodes without CF matrix. This study provides a new approach of enhancing electrochemical performance of carbon-based electrodes by structural design using macro-size scale, affordable materials.

Electrochemical quantification of levothyroxine at disposable screen-printed electrodes

The concentration of thyroxine hormone is linked to a large variety of medical conditions, where the best therapy is hormone substitution, through administration of levothyroxine (LT4) medication. Herewith, the detection of these biomolecules still lacks a simple, reliable tool, such as label-free sensors. In this work, the performances of commercial screen-printed carbon electrodes, containing different nanostructured materials (carbon nanotubes, graphene, and gold nanoparticles), used as sensors for LT4 detection, were described and compared. Electrochemical methods were used for the characterization of the nanostructure-based sensors. Several optimization steps were undertaken to achieve optimum performances for selective LT4 quantification. The redox behaviour of LT4 at sensors surface together with the interfacial changes, which occur due to the interaction between nanostructures and LT4, were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Differential pulse voltammetry (DPV) was used for LT4 detection, where best performances were obtained in the presence of carbon nanotubes, with a detection limit of 30 nM.

Electrochemical Detection Platform Based on RGO Functionalized with Diazonium Salt for DNA Hybridization.

In this paper, we propose an improved electrochemical platform based on graphene for the detection of DNA hybridization. Commercial screen-printed carbon electrodes (SPCEs) were used for this purpose due to their ease of functionalization and miniaturization opportunities. SPCEs were modified with reduced graphene oxide (RGO), offering a suitable surface for further functionalization. Therefore, aryl-carboxyl groups were integrated onto RGO-modified electrodes by electrochemical reduction of the corresponding diazonium salt to provide enough reaction sites for the covalent immobilization of amino-modified DNA probes. Our final goal was to determine the optimum conditions needed to fabricate a simple, label-free RGO-based electrochemical platform to detect the hybridization between two complementary single-stranded DNA molecules. Each modification step in the fabrication process was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3−/4− as a redox reporter. Although, the diazonium electrografted layer displayed the expected blocking effect of the charge transfer, the next steps in the modification procedure resulted in enhanced electron transfer properties of the electrode interface. We suggest that the improvement in the charge transfer after the DNA hybridization process could be exploited as a prospective sensing feature. The morphological and structural characterization of the modified electrodes performed by scanning electron microscopy (SEM) and Raman spectroscopy, respectively, were used to validate different modification steps in the platform fabrication process.

Disposable carbon nanotube-based antifouling electrochemical sensors for detection of morphine in unprocessed coffee and milk

The direct on-site detection of illegal additives in unprocessed food samples is usually a great challenge for electrochemical sensors because of electrode biofouling. In this work, a simple filtration method for the scalable fabrication of disposable single-walled carbon nanotubes (SWCNTs)-based antifouling electrochemical sensors is reported. This method employs flash foam stamp-assisted polydimethylsiloxane (PDMS) patterns to control the region-selective deposition of SWCNTs on polyvinylidene fluoride (PVDF) membranes during filtration, which enables the scalable fabrication of a SWCNTs three-electrode-based sensor with high conductivity, good reproducibility and excellent flexibility. The resulting SWCNTs sensor exhibits a sensitive response towards morphine with a calibration range of 0.2 ∼ 100 μg mL−1 and a detection limit of 0.06 μg mL−1 (S/N = 3). Moreover, probably owing to its unique nanoporous structure, this SWCNTs sensor possesses apparently improved antifouling ability as compared with the widely used glassy carbon electrode (GCE), and allows the direct detection of morphine in unprocessed complex foods such as milk and coffee. The present work thus establishes a simple approach to the scalable production of self-designed SWCNTs electrode arrays suitable for on-site food analysis, which may also provide an alternative to commercial screen-printed carbon electrodes (SPCEs) for electrochemical sensing applications.

Laser-activated screen-printed carbon electrodes for enhanced dopamine determination in the presence of ascorbic and uric acid

Commercial screen-printed carbon electrodes have been treated with a CO2 laser energy of 12.8 mJ cm−2 in air. This thermal treatment resulted in an increase in the crystallinity of the graphite and an enhancement in electron transfer rates, determined by Raman spectroscopy and cyclic voltammetry, respectively. Laser treatment also facilitated the introduction of oxygen groups by anodization at a potential of 1.55 V vs Ag, which was highly beneficial for the simultaneous detection of dopamine (DA), even in the presence of ascorbic acid (AA), and uric acid (UA) by differential pulse voltammetry (DPV). Anodized laser-treated electrodes were much better at resolving the oxidation peaks of these three substances compared to the as-received commercial electrodes. A linear response from 0.34 to 1.6 µM and a detection limit of 80 nM were obtained for DA in the presence of 20 µM uric acid and 160 µM ascorbic acid. This work demonstrates a suitable method to improve sensitivity in carbon-based printable sensors for the simultaneous analysis of oxygen surface-sensitive substances.

Fabrication, Characterization and Performance Evaluation of Screen-printed Carbon Electrodes: Determination of Acetaminophen in Tylenol

Screen-printed carbon electrodes (SPCEs) were fabricated and compared with the commercial DS 110 (DropSens). In addition to the classic cyclic voltammetry (CV) of K 3 [Fe(CN) 6 ], a method using widely available Bausch + Lomb and Tylenol was developed for comprehensive evaluation of the electrochemical performance of SPCEs. Scanning electron microscope (SEM) images showed that the graphite surface of the in-house SPCEs, which acted as reaction surface, was covered by grainy binders thus less reactive than DS 110. X-ray photoelectron (XPS) spectra indicated that both were composed primarily of graphite (> 85%), but the concentrations of S (detected in DS110 only), N and Cl in the less-electroactive binders differed. The CV using K 3 [Fe(CN) 6 ] as probe revealed that the peak-to-peak separation of the in-house SPCE (0.140 V) was further apart than that of DS 110 (0.075 V). The oxidation and reduction peak currents of the in-house SPCE were 73% and 82% of that of the DS 110, respectively. When CV was applied to the determination of acetaminophen in Tylenol (product label concentration: 661 mmol/L) using Bausch + Lomb solution with 1 mol/L KCl as the buffer, DS 110 showed better sensitivity, but the in-house SPCE was stable and more precise. Though DS 110 displayed higher current and thus more sensitive, the in-house SPCE current was stable and thus more precise. The concentrations obtained from oxidation and reduction peaks were (775 ± 80) mmol/L and (686 ± 322) mmol/L for DS 110, and (637 ± 39) mmol/L and (713 ± 139) mmol/L for in-house SPCE, respectively. Moreover, DS 110 exhibited two large unknown peaks and thus less reliable in the acetaminophen-in-Tylenol CV test. Determination of acetaminophen in real Tylenol sample was helpful as additional quality control in SPCEs fabrication. To evaluate the electrochemical performance of in-house screen-printed electrode (SPCE) and commercial SPCE (DS 110), a fast and inexpensive method to analyze concentration of acetaminophen in Tylenol using Bausch + Lomb as buffer was developed, in addition to the classic K 3 [Fe(CN) 6 ]. The results were relatively accurate. Meanwhile, surface characterizations showed that both SPCEs contained major amount of graphite but with different configurations, which might result in a less sensitivity but more precision of the in-house SPCEs compared to DS110.

3D-printing pen versus desktop 3D-printers: Fabrication of carbon black/polylactic acid electrodes for single-drop detection of 2,4,6-trinitrotoluene

The fabrication of carbon black/polylactic acid (PLA) electrodes using a 3D printing pen is presented and compared with electrodes obtained by a desktop fused deposition modelling (FDM) 3D printer. The 3D pen was used for the fast production of electrodes in two designs using customized 3D printed parts to act as template and guide the reproducible application of the 3D pen: (i) a single working electrode at the bottom of a 3D-printed cylindrical body and (ii) a three-electrode system on a 3D-printed planar substrate. Both devices were electrochemically characterized using the redox probe [Fe(CN)6]3−/4- via cyclic voltammetry, which presented similar performance to an FDM 3D-printed electrode or a commercial screen-printed carbon electrode (SPE) regarding peak-to-peak separation (ΔEp) and current density. The surface treatment of the carbon black/PLA electrodes fabricated by both 3D pen and FDM 3D-printing procedures provided substantial improvement of the electrochemical activity by removing excess of PLA, which was confirmed by scanning electron microscopic images for electrodes fabricated by both procedures. Structural defects were not inserted after the electrochemical treatment as shown by Raman spectra (iD/iG), which indicates that the use of 3D pen can replace desktop 3D printers for electrode fabrication. Inter-electrode precision for the best device fabricated using the 3D pen (three-electrode system) was 4% (n = 5) considering current density and anodic peak potential for the redox probe. This device was applied for the detection of 2,4,6-trinitrotoluene (TNT) via square-wave voltammetry of a single-drop of 100 μL placed upon the thee-electrode system, resulting in three reduction peaks commonly verified for TNT on carbon electrodes. Limit of detection of 1.5 μmol L−1, linear range from 5 to 500 μmol L−1 and RSD lower than 4% for 10 repetitive measurements of 100 μmol L−1 TNT were obtained. The proposed devices can be reused after polishing on sandpaper generating new electrode surfaces, which is an extra advantage over chemically-modified electrochemical sensors applied for TNT detection.

Quantitative trace level voltammetry in the presence of electrode fouling agents: Comparison of single-walled carbon nanotube network electrodes and screen-printed carbon electrodes

Single walled carbon nanotube (SWNT) network electrodes, in which a planar arrangement of SWNTs on an inert surface serve as a working electrode for voltammetry, offer considerable attributes for electroanalysis. Here, the effect of SWNT network density on the trace voltammetric analysis of a water-soluble ferrocene derivative (FcCOOH) is investigated in the presence of polyethylene glycol (PEG) or albumin, species that can foul (block) an electrode via adsorption. Fc-based analytes typically find use in redox labelling or redox shuttling, point-of-care electrochemical detection devices. Comparison is made between SWNT electrodes, grown by catalyzed chemical vapour deposition at three different surface coverages, 5, ~20 and ~30 μmSWNT μm-2, and commercial screen-printed carbon electrodes (SPCEs). In the presence of PEG (8% 2 K), for cyclic voltammetry, the lowest detectable concentration decreases as SWNT network density decreases. However, when employing differential pulse voltammetry, all three networks show a 1 nM FcCOOH limit of detection, three orders of magnitude smaller than achievable with SPCEs. This is attributed to the low capacitance of the SWNTs and absence of amorphous carbon structures which can contribute a pseudo-capacitive response. For both polyethylene glycol (PEG) and albumin (4%), repeat cycling shows the higher density SWNT network electrodes (≥20 μmSWNT μm-2) are far less susceptible to electrode fouling. Toward practical devices, a three-electrode chip, similar in design to that used in SPCEs, but using high density SWNT network electrodes, is also demonstrated to have impressive detection sensitivity for FcCOOH (nM level) in PEG solutions. The simplicity and practicality of the design widens the potential applications of these ultra-sensitive diagnostic tools based on planar network SWNTs.