Carbon-based Screen-printed Electrodes Research Articles

In-Depth Characterization of Natural Clays from Southeast Albania

Clays have been exploited in the manufacture of diverse products from ceramics to paints, pharmaceuticals, plastics, cosmetics, and more. Thus, they can be used in many industrial applications, showing good adsorbent ability thanks to their lamellar structure, high cation exchange capacity, pore size distribution, and large surface area. For this reason, considerable attention has been paid to their in-depth characterization, for further integration in sectors such as biomedicine, construction, remediation, aerospace, and nanotechnology. For this aim, two samples of natural clays, ALO1 and PRE4, from the southeast part of Albania, were subject to a multi-methodological characterization, with the aim of addressing the use of such geomaterials in possible sensing applications. X-ray fluorescence analysis, morphological characterization of the samples, and energy-dispersive system spectroscopy pointed to an extreme mineralogical variety, with kaolinite in AL01 and montmorillonite in PRE4 as the most abundant phases. This fact was further confirmed by powder X-ray diffraction, showing a quartz content of 20%, a kaolinite content of 64%, and a muscovite content of 16% for ALO1; meanwhile, for PRE4, we found a content of quartz of 45%, a content of montmorillonite of 34.9%, and a content of clinochlore of 20%. Infrared spectroscopy and thermal analyses confirmed the presence of hydroxyl groups in both samples, suggesting a higher content in ALO1. Measurement of N2 adsorption isotherms on the clay samples yields specific surface areas of 87 m2/g for PRE4 and 32 m2/g for ALO1, pore volumes of 0.721 cm3/g for PRE4 and 0.637 cm3/g for ALO1, and similar pore sizes in the range of 6–12 nm. Electrochemical analysis highlighted a good conductivity of ALO1 and PRE4 when used for the modification of commercial carbon-based screen-printed electrodes. In detail, higher currents were registered by differential pulse voltammetry for the electrodes modified with the clays with respect to bare electrodes, as well as good repeatability of the measurements. In addition, a comparative study with nanomaterials, known for their good conductivity, was achieved, using carbon black and gold nanoparticles as a reference, showing that the conductivity of the clays was lower than but not so different from those of the reference materials.

Microfluidic Reservoir Integrated with Optimized Screen-Printed Electrode for Simultaneous Detection of Ascorbic Acid and L-Cysteine

Abstract iomarker detection is crucial in the healthcare industry as it gives important insights into the field of disease diagnosis, prognosis, and treatment. This work demonstrates a flexible carbon-based screen-printed electrode (CSPE) modified with carboxylic acid functionalized multiwalled carbon nanotube (MWCNT-COOH) for simultaneous detection of Ascorbic acid (AA) and L-Cysteine (CySH). The electrochemical properties of the fabricated film are studied using the Cyclic voltammetry (CV) and Amperometry technique. The MWCNT-COOH/CSPE showed good electrocatalytic activity for oxidation of CySH and AA. Favorable ionic interaction, or electrostatic attraction, between the analytes and MWCNT-COOH increased the detection capability. The fabricated electrode is incorporated with a microfluidic reservoir to hold the analyte that can separately detect AA and CySH using the device. The device is tested for a linear range of 0.01 mM to 20 mM for both analytes. The detection limit for AA and CySH obtained using amperometry analysis is 3.07 µM and 5.72 µM, respectively. Also, the calculated quantification limits values are 9.11 µM and 17.3 µM, respectively for AA and CySH. Further, the device demonstrates appreciable results in both real sample analysis and interference analysis. The device, enabled with screen printed electrodes and microfluidic reservoir, opens a new method for simultaneous multiplexed detection enabling the detection of many different biomarkers on the same experimental setup.

Selecting optimal carbon inks for fabricating high-performance screen-printed electrodes for diverse electroanalytical applications

Carbon-based screen-printed electrodes (SPEs) are extensively employed in electrochemistry due to their reproducibility, low-cost production, disposability and versatility. It is commonly accepted that batch to batch variations may occur due to variations in the ink formulation or the use of a different ink to print the electrodes. In this paper, three different commercial carbon-based inks (DuPont, Loctite and SunChemical) were used to manufacture SPEs, referred to respectively as Dup-SPE, Loc-SPE and Sun-SPE, using a semi-automated screen-printing technology. This study focuses on evaluating the quality, characteristics and electrochemical performance of the fabricated SPEs. Furthermore, the study aimed to investigate potential correlations between the ink composition and the nature of different target molecules, as well as their electroanalytical responses. Specifically, phenolic compounds and cocaine cutting agents are tested in alkaline conditions, while benzodiazepines and cephalosporine antibiotics are investigated in acidic media using square wave voltammetry (SWV). This aims to extract insights for the proper selection of inks and SPEs in both conditions. Additionally, a scan rate study of cephalosporine antibiotics using linear sweep voltammetry (LSV) is performed confirming the ion-exchange polymer layer on the electrode surface of Loc-SPE, which impact surface and electrochemical properties, leading to drawbacks in alkaline SWV sensing, but strategic benefits in reductive sensing resulting in an enhanced selective detection of specific targets. The insights on ink-specific influences on the surface and electrochemical properties of the SPEs obtained, may be useful for facilitating the electrode selection in diverse electrochemical applications, emphasizing the critical role of ink composition in achieving desired sensing capabilities.

Electrochemical Biosensor Enabling Sensitive Detection of miRNA Biomarkers

Biomarkers are becoming increasingly important for early diagnosis, exploration of responses to medication, and assessment of therapeutic efficacy of various diseases [1]. Increasing evidence shows that miRNAs can be employed as biomarkers for cancer and cardiovascular diseases. In this context, the development of powerful electrochemical diagnostic tools has grown in interest due to their sensitivity, speed, and low cost [1]. Additionally, electrochemical technologies offer a facile means to fabricate well-defined nanostructured surfaces in a controlled environment. The gold (Au)-based surface stands out for its ability to improve charge transfer characteristics, enhancing conductivity. It also serves as a stable substrate for further modification, enabling the detection of target analytes [2]. Here, we utilized an electrochemical platform by using a 3-electrode carbon-based screen-printed electrode (SPE) electrochemically modified with gold and subsequently attached a specific DNA-based redox probe to detect low levels of miRNAs as a biomarker. Our design was applied to detect miRNA-1 (5′-TGG AAT GTA AAG AAG TAT GTA T-3′), demonstrating exceptional sensitivity and a low detection limit (LOD) of 120 fM. We also discuss how the developed platform broadly benefits numerous other miRNA sequences. Device preparation method: A screen-printed electrode (SPE) consisting of a 3 mm diameter carbon working electrode, an Ag reference electrode, and a carbon counter electrode was used as a base for device development. The bare SPE was activated during 10 cycles of cyclic voltammetry (CV) with potentials ranging from -0.5 to +1 V at a scan rate of 20 mVs-1 using PBS as the electrolyte. Before gold electrodeposition, the activated SPE was rinsed with PBS and deionized water. The electrode was submerged in a solution of 115 mM HAuCl4 (in 0.5 M H2SO4) during 10 CV cycles with the same parameters described above. Next, the DNA-probe sequence was attached to the working surface of the Au-decorated screen-printed electrode (Au-SPE). The DNA-probe sequence was modified in advance with C6-S-S-R at the 5′ end (enabling covalent binding onto Au) and methylene blue (MB) at the 3′ end (allowing electron transport at the electrode). Before modification of SPE, the disulfide bond was reduced using tris(2-carboxyethyl)-phosphine hydrochloride) (TCEP) to enable covalently attachment of the HS-DNA-MB probe to the Au-SPE [2]. The attachment of the DNA-probe sequence was achieved by placing 10 µL of the diluted probe onto the working electrode area and allowing for 1 hour of modification at room temperature to take place, as shown in Fig. 1(A). Results & Discussion: The device was evaluated for analytical performance in the presence of increasing target concentrations, as shown in Fig. 1 (A). In the absence of a miRNA-1 target, the stem-loop structure of the DNA probe remains closed, forcing the redox MB-reporter into proximity to the electrode, allowing for efficient electron transport. In the presence of miRNA-1, the target molecule binds to a complementary sequence of the DNA probe, opening the loop. The structure assumes a relatively rigid conformation where MB is farther from the gold surface, reducing the observed signal, Fig. 1 (B). The observed current gradually decreases upon the successive addition of miRNA target molecules for both cathodic, Ipc, and anodic, Iac, peaks. Using the dependence of anodic peak, Iac, the sensor was calibrated as a function of added miRNA-1 concentration in the range between 0 and 4 nM. Using the calibration curve shown in Fig. 1 (C), the detection limit was estimated to be 120 femtoM. The device was further tested for stability and exhibited robust performance over an extended period displaying minimal fluctuations in the recorded current. While we demonstrate the sensitive detection of miRNA-1, the design can be easily adapted for other miRNA sequences [3]. Additionally, it introduces exciting prospects for multiplexing, where multiple miRNA sequences can be easily detected with only minor adjustments to the established design. Fig. 1 (A) Schematics of the device fabrication process and mechanism for the development of Smart Electrochemical Sensors setup; (B) Cyclic Voltammetry (CV) responses during Au electrodeposition (black) in the absence of miRNA-1 target (red) and presence of miRNA-1 target (blue); (C) The device response curve concerning successive addition of miRNA-1 target molecule into the device chamber (different concentrations of target from 0 to ~ 4000 pM), the inset shows CV response used to plot the calibration curve. Acknowledgment: NSF DMR 2204027, US DOE EPSCoR DE-SC0024284

A comparative study of graphene-based electrodes for electrochemical detection of visceral leishmaniasis in symptomatic and asymptomatic patients

BackgroundVisceral Leishmaniasis is a neglected tropical disease with a high rate of infection and mortality in affected areas. Around 50,000 to 90,000 new cases of visceral leishmaniasis (VL) are estimated every year. Individuals asymptomatic for the disease should also be considered in epidemiological surveillance of the disease, as they can help spread the parasite. Thus, the development of low-cost diagnosis methods that allow the identification of infected and asymptomatic individuals is required, especially in developing countries where this disease is endemic. ResultsIn this work, we developed an immunosensor for recognizing anti-Leishmania antibodies in asymptomatic individuals and avoiding cross-reaction with Chagas disease (CD). For that, we used carbon-based screen-printed electrodes, modified with graphene oxide and gold. Reproducibility was assessed by calculating the relative standard deviation (RSD < 5 %) from cyclic voltammograms of [Fe(CN)6]3-/4− using three different electrodes, screen-printed carbon electrodes (DPR-110) and graphene modified screen-printed electrodes (DPR-110 GPH) were purchased from DropSens (Oviedo, Asturias, Spain). SignificanceAs an electrochemical methodology, we use cyclic voltammetry. After the tests were carried out, we considered that carbon electrodes adsorbed with reduced graphene oxide and modified with gold nanoparticles were the best platforms for detecting anti-Leishmania antibodies. In the study carried out, the limit of quantification (LOQ) for anti-Leishmania antibodies was established at 16.75 mg/mL, while the limit of detection (LOD) was 5.58 mg/mL. These limits indicate the minimum antibody concentration values that can be quantified and detected accurately and reliably in the analyzed sera.

Functionalization of Carbon Nanofibers with an Aromatic Diamine: Toward a Simple Electrochemical-Based Sensing Platform for the Selective Sensing of Glucose.

Despite a variety of glucose sensors being available today, the development of nonenzymatic devices for the determination of this biologically relevant analyte is still of particular interest in several applicative sectors. Here, we report the development of an impedimetric, enzyme-free electrochemical glucose sensor based on carbon nanofibers (CNFs) functionalized with an aromatic diamine via a simple wet chemistry functionalization. The electrochemical performance of the chemically modified carbon-based screen-printed electrodes (SPCEs) was evaluated by electrical impedance spectroscopy (EIS), demonstrating a high selectivity of the sensor for glucose with respect to other sugars, such as fructose and sucrose. The sensing parameters to obtain a reliable calibration curve and the selective glucose sensing mechanism are discussed here, highlighting the performance of this novel electrochemical sensor for the selective sensing of this important analyte. Two linear trends were noted, one at low concentrations (0-1200 μM) and the other from 1200 to 5000 μM. The limit of detection (LOD), calculated as the (standard error/slope)*3.3, was 18.64 μM. The results of this study highlight the performance of the developed novel electrochemical sensor for the selective sensing of glucose.

Rapid integration of screen-printed electrodes into thermoplastic organ-on-a-chip devices for real-time monitoring of trans-endothelial electrical resistance.

Trans-endothelial electrical resistance (TEER) is one of the most widely used indicators to quantify thebarrier integrity of endothelial layers. Over the last decade, the integration of TEER sensors into organ-on-a-chip (OOC) platforms has gained increasing interest for its efficient and effective measurement of TEERin OOCs. To date, microfabricated electrodes or direct insertion of wires has been used to integrate TEERsensors into OOCs, with each method having advantages and disadvantages. In this study, we developed aTEER-SPE chip consisting of carbon-based screen-printed electrodes (SPEs) embedded in a poly(methylmethacrylate) (PMMA)-based multi-layered microfluidic device with a porous poly(ethylene terephthalate)membrane in-between. As proof of concept, we demonstrated the successful cultures of hCMEC/D3 cellsand the formation of confluent monolayers in the TEER-SPE chip and obtained TEER measurements for 4days. Additionally, the TEER-SPE chip could detect changes in the barrier integrity due to shear stress oran inflammatory cytokine (i.e., tumor necrosis factor-α). The novel approach enables a low-cost and facilefabrication of carbon-based SPEs on PMMA substrates and the subsequent assembly of PMMA layers forrapid prototyping. Being cost-effective and cleanroom-free, our method lowers the existing logistical andtechnical barriers presenting itself as another step forward to the broader adoption of OOCs with TEERmeasurement capability.

Smartphone-Based Electrochemical Biosensor for On-Site Nutritional Quality Assessment of Coffee Blends.

This work aimed to develop an easy-to-use smartphone-based electrochemical biosensor to quickly assess a coffee blend's total polyphenols (Phs) content at the industrial and individual levels. The device is based on a commercial carbon-based screen-printed electrode (SPE) modified with multi-walled carbon nanotubes (CNTs) and gold nanoparticles (GNPs). At the same time, the biological recognition element, Laccase from Trametes versicolor, TvLac, was immobilized on the sensor surface by using glutaraldehyde (GA) as a cross-linking agent. The platform was electrochemically characterized to ascertain the influence of the SPE surface modification on its performance. The working electrode (WE) surface morphology characterization was obtained by scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) imaging. All the measurements were carried out with a micro-potentiostat, the Sensit Smart by PalmSens, connected to a smartphone. The developed biosensor provided a sensitivity of 0.12 μA/μM, a linear response ranging from 5 to 70 μM, and a lower detection limit (LOD) of 2.99 μM. Afterward, the biosensor was tested for quantifying the total Phs content in coffee blends, evaluating the influence of both the variety and the roasting degree. The smartphone-based electrochemical biosensor's performance was validated through the Folin-Ciocâlteu standard method.

A carbon based-screen-printed electrode amplified with two-dimensional reduced graphene/Fe3O4 nanocomposite as electroanalytical sensor for monitoring 4-aminophenol in environmental fluids

The analysis water pollutants are so important strategy for investigation of water quality. On the other hand, 4-aminophenol is known as a hazardous and high-risk compound for humans, and its detection and measurement is very important for investigating the quality of surface and groundwater. In this study, graphene/Fe3O4 nanocomposite was synthesized by a simple chemical method and characterized by EDS and TEM methods and results showed Nano spherical shape of Fe3O4 nanoparticle with diameter about 20 nM decorated at surface of 2D reduce graphene nanosheet (2D-rG-Fe3O4). The 2D-rG-Fe3O4 was used as excellent catalyst at surface of carbon-based screen-printed electrode (CSPE) and used as electroanalytical sensor in monitoring and determination of 4-aminophenol in waste water sample. The results confirmed improving ∼4.0 times in oxidation signal and reducing 120 mV in oxidation potential of 4-aminophenol at surface of 2D-rG-Fe3O4/CSPE compare to CSPE, respectively. The electrochemical investigation showed pH dependence behavior with equal value of electron and proton for -aminophenol at surface of 2D-rG-Fe3O4/CSPE. Using square wave voltammetry method (SWV), the 2D-rG-Fe3O4/CSPE successfully monitored 4-aminophenol in the concentration range 1.0 nM–200 μM. Finally, 2D-rG-Fe3O4/CSPE monitored 4-aminophenol in the different environmental fluids such as urban waste water, industrial waste water and river samples with recovery range 97.2%–104.3% that confirm powerful ability of 2D-rG-Fe3O4/CSPE as analytical tool.

Sensitive Detection of Hydroxytyrosol in Extra Virgin Olive Oils with a Novel Biosensor Based on Single-Walled Carbon Nanotubes and Tyrosinase.

Hydroxytyrosol (HT) is an important marker for the authenticity and quality assessment of extra virgin olive oils (EVOO). The aim of the study was the qualitative and quantitative determination of hydroxytyrosol in commercial extra virgin olive oils of different origins and varieties using a newly developed biosensor based on a screen-printed electrode modified with single-layer carbon nanotubes and tyrosinase (SPE-SWCNT-Ty). The enzyme was immobilized on a carbon-based screen-printed electrode previously modified with single-layer carbon nanotubes (SPE-SWCNT-Ty) by the drop-and-dry method, followed by cross-linking with glutaraldehyde. The modified electrode surface was characterized by different methods, including electrochemical (cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS)) and spectrometric (Fourier transform infrared (FTIR) spectroscopy) methods. Cyclic voltammetry was used for the quantitative determination of HT, obtaining a detection limit of 3.49 × 10−8 M and a quantification limit of 1.0 × 10−7 M, with a wide linearity range (0.49–15.602 µM). The electrochemical performance of the SPE-SWCNT-Ty biosensor was compared with that of the modified SPE-SWCNT sensor, and the results showed increased selectivity and sensitivity of the biosensor due to the electrocatalytic activity of tyrosinase. The results obtained from the quantitative determination of HT showed that commercial EVOOs contain significant amounts of HT, proving the high quality of the finished products. The determination of the antiradical activity of HT was carried out spectrophotometrically using the free reagent galvinoxyl. The results showed that there is a very good correlation between the antiradical capacity of EVOOs, the voltammetric response and implicitly the increased concentration of HT. SPE-SWCNT-Ty has multiple advantages such as sensitivity, selectivity, feasibility and low cost and could be used in routine analysis for quality control of food products such as vegetable oils.

Glycerol oxidation at Pd nanocatalysts obtained through spontaneous metal deposition on carbon substrates

Spontaneous deposition of Pd is carried out on five different carbon-based screen-printed electrodes (SPEs) in the absence of solute reductant species in the Pd ions solution. Pd nanoparticles (NPs) with mean sizes ranging between 11.2 and 17.9 nm and homogeneous distribution are obtained on the carbon supports. The NPs mean size and amount of available metal are found to depend on the type of the carbon SPE, i.e. carbon (C110), mesoporous carbon (MC), carbon nanofibers (CNF), single- or multi-walled carbon nanotubes (SWCNT or CNT). Overlapping and agglomerating particles are found only in the SWCNT case whereas for all other electrodes the individual NPs are well isolated. Glycerol oxidation is studied at the five types of Pd nanocatalysts and data for the mass activity are obtained for glycerol and KOH concentrations used in fuel cells applications. The data for the mass activity correlate with the electroactive surface area (EASA) of the metallic particles for three of the electrodes (C110, MC and CNF) whereas Pd NPs supported by multi walled CNTs show a very high mass activity not to be associated with increased EASA alone. In separate experiments the applicability of the Pd-carbon-based SPEs is studied in view of electroanalytical detection of glycerol. A stable electroanalytical response is found for the MC, CNT and CNF SPEs. The concentration dependence of the glycerol oxidation peak current is modeled by a Langmuir type function that allows for detection of glycerol in the 0.2 to 15 mmol/l concentration range. The ease of preparation of the Pd nanocatalysts and the use of disposable SPEs present a good prospect for practical applications.

An ultra-sensitive electrochemical biosensor using the Spike protein for capturing antibodies against SARS-CoV-2 in point-of-care.

This work presents an innovative ultra-sensitive biosensor having the Spike protein on carbon-based screen-printed electrodes (SPEs), for monitoring in point-of-care antibodies against SARS-CoV-2, a very important tool for epidemiological monitoring of COVID-19 infection and establishing vaccination schemes. In an innovative and simple approach, a highly conductive support is combined with the direct adsorption of Spike protein to enable an extensive antibody capture. The high conductivity was ensured by using carboxylated carbon nanotubes on the carbon electrode, by means of a simple and quick approach, which also increased the surface area. These were then modified with EDC/NHS chemistry to produce an amine layer and undergo Spike protein adsorption, to generate a stable layer capable of capturing the antibodies against SARS-CoV-2 in serum with great sensitivity. Electrochemical impedance spectroscopy was used to evaluate the analytical performance of this biosensor in serum. It displayed a linear response between 1.0 ​pg/mL and 10 ​ng/mL, with a detection limit of ∼0.7 ​pg/mL. The analysis of human positive sera containing antibody in a wide range of concentrations yielded accurate data, correlating well with the reference method. It also offered the unique ability of discriminating antibody concentrations in sera below 2.3 ​μg/mL, the lowest value detected by the commercial method. In addition, a proof-of-concept study was performed by labelling anti-IgG antibodies with quantum dots to explore a new electrochemical readout based on the signal generated upon binding to the anti-S protein antibodies recognised on the surface of the biosensor. Overall, the alternative serologic assay presented is a promising tool for assessing protective immunity to SARS-CoV-2 and a potential guide for revaccination.

Label-Free Electrochemical Aptasensor for the Detection of the 3-O-C12-HSL Quorum-Sensing Molecule in Pseudomonas aeruginosa.

Pseudomonas aeruginosa, an opportunistic Gram-negative bacterium, is one of the main sources of infections in healthcare environments, making its detection very important. N-3-oxo-dodecanoyl L-homoserine lactone (3-O-C12-HSL) is a characteristic molecule of quorum sensing—a form of cell-to-cell communication between bacteria—in P. aeruginosa. Its detection can allow the determination of the bacterial population. In this study, the development of the first electrochemical aptasensor for the detection of 3-O-C12-HSL is reported. A carbon-based screen-printed electrode modified with gold nanoparticles proved to be the best platform for the aptasensor. Each step in the fabrication of the aptasensor (i.e., gold nanoparticles’ deposition, aptamer immobilization, incubation with the analyte) was optimized and characterized using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Different redox probes in solution were evaluated, the best results being obtained in the presence of [Fe(CN)6]4−/[Fe(CN)6]3−. The binding affinity of 106.7 nM for the immobilized thiol-terminated aptamer was determined using surface plasmon resonance. The quantification of 3-O-C12-HSL was performed by using the electrochemical signal of the redox probe before and after incubation with the analyte. The aptasensor exhibited a logarithmic range from 0.5 to 30 µM, with a limit of detection of 145 ng mL−1 (0.5 µM). The aptasensor was successfully applied for the analysis of real samples (e.g., spiked urine samples, spiked microbiological growth media, and microbiological cultures).

Disposable screen-printed carbon-based electrodes in amperometric detection for simultaneous determination of parabens in complex-matrix personal care products by HPLC

Parabens are chemicals widely used as preservatives in different types of industrial products. In recent years, the concern about the safety of these compounds has increased due to their endocrine disrupting activity. For this reason, their use is highly regulated and even some of them have already been banned. Thus, methods for the sensitive and selective detection of these compounds are required to control their presence in food, cosmetic, and pharmaceutical products. This paper presents an HPLC method with electrochemical detection using disposable screen-printed electrodes (SPE) for simultaneous determination of 6 different parabens in personal care products. Electrochemical behaviour of parabens was studied on SPE with different carbon-based materials as working electrode: carbon, ordered mesoporous carbon and graphene. From these studies, pH, detection potential, and the most adequate SPE were chosen. Due to the wide range of textures and viscosities (e.g., liquid, solid, and semi-solid) of personal care products, adequate sample pretreatments are required before chromatographic measurement. Here, a fast ultrasound-assisted extraction method was applied to simultaneously extract 6 parabens (methyl-, ethyl-, isopropyl-, propyl-, butyl-and benzyl-paraben) from different complex-matrix cosmetic products. Instrumental limits of detection between 20 and 115 μg L−1 were obtained applying +1.0 V (vs. Ag) as detection potential on carbon-based SPE. The total analysis time, including sample extraction and HPLC run, was shorter than 35 min. The proposed method is more versatile and faster than the current available methods and has been successfully applied to determine parabens in commercial samples such as shampoos, body creams, facial tonics, and toothpastes.

Nitrites Detection with Sensors Processed via Matrix-Assisted Pulsed Laser Evaporation

This work is focused on the application of a laser-based technique, i.e., matrix-assisted pulsed laser evaporation (MAPLE) for the development of electrochemical sensors aimed at the detection of nitrites in water. Commercial carbon-based screen-printed electrodes were modified by MAPLE via the application of a newly developed composite coating with different concentrations of carbon nanotubes (CNTs), chitosan, and iron (II) phthalocyanine (C32H16FeN8). The performance of the newly fabricated composite coatings was evaluated both by investigating the morphology and surface chemistry of the coating, and by determining the electro-catalytic oxidation properties of nitrite with bare and modified commercial carbon-based screen-printed electrode. It was found that the combined effect of CNTs with chitosan and C32H16FeN8 significantly improves the electrochemical response towards the oxidation of nitrite. In addition, the MAPLE modified screen-printed electrodes have a limit of detection of 0.12 µM, which make them extremely useful for the detection of nitrite traces.

An Electrochemical Impedance Spectroscopy-Based Aptasensor for the Determination of SARS-CoV-2-RBD Using a Carbon Nanofiber-Gold Nanocomposite Modified Screen-Printed Electrode.

Worldwide, human health is affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hence, the fabrication of the biosensors to diagnose SARS-CoV-2 is critical. In this paper, we report an electrochemical impedance spectroscopy (EIS)-based aptasensor for the determination of the SARS-CoV-2 receptor-binding domain (SARS-CoV-2-RBD). For this purpose, the carbon nanofibers (CNFs) were first decorated with gold nanoparticles (AuNPs). Then, the surface of the carbon-based screen-printed electrode (CSPE) was modified with the CNF–AuNP nanocomposite (CSPE/CNF–AuNP). After that, the thiol-terminal aptamer probe was immobilized on the surface of the CSPE/CNF–AuNP. The surface coverage of the aptamer was calculated to be 52.8 pmol·cm−2. The CSPE/CNF–AuNP/Aptamer was then used for the measurement of SARS-CoV-2-RBD by using the EIS method. The obtained results indicate that the signal had a linear–logarithmic relationship in the range of 0.01–64 nM with a limit of detection of 7.0 pM. The proposed aptasensor had a good selectivity to SARS-CoV-2-RBD in the presence of human serum albumin; human immunoglobulins G, A, and M, hemagglutinin, and neuraminidase. The analytical performance of the aptasensor was studied in human saliva samples. The present study indicates a practical application of the CSPE/CNF-AuNP/Aptamer for the determination of SARS-CoV-2-RBD in human saliva samples with high sensitivity and accuracy.

An innovative autonomous robotic system for on-site detection of heavy metal pollution plumes in surface water

Smart monitoring has been studied and developed in recent years to create faster, cheaper, and more user-friendly on-site methods. The present study describes an innovative technology for investigative monitoring of heavy metal pollution (Cu and Pb) in surface water. It is composed of an autonomous surface vehicle capable of semiautonomous driving and equipped with a microfluidic device for detection of heavy metals. Detection is based on the method of square wave anodic stripping voltammetry using carbon-based screen-printed electrodes (SPEs). The focus of this work was to validate the ability of the integrated system to perform on-site detection of heavy metal pollution plumes in river catchments. This scenario was simulated in laboratory experiments. The main performance characteristics of the system, which was evaluated based on ISO 15839 were measurement bias (Pb 75%, Cu 65%), reproducibility (in terms of relative standard deviation: Pb 11–18%, Cu 6–10%) and the limit of detection (4 µg/L for Pb and 7 µg/L for Cu). The lowest detectable change (LDC), which is an important performance characteristic for this application, was estimated to be 4–5 µg/L for Pb and 6–7 µg/L for Cu. The life span of an SPE averaged 39 measurements per day, which is considered sufficient for intended monitoring campaigns. This work demonstrated the suitability of the integrated system for on-site detection of Pb and Cu emissions from large and medium urban areas discharging into small water bodies.

Gold-based nanostructured platforms for oxytetracycline detection from milk by a “signal-on” aptasensing approach

Several gold platforms of different morphologies were investigated in the elaboration of a new aptasensor for oxytetracycline. Au-nanostructures were electrochemically synthesized from solutions of different concentrations of HAuCl4 in different media by chronoamperometry, multipulse amperometry, and chronopotentiometry, respectively at carbon-based screen-printed electrodes (C-SPE). The nano-/micro-scale morphologies of the patterned surfaces and elemental composition were examined by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy, respectively. The electrochemical properties of the obtained gold nanostructured platforms (AuNSs|C-SPE) were investigated to achieve optimal aptamer coverage. The results showed that the aptasensor developed using the platform with thistle-like AuNSs exhibited the highest conductivity in terms of ferrocene signal and the largest effective area. Under optimal conditions, a linear range from 5.0 × 10−8 M to 1.2 × 10−6 M, with a limit of detection (LOD) of 8.7 × 10−9 M OXT were obtained, which is about 20 times lower than the EU regulations for OXT residues in milk. The electrochemical aptasensor was able to discriminate other antibacterial agents, such as amoxicillin, ampicillin, gentamicin, tetracycline, and vancomycin and was successfully applied in milk samples. This “signal-on” aptasensing approach provides a simple and cost-effective disposable sensor that could be easily applied for the on-site determination of antibiotics.

Carbon screen-printed electrodes for substrate-assisted electroless deposition of palladium

Five types of carbon-based screen-printed electrodes (SPE) – carbon (C110), mesoporous carbon (MC), single walled carbon nanotubes (SWCNT)-, carbon nanotubes (CNT)-, and carbon nanofibers (CNF)-modified electrodes – are characterized with respect to surface roughness, true surface area (TSA), electrochemical activity and electrochemical impedance (EIS) behavior and further used for electroless deposition of Pd. Structural characterization was performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Investigation of the surfaces with AFM revealed an increasing root mean square (RMS) roughness in the order C110, SWCNT, CNT, CNF, and MC. EIS studies demonstrate significant difference in the resistance of the SPEs with largest value found for the carbon electrode (C110), followed by the carbon nanofiber (CNF)-modified electrode. MC, CNT- and SWCNT-modified electrodes exhibit close, significantly lower resistance values. The capacitance of the carbon-based SPEs is found to be rather high for all electrodes even if accounting for the TSA which has been determined with AFM. This implies a significant effect of nanoroughness and/or of a large internal porous structure especially for CNF and MC SPEs. Pd electroless deposition occurs at all carbon-based SPEs after reductive pre-treatment in supporting electrolytes (0.5 mol dm−3 H2SO4 or 0.1 mol dm−3 LiClO4) without using a solute chemical reductant in the metal plating solution. The amount and characteristics of the deposited Pd is estimated by anodic stripping voltammetry, EDX analysis, and SEM. It is established that the type and amount of Pd deposit depends on the structure of the carbon-based electrodes with nanostructured carbon coatings (consisting of CNT, SWCNT, or CNF) providing higher amounts of deposited Pd (in the range of 4.4 to 5.8 µg cm−2) and smaller size of the obtained metal particles.

On the performance of carbon-based screen-printed electrodes for (in)organic hydroperoxides sensing in rainwater

Hydroperoxides play important roles in atmospheric chemical processes since they act as strong oxidants. This paper details with the modification, characterization and performance of different carbon-based screen-printed electrodes to develop a sensor that allows to analyze organic and inorganic hydroperoxides in atmospheric samples. Commercial electrodes made up of graphite, graphene, carbon nanotubes and graphene oxide were electrochemically activated and subsequently modified by layer-by-layer method with a conducting polymer of azure-A and electrodeposited platinum nanoparticles. Characterization of modified electrodes was performed by FE-SEM, XPS, Raman spectroscopy, cyclic voltammetry, and impedance spectroscopy. Even though all modified carbonaceous substrates enabled the development of competitive electrochemical sensors for (in)organic hydroperoxides detection, carbon nanotubes underlying substrate exhibited the best performances in terms of sensitivity, stability, limit of detection and linear range. This amperometric sensor displayed linear responses to hydroperoxides over 0.081–450 μM with detection limits in the range of 24–558 nM and sensitivity values among 0.0628±1.6E-4 and 0.0112±0.71E-4 μA/μM for the different hydroperoxides herein studied. The developed electrochemical sensor was successfully applied to the analysis of (in)organic hydroperoxides in rainwater samples. Measurements in rainwater were performed in a city located in the East of Spain and collected at two different sites (downtown and suburban area) on two different dates (July and November 2020). The presented results demonstrated high sensitivity and selectivity for the detection of hydroperoxides among a plethora of substances naturally present in rainwater.