A lab-made screen-printed electrode as a platform to study the effect of the size and functionalization of carbon nanotubes on the voltammetric determination of caffeic acid

Smart and emerging point of care electrochemical sensors based on nanomaterials for SARS-CoV-2 virus detection: Towards designing a future rapid diagnostic tool

In the recent years, researchers from all over the world have become interested in the fabrication of advanced and innovative electrochemical and/or biosensors for respiratory virus detection with the use of nanotechnology. These fabricated sensors demonstrated a number of benefits, including precision, affordability, accessibility, and miniaturization which makes them a promising test method for point-of-care (PoC) screening for SARS-CoV-2 viral infection. In order to comprehend the principles of electrochemical sensing and the role of various types of sensing interfaces, we comprehensively explored the underlying principles of electroanalytical methods and terminologies related to it in this review. In addition, it is addressed how to fabricate electrochemical sensing devices incorporating nanomaterials as graphene, metal/metal oxides, metal organic frameworks (MOFs), MXenes, quantum dots, and polymers. We took an effort to carefully compile current developments, advantages, drawbacks, possible solutions in nanomaterials based electrochemical sensors.

Electrochemical Paper-Based Nanobiosensor for Rapid and Sensitive Detection of Monkeypox Virus

Monkeypox virus (MPXV) infection was classified as a public health emergency of international concern by the World Health Organization (WHO) in 2022, being transmitted between humans by large respiratory droplets, in contact with skin lesions, fomites, and sexually. Currently, there are no available accessible and simple-to-use diagnostic tests that accurately detect MPXV antigens for decentralized and frequent testing. Here, we report an electrochemical biosensor to detect MPXV antigens in saliva and plasma samples within 15 min using accessible materials. The electrochemical system was manufactured onto a paper substrate engraved by a CO2 laser machine, modified with gold nanostructures (AuNS) and a monoclonal antibody, enabling sensitive detection of A29 viral protein. The diagnostic test is based on the use of electrochemical impedance spectroscopy (EIS) and can be run by a miniaturized potentiostat connected to a smartphone. The impedimetric biosensing method presented excellent analytical parameters, enabling the detection of A29 glycoprotein in the concentration ranging from 1 × 10-14 to 1 × 10-7 g mL-1, with a limit of detection (LOD) of 3.0 × 10-16 g mL-1. Furthermore, it enabled the detection of MPXV antigens in the concentration ranging from 1 × 10-1 to 1 × 104 PFU mL-1, with an LOD of 7.8 × 10-3 PFU mL-1. Importantly, no cross-reactivity was observed when our device was tested in the presence of other poxvirus and nonpoxvirus strains, indicating the adequate selectivity of our nanobiosensor for MPXV detection. Collectively, the nanobiosensor presents high greenness metrics associated with the use of a reproducible and large-scale fabrication method, an accessible and sustainable paper substrate, and a low volume of sample (2.5 μL), which could facilitate frequent testing of MPXV at point-of-care (POC).

Sulfanilamide Electrochemical Sensor Using Phenolic Substrates and CO2 Laser Pyrolysis

The concentration of environmental pollutants needs to be monitored constantly by reliable analytical methods since they pose a public health risk. Developing simple and affordable sensors for such pollutants can allow for large-scale monitoring economically. Here, we develop a simple electrochemical sensor for sulfanilamide (SFD) quantification using a phenolic resin substrate and a CO2 laser to pyrolyze the sensor geometry over the substrate. The sensors are modified with carbon nanotubes via a simple drop-casting procedure. The carbon nanotube loading effect the electrochemical performance toward a redox probe and analytical performance for SFD detection is investigated, showing no net benefit beyond 1 mg L-1 of carbon nanotubes. The effects of the modification on the SFD oxidation are shown to be more than just an electrode area effect and possibly attributed to the fast electron transfer kinetics of the carbon nanotubes. SFD detection is performed at small solution volumes under static (800 μL) and hydrodynamic conditions (3 mL) in a fully integrated, miniaturized batch-injection analyses cell. Both methods have a similar linear range from 10.0 to 115.0 μmol L-1 and high selectivity for SFD determination. Both systems are used to quantify SFD in real samples as a proof of concept, showcasing the proposed device's applicability as a sensor for environmental and public health monitoring of SFD.

Paper-based analytical devices for point-of-need applications

Paper-based analytical devices (PADs) are powerful platforms for point-of-need testing since they are inexpensive devices fabricated in different shapes and miniaturized sizes, ensuring better portability. Additionally, the readout and detection systems can be accomplished with portable devices, allying with the features of both systems. These devices have been introduced as promising analytical platforms to meet critical demands involving rapid, reliable, and simple testing. They have been applied to monitor species related to environmental, health, and food issues. Herein, an outline of chronological events involving PADs is first reported. This work also introduces insights into fundamental parameters to engineer new analytical platforms, including the paper type and device operation. The discussions involve the main analytical techniques used as detection systems, such as colorimetry, fluorescence, and electrochemistry. It also showed recent advances involving PADs, especially combining optical and electrochemical detection into a single device. Dual/combined detection systems can overcome individual barriers of the analytical techniques, making possible simultaneous determinations, or enhancing the devices' sensitivity and/or selectivity. In addition, this review reports on distance-based detection, which is also considered a trend in analytical chemistry. Distance-based detection offers instrument-free analyses and avoids user interpretation errors, which are outstanding features for analyses at the point of need, especially for resource-limited regions. Finally, this review provides a critical overview of the practical specifications of the recent analytical platforms involving PADs, demonstrating their challenges. Therefore, this work can be a highly useful reference for new research and innovation.

Rapid pretreatment-free evaluation of antioxidant capacity in extra virgin olive oil using a laser-nanodecorated electrochemical lab-on-strip

An electroanalytical lab-on-a-strip device for the direct extra-virgin olive oil (EVOO) antioxidant capacity evaluation is proposed. The lab-made device is composed of a CO₂ laser nanodecorated sensor combined with a cutter-plotter molded paper-strip designed for EVOOs sampling and extraction. Satisfactory performance towards the most representative o-diphenols of EVOOs i.e., hydroxytyrosol (HY) and oleuropein (OL) were achieved; good sensitivity (LOD_HY = 2 µM; LOD_OL = 0.6 µM), extended linear ranges (HY: 10-250 µM; OL: 2.5-50 µM) and outstanding reproducibility (RSD < 5%, n = 3) were obtained in rectified oil. The device was challenged for the extraction-free analysis of 15 different EVOO samples, with satisfactory recoveries (90-94%; RSD < 5%, n = 3) and correlation with classical photometric assays (r ≥ 0.91). The proposed device includes all analysis steps, needs 4 µL of sample, and returns reliable results in 2 min, resulting portable and usable with a smartphone.

Carbon Nanomaterials-Based Screen-Printed Electrodes for Sensing Applications

Electrochemical sensors consisting of screen-printed electrodes (SPEs) are recurrent devices in the recent literature for applications in different fields of interest and contribute to the expanding electroanalytical chemistry field. This is due to inherent characteristics that can be better (or only) achieved with the use of SPEs, including miniaturization, cost reduction, lower sample consumption, compatibility with portable equipment, and disposability. SPEs are also quite versatile; they can be manufactured using different formulations of conductive inks and substrates, and are of varied designs. Naturally, the analytical performance of SPEs is directly affected by the quality of the material used for printing and modifying the electrodes. In this sense, the most varied carbon nanomaterials have been explored for the preparation and modification of SPEs, providing devices with an enhanced electrochemical response and greater sensitivity, in addition to functionalized surfaces that can immobilize biological agents for the manufacture of biosensors. Considering the relevance and timeliness of the topic, this review aimed to provide an overview of the current scenario of the use of carbonaceous nanomaterials in the context of making electrochemical SPE sensors, from which different approaches will be presented, exploring materials traditionally investigated in electrochemistry, such as graphene, carbon nanotubes, carbon black, and those more recently investigated for this (carbon quantum dots, graphitic carbon nitride, and biochar). Perspectives on the use and expansion of these devices are also considered.

A lab-made screen-printed sensing strip for sensitive and selective electrochemical detection of butylated hydroxyanisole

This study describes the fabrication of a lab-made screen-printed electrode (LabSPE) and its sensing ability for the detection of butylated hydroxyanisole (BHA) which is a synthetic antioxidant utilized widely in food industries. The lab-made screen-printed electrodes were printed on a polycarbonate substrate stepwise via a screen-printing technique using various inks suitable for electrode templates and then modified for the detection of BHA. As for the design of the sensor, firstly, graphitic carbon nitride (g-C₃N₄) was synthesized electrochemically through the one-pot synthesis method. After the synthesis of Fe₃O₄ nanoparticles (Fe₃O₄ NPs), the surface of SPE was modified with the dual composite consisting of g-C₃N₄ and Fe₃O₄ NPs. Lastly, platinum nanoparticles (Pt NPs) were deposited electrochemically on the modified electrode in 0.5 M HCl solution containing 2 mM H₂PtCl₆ at a constant potential of 0.25 V for 45 s. After optimization of varied parameters such as pH of the electrolyte solution, deposition time, and deposition potential, the current responses of the sensor (Pt/g-C₃N₄-Fe₃O₄/LabSPE) toward BHA displayed linearity in the wide concentration range of 0.25 μM to 90 μM with a low detection limit of 0.053 μM. The selectivity of Pt/g-C₃N₄-Fe₃O₄/SPE was tested successfully in the presence of other antioxidants (BHT, TBHQ, GA, and PG). Moreover, the applicability of the proposed sensor for practical tests was verified by the detection of BHA in commercial samples.

A pencil graphite-based disposable device for electrochemical monitoring of sulfanilamide in honey and water samples

The present paper reports a simple, fast, and inexpensive process of manufacturing a disposable pencil graphite electrode (PGE) from widely available materials, which showed a reproducibility of at least 7.5%. The electrode was compared to the commercial glassy carbon electrode (GCE) and showed superior electroanalytical performance for sulfanilamide (SFA) with approximately 3.9-fold higher current density. Additionally, a displacement of the oxidation peak from approximately 80 mV to more cathodic regions was observed. Therefore, a method based on square wave voltammetry (SWV) was developed for the determination of the antimicrobial SFA in honey and tap water samples using the proposed sensor. The optimized method presented good detectability (LOD = 2.37 μmol L^-1), with excellent precision and accuracy (relative standard deviation < 4.2%) and percent recovery from spiked samples ranging from 92 to 97%. In addition, the sensor did not suffer significant interference from sample matrix components and other commonly evaluated antimicrobials, which demonstrates the potential of these electrodes for implementation in routine analysis and quality control.

Development of New Simple Compositions of Silver Inks for the Preparation of Pseudo-Reference Electrodes

Silver materials are known to present excellent properties, such as high electrical and thermal conductivity as well as chemical stability. Silver-based inks have drawn a lot of attention for being compatible with various substrates, which can be used in the production uniform and stable pseudo-reference electrodes with low curing temperatures. Furthermore, the interest in the use of disposable electrodes has been increasing due to the low cost and the possibility of their use in point-of-care and point-of-need situations. Thus, in this work, two new inks were developed using Ag as conductive material and colorless polymers (nail polish (NP) and shellac (SL)), and applied to different substrates (screen-printed electrodes, acetate sheets, and 3D-printed electrodes) to verify the performance of the proposed inks. Measurements attained with open circuit potential (OCP) attested to the stability of the potential of the pseudo-reference proposed for 1 h. Analytical curves for β-estradiol were also obtained using the devices prepared with the proposed inks as pseudo-references electrodes, which presented satisfactory results concerning the potential stability (RSD < 2.6%). These inks are simple to prepare and present great alternatives for the development of pseudo-reference electrodes useful in the construction of disposable electrochemical systems.

Nanomaterials-based electrochemical sensors for the detection of natural antioxidants in food and biological samples: research progress

Antioxidants are healthy substances that are beneficial to the human body and exist mainly in natural and synthetic forms. Among many kinds of antioxidants, the natural antioxidants have great applications in many fields such as food chemistry, medical care, and clinical application. In recent years, many efforts have been made for the determination of natural antioxidants. Nano-electrochemical sensors combining electrochemistry and nanotechnology have been widely used in the determination of natural antioxidants due to their unique advantages. Therefore, a large number of nanomaterials such as metal oxide, carbon materials, and conducting polymer have attracted much attention in the field of electrochemical sensors due to their good catalytic effect and stable performance. This review mainly introduces the construction of electrochemical sensors based on different nanomaterials, such as metallic nanomaterials, metal oxide nanomaterials, carbon nanomaterials, metal-organic frameworks, polymer nanomaterials, and other nanocomposites, and their application to the detection of natural antioxidants, including ascorbic acid, phenolic acids, flavonoid, tryptophan, citric acid, and other natural antioxidants. In the end, the limitations of the existing nano-sensing technology, the latest development trend, and the application prospect for various natural antioxidant substances are summarized and analyzed. We expect that this review will be helpful to researchers engaged in electrochemical sensors.

Simultaneous Determination of Caffeic Acid and Ferulic Acid Using a Carbon Nanofiber-Based Screen-Printed Sensor

This work aims to achieve the simultaneous qualitative and quantitative determination of two hydroxycinnamic acids (ferulic acid and caffeic acid) from standard solutions and from a phyto-homeopathic product using a carbon nanofiber-based screen-printed sensor (CNF/SPE). The two compounds are mentioned in the manufacturer's specifications but without indicating their concentrations. The stability and reproducibility of the CNF/SPE were found to be effective and the sensitivity was high for both caffeic acid-CA (limit of detection 2.39 × 10^-7 M) and ferrulic acid-FA (limit of detection 2.33 × 10^-7 M). The antioxidant capacity of the compounds in the analyzed product was also determined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. The electrochemical method was efficient and less expensive than other analytical methods; therefore, its use can be extended for the detection of these phenolic compounds in various dietary supplements or pharmaceutical products.

Electrochemical Sensors and Biosensors for the Analysis of Tea Components: A Bibliometric Review

Tea is a popular beverage all around the world. Tea composition, quality monitoring, and tea identification have all been the subject of extensive research due to concerns about the nutritional value and safety of tea intake. In the last 2 decades, research into tea employing electrochemical biosensing technologies has received a lot of interest. Despite the fact that electrochemical biosensing is not yet the most widely utilized approach for tea analysis, it has emerged as a promising technology due to its high sensitivity, speed, and low cost. Through bibliometric analysis, we give a systematic survey of the literature on electrochemical analysis of tea from 1994 to 2021 in this study. Electrochemical analysis in the study of tea can be split into three distinct stages, according to the bibliometric analysis. After chromatographic separation of materials, electrochemical techniques were initially used only as a detection tool. Many key components of tea, including as tea polyphenols, gallic acid, caffeic acid, and others, have electrochemical activity, and their electrochemical behavior is being investigated. High-performance electrochemical sensors have steadily become a hot research issue as materials science, particularly nanomaterials, and has progressed. This review not only highlights these processes, but also analyzes and contrasts the relevant literature. This evaluation also provides future views in this area based on the bibliometric findings.

Applications of electrochemical biosensors based on functional antibody-modified screen-printed electrodes: a review

The detection of biomolecular analytes is of great importance in clinical, environmental, and argo-food areas, among which the electrochemical methodology is attracting much attention. In particular, screen-printed electrode (SPE)-based sensing applications have exhibited potential possibility for on-site detection, especially for fast clinical biomarker detection, since they provide a miniaturized but robust and portable electrode detection system. In this context, we focused on the modification of SPE with functional antibodies to improve the electrochemical detection performance in versatile sensing applications, particularly for COVID-19 detection. These antibodies were immobilized onto the electrode surface via various methodologies, through which the powerful potential from the modification of SPE was revealed. Finally, more novel and excellent works on the biomolecular modification of SPE and the prospects of this technology from its state-of-art status to commercialization are previewed and future perspectives in this field are mentioned.

A novel miniaturized electroanalytical device integrated with gas extraction for the voltammetric determination of sulfite in beverages

Voltammetry and amperometry are inexpensive and high-performance analytical techniques. However, their lack of selectivity limits their use in complex matrices such as biological, environmental, and food samples. Therefore, voltammetric and amperometric analyses of these samples usually require time-consuming and laborious sample pretreatments. In this study, we present a simple and cost-effective approach to fabricate a miniaturized electrochemical cell that can be easily coupled to a head space-like gas extraction procedure in such a way the sample pretreatment and voltammetric detection are performed in a single step. As a proof of concept, we have used the proposed system to quantify sulfite in beverage samples after its conversion to SO_2(g). Despite the simplicity and low cost of the proposed system, it provided good analytical performance and a limit of detection of 4.0 μmol L^-1 was achieved after only 10 min of extraction. The proposed system is quite versatile since it can be applied to quantify any volatile electroactive species. Also, the proposed system provides a unique way to assess real-time extraction curves, which are essential to study and optimize new gas extraction procedures. Therefore, the approach described in this study could contribute to both applied and fundamental Analytical Chemistry.

Fabrication of paper-based analytical devices using a PLA 3D-printed stencil for electrochemical determination of chloroquine and escitalopram

In recent years, the use of prescribed and non-prescribed drugs has increased. Therefore, advances in new technologies and sensors for detecting molecules in natural environments are required. In this work, a 3D-printed polylactic acid stencil is used to fabricate paper-based analytical devices (ePADs). Herein, we report the use of carbon-based lab-manufactured conductive ink for the fabrication of sensors towards the detection of chloroquine and escitalopram. For each batch, eight ePADs were successfully fabricated. Firstly, the fabricated sensors were evaluated morphologically by scanning electron microscopy and electrochemically by cyclic voltammetry and electrochemical impedance spectroscopy experiments. The sensors displayed a well-defined voltammetric profile in the presence of the redox couple, when compared to a commercial carbon screen-printed electrode. Differential pulse voltammetry conducted the detection of chloroquine and escitalopram with detection limits of 4.0 and 0.5 µmol L⁻¹, respectively. The ePADs fabricated using the 3D stencil are here presented as alternatives for the fabrication of electrochemical analytical devices.

Disposable and low-cost electrochemical sensor based on the colorless nail polish and graphite composite material for tartrazine detection

A new method to manufacture electrochemical devices based on the graphite and colorless nail polish (N-grap) film was developed for tartrazine (Tz) detection. Scanning Electron Microscopy (SEM) demonstrates that the composite material presents a high porous carbon structure. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were employed to electrochemically characterize the electrode material, which corroborates the porous structure of the N-graph due to the enhanced electroactive area (5.4-fold increase) and presented a heterogeneous electron transfer rate constant (k0) of 5.82 × 10-3 cm s-1 for potassium ferricyanide. The electrochemical determination of the Tz was carried out using square-wave voltammetry (SWV), under the optimized experimental conditions, which showed high sensitivity (0.793 A L mol-1) and a lower limit of detection (LOD) of 2.10 × 10-8 mol L-1 with a linear concentration ranging from 2.0 to 50.0 μmol L-1. The developed sensor was applied for the analysis of Tz in sports drink samples and the result obtained by N-grap device was statistically compared with a spectrophotometric method demonstrating good accordance and the accuracy of the proposed method. Based on these results, we believe that this new fabrication method to produce disposable and low-cost electrochemical devices can be an alternative method for in-field analysis of dye in commercial sport drink samples and other relevant applications.

Electropolymerization of poly(methylene blue) on flower-like nickel-based MOFs used for ratiometric electrochemical sensing of total polyphenolic content in chrysanthemum tea

A ratiometric electrochemical sensor for caffeic acid (CAE) detection was constructed using a glassy carbon electrode modified with poly(methylene blue) and flower-like nickel-based metal organic frameworks (PMB@Ni-TPA/GCE). The electrochemical behavior of CAE was investigated at the PMB@Ni-TPA/GCE, and was found to follow a two-electron, two-proton electrooxidation process. PMB was used as the internal reference probe, and Ni-TPA can enhance the electrochemical signals of both CAE and PMB. As the CAE concentration increases, the oxidation peak current of CAE is enhanced but that of PMB keeps almost unchanged. The oxidation peak current ratio between CAE and PMB recorded by differential pulse voltammetry changes linearly with CAE concentration over the range of 0.25-15.0 μM, with a detection limit of 0.2 μM. The proposed sensor was successfully employed to evaluate the total polyphenolic content as CAE equivalent in chrysanthemum tea, and the results were comparable with those given by the reference Folin-Ciocalteu spectrophotometry.

Voltamperometric Sensors and Biosensors Based on Carbon Nanomaterials Used for Detecting Caffeic Acid-A Review

Caffeic acid is one of the most important hydroxycinnamic acids found in various foods and plant products. It has multiple beneficial effects in the human body such as antioxidant, antibacterial, anti-inflammatory, and antineoplastic. Since overdoses of caffeic acid may have negative effects, the quality and quantity of this acid in foods, pharmaceuticals, food supplements, etc., needs to be accurately determined. The present paper analyzes the most representative scientific papers published mostly in the last 10 years which describe the development and characterization of voltamperometric sensors or biosensors based on carbon nanomaterials and/or enzyme commonly used for detecting caffeic acid and a series of methods which may improve the performance characteristics of such sensors.

Printing-Based Assay and Therapy of Antioxidants

Antioxidants are essential in regulating various physiological functions and oxidative deterioration. Over the past decades, many researchers have paid attention to antioxidants and studied the screening of antioxidants from natural products and their utilization for treatments in diverse pathological conditions. Nowadays, as printing technology progresses, its influence in the field of biomedicine is growing significantly. The printing technology has many advantages. Especially, the capability of designing sophisticated platforms is useful to detect antioxidants in various samples. The high flexibility of 3D printing technology is advantageous to create geometries for customized patient treatment. Recently, there has been increasing use of antioxidant materials for this purpose. This review provides a comprehensive overview of recent advances in printing technology-based assays to detect antioxidants and 3D printing-based antioxidant therapy in the field of tissue engineering. This review is divided into two sections. The first section highlights colorimetric assays using the inkjet-printing methods and electrochemical assays using screen-printing techniques for the determination of antioxidants. Alternative screen-printing techniques, such as xurography, roller-pen writing, stamp contact printing, and laser-scribing, are described. The second section summarizes the recent literature that reports antioxidant-based therapy using 3D printing in skin therapeutics, tissue mimetic 3D cultures, and bone tissue engineering.