Low-cost screen-printed electrodes based on electrochemically reduced graphene oxide-carbon black nanocomposites for dopamine, epinephrine and paracetamol detection

Portable electrochemical sensor for adrenaline detection using CoNi-MOF-based CS-PAM hydrogel

The development of a portable smartphone-based electrochemical sensor for analyzing adrenaline levels in real samples can make a great contribution to the research community worldwide. In order to achieve this goal, the key challenge is to build sensing interfaces with excellent electrocatalytic properties. In this work, microspherical bimetallic metal-organic frameworks (CoNi-MOF) consisting of nanoclusters were first synthesized using a hydrothermal method. On this basis, the catalytic activity of pure chitosan-polyacrylamide hydrogel (CS-PAM) was modulated by adding different amounts of CoNi-MOF during the in-situ synthesis of CS-PAM. Finally, a portable electrochemical detection system based on CS-PAM was established for the detection of adrenaline. A series of resulting composite hydrogels with a large specific surface area, abundant active sites, and unique network structure facilitate the enrichment and catalysis of adrenaline molecules. Under optimal conditions, the analytical platform constructed by using CoNi-MOF-based CS-PAM has the advantages of a wide detection range (0.5-10 and 10-2500 μM), a low detection limit (0.167 μM), and high sensitivity (0.182 and 0.133 μA·μM·cm-2). In addition, the sensor maintains selective detection of the target in the presence of many different types of interferences, and the current response is not significantly reduced even after 60 cycles of testing. We strongly believe that the designed smart portable sensing can realize the accurate determination of adrenaline in complex systems, and this study can provide new ideas for the research of MOFs-based hydrogels in electrochemical analysis.

Ultrafast Laser Processing of 2D Materials: Novel Routes to Advanced Devices

Ultrafast laser processing has emerged as a versatile technique for modifying materials and introducing novel functionalities. Over the past decade, this method has demonstrated remarkable advantages in the manipulation of 2D layered materials, including synthesis, structuring, functionalization, and local patterning. Unlike continuous-wave and long-pulsed optical methods, ultrafast lasers offer a solution for thermal heating issues. Nonlinear interactions between ultrafast laser pulses and the atomic lattice of 2D materials substantially influence their chemical and physical properties. This paper highlights the transformative role of ultrafast laser pulses in maskless green technology, enabling subtractive, and additive processes that unveil ways for advanced devices. Utilizing the synergetic effect between the energy states within the atomic layers and ultrafast laser irradiation, it is feasible to achieve unprecedented resolutions down to several nanometers. Recent advancements are discussed in functionalization, doping, atomic reconstruction, phase transformation, and 2D and 3D micro- and nanopatterning. A forward-looking perspective on a wide array of applications of 2D materials, along with device fabrication featuring novel physical and chemical properties through direct ultrafast laser writing, is also provided.

An electrochemical immunosensor based on a carboxylated multiwalled carbon nanotube-silver nanoparticle-chitosan functional layer for the detection of fipronil

Fipronil (FP) is a very effective phenylpyrazole insecticide and is now widely used in agriculture. At the same time, the water and soil in the environment are polluted by FP. For the rapid detection of FP toxicants in food and the environment, we have designed an entirely novel electrochemical immunosensor that employs the combined functionalities of a cMWCNTs-AgNPs-CS-FAb-BSA layer to modify an SPCE by the freeze-drying technique. The high porosity of chitosan (CS) coupled with an excellent electron transfer enabled by the cMWCNTs and AgNPs increased the surface area for anti-fipronil (FAb) antibody immobilization and enhanced the current signal of the immunosensor. Cyclic voltammetry (CV) was applied for the quantitative determination of FP under optimized conditions (0.1 M PBS, pH 7.5, 35 °C incubation temperature, and 40 min incubation duration). The modified electrochemical immunosensor displayed excellent analytical performance, including a wide linear concentration range from 0.1 to 1000 ng mL-1 with a very low limit of detection of 0.021 ng mL-1 and good reproducibility (RSD = 2.58%, n = 6), stability (80.4% sensitivity after 5 days), and selectivity. Not only could the modified electrochemical immunosensor be applied in the FP residue analysis of agricultural products, but the present immobilization strategy can also potentially be applied to different biomolecules.

Improving the performance and versatility of microfluidic thread electroanalytical devices by automated injection with electronic pipettes: a new and powerful 3D-printed analytical platform

Microfluidic cotton thread-based electroanalytical devices (μTEDs) are analytical systems with attractive features such as spontaneous passive flow, low cost, minimal waste production, and good sensitivity. Currently, sample injection in µTEDs is performed by hand using manual micropipettes, which have drawbacks such as inconstant speed and position, dependence of skilled analysts, and need of physical effort of operator during prolonged times, leading to poor reproducibility and risk of strain injury. As an alternative to these inconveniences, we propose, for the first time, the use of electronic micropipettes to carry out automated injections in µTEDs. This new approach avoids all disadvantages of manual injections, while also improving the performance, experience, and versatility of µTEDs. The platform developed here is composed by three 3D-printed electrodes (detector) attached to a 3D-printed platform containing an adjustable holder that keeps the electronic pipette in the same x/y/z position. As a proof-of-concept, both injection modes (manual and electronic) were compared using three model analytes (nitrite, paracetamol, and 5-hydroxytryptophan) on µTED with amperometric detection. As result, improved analytical performance (limits of detection between 2.5- and 5-fold lower) was obtained when using electronic injections, as well as better repeatability/reproducibility and higher analytical frequencies. In addition, the determination of paracetamol in urine samples suggested better precision and accuracy for automated injection. Thus, electronic injection is a great advance and changes the state-of-art of µTEDs, mainly considering the use of more modern and versatile electronic pipettes (wider range of pre-programmed modes), which can lead to the development of even more automated systems.

Laser-induced porous graphene electrodes from polyketimine membranes for paracetamol sensing

The development of cost-effective materials for fabricating electrodes is crucial for drug, pharmaceutical and environmental applications. This paper presents the synthesis and characterization of a novel polyketimine (PKI) membrane obtained by condensing partially of different weight percentages of oxidized polyvinyl alcohol and aminated polyether sulfone. Using the PKI membrane as a scaffold, we introduced laser-induced graphene electrodes (LIGEs) for the efficient electrochemical sensing of paracetamol (PCM), which serves as a model drug. Electrochemical measurements were conducted to assess the physico-chemical properties, including laser-induced porous graphene features, such as the heterogeneous electron transfer (HET) rate and electrochemically active surface area (ECSA). The obtained results demonstrate that the LIGEs exhibit excellent performance in PCM sensing, showing a linear detection range of 50-600 µM with a detection limit (LOD) as low as 14.3 µM and a good selectivity toward uric acid. Furthermore, the functionalization of the electrode surface with AuNPs improved the electrode physico-chemical properties (HET and ECSA) and lowered the detection limit down to 1.1 µM. Consequently, these affordable electrodes hold great potential for analysing other drugs and detecting heavy metal cations in various applications.

Tunable graphene oxide for the low-fouling electrochemical sensing of uric acid in human serum

Numerous studies have been reported to improve the selectivity of uric acid (UA) by eliminating the interference from other electroactive species that coexist in biological fluids. However, two main challenges associated with the nonenzymatic electrochemical detection of UA need to be overcome to achieve practical applications in biological samples. Those are the chemical fouling of electrodes caused by the oxidation product of UA and biofouling due to the non-specific absorption of biological macromolecules. It was found that the residual oxo-functional groups and defects on graphene played a crucial part in both electrocatalysis and anti-biofouling. Here, graphene oxide (GO) was tuned by electro-oxidation and electro-reduction and was investigated in antifouling and electrocatalytic performances for the electrochemical sensing of UA by using pristine GO, BSA bound GO, electro-reduction-treated GO and electro-oxidation-treated GO. The electro-oxidation-treated GO was explored in electrochemical sensing for the first time and exhibited the highest sensitivity and low fouling properties. Holey GO might be formed on the electrode surface by the electrochemical oxidation method in a mild and green solution without the use of an acid. The different electrode interfaces as well as the interaction with BSA were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, contact angle measurements, scanning electron microscopy, electrochemistry, and electrochemical impedance spectroscopy.

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.

Cell viability and drug evaluation biosensing system based on disposable AuNPs/MWCNT nanocomposite modified screen-printed electrode for exocytosis dopamine detection

Cell viability, as an important index to evaluate drug effects, usually was measured by tetrazolium colorimetric assay, playing a key role in drug development and drug screening. Tedious operating procedures, unsatisfactory sensitivity and abominable environments perplex researchers to acquire more detailed in vivo-relevant biological information. Herein, a simple and low-cost cell viability and drug evaluation biosensing system-based on multiwalled carbon nanotubes, gold nanoparticles and Nafion modified screen-printed electrode (SPE) biosensor was constructed for detection of dopamine (DA) released from living cells to evaluate cytotoxicity of antineoplastic drugs such as cisplatin and resveratrol. The biosensing system was demonstrated to display exceptional selectivity, excellent flexibility and good stability toward DA measurement in complex bio-samples. Additionally, the satisfactory recoveries of DA in real samples revealed the reliability and accuracy of the biosensing system in practical application. The IC₅₀ curves respectively obtained by the biosensing system and tetrazolium colorimetric assay provided similar IC₅₀ value but distinctly different dose-effect relationship, which confirmed the enormous potential of the biosensor in cell viability and described drug efficacy profiles in cell function. In short, the cell viability and drug evaluation system using SPE biosensor paves a new way in drug screening and pharmaceutical application to measure bioactive molecule such as DA.

A bibliometric analysis of graphene in acetaminophen detection: Current status, development, and future directions

Acetaminophen is a widely used analgesic throughout the world. Detection of acetaminophen has particular value in pharmacy and clinics. Electrochemical sensors assembled with advanced materials are an effective method for the rapid detection of acetaminophen. Graphene-based carbon nanomaterials have been extensively investigated for potential analytical applications in the last decade. In this article, we selected papers containing both graphene and acetaminophen. Bibliometrics was used to analyze the relationships and trends among these papers. The results show that the topic has grown at a high rate since 2009. Among them, the detection of acetaminophen by an electrochemical sensor based on graphene is the most important direction. Graphene has moved from being a primary sensing material to a substrate for immobilization of other active ingredients. In addition, the degradation of acetaminophen using graphene-modified electrodes is also an important direction. We analyzed the research history and current status of this topic through bibliometrics. Authors, institutions, countries, and key literature were discussed. We also proposed perspectives for this topic.

A Voltammetric Sensor for the Determination of Hydroxylamine Using a Polypyrrole Nanotubes-Modified Electrode

In this work, we develop an electrochemical sensor using a polypyrrole nanotubes-modified graphite screen-printed electrode (PPy NTs/GSPE) for sensing hydroxylamine. The PPy NTs/GSPE-supported sensor has an appreciable electrocatalytic performance and great stability for hydroxylamine oxidation. Compared to a bare graphite screen-printed electrode, we demonstrate that using the PPy NTs/GSPE leads to a significant reduction in the oxidation potential of hydroxylamine. The standard curve shows a linear relationship ranging from 0.005 to 290.0 μM (R2  =  0.9998), with a high sensitivity (0.1349 μA/μM) and a narrow limit of detection (LOD) of 0.001 μM. In addition, the PPy NTs/GSPE has satisfactory outcomes for hydroxylamine detection in real specimens.

Electrochemical immunosensors using electrodeposited gold nanostructures for detecting the S proteins from SARS-CoV and SARS-CoV-2

This paper reports the development of a low-cost (< US$ 0.03 per device) immunosensor based on gold-modified screen-printed carbon electrodes (SPCEs). As a proof of concept, the immunosensor was tested for a fast and sensitive determination of S proteins from both SARS-CoV and SARS-CoV-2, by a single disposable device. Gold nanoparticles were electrochemically deposited via direct reduction of gold ions on the electrode using amperometry. Capture antibodies from spike (S) protein were covalently immobilized on carboxylic groups of self-assembled monolayers (SAM) of mercaptoacetic acid (MAA) attached to the gold nanoparticles. Label-free detection of S proteins from both SARS-CoV and SARS-CoV-2 was performed with electrochemical impedance spectroscopy (EIS). The immunosensor fabricated with 9 s gold deposition had a high performance in terms of selectivity, sensitivity, and low limit of detection (LOD) (3.16 pmol L^-1), thus permitting the direct determination of the target proteins in spiked saliva samples. The complete analysis can be carried out within 35 min using a simple one-step assay protocol with small sample volumes (10 µL). With such features, the immunoplatform presented here can be deployed for mass testing in point-of-care settings.

Diamine Oxidase-Conjugated Multiwalled Carbon Nanotubes to Facilitate Electrode Surface Homogeneity

Carbon nanomaterials have gained significant interest over recent years in the field of electrochemistry, and they may be limited in their use due to issues with their difficulty in dispersion. Enzymes are prime components for detecting biological molecules and enabling electrochemical interactions, but they may also enhance multiwalled carbon nanotube (MWCNT) dispersion. This study evaluated a MWCNT and diamine oxidase enzyme (DAO)-functionalised screen-printed electrode (SPE) to demonstrate improved methods of MWCNT functionalisation and dispersion. MWCNT morphology and dispersion was determined using UV-Vis spectroscopy (UV-Vis) and scanning electron microscopy (SEM). Carboxyl groups were introduced onto the MWCNT surfaces using acid etching. MWCNT functionalisation was carried out using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS), followed by DAO conjugation and glutaraldehyde (GA) crosslinking. Modified C-MWNCT/EDC-NHS/DAO/GA was drop cast onto SPEs. Modified and unmodified electrodes after MWCNT functionalisation were characterised using optical profilometry (roughness), water contact angle measurements (wettability), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) (vibrational modes and elemental composition, respectively). The results demonstrated that the addition of the DAO improved MWCNT homogenous dispersion and the solution demonstrated enhanced stability which remained over two days. Drop casting of C-MWCNT/EDC-NHS/DAO/GA onto carbon screen-printed electrodes increased the surface roughness and wettability. UV-Vis, SEM, Raman and EDX analysis determined the presence of carboxylated MWCNT variants from their non-carboxylated counterparts. Electrochemical analysis demonstrated an efficient electron transfer rate process and a diffusion-controlled redox process. The modification of such electrodes may be utilised for the development of biosensors which could be utilised to support a range of healthcare related fields.

An electrochemical sensor based on a Co3O4-ERGO nanocomposite modified screen-printed electrode for detection of uric acid in artificial saliva

In this study, we report the fabrication of a nanocomposite consisting of Co₃O₄ nanoparticles (Co₃O₄ NPs) and electrochemically reduced graphene oxide (ERGO) on a screen-printed electrode (SPE) and its sensing performance in the electrochemical detection of uric acid (UA). The surface modification of the electrode was confirmed by using a variety of characterization techniques (FE-SEM, XRD, AFM, EDX, WCA, FTIR, and Raman spectroscopy). In addition, the surface modification was electrochemically characterized step by step through CV, EIS and DPV techniques, and the results showed that the Co₃O₄-ERGO nanocomposite exhibited highly sensitive and selective sensing performance towards the oxidation of UA in 0.1 M (pH 7.0) phosphate buffer solution (PBS). The sensor (Co₃O₄-ERGO/SPE) signals were observed to be linear to the UA concentration in the range of 5 μM to 500 μM (R² = 0.9985). After revealing its other performance characteristics, such as repeatability, reproducibility, stability, sensitivity, and selectivity, the sensor was successfully applied to the analysis of UA in artificial saliva samples.

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.

Carbon-Based Electrochemical Sensors for In Vivo and In Vitro Neurotransmitter Detection

As essential neurological chemical messengers, neurotransmitters play an integral role in the maintenance of normal mammalian physiology. Aberrant neurotransmitter activity is associated with a range of neurological conditions including Parkinson's disease, Alzheimer's disease, and Huntington's disease. Many studies to date have tested different approaches to detecting neurotransmitters, yet the detection of these materials within the brain, due to the complex environment of the brain and the rapid metabolism of neurotransmitters, remains challenging and an area of active research. There is a clear need for the development of novel neurotransmitter sensing technologies capable of rapidly and sensitively monitoring specific analytes within the brain without adversely impacting the local microenvironment in which they are implanted. Owing to their excellent sensitivity, portability, ease-of-use, amenability to microprocessing, and low cost, electrochemical sensors methods have been widely studied in the context of neurotransmitter monitoring. The present review, thus, surveys current progress in this research field, discussing developed electrochemical neurotransmitter sensors capable of detecting dopamine (DA), serotonin (5-HT), acetylcholine (Ach), glutamate (Glu), nitric oxide (NO), adenosine (ADO), and so on. Of these technologies, those based on carbon nanostructures-modified electrodes including carbon nanotubes (CNTs), graphene (GR), gaphdiyne (GDY), carbon nanofibers (CNFs), and derivatives thereof hold particular promise owing to their excellent biocompatibility and electrocatalytic performance. The continued development of these and related technologies is, thus, likely to lead to major advances in the clinical diagnosis of neurological diseases and the detection of novel biomarkers thereof.

A novel electrochemical sensor based on TAPT-TFP-COF/COOH-MWCNT for simultaneous detection of dopamine and paracetamol

In this work, a covalent organic framework (COF) TAPT-TFP-COF containing a triazine ring was prepared by a typical Schiff base condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) and 1,3,5-triformyl phloroglucinol (TFP). The TAPT-TFP-COF and carboxyl-functionalized multi-wall carbon nanotubes (COOH-MWCNTs) were drip-coated on glassy carbon electrode respectively to develop a novel and simple electrochemical sensor in order to simultaneously detect dopamine (DA) and paracetamol (PA). COOH-MWCNTs interconnected the TAPT-TFP-COF and acted as bridges between the COF particles, which had a good synergistic effect and accelerated electron transfer. Under optimal conditions, linear responses were obtained over the concentration range 1-190 μM for DA and PA with limits of detection (LOD) of 0.14 μM and 0.19 μM, respectively. Furthermore, the fabricated sensor possesses outstanding repeatability and high selectivity, and can be applied for the determination of DA and PA in dopamine injection and acetaminophen drugs with satisfactory recoveries.

Selective Electrochemical Sensing Platform Based on the Synergy between Carbon Black and Single-Crystalline Bismuth Sulfide for Rapid Analysis of Antipyretic Drugs

Nanomaterials are of significant interest in acetaminophen (APAP) detection in pharmaceutical samples. Herein, a carbon black/single-crystalline rodlike bismuth sulfide (CB/Bi₂S₃) composite prepared by an ultrasonic method is reported and utilized for the rapid analysis of APAP. The highly oriented edge reactive sites of the CB/Bi₂S₃ composite promoted synergy and good electrochemical sensing performance with a fast electron transfer rate and low overpotential (0.35 V). Therefore, a CB/Bi₂S₃ composite-modified glassy carbon electrode (GCE) was applied to the selective determination of APAP by the voltammetric technique. The CB/Bi₂S₃ composite-modified electrode showed the lowest limit of detection of APAP (1.9 nM) with excellent sensitivity. The proposed CB/Bi₂S₃/GCE platform exhibited high selectivity, excellent stability (87.15%), and reproducibility. Also, the CB/Bi₂S₃/GCE sensor was then successfully used to analyze an APAP pharmaceutical sample and exhibited satisfactory outcomes. Therefore, the CB/Bi₂S₃-modified GCE sensor platform would be a low-cost and robust GCE electrode material for APAP detection.

Electrochemically Activated Screen-Printed Carbon Sensor Modified with Anionic Surfactant (aSPCE/SDS) for Simultaneous Determination of Paracetamol, Diclofenac and Tramadol

In this work, an electrochemically activated screen-printed carbon electrode modified with sodium dodecyl sulfate (aSPCE/SDS) was proposed for the simultaneous determination of paracetamol (PA), diclofenac (DF), and tramadol (TR). Changes of surface morphology and electrochemical behaviour of the electrode after the electrochemical activation with H₂O₂ and SDS surface modification were studied by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The influence of various parameters on the responses of the aSPCE/SDS such as pH and concentration of the buffer, SDS concentration, and techniques parameters were investigated. Using optimised conditions (E_acc. of −0.4 V, t_acc. of 120 s, ΔE_A of 150 mV, ν of 250 mV s⁻¹, and t_m of 10 ms), the aSPCE/SDS showed a good linear response in the concentration ranges of 5.0 × 10⁻⁸–2.0 × 10⁻⁵ for PA, 1.0 × 10⁻⁹–2.0 × 10⁻⁷ for DF, and 1.0 × 10⁻⁸–2.0 × 10⁻⁷ and 2.0 × 10⁻⁷–2.0 × 10⁻⁶ mol L⁻¹ for TR. The limits of detection obtained during the simultaneous determination of PA, DF, and TR are 1.49 × 10⁻⁸ mol L⁻¹, 2.10 × 10⁻¹⁰ mol L⁻¹, and 1.71 × 10⁻⁹ mol L⁻¹, respectively. The selectivity of the aSPCE/SDS was evaluated by examination of the impact of some inorganic and organic substances that are commonly present in environmental and biological samples on the responses of PA, DF, and TR. Finally, the differential pulse adsorptive stripping voltammetric (DPAdSV) procedure using the aSPCE/SDS was successfully applied for the determination of PA, DF, and TR in river water and serum samples as well as pharmaceuticals.

Semi-transparent reduced graphene oxide photodetectors for ultra-low power operation

The emerged demand for high-performance systems promotes the development of two-dimensional (2D) graphene-based photodetectors. However, these graphene-based photodetectors are usually fabricated by an expensive photolithography and complicated transferred process. Here, a semi-transparent reduced graphene oxide (rGO) photodetector on a polyethylene terephthalate (PET) substrate with ultra-low power operation by simple processes is developed. The photodetector has achieved a transmittance about 60%, a superior responsivity of 375 mA/W and a high detectivity of 10¹² Jones at a bias of -1.5 V. Even the photodetector is worked at zero bias, the photodetector exhibits a superior on/off ratio of 12. Moreover, the photoresponse of such photodetector displays little reduction after hundred times bending, revealing that the photodetector is reliable and robust. The proposed fabrication strategy of the photodetector will be beneficial to the integration of semi-transparent and low-power wearable devices in the future.

Studying the preparation, electrochemical performance testing, comparison and application of a cost-effective flexible graphene working electrode

-A cost-effective flexible graphene working electrode (FGWE) was fabricated using overhead projector transparent film (OPTF) and a screen-printing technique. The surface morphology and electrochemical behavior of the electrode were characterized by scanning electron microscopy and cyclic voltammetry. The electrode presented a very thin layer of conductive ink (16.0 ± 0.7 µm) on a large effective surface area (0.301 ± 0.001 cm^-2). The anodic peak current density (j_pa) of acetaminophen (ACT) in FGWE was 5.2, 3.7, 3.5 and 6.0 times greater than the j_pa of glassy carbon electrode (GCE), flexible carbon working electrode (FCWE), SPE1, and SPE2, respectively. The electrochemical performance of FGWE toward ACT was evaluated by differential pulse voltammetry. Under optimized condition, ACT was quantified in a range of  4-100 µM, with good sensitivity, good accuracy (recovery = 82.3 ± 0.4 to 106 ± 3%), and excellent precision. FGWE was applied to determine ACT in commercial pharmaceutical formulations. The results of the study are in good agreement with those obtained by the standard spectrophotometric method. These results indicate that disposable FGWE is particularly useful for the detection of ACT, and its performance may serve as a platform for cost-effective flexible electrochemical sensors.

Ultrasensitive determination of chloramphenicol in pork and chicken meat samples using a portable electrochemical sensor: effects of 2D nanomaterials on the sensing performance and stability

This work contributes to a deeper understanding of the effects of functional 2D nanomaterials on the electrochemical sensing performance of SPE-based portable sensors for the rapid, accurate, and on-site determination of CAP in food samples.

Exploring carbon particle type and plasma treatment to improve electrochemical properties of stencil-printed carbon electrodes

Stencil-printing conductive carbon inks has revolutionized the development of inexpensive, disposable and portable electrochemical sensors. However, stencil-printed carbon electrodes (SPCEs) typically suffer from poor electrochemical properties. While many surface pretreatments and modifications have been tested to improve the electrochemical activity of SPCEs, the bulk composition of the inks used for printing has been largely ignored. Recent studies of other carbon composite electrode materials show significant evidence that the conductive carbon particle component is strongly related to electrochemical performance. However, such a study has not been carried out with SPCEs. In this work, we perform a systematic characterization of SPCEs made with different carbon particle types including graphite particles, glassy carbon microparticles and carbon black. The relationship between carbon particle characteristics including particle size, particle purity, and particle morphology as well as particle mass loading on the fabrication and electrochemical properties of SPCEs is studied. SPCEs were plasma treated for surface activation and the electrochemical properties of both untreated and plasma treated SPCEs are also compared. SPCEs displayed distinct analytical utilities characterized through solvent window and double layer capacitance. Cyclic voltammetry (CV) of several standard redox probes, FcTMA+, ferri/ferrocyanide, and pAP was used to establish the effects of carbon particle type and plasma treatment on electron transfer kinetics of SPCEs. CV of the biologically relevant molecules uric acid, NADH and dopamine was employed to further illustrate the differences in sensing and fouling characteristics of SPCEs fabricated with different carbon particle types. SEM imaging revealed significant differences in the SPCE surface microstructures. This systematic study demonstrates that the electrochemical properties of SPCEs can be tuned and significantly improved through careful selection of carbon particle type and plasma cleaning with a goal toward the development of better performing electrochemical point-of-need sensors.

Density Functional Theory-Assisted Electrochemical Assay Manipulated by a Donor-Acceptor Structure toward Pharmaceutical Diagnostic

Oxidative stress is a state of stress injury, which leads to the pathogenesis of most neurodegenerative diseases. Moreover, this is also one of the main reasons for the loss of dopaminergic neurons and the abnormal content of dopamine (DA). In the past decades, a number of studies have found that acetaminophen (AP) is metabolized and distributed in the brain when it is used as a neuroprotective compound. In this context, we proposed an electrochemical sensor based on 9-(4-(10-phenylanthracen-9-yl)phenyl)-9H-carbazole with the goal of diagnosing these two drugs in the body. Carbazole groups can easily be formed into large π-conjugated systems by electropolymerization. The introduction of anthracene exactly combined the carbazole group to establish an efficient electron donor-acceptor pattern, which enhanced π-π interaction with the electrode surface and charge transporting ability. The diagnostic platform showed good sensing activity toward the oxidation of DA and AP. The detection range for DA and AP is from 0.2 to 300 μM and from 0.2 to 400 μM, respectively. The simultaneous detection range is from 0.5 to 250 μM, which is wider than most reports. After a series of electrochemical assessments were determined, the sensor was finally developed to the analysis of pharmaceutical and human serum, displaying a meaningful potential in clinical evaluation.

Electrochemical properties of vertically aligned graphenes: tailoring heterogeneous electron transfer through manipulation of the carbon microstructure

The electrochemical response of different morphologies (microstructures) of vertically aligned graphene (VG) configurations is reported. Electrochemical properties are analysed using the outer-sphere redox probes Ru(NH₃)₆ ^2+/3+ (RuHex) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), with performances de-convoluted via accompanying physicochemical characterisation (Raman, TEM, SEM, AFM and XPS). The VG electrodes are fabricated using an electron cyclotron resonance chemical vapour deposition (ECR-CVD) methodology, creating vertical graphene with a range of differing heights, spacing and edge plane like-sites/defects (supported upon underlying SiO₂/Si). We correlate the electrochemical reactivity/response of these novel VG configurations with the level of edge plane sites (%-edge) comprising their structure and calculate corresponding heterogeneous electron transfer (HET) rates, k ⁰. Taller VG structures with more condensed layer stacking (hence a larger global coverage of exposed edge plane sites) are shown to exhibit improved HET kinetics, supporting the claims that edge plane sites are the predominant source of electron transfer in carbon materials. A measured k ⁰ _eff of ca. 4.00 × 10^-3 cm s^-1 (corresponding to an exposed surface coverage of active edge plane like-sites/defects (% θ _edge) of 1.00%) was evident for the tallest and most closely stacked VG sample, with the inverse case true, where a VG electrode possessing large inter-aligned-graphene spacing and small flake heights exhibited only 0.08% of % θ _edge and a k ⁰ _eff value one order of magnitude slower at ca. 3.05 × 10^-4 cm s^-1. Control experiments are provided with conventional CVD (horizontal) grown graphene and the edge plane of highly ordered pyrolytic graphite (EPPG of HOPG), demonstrating that the novel VG electrodes exhibit ca. 3× faster k ⁰ than horizontal CVD graphene. EPPG exhibited the fastest HET kinetics, exhibiting ca. 2× larger k ⁰ than the best VG. These results are of significance to those working in the field of 2D-carbon electrochemistry and materials scientists, providing evidence that the macroscale electrochemical response of carbon-based electrodes is dependent on the edge plane content and showing that a range of structural configurations can be employed for tailored properties and applications.

Chemically modified carbon-based electrodes for the determination of paracetamol in drugs and biological samples

Paracetamol is a non-steroidal, anti-inflammatory drug widely used in pharmaceutical applications for its sturdy, antipyretic and analgesic action. However, an overdose of paracetamol can cause fulminant hepatic necrosis and other toxic effects. Thus, the development of advantageous analytical tools to detect and determine paracetamol is required. Due to simplicity, higher sensitivity and selectivity as well as costefficiency, electrochemical sensors were fully investigated in last decades. This review describes the advancements made in the development of electrochemical sensors for the paracetamol detection and quantification in pharmaceutical and biological samples. The progress made in electrochemical sensors for the selective detection of paracetamol in the last 10 years was examined, with a special focus on highly innovative features introduced by nanotechnology. As the literature is rather extensive, we tried to simplify this work by summarizing and grouping electrochemical sensors according to the by which manner their substrates were chemically modified and the analytical performances obtained.

Chemically synthesized chevron-like graphene nanoribbons for electrochemical sensors development: determination of epinephrine

We employ chevron-like graphene nanoribbons (GNRs) synthesized by a solution-based chemical route to develop a novel electrochemical sensor for determination of the neurotransmitter epinephrine (EPI). The sensor surface, a glassy carbon electrode modified with GNRs, is characterized by atomic force microscopy, scanning electron microscopy and Raman spectroscopy, which show that the electrode surface modification comprises of bi-dimensional multilayer-stacked GNRs that retain their molecular structure. The charge transfer process occurring at the electrode interface is evaluated by electrochemical impedance spectroscopy. The sensor is applied to the determination of EPI, employing as an analytical signal the reduction peak corresponding to the epinephrinechrome–leucoepinephrinechrome transition (E = − 0.25 V) instead of the oxidation peak usually employed in the literature (E =  + 0.6 V) in order to minimize interferences. The results obtained demonstrate that chevron-like nanoribbons synthesized by solution methods exhibit reliable electrocatalytic activity for EPI determination. Using differential pulse voltammetry, we obtain a linear concentration range from 6.4 × 10^–6 to 1.0 × 10^–4 M and a detection limit of 2.1 × 10^–6 M. The applicability of the sensor was evaluated by determining EPI in pharmaceutical samples with satisfactory results.

Fully-printed electrochemical sensors made with flexible screen-printed electrodes modified by roll-to-roll slot-die coating

The manufacture of sensors using large-scale production techniques, such as roll-to-roll (R2R) processing, may fulfill requirements of low-cost disposable devices. Herein, we report the fabrication of fully-printed electrochemical sensors using screen-printed carbon electrodes coated with carbon black inks through slot-die coating within an R2R process. As a proof of concept, sensors were produced to detect the neurotransmitter dopamine with high reproducibility and low limit of detection (0.09 μmol L^-1). Furthermore, fully-printed biosensors made with a tyrosinase-containing ink were used to detect catechol in natural water samples. Since slot-die deposition enables printing enzymes without significant activity loss, the biosensors exhibited high stability over a period of several weeks. Even more important, R2R slot-die coating may be extended to any type of sensors and biosensors with the possibility of large-scale manufacturing.

Stone Paper as a New Substrate to Fabricate Flexible Screen-Printed Electrodes for the Electrochemical Detection of Dopamine

Flexible screen-printed electrodes (HP) were fabricated on stone paper substrate and amperometrically modified with gold nanoparticles (HP-AuNPs). The modified electrode displayed improved electronic transport properties, reflected in a low charge-transfer resistance (1220 Ω) and high apparent heterogeneous electron transfer rate constant (1.94 × 10⁻³ cm/s). The voltammetric detection of dopamine (DA) was tested with HP and HP-AuNPs electrodes in standard laboratory solutions (pH 6 phosphate-buffered saline (PBS)) containing various concentrations of analyte (10⁻⁷–10⁻³ M). As expected, the modified electrode exhibits superior performances in terms of linear range (10⁻⁷–10⁻³ M) and limit of detection (3 × 10⁻⁸ M), in comparison with bare HP. The determination of DA was tested with HP-AuNPs in spiked artificial urine and in pharmaceutical drug solution (ZENTIVA) that contained dopamine hydrochloride (5 mg/mL). The results obtained indicated a very good DA determination in artificial urine without significant matrix effects. In the case of the pharmaceutical drug solution, the DA determination was affected by the interfering species present in the vial, such as sodium metabisulfite, maleic acid, sodium chloride, and propylene glycol.

Carbonaceous Nanomaterials Employed in the Development of Electrochemical Sensors Based on Screen-Printing Technique—A Review

This paper aims to revise research on carbonaceous nanomaterials used in developing sensors. In general, nanomaterials are known to be useful in developing high-performance sensors due to their unique physical and chemical properties. Thus, descriptions were made for various structural features, properties, and manner of functionalization of carbon-based nanomaterials used in electrochemical sensors. Of the commonly used technologies in manufacturing electrochemical sensors, the screen-printing technique was described, highlighting the advantages of this type of device. In addition, an analysis was performed in point of the various applications of carbon-based nanomaterial sensors to detect analytes of interest in different sample types.

Screen-printed disposable electrodes using graphite-polyurethane composites modified with magnetite and chitosan-coated magnetite nanoparticles for voltammetric epinephrine sensing: a comparative study

Disposable screen-printed electrodes based on the use of graphite-polyurethane composites modified with magnetite nanoparticles (MNP-SPE) or chitosan-coated magnetite nanoparticles (CHMNP-SPE) are described. The MNP and CHMNP were synthetized and comparatively characterized by TEM, XRD, FTIR, and TGA/DTG. The MNP-SPE and CHMNP-SPE were characterized by SEM and EDX. After optimization of the MNP percentage in MNP-SPE, the materials were electrochemically characterized by cyclic voltammetry, EIS, and chronocoulometry. The electrodes were tested for their performance towards sensing of epinephrine (EP). The CHMNP-SPE is found to have better electrochemical responses in comparison to the MNP-SPE. This is assumed to be due to the chitosan coating which also protects the MNPs from oxidation under air and at different applied potential fields. The performances of the MNP-SPE and CHMNP-SPE were studied by DPV after optimization of equilibration time and DPV parameters. Response is linear in the 0.1-0.8 μM EP concentration range, at 0.03 V (vs. pseudo-Ag/AgCl), and the detection limit is 25 nM for the MNP-SPE. The linear response for the CHMNP-SPE was 0.1-0.6 μM, at 0.0 V (vs. pseudo-Ag/AgCl), and a LOD of 14 nM was achieved. The devices were used for the quantification of EP in synthetic urine and in cerebrospinal synthetic fluids. Recoveries from spiked samples are in the 95.6-102.2% range for the CHMNP-SPE and in the 98.3-109% range for MNP-SPE. The stability of the respective sensors was investigated and compared over a period of 5 months. The EP peak currents were found to decrease by only 4% for the CHMNP-SPE, while the MNP-SPE lost 23% of its EP peak current. Accordingly, the CHMNP-SPE was chosen as the most stable and sensitive sensor for EP. Graphical abstract Schematic figure of modification of a graphite-polyurethane screen-printed composite electrode with magnetite nanoparticles (MNPs) and chitosan-coated magnetite nanoparticles (CHMNPs) for the voltammetric determination of epinephrine (EP). Improved response of CHMNP-SPE (black voltammogram) in comparison to MNP-SPE (red voltammogram) was attributed to the protection of MNP from oxidation.

Electrochemical (Bio)Sensors for Pesticides Detection Using Screen-Printed Electrodes

Pesticides are among the most important contaminants in food, leading to important global health problems. While conventional techniques such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS) have traditionally been utilized for the detection of such food contaminants, they are relatively expensive, time-consuming and labor intensive, limiting their use for point-of-care (POC) applications. Electrochemical (bio)sensors are emerging devices meeting such expectations, since they represent reliable, simple, cheap, portable, selective and easy to use analytical tools that can be used outside the laboratories by non-specialized personnel. Screen-printed electrodes (SPEs) stand out from the variety of transducers used in electrochemical (bio)sensing because of their small size, high integration, low cost and ability to measure in few microliters of sample. In this context, in this review article, we summarize and discuss about the use of SPEs as analytical tools in the development of (bio)sensors for pesticides of interest for food control. Finally, aspects related to the analytical performance of the developed (bio)sensors together with prospects for future improvements are discussed.