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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. [ABSTRACT FROM AUTHOR]

A porous diamond-like carbon film deposited on vertically aligned multi-walled carbon nanotubes (DLC:VAMWCNT) was evaluated as an electrode material in flow injection analysis (FIA) with amperometric detection. The redox behavior of hydroquinone (H 2 Q) was carried out as proof of concept. From cyclic voltammetry tests, H 2 Q gave a heterogeneous electron transfer rate constant (k 0) of 4.9 × 10−3 cm s−1, which is comparable or better than those obtained with conventional electrodes. For the H 2 Q determination with the FIA-amperometry system, optimizations were performed regarding the supporting electrolyte, applied potential and FIA parameters (flow rate and sample injection volume). Under optimal conditions, the amperometric response of the DLC:VAMWCNT electrode was linear in the H 2 Q concentration range from 1.0 × 10−6 to 1.0 × 10−4 mol L−1, with a limit of detection (LOD) of 7.7 × 10−7 mol L−1. Interestingly, the DLC:VAMWCNT electrode displayed a very stable response under hydrodynamic conditions, with no memory effect while retaining accuracy towards the analysis of commercial H 2 Q-based dermatological creams. From these findings, DLC:VAMWCNT appears to be an outstanding candidate for flow injection analysis systems coupled to electrochemical detection. [Display omitted] • Porous diamond-like carbon prepared on vertically aligned carbon nanotubes • Amperometric flow injection analysis with porous diamond-like carbon electrode • Porous-diamond like carbon electrodes display stable response under flow conditions. • Hydroquinone amperometric determination in cosmetic samples [ABSTRACT FROM AUTHOR]

Carbon black (CB) is a nanostructured material widely used in several industrial processes. This nanomaterial features a set of remarkable properties including high surface area, high thermal and electrical conductivity, and very low cost. Several studies have explored the applicability of CB in electrochemical fields. Recent data showed that modified electrodes based on CB present fast charge transfer and high electroactive surface area, comparable to carbon nanotubes and graphene. These characteristics make CB a promising candidate for the design of electrochemical sensors and biosensors. In this review, we highlight recent advances in the use of CB as a template for biosensing. As will be seen, we discuss the main biosensing strategies adopted for enzymatic catalysis for several target analytes, such as glucose, hydrogen peroxide, and environmental contaminants. Recent applications of CB on DNA-based biosensors are also described. Finally, future challenges and trends of CB use in bioanalytical chemistry are discussed. [ABSTRACT FROM AUTHOR]

A porous electrode material combining the features of vertically aligned multi-walled carbon nanotubes (VAMWCNT) and diamond-like carbon films (DLC) have been developed for a highly sensitive electrochemical sensor. For working electrode preparation, DLC has been grown onto VAMWCNT, forming a porous, conductive and stable composite. The electrochemical performance of this DLC:VAMWCNT electrode has been investigated toward detection and analysis of three well-known molecules, namely paracetamol, codeine and caffeine. A ternary mixture of these analytes was simultaneously determined under optimum experimental conditions using square-wave voltammetry. Wide linear concentration ranges and the limits of detection of 3.34×10−7 mol L−1, 1.57×10−7 mol L−1 and 3.67×10−7 mol L−1 were obtained for paracetamol, codeine and caffeine, respectively. We conclude that the proposed voltammetric method and the DLC:VAMWCNT electrode comprise a reliable methodology for simultaneous determination of paracetamol, codeine and caffeine in biological matrix samples. [ABSTRACT FROM AUTHOR]

Porous boron-doped diamond (p-BDD) electrodes of high-surface-area have been prepared on vertically aligned carbon nanotube substrates, and their electrochemical performance has demonstrated promising results for application in electroanalysis. The electrochemical features of the p-BDD electrodes were investigated and compared with those of a conventional flat BDD electrode (f-BDD). From cyclic voltammetry studies performed for the electrochemical probes [Fe(CN)] and N, N, N′, N′-tetramethyl- para-phenylenediamine (TMPD), a fast charge transfer was observed at the p-BDD/electrolyte interface. For the [Fe(CN)] redox probe, the heterogeneous electron-transfer rate constant ( k ) value obtained for p-BDD was 10.9 times higher than that obtained using a f-BDD electrode. Moreover, the p-BDD electrodes also gave a smaller peak potential separation, Δ E , and larger analytical signal magnitude for different biomolecules, such as dopamine (DA), acetaminophen (AC), and epinephrine (EP). These set of results demonstrated that the p-BDD electrode is a suitable candidate for applications in electroanalytical chemistry. [ABSTRACT FROM AUTHOR]

Carbon paste electrodes (CPE) were modified with nitrogen-doped carbon nanotubes (N-CNTs) synthesized at 750 °C (N-CNT 750) and 850 °C (N-CNT 850), carboxyl functionalized carbon nanotubes (MWCNT COOH), and pristine carbon nanotubes (MWCNT). Their electrochemical properties were investigated and compared towards a common redox probe, potassium ferricyanide (K 3 [Fe(CN) 6 ]). The electrochemical responses were probed using cyclic voltammetry, and the results unveiled that modification with carbon nanotubes enhanced anodic peak currents (I pa) for the electrodes CPE/MWCNT COOH , CPE/N-CNT 750 and CPE/N-CNT 850 (I pa , p < 0.05 in relation to pure CPE). In particular, CPE modified with N-CNTs synthesized at 850 °C (CPE/N-CNT 850) exhibited better electrochemical response, with lower peak-to-peak potential separation (ΔE p , p < 0.05 in relation to pure CPE). Complementary studies were conducted to investigate the electroactive area (A) and heterogeneous electron-transfer kinetics (k 0). CPE/N-CNT 850 (0.034 ± 0.005 cm2) and CPE/MWCNT COOH (0.057 ± 0.002 cm2) presented more satisfactory results for the anodic and cathodic electroactive area (A), respectively. Kinetic studies revealed a higher k 0 (1.03 × 10−3 cm.s−1) for the CPE/N-CNT 850 electrode. Differential pulse voltammetry was employed for the electrochemical detection of Acetaminophen (AC). The response was linear for an AC concentration range from 66.2 to 259.7 μmol L−1, with the lowest detection limit (LOD) of 0.37 μmol L−1 and the highest sensitivity of 0.244 ± 0.002 μA L μmol−1 for the respective electrodes CPE/N-CNT 850 and CPE/MWCNT COOH. The CPE/N-CNT 850 and CPE/MWCNT COOH electrodes show the best correlation of results, the presence of polar groups on the surface of MWCNT COOH and a higher amount of graphitic nitrogen bond of N-CNT 850 suggest that these CNTs are particularly promising for applications in electrochemical fields. [Display omitted] • CNTs synthesized in different conditions were employed as modifiers in carbon paste electrode. • CPE/N-CNT 850 and CPE/MWCNT COOH displayed more satisfactory results regarding the electroactive area using [Fe(CN) 6 ]3−/4−. • CPE/N-CNT 850 exposed a higher k 0 for the redox probe. • Electrodes modified with N-CNT 850 and MWCNT COOH exhibited improved sensing capabilities for acetaminophen determination. • MWCNT COOH with polar groups and N-CNT 850 with a higher amount of graphitic nitrogen bond could improve their electrochemical properties. [ABSTRACT FROM AUTHOR]

A novel electrochemical method for the determination of rosuvastatin calcium (RC) using a composite of vertically aligned carbon nanotubes and graphene oxide (VACNT-GO) as the electrode material is proposed. The VACNT-GO electrode was synthesized using a microwave-assisted chemical vapor deposition method followed by oxygen plasma treatment. The VACNT-GO electrode presented superhydrophilic behavior and fast charge transfer, which are very attractive for electrochemical applications. The RC molecule presented an oxidation process at +1.26 V vs. Ag/AgCl (3.0 mol L −1 KCl) in phosphate buffer solution (pH 2), and this redox behavior was explored for its voltammetric determination. Using square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized conditions, the analytical curve was linear in RC concentration range from 0.48 to 46.72 μmol L −1 with a limit of detection of 0.06 μmol L −1 . The developed SWAdASV method was applied for RC quantification in commercial pharmaceutical samples, and the results are consistent with those obtained by the comparative spectrophotometric method at a confidence level of 95%. Moreover, RC was determined in human body fluid samples of urine and human serum. [ABSTRACT FROM AUTHOR]

In this work, an alternative voltammetric procedure for the determination of Pb(II) was developed using a carbon nanotube paste electrode modified with crosslinked chitosan with glutaraldehyde (GA-CTS-CNTPE). Square-wave adsorptive stripping voltammetry (SWAdSV) was used and the relevant experimental parameters were optimized. Under optimal experimental conditions, the voltammetric response was linear in the range of 9.90×10−8 to 2.00×10−6 molL−1 with a detection limit of 5.70×10−8 molL−1. The proposed voltammetric method showed good repeatability and low interference from other metallic species. It was successfully applied in the determination of Pb(II) in natural water samples and the results were in very close agreement with those obtained using a comparative method (inductively coupled plasma optical emission spectrometry (ICP-OES)). [ABSTRACT FROM AUTHOR]

Voltammetric studies have been carried out using a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and the ionic liquid 1-butyl-3-methylimidazolium chloride (IL). Studies on the electrochemical properties of GCEs modified with MWCNTs and IL within different polymeric films (dihexadecylphosphate (DHP), Nafion, and chitosan (CTS)) were performed using a [Fe(CN)6]4−/3− electrochemical probe. The modified GCE with different polymeric films was also tested for ciprofibrate (CPF) sensing in the presence and absence of IL in the film. The presence of IL and the MWCNTs improved the electrochemical response for CPF in all cases due to a synergic effect, and the IL-MWCNTs-DHP/GCE showed a great voltammetric profile for CPF detection. The IL-MWCNTs-DHP/GCE and differential pulse voltammetry (DPV) were used for the determination of CPF. An analytical curve was obtained for CPF in the concentration range of 2.50 × 10−7 to 7.41 × 10−6 mol L−1 with a detection limit of 9.20 × 10−8 mol L−1. The proposed DPV method was successfully applied for CPF determination in pharmaceutical samples, and the results obtained agree with the results obtained using a spectrophotometric method at a confidence level of 95%. [ABSTRACT FROM AUTHOR]

Abstract: Vertically aligned carbon nanotubes/graphene oxide nanocomposite (VACNT-GO) has been prepared and applied as electrode material. First, dense packets of VACNT were prepared in microwave chemical vapor deposition reactor, and then functionalized by oxygen plasma etching. We observed that oxygen plasma could exfoliate carbon nanotubes tips and provide oxygen group attachment on its surface, changing its wettability as well. This change in wettability of the VACNT is crucial for its electrochemical application, since as-grown VACNT is super-hydrophobic. After exfoliation and functionalization, the electrochemical tests were performed using potassium ferrocyanide. The cyclic voltammetry (CV) and impedance spectroscopy revealed fast electron transfer kinetics on this new material. The CV peak potential separation was 59mV, suggesting ideal reversibility at the electrode. The Nyquist and Bode plots were well-fitted as modified Randles equivalent electrical circuits with non-charge transfer impedance. This new highly porous nanostructures have been intensively characterized by scanning electron microscopy, Brunauer–Emmett–Teller surface area, surface wettability, Raman and X-ray photoemission spectroscopy. Our results suggest this new material has a relevant potential for future applications in electrocatalysis and (bio)sensors. [Copyright &y& Elsevier]

A sensitive way to determine levofloxacin using a sensor based on vertical aligned carbon nanotubes is described. The morphology and the electrochemical performance of the electrodes were characterised by atomic force microscopy, cyclic voltammetry and square wave voltammetry. A scan-rate study and electrochemical impedance spectroscopy showed that the levofloxacin oxidation product is adsorbed on the electrode surface. Differential pulse voltammetry in phosphate-buffer solution allowed the development of a method to determine levofloxacin levels in the range of 1.0-10.0 µmol L−1, with a detection limit of 75.2 nmol L−1. The proposed sensor was successfully applied in the determination of levofloxacin in urine, and the obtained results were in full agreement with those from the HPLC procedure. [ABSTRACT FROM AUTHOR]

Abstract: This communication reports a comparison study between sensors based on vertically aligned and dispersed single-walled carbon nanotubes on the electrochemical determination of an endocrine disruptor. The vertical alignment of carbon nanotubes enabled an electrocatalytic effect and enhanced the sensitivity of bisphenol A oxidation compared with an electrode modified with dispersed carbon nanotubes. The vertically aligned surface had a remarkable influence on the limit-of-detection obtained for bisphenol A. [Copyright &y& Elsevier]

Porous boron-doped diamond (p-BDD) electrodes were prepared and explored as a potential electrochemical sensor for applications in flow-injection analysis (FIA) coupled to amperometric detection systems. Porous BDD films were grown by Hot Filament Chemical Vapor Deposition (HFCVD) over oxygen plasma functionalized carbon nanotubes and, morphological and chemical characterizations of the obtained composite material were carried out by Field Emission Gun Scanning Electron Microscopy (FEG-SEM) and Raman spectroscopy. The analytical performance of the designed p-BDD electrode under FIA conditions was investigated using two model electroactive analytes, epinephrine (EP, an important neurotransmitter) and acetaminophen (AC, a commonly consumed analgesic). All experimental parameters, such as applied potential, flow-rate and injection volume for both analytes were optimized. Under the best experimental conditions, the analytical curves for EP and AC were linear from 0.60 to 30.0 μmol L − 1 (EP) and from 0.80 to 70.0 μmol L − 1 (AC), with detection limits of 0.50 μmol L − 1 and 0.70 μmol L − 1 for EP and AC, respectively. Measurement precision was demonstrated from a number of amperometric measurements performed for successive injections of standard AC and EP solutions. In addition, the applicability of the developed FIA procedure was reported for the AC and EP determination in human serum fluid. [ABSTRACT FROM AUTHOR]

In this work, an electrochemical sensor based on vertically oriented carbon nanotubes (voMWCNT), electrically wired via connection upon a copper plate, for the detection of tadalafil (TD) is reported. The voMWCNT is easily prepared via microwave plasma reactor with no additional post-treatment. The voMWCNT was characterized by scanning and transmission electron microscopy in addition to electrochemical characterization with cyclic voltammetry. Once TD is of easy access and used in the treatment of erectile dysfunction and related diseases, the quality control of this drug is of high importance. Using linear sweep voltammetry, the detection of TD was found to be possible from 0.85 to 8.9 μmol L−1, with an R2 of 0.992 with a limit of detection found to correspond to 78 nmol L−1. The quantification of TD in different pharmaceutical drugs, as well as the device stability, indicates that the voMWCNT has potential for the routine sensing of TD. Unlabelled Image [ABSTRACT FROM AUTHOR]