α-Fe2O3/, Co3O4/, and CoFe2O4/MWCNTs/Ionic Liquid Nanocomposites as High-Performance Electrocatalysts for the Electrocatalytic Hydrogen Evolution Reaction in a Neutral Medium.

Transition metal oxides are a great alternative to less expensive hydrogen evolution reaction (HER) catalysts. However, the lack of conductivity of these materials requires a conductor material to support them and improve the activity toward HER. On the other hand, carbon paste electrodes result in a versatile and cheap electrode with good activity and conductivity in electrocatalytic hydrogen production, especially when the carbonaceous material is agglomerated with ionic liquids. In the present work, an electrode composed of multi-walled carbon nanotubes (MWCNTs) and cobalt ferrite oxide (CoFe2O4) was prepared. These compounds were included on an electrode agglomerated with the ionic liquid N-octylpyridinium hexafluorophosphate (IL) to obtain the modified CoFe2O4/MWCNTs/IL nanocomposite electrode. To evaluate the behavior of each metal of the bimetallic oxide, this compound was compared to the behavior of MWCNTs/IL where a single monometallic iron or cobalt oxides were included (i.e., α-Fe2O3/MWCNTs/IL and Co3O4/MWCNTs/IL). The synthesis of the oxides has been characterized by X-ray diffraction (XRD), RAMAN spectroscopy, and field emission scanning electronic microscopy (FE-SEM), corroborating the nanometric character and the structure of the compounds. The CoFe2O4/MWCNTs/IL nanocomposite system presents excellent electrocatalytic activity toward HER with an onset potential of -270 mV vs. RHE, evidencing an increase in activity compared to monometallic oxides and exhibiting onset potentials of -530 mV and -540 mV for α-Fe2O3/MWCNTs/IL and Co3O4/MWCNTs/IL, respectively. Finally, the system studied presents excellent stability during the 5 h of electrolysis, producing 132 µmol cm-2 h-1 of hydrogen gas.

Electrochemical sensing at the fingertips: Wearable glove-based sensors for detection of 4-nitrophenol, picric acid and diazepam.

A wearable glove-based sensor is a portable and practical approach for onsite detection/monitoring of a variety of chemical threats. Herein, we report a flexible and sensitive wearable sensor fabricated on the nitrile glove fingertips by stencil-printing technique. The working electrodes were modified with multiwalled carbon nanotubes (MWCNTs)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) for sensitive and real-time analyses of hazardous or chemical treats, as picric acid (PA) explosive, diazepam (DZ) as drug-facilitated crimes and the emerging pollutant 4-nitrophenol (4-NP). The multi-sensing platform towards PA, 4-NP, and DZ offers the ability of in-situ qualitative and quantitative analyses of powder and liquid samples. A simple sampling by touching or swiping the fingertip sensor on the sample or surface under investigation using an ionic hydrogel combined with fast voltammetry measurement provides timely point-of-need analyses. The wearable glove-based sensor uses the square wave voltammetry (SWV) technique and exhibited excellent performance to detect PA, 4-NP, and DZ, resulting in limits of detection (LOD) of 0.24 µM, 0.35 µM, 0.06 µM, respectively, in a wide concentration range (from 0.5 µM to 100 µM). Also, we obtained excellent manufacturing reproducibility with relative standard deviations (RSD) in the range of 3.65%-4.61% using 7 different wearable devices (n = 7) and stability in the range of 4.86%-6.61% using different electrodes stored for 10 days at room temperature (n = 10), demonstrating the excellent sensor-to-sensor reproducibility and stability for reliable in-field measurements. The stretchable sensor presented great mechanical robustness, supporting up to 80 bending or stretching deformation cycles without significant voltammetric changes. Collectively, our wearable glove-based sensor may be employed for analyses of chemical contaminants of concern, such as explosives (PA), drugs (DZ), and emerging pollutants (4-NP), helping in environmental and public safety control.

Disposable electrochemical sensor: Highly sensitive determination of nitrofurazone antibiotic in environmental samples and pharmaceutical formulations.

The study presents the successful development of a new electrochemical sensor with low cost and disposability for application in nitrofurazone detection in environmental and pharmaceutical samples. The sensors were fabricated using materials obtained from local storage and conductive carbon ink. The modification of the screen-printed electrodes with the hybrid nanomaterial based on silver nanoparticles, carbon quantum dots, and carbon nanotubes showed synergistic contributions in the nitrofurazone electrooxidation, as observed in the wide linear range (0.008 at 15.051 µM), with a sensitivity of 0.650 µA/µM. The limit of detection obtained was 4.6 nM. Differential pulse voltammetry, cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, and high-resolution transmission electron microscopy were used to evaluate the electrochemical and structural characteristics. Studies of possible interferences were considered with nitrofurazone in the presence of the ions and organic molecules. The results were satisfactory, with a variation of 93.3% ± 4.39% at 100% ± 2.40%. The low volume used in the analyses (50 µL), disposability, high sensibility, selectivity, and low limit of detection are advantages that make the proposed sensor an electrochemical tool of high viability for the NFZ detection in environmental matrices and pharmaceutical formulations.

Design and Fabrication of a Biomimetic Smart Material for Electrochemical Detection of Carbendazim Pesticides in Real Samples with Enhanced Selectivity.

Agricultural products are vitally important for sustaining life on earth and their production has notably grown over the years worldwide in general and in Brazil particularly. Elevating agricultural practices consequently leads to a proportionate increase in the usage of pesticides that are crucially important for enhanced crop yield and protection. These compounds have been employed excessively in alarming concentrations, causing the contamination of soil, water, and air. Additionally, they pose serious threats to human health. The current study introduces an innovative tool for producing appropriate materials coupled with an electrochemical sensor designed to measure carbendazim levels. The sensor is developed using a molecularly imprinted polymer (MIP) mounted on a glassy carbon electrode. This electrode is equipped with multi-walled carbon nanotubes (MWCNTs) for improved performance. The combined system demonstrates promising potential for accurately quantifying carbendazim. The morphological characteristics of the synthesized materials were investigated using field emission scanning electron microscopy (FESEM) and the Fourier-transform infrared (FTIR) technique. The analytical curve was drawn using the electrochemical method in the range of 2 to 20 ppm while for HPLC 2-12 ppm; the results are presented as the maximum adsorption capacity of the MIP (82.4%) when compared with NIP (41%) using the HPLC method. The analysis conducted using differential pulse voltammetry (DPV) yielded a limit of detection (LOD) of 1.0 ppm and a repeatability of 5.08% (n = 10). The results obtained from the analysis of selectivity demonstrated that the proposed electrochemical sensor is remarkably efficient for the quantitative assessment of carbendazim, even in the presence of another interferent. The sensor was successfully tested for river water samples for carbendazim detection, and recovery rates ranging from 94 to 101% were obtained for HPLC and 94 to 104% for the electrochemical method. The results obtained show that the proposed electrochemical technique is viable for the application and quantitative determination of carbendazim in any medium.

Magnetic carbon nanotubes modified with proteins and hydrophilic monomers: Cytocompatibility, in-vitro toxicity assays and permeation across biological interfaces.

Carbon nanotubes are promising materials for biomedical applications like delivery systems and tissue scaffolds. In this paper, magnetic carbon nanotubes (M-CNTs) covered with bovine serum albumin (M-CNTs-BSA) or functionalized with hydrophilic monomers (M-CNTs-HL) were synthesized, characterized, and evaluated concerning their interaction with Caco-2 cells. There is no comparison between these two types of functionalization, and this study aimed to verify their influence on the material's interaction with the cells. Different concentrations of the nanotubes were applied to investigate cytotoxicity, cell metabolism, oxidative stress, apoptosis, and capability to cross biomimetic barriers. The materials showed cytocompatibility up to 100 µg mL-1 and a hemolysis rate below 2 %. Nanotubes' suspensions were allowed to permeate Caco-2 monolayers for up to 8 h under the effect of the magnetic field. Magnetic nanoparticles associated with the nanotubes allowed estimation of permeation through the monolayers, with values ranging from 0.50 to 7.19 and 0.27 to 9.30 × 10-3 µg (equivalent to 0.43 to 6.22 and 0.23 to 9.54 × 10-2 % of the initially estimated mass of magnetic nanoparticles) for cells exposed and non-exposed to the magnets, respectively. Together, these results support that the developed materials are promising for applications in biomedical and biotechnological fields.

Platinum Nanoparticles Supported by Carbon Nanotubes: Improvement in electrochemical sensor performance for caffeine determination.

Platinum nanoparticles supported by carbon nanotubes were obtained by a simple chemical route and used for preparation of electrochemical sensor towards caffeine determination. Carbon nanotubes were used before and after an acid treatment, yielding two different materials. Morphological and structural characterization of these materials showed platinum nanoparticles (size around 12 nm) distributed randomly along carbon nanotubes. Modified electrodes were directly prepared through a dispersion of these materials. Voltammetric studies in the presence of caffeine revealed an electrocatalytic effect of platinum oxides, electrochemically produced from the chemical oxidation of the platinum nanoparticles. This behavior was explored in the development a selective method for caffeine determination based on platinum oxide reduction at a lower potential value (+0.45 V vs. Ag/AgCl). Using the best set of experimental conditions, it was shown a linear relationship for the caffeine concentration ranging from 5.0 to 25 µmol L-1 with a sensitivity of 449 nA L µmol-1. Limits of detection and quantification of 0.54 and 1.80 µmol L-1 were calculated, respectively. Recovery values for real samples of caffeine pharmaceutical formulations between 98.6% and 101.0% (n = 3) were obtained using the proposed procedure. Statistical calculations showed good concordance (95% confidence level) between the added and recovery values.

L-Lactate Electrochemical Biosensor Based on an Integrated Supramolecular Architecture of Multiwalled Carbon Nanotubes Functionalized with Avidin and a Recombinant Biotinylated Lactate Oxidase.

L-Lactate is an important bioanalyte in the food industry, biotechnology, and human healthcare. In this work, we report the development of a new L-lactate electrochemical biosensor based on the use of multiwalled carbon nanotubes non-covalently functionalized with avidin (MWCNT-Av) deposited at glassy carbon electrodes (GCEs) as anchoring sites for the bioaffinity-based immobilization of a new recombinant biotinylated lactate oxidase (bLOx) produced in Escherichia coli through in vivo biotinylation. The specific binding of MWCNT-Av to bLOx was characterized by amperometry, surface plasmon resonance (SPR), and electrochemical impedance spectroscopy (EIS). The amperometric detection of L-lactate was performed at -0.100 V, with a linear range between 100 and 700 µM, a detection limit of 33 µM, and a quantification limit of 100 µM. The proposed biosensor (GCE/MWCNT-Av/bLOx) showed a reproducibility of 6.0% and it was successfully used for determining L-lactate in food and enriched serum samples.

Enhanced degradation and removal of ciprofloxacin and ofloxacin through advanced oxidation and adsorption processes using environmentally friendly modified carbon nanotubes.

This study explores the utilization of adsorption and advanced oxidation processes for the degradation of ofloxacin (OFL) and ciprofloxacin (CIP) using a green functionalized carbon nanotube (MWCNT-OH/COOH-E) as adsorbent and catalyst material. The stability and catalytic activity of the solid material were proved by FT-IR and TG/DTG, which also helped to elucidate the reaction mechanisms. In adsorption kinetic studies, both antibiotics showed similar behavior, with an equilibrium at 30 min and 60% removal. The adsorption kinetic data of both antibiotics were well described by the pseudo-first-order (PFO) model. Different advanced oxidation processes (AOPs) were used, and the photolytic degradation was not satisfactory, whereas heterogeneous photocatalysis showed high degradation (⁓ 70%), both processes with 30 min of reaction. Nevertheless, ozonation and catalytic ozonation have resulted in the highest efficiencies, 90%, and 70%, respectively, after 30-min reaction. For AOP data modeling, the first-order model better described CIP and OFL in photocatalytic and ozonation process. Intermediates were detected by MS-MS analysis, such as P313, P330, and P277 for ciprofloxacin and P391 and P332 for ofloxacin. The toxicity test demonstrated that a lower acute toxicity was observed for the photocatalysis method samples, with only 3.1 and 1.5 TU for CIP and OFL, respectively, thus being a promising method for its degradation, due to its lower risk of inducing the proliferation of bacterial resistance in an aquatic environment. Ultimately, the analysis of MWCNT reusability showed good performance for 2 cycles and regeneration of MWCNT with ozone confirmed its effectiveness up to 3 cycles.

Green synthesis of carbon nanotubes functionalized with iron nanoparticles and coffee husk biomass for efficient removal of losartan and diclofenac: Adsorption kinetics and ANN modeling studies.

The presence of emerging contaminants in wastewater poses a global environmental challenge, requiring the development of innovative materials or methods for their treatment. This study focused on the production of green functionalized carbon nanotubes (CNTs) and using them in the adsorption of the pharmaceuticals Losartan (LOS) and Diclofenac (DIC). The efficiency of the methodology was verified by characterization techniques. Elemental composition analysis indicated a significant increase in the iron content after the green functionalization, proving the effectiveness of the method. Thermogravimetric analysis showed similar thermal degradation profiles for pristine CNTs and functionalized CNTs, indicating better post-functionalization thermal stability. BET analysis revealed mesoporous characteristics of CNTs, with increased surface area and pore volumes after functionalization. X-Ray diffraction confirmed the preservation of the lattice structure of the CNTs post-functionalization and post-adsorption, with changes in peak broadening suggesting surface modifications. LOS and DIC adsorption were evaluated via kinetic studies at four different concentrations (0.1-0.4 mmol/L) that were best represented by the pseudo-second order model, suggesting chemisorption mechanisms, with faster and higher uptakes for DIC (0.084-0.261 mmol/g; teq = 5 min) when compared to LOS (0.058-0.235 mmol/g; teq = 20 min). The curves were also studied via artificial neural networks (ANN) and revealed that the best ANN architecture for representing the experimental data is a network with [3 5 5 2] neurons trained using the Bayesian-Regularization algorithm and the Log-sigmoid (hidden layers) and Linear (output layer) transfer functions. The desorption study showed that CaCl2 had better performance in CNT regeneration, reaching its removal capacity above 50% up to 3 cycles, for both pharmaceuticals. These findings reveal the potential of the developed material as a promising adsorbent for targeted removal of pollutants, contributing to advances in the remediation of emerging contaminants and the application of artificial intelligence in adsorption research.

Layer-by-layer assembly of PDDA/MWCNTs thin films as an efficient strategy for extraction of organic compounds from complex samples.

This article presents the assembly and characterization of poly(diallyldimethylammonium chloride)/multi-walled carbon nanotubes (PDDA/MWCNTs) thin films on borosilicate bottles using a layer-by-layer (LBL) approach. The thin films, consisting of 10 bilayers of coating materials, were thoroughly characterized using UV-VIS spectroscopy, scanning electron microscopy (SEM), and zeta potential measurements. The modified bottles were then utilized for the extraction of analytes with diverse acid-base characteristics, including drugs, illicit drugs, and pesticides, from saliva, urine, and surface water samples. The studied analytes can be adsorbed on the surface of the LBL film mainly through hydrogen bonding and/or hydrophobic interactions. Remarkably high extraction percentages of up to 92 % were achieved, accompanied by an impressive enhancement in the analytical signal of up to 12 times when the sample volume was increased from 0.7 to 10 mL. These results highlight the outstanding extraction and sorption capabilities of the developed material. Additionally, the (PDDA/MWCNTs)10 films exhibited notable resistance to extraction and desorption processes, enabling their reuse for at least 5 cycles. The straightforward and cost-effective fabrication of these sorbent materials using the LBL technique, combined with the ability to extract target compounds during sample transportation and/or storage, renders this sample preparation method a promising alternative.

Exploring novel electroanalytical approach using MWCNT nanostructures to quantify nimodipine.

A new type of buckypaper of MWCNT with entrapped Nimodipine (NMD) drug was constructed. NMD features a nitroaromatic group that is electroreducible, and a dihydropyridine ring that can be electrooxidized. From the perspective of the nitroaromatic group's reductive capability, we have devised amperometric and voltammetric analytical strategies, including both differential pulse and linear voltammetric techniques. These methods are implemented using glassy carbon electrodes (GCE) modified with buckypaper (BP) disks composed of multiwalled carbon nanotubes (MWCNT), which are capable of adsorbing NMD. Furthermore, by capitalizing on the oxidative capacity of the dihydropyridine ring, we have designed strategies that involve amperometry using screen-printed electrodes (SPE) modified with BP-MWCNT mini discs within a Batch Injection Analysis Cell (BIAS) designed for SPE. The developed sensor was applied successfully to determine the drug in commercial tablets. The analytical parameters of this sensor were adequate, with a recovery value of 98.24 % and detection and quantification limits of 7.01 mgL-1 and 23.35 mgL-1, respectively using the DPV method.

Nanomaterials-combined methacrylated gelatin hydrogels (GelMA) for cardiac tissue constructs.

Among non-communicable diseases, cardiovascular diseases are the most prevalent, accounting for approximately 17 million deaths per year. Despite conventional treatment, cardiac tissue engineering emerges as a potential alternative for the advancement and treatment of these patients, using biomaterials to replace or repair cardiac tissues. Among these materials, gelatin in its methacrylated form (GelMA) is a biodegradable and biocompatible polymer with adjustable biophysical properties. Furthermore, gelatin has the ability to replace and perform collagen-like functions for cell development in vitro. The interest in using GelMA hydrogels combined with nanomaterials is increasingly growing to promote the responsiveness to external stimuli and improve certain properties of these hydrogels by exploring the incorporation of nanomaterials into these hydrogels to serve as electrical signaling conductive elements. This review highlights the applications of electrically conductive nanomaterials associated with GelMA hydrogels for the development of structures for cardiac tissue engineering, by focusing on studies that report the combination of GelMA with nanomaterials, such as gold and carbon derivatives (carbon nanotubes and graphene), in addition to the possibility of applying these materials in 3D tissue engineering, developing new possibilities for cardiac studies.

Comprehensive detection of lysergic acid diethylamide (LSD) in forensic samples using carbon nanotube screen-printed electrodes.

Lysergic acid diethylamide (LSD) is a prevalent psychoactive substance recognized for its hallucinogenic properties, often encountered in blotter papers for illicit consumption. Given that LSD ranks among the most widely abused illicit drugs globally, its prompt identification in seized samples is vital for forensic investigations. This study presents, for the first time, an electrochemical screening method for detecting LSD in forensic samples, utilizing a multi-wall carbon nanotube screen-printed electrode (SPE-MWCNT). The LSD detection process was optimized on SPE-MWCNT in a phosphate buffer solution (0.1 mol L-1, pH 12.0) using square wave voltammetry (SWV). The combined use of SPE-MWCNT with SWV displayed robust stability in electrochemical responses for both qualitative (peak potential) and quantitative (peak current) LSD assessment, with a relative standard deviation (RSD) of less than 5% across the same or different electrodes (N = 3). A linear detection range was established between 0.16 and 40.0 µmol L-1 (R2 = 0.998), featuring a low limit of detection (LOD) of 0.05 µmol L-1. Interference studies with twenty-three other substances, including groups of phenethylamines typically found in blotting papers (e.g., NBOHs and NBOMes) and traditional illicit drugs, were performed, revealing a highly selective response for LSD using the proposed method. Consequently, the integration of SPE-MWCNT with SWV offers a robust tool for qualitative and quantitative LSD analysis in forensic applications, providing rapid, sensitive, selective, reproducible, and straightforward preliminary identification in seized samples.

Quint points lattice and multistability in a damped-driven curved carbon nanotube oscillator model.

Single-walled carbon nanotubes (SWCNTs) can undergo arbitrarily large nonlinear deformations without permanent damage to the atomic structure and mechanical properties. The dynamic response observed in curved SWCNTs under externally driven forces has fundamental implications in science and technology. Therefore, it is interesting to study the nonlinear dynamics of a damped-driven curved SWCNT oscillator model if two control parameters are varied simultaneously, e.g., the external driven strength and damping parameters. For this purpose, we construct high-resolution two-dimensional stability diagrams and, unexpectedly, we identify (i) the existence of a quint points lattice merged in a domain of periodic dynamics, (ii) the coexistence of different stable states for the same parameter combinations and different initial conditions (multistability), and (iii) the existence of infinite self-organized generic stable periodic structures (SPSs) merged into chaotic dynamics domains. The quint points lattice found here is composed of five distinct stability domains that coalesce and are associated with five different periodic attractors. The multistability is characterized by the coexistence of three different multi-attractors combinations for three exemplary parameter sets: two periodic attractors, two chaotic attractors, or one periodic and one chaotic attractor. This study demonstrates how complex the dynamics of a damped-driven curved SWCNT oscillator model can be when parameters and initial conditions are varied. For this reason, it may have a relevant impact on new theoretical and experimental applications of damped-driven curved SWCNTs.

Dopamine removal from water by advanced oxidative processes with Fe/N-doped carbon nanotubes.

Dopamine (DA) is an important neurotransmitter in the human body, and a subnormal level is associated with some neurological problems, such as Alzheimer's and Parkinson's diseases. Its use as medicine has progressively increased, as well as its appearance in water bodies, such as domestic or hospital effluents. Dopamine has been found to produce neurological and cardiac damage to the animals that have consumed water with its content, so the removal of dopamine from water is of utmost importance to ensure water safety. Advanced oxidative processes (AOPs) are one of the most effective technologies to eliminate hazardous and toxic compounds in wastewater. In this work, Fe-based multi-walled carbon nanotubes (MWCNTs) were synthesized by aerosol-assisted catalytic chemical vapor deposition to be applied in the AOP of DA. MWCNTs (carbon nanotubes) exhibited high catalytic activity in removing DA with 99% of elimination.By increasing 4 times the initial concentration of DA, the removal percentage of the molecule was lower than the original one, which was attributed to the DA saturation of active sites. Even so, the percentage of degradation was high (76.2%).

Adsorptive behavior of multi-walled carbon nanotubes immobilized magnetic nanoparticles for removing selected pesticides from aqueous matrices.

The present work synthesized two new materials of functionalized multi-walled carbon nanotubes (MWCNT-OH and MWCNT-COOH) impregnated with magnetite (Fe3O4) using solution precipitation methodology. The resulting MWCNT-OH-Mag and MWCNT-COOH-Mag materials were characterized by scanning electron microscopy coupled with energy dispersion X-ray spectroscopy, Fourier transform infrared, X-ray diffraction, atomic force microscopy, and electrical force microscopy. The characterization results indicate that the -OH functional groups in the MWCNT interact effectively with magnetite iron favoring impregnation and indicating the regular distribution of nanoparticles on the surface of the synthesized materials. The adsorption efficiency of the MWCNT-OH-Mag and MWCNT-COOH-Mag materials was tested using the pollutants 2,4-D and Atrazine. Over batch studies carried out under different pH ranges, it was found that the optimal condition for 2,4-D adsorption was at pH 2, while for Atrazine, it was found at pH 6. The rapid adsorption kinetics of 2,4-D and Atrazine reaches equilibrium within 30 min. The pseudo-first-order model described 2,4-D adsorption well. The General-order model described better atrazine adsorption. The magnetically doped adsorbent functionalized with -OH surface groups (MWCNT-OH-Mag) demonstrated superior adsorption performance and increased Fe-doped sites. The Sips model described the adsorption isotherms accurately. MWCNT-OH-Mag presented the greatest adsorption capacity at 51.4 and 47.7 mg g-1 for 2,4-D and Atrazine, respectively. Besides, electrostatic forces and complexation rule the molecular interactions between metals and pesticides. The leaching and regeneration tests of the synthesized materials indicate high stability in an aqueous solution. Furthermore, experiments with wastewater samples contaminated with the model pollutants indicate that the novel adsorbents are highly promising for enhancing water purification by adsorptive separation.

A low-cost carbon-based electrochemical platform for determining 2,3-dihydroxyphenol: applications in natural water and biodiesel samples.

2,3-Dihydroxyphenol (DHP) is a phenolic compound that has been used as an additive in biodiesel to avoid the auto-oxidation of biofuels and also in the production of cosmetic products. However, this substance can be released into the environment during its manufacture, transport, disposal and industrial use and can be harmful to health due to its toxicity, and hence, monitoring its presence in different samples is very important. Therefore, this work describes an electroanalytical study of DHP using different carbon-based pastes prepared to evaluate which one would be more promising to be used as an electrochemical platform for DHP quantification. The materials studied (graphite, carbon black and carbon nanotubes) in this work were characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and the Boehm method. Voltammetric studies showed that pure carbon black presented a higher current density for detecting DHP than the other materials tested (graphite, carbon black + graphite, carbon nanotubes, carbon nanotubes + graphite). In studying the medium's pH, the highest currents occurred in acid media and acetate buffer solutions. After optimizing the experimental parameters, it was possible to obtain a wide range of linear responses from 0.1 to 10 000 µmol L-1 for DHP and a good limit of detection (LOD) of 0.03 µmol L-1. The selectivity of the electrode was tested for different species that may be present in samples containing DHP. Finally, the electrode was applied to determine DHP in natural water and biodiesel samples, showing recovery values between 98 and 102%, indicating good accuracy.

Two birds with one stone: integrating exfoliation and immunoaffinity properties in multi-walled carbon nanotubes by non-covalent functionalization with human immunoglobulin G.

An innovative strategy is proposed to simultaneously exfoliate multi-walled carbon nanotubes (MWCNTs) and generate MWCNTs with immunoaffinity properties. This strategy was based on the non-covalent functionalization of MWCNTs with human immunoglobulin G (IgG) by sonicating 2.5 mg mL-1 MWCNTs in 2.0 mg mL-1 IgG for 15 min with sonicator bath. Impedimetric experiments performed at glassy carbon electrodes (GCE) modified with the resulting MWCNT-IgG nanohybrid in the presence of anti-human immunoglobulin G antibody (Anti-IgG) demonstrated that the immunoglobulin retains their biorecognition properties even after the treatment during the MWCNT functionalization. We proposed, as proof-of-concept, two model electrochemical sensors, a voltammetric one for uric acid quantification by taking advantages of the exfoliated MWCNTs electroactivity (linear range, 5.0 × 10-7 M - 5.0 × 10-6 M; detection limit, 165 nM) and an impedimetric immunosensor for the detection of Anti-IgG through the use of the bioaffinity properties of the IgG present in the nanohybrid (linear range, 5-50 µg mL-1; detection limit, 2 µg mL-1).

Development of an inexpensive and rapidly preparable enzymatic pencil graphite biosensor for monitoring of glyphosate in waters.

Glyphosate (GLY) is the most widely used non-selective broad-spectrum herbicide worldwide under well-reported side effects on the environment and human health. That's why it's necessary to control its presence in the environment. This work describes the development of an affordable, simple, and accurate electrochemical biosensor using a pencil graphite electrode as support, a horseradish peroxidase enzyme immobilized on a polysulfone membrane doped with multi-walled carbon nanotubes. The developed electrochemical sensor was used in the determination of GLY in river and drinking water samples. Cyclic voltammetry and amperometry were used as electrochemical detection techniques for the characterization and analytical application of the developed biosensor. The working mechanism of the biosensor is based on the inhibition of the peroxidase enzyme by GLY. Under optimal experimental conditions, the biosensor showed a linear response in the concentration range of 0.1 to 10 mg L-1. The limits of detection and quantification are 0.025 ± 0.002 and 0.084 ± 0.007 mg L-1, respectively, which covers the maximum residual limit established by the EPA for drinking water (0.7 mg L-1). The proposed biosensor demonstrated high reproducibility, excellent analytical performance, repeatability, and accuracy. The sensor proved to be selective against other pesticides, organic acids, and inorganic salts. Application on real samples showed recovery rates ranging between 98.18 ± 0.11 % and 97.32 ± 0.23 %. The analytical features of the proposed biosensor make it an effective and useful tool for the detection of GLY for environmental analysis.

Electrochemical Sensor Based on Multi-Walled Carbon Nanotubes and N-Doped TiO2 Nanoparticles for Voltametric Simultaneous Determination of Benserazide and Levodopa.

An electrochemical sensor for simultaneous determination of Benserazide (BEZ) and levodopa (L-dopa) was successfully developed using a glassy carbon electrode (GCE) modified with multi-walled carbon nanotube and nitrogen-doped titanium dioxide nanoparticles (GCE/MWCNT/N-TiO2). Cyclic voltammetry and square wave voltammetry were employed to investigate the electrochemical behavior of different working electrodes and analytes. In comparison with unmodified GCE, the modified electrode exhibited better electrocatalytic activity towards BEZ and L-dopa and was efficient in providing a satisfactory separation for oxidation peaks, with a potential difference of 140 mV clearly allows the simultaneous determination of these compounds. Under the optimized conditions, linear ranges of 2.0-20.0 and 2.0-70.0 µmol L-1 were obtained for BEZ and L-dopa, respectively, with a limit of detection of 1.6 µmol L-1 for BEZ and 2.0 µmol L-1 for L-dopa. The method was applied in simultaneous determination of the analytes in pharmaceutical samples, and the accuracy was attested by comparison with HPLC-DAD as the reference method, with a relative error lower than 4.0%.