(Bio)Sensing Strategies Based on Ionic Liquid-Functionalized Carbon Nanocomposites for Pharmaceuticals: Towards Greener Electrochemical Tools.

The interaction of carbon-based nanomaterials and ionic liquids (ILs) has been thoroughly exploited for diverse electroanalytical solutions since the first report in 2003. This combination, either through covalent or non-covalent functionalization, takes advantage of the unique characteristics inherent to each material, resulting in synergistic effects that are conferred to the electrochemical (bio)sensing system. From one side, carbon nanomaterials offer miniaturization capacity with enhanced electron transfer rates at a reduced cost, whereas from the other side, ILs contribute as ecological dispersing media for the nanostructures, improving conductivity and biocompatibility. The present review focuses on the use of this interesting type of nanocomposites for the development of (bio)sensors specifically for pharmaceutical detection, with emphasis on the analytical (bio)sensing features. The literature search displayed the conjugation of more than 20 different ILs and several carbon nanomaterials (MWCNT, SWCNT, graphene, carbon nanofibers, fullerene, and carbon quantum dots, among others) that were applied for a large set (about 60) of pharmaceutical compounds. This great variability causes a straightforward comparison between sensors to be a challenging task. Undoubtedly, electrochemical sensors based on the conjugation of carbon nanomaterials with ILs can potentially be established as sustainable analytical tools and viable alternatives to more traditional methods, especially concerning in situ environmental analysis.

Electrochemical sensor based on multi-walled carbon nanotubes for imidacloprid determination.

A simple and robust sensor (fMWCNT-Nafion®0.5%/GCE) for determination of imidacloprid (IMI), a widely used neonicotinoid, was developed using a glassy carbon electrode (GCE) modified with functionalized multi-walled carbon nanotubes (fMWCNT) and Nafion®. The obtained data suggest that IMI reduction is an irreversible process, due to the reduction of the nitro group to hydroxylamine derivatives, with the participation of two protons and four electrons, and a charge transfer coefficient of 0.141. The optimized square-wave voltammetric conditions were: McIlvaine buffer at pH 6.0, 0.5% of Nafion® in the fMWCNT suspension, -0.6 V and 180 s as accumulation potential and time, respectively. A linearity in the range of 2.00 × 10-7 to 1.77 × 10-6 mol L-1 IMI, with the values of limit of detection and limit of quantification were equal to 3.74 × 10-8 mol L-1 and 1.25 × 10-7 mol L-1, respectively. Repeatability and reproducibility displayed relative standard deviations lower than 5%. Recovery tests performed in tap water, melon, and shrimp yielded mean values of 94 ± 6%, 97 ± 10% and 93 ± 10%, respectively. Moreover, several inorganic and organic compounds did not significantly interfere (0.6 to 4.5%) on the IMI signal, proving the selectivity and applicability of the developed sensor for IMI detection in complex samples.

Molecular approach about the effect of water on the electrochemical behaviour of Ag+ ions in urea-choline chloride-water mixture.

The water influence on electrochemical behaviour of Ag+ ions in urea and choline chloride mixture was investigated by cyclic voltammetry technique, while the molecular insights about the investigated systems were obtained from molecular dynamic (MD) simulation. The water content was variated from 0 up to 10% (v/v). Cyclic voltammetry technique showed that the peak potential for Ag+/Ag redox couples shifted in direction to more positive potentials with the gradual increase of water content in solution, indicating that the addition of water electrocatalyses the kinetics of the reduction of Ag+ ions. The MD simulations demonstrated that water molecules do not interact strongly with Ag+ ions but induce a small reduction in the number of urea molecules around of the ion and that the water molecules adjust to free spaces in the mixture.

Application of Nanostructured Carbon-Based Electrochemical (Bio)Sensors for Screening of Emerging Pharmaceutical Pollutants in Waters and Aquatic Species: A Review.

Pharmaceuticals, as a contaminant of emergent concern, are being released uncontrollably into the environment potentially causing hazardous effects to aquatic ecosystems and consequently to human health. In the absence of well-established monitoring programs, one can only imagine the full extent of this problem and so there is an urgent need for the development of extremely sensitive, portable, and low-cost devices to perform analysis. Carbon-based nanomaterials are the most used nanostructures in (bio)sensors construction attributed to their facile and well-characterized production methods, commercial availability, reduced cost, high chemical stability, and low toxicity. However, most importantly, their relatively good conductivity enabling appropriate electron transfer rates-as well as their high surface area yielding attachment and extraordinary loading capacity for biomolecules-have been relevant and desirable features, justifying the key role that they have been playing, and will continue to play, in electrochemical (bio)sensor development. The present review outlines the contribution of carbon nanomaterials (carbon nanotubes, graphene, fullerene, carbon nanofibers, carbon black, carbon nanopowder, biochar nanoparticles, and graphite oxide), used alone or combined with other (nano)materials, to the field of environmental (bio)sensing, and more specifically, to pharmaceutical pollutants analysis in waters and aquatic species. The main trends of this field of research are also addressed.

Understanding the dipyrone oxidation allying electrochemical and computational approaches.

Electroanalytical methodology by boron-doped diamond electrode (BDDE) associated to the square-wave voltammetry (SWV) for the determination of hydrolyzed dipyrone (DIP) in commercial formulations, raw natural waters and in human urine was developed. Through cyclic voltammetry (CV), it was shown that the oxidation of the DIP on the BDDE was irreversible with diffusional control. Computational studies suggested that the oxidation mechanism of DIP occurred with participation of two electrons and one proton. The analytical curves were obtained for concentrations of DIP ranging from 1.0 × 10-6 to 6.5 × 10-5 mol L-1 (r = 0.9994). The values of detection limit (LOD) and quantification limit (LOQ) of DIP were calculated from SWV and found to be 2.6 × 10-7 mol L-1 and 8.8 × 10-7 mol L-1. The methodology was effectively applied to real samples with the values of calculated recoveries varying between 91.0% and 117.3% and validated by iodometric titration experiments whose values were between 93.3% and 106.9%. The proposed methodology with BDDE represents an alternative tool and it has advantageous, such as very easy handling, low cost, no need for modification, low detection limit. Furthermore, it can be used for the routine analysis of DIP in different real samples.

Chitosan-magnetite nanocomposite as a sensing platform to bendiocarb determination.

A novel platform for carbamate-based pesticide quantification using a chitosan/magnetic iron oxide (Chit-Fe3O4) nanocomposite as a glassy carbon electrode (GCE) modifier is shown for an analytical methodology for determination of bendiocarb (BND). The BND oxidation signal using GCE/Chit-Fe3O4 compared with bare GCE was catalyzed, showing a 37.5% of current increase with the peak potential towards less positive values, showing method's increased sensitivity and selectivity. Using square-wave voltammetry (SWV), calibration curves for BND determination were obtained (n = 3), and calculated detection and quantification limits values were 2.09 × 10-6 mol L-1 (466.99 ppb) and 6.97 × 10-6 mol L-1 (1555.91 ppb), respectively. The proposed electroanalytical methodology was successfully applied for BND quantification in natural raw waters without any sample pretreatment, proving that the GCE/Chit-Fe3O4 modified electrode showed great potential for BND determination in complex samples. ᅟ Graphical abstract.

Dispersion of multi-walled carbon nanotubes in [BMIM]PF6 for electrochemical sensing of acetaminophen.

The influence of functionalized multi-walled carbon nanotubes (fMWCNT) in the presence of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) in different ratios was investigated on the acetaminophen (ACOP) electrochemical determination. The electrochemical behavior of the ACOP exhibited a pair of well-defined redox peaks, suggesting that the reversibility of ACOP was significantly improved in comparison to irreversible oxidation peak on bare GCE. The redox process was controlled by adsorption, involves two electrons and the value of apparent rate constant (ks) was equal to 14.7 s-1 ±â€¯3.6 s-1. The analytical curves were obtained for concentrations of ACOP ranging from 0.3 to 3.0 µmol L-1. The values of the detection limit were calculated from SWV and found to be 6.73 × 10-8 mol L-1. The proposed electrochemical sensor exhibited good stability and reproducibility and was applied for ACOP determination in tablets (Tylenol® and Tylenol®DC) with satisfactory results.

The effect of water on the physicochemical properties of an ethylene glycol and choline chloride mixture containing Cu2+ ions: electrochemical results and dynamic molecular simulation approach.

The effect of water on the physicochemical properties of an ethylene glycol and choline chloride mixture containing Cu2+ ions was investigated by electrochemical techniques and molecular dynamics simulation. The experiments and computational calculations were carried out by increasing the water content from 0 up to 10% (v/v). The cyclic voltammetry and chronopotentiometry techniques showed that the diffusion coefficient of Cu2+ ions increased and that the peak potentials for both the Cu2+/Cu+ and Cu+/Cu redox couples shifted towards more positive potentials with the increase in the water content in the solution. The molecular dynamics simulation indicated that the water molecules replaced the ethylene glycol molecules that were coordinated with Cu2+ ions, while the interactions between Cu2+ and Cl- ions were not influenced by the presence of water.

Morphological dependence of silver electrodeposits investigated by changing the ionic liquid solvent and the deposition parameters.

The low toxicity and environmentally compatible ionic liquids (ILs) are alternatives to the toxic and harmful cyanide-based baths used in industrial silver electrodeposition. Here, we report the successful galvanostatic electrodeposition of silver films using the air and water stable ILs 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIM]TfO) and 1-H-3-methylimidazolium hydrogen sulphate ([HMIM(+)][HSO4(-)]) as solvents and AgTfO as the source of silver. The electrochemical deposition parameters were thoughtfully studied by cyclic voltammetry before deposition. The electrodeposits were characterized by scanning electron microscopy coupled with X-ray energy dispersive spectroscopy and X-ray diffraction. Molecular dynamics (MD) simulations were used to investigate the structural dynamic and energetic properties of AgTfO in both ILs. Cyclic voltammetry experiments revealed that the reduction of silver is a diffusion-controlled process. The morphology of the silver coatings obtained in [EMIM]TfO is independent of the applied current density, resulting in nodular electrodeposits grouped as crystalline clusters. However, the current density significantly influences the morphology of silver electrodeposits obtained in [HMIM(+)][HSO4(-)], thus evolving from dendrites at 15 mA cm(-2) to the coexistence of dendrites and columnar shapes at 30 mA cm(-2). These differences are probably due to the greater interaction of Ag(+) with [HSO4(-)] than with TfO(-), as indicated by the MD simulations. The morphology of Ag deposits is independent of the electrodeposition temperature for both ILs, but higher values of temperature promoted increased cluster sizes. Pure face-centred cubic polycrystalline Ag was deposited on the films with crystallite sizes on the nanometre scale. The morphological dependence of Ag electrodeposits obtained in the [HMIM(+)][HSO4(-)] IL on the current density applied opens up the opportunity to produce different and predetermined Ag deposits.

Modeling of laccase inhibition by formetanate pesticide using theoretical approaches.

The inhibition of laccase enzymatic catalytic activity by formetanate hydrochloride (FMT) was investigated by cyclic voltammetry and by quantum chemical calculations based on density functional theory with a protein fragmentation approach. The cyclic voltammograms were obtained using a biosensor prepared by enzyme immobilization on gold electrodes modified with gold nanoparticles and 4-aminophenol as the target molecule. The decrease in the peak current in the presence of FMT was used to characterize the inhibition process. The calculations identified Asp206 as the most relevant moiety in the interaction of FMT with the laccase enzymatic ligand binding domain. The amino acid residue Cys453 was important, because the Cys453-FMT interaction energy was not affected by the dielectric constant, although it was not a very close residue. This study provides an overview of how FMT inhibits laccase catalytic activity.

Diclofenac on boron-doped diamond electrode: from electroanalytical determination to prediction of the electrooxidation mechanism with HPLC-ESI/HRMS and computational simulations.

Using square-wave voltammetry coupled to the boron-doped diamond electrode (BDDE), it was possible to develop an analytical methodology for identification and quantification of diclofenac (DCL) in tablets and synthetic urine. The electroanalytical procedure was validated, with results being statistically equal to those obtained by chromatographic standard method, showing linear range of 4.94 × 10(-7) to 4.43 × 10(-6) mol L(-1), detection limit of 1.15 × 10(-7) mol L(-1), quantification limit of 3.85 × 10(-7) mol L(-1), repeatability of 3.05% (n = 10), and reproducibility of 1.27% (n = 5). The association of electrochemical techniques with UV-vis spectroscopy, computational simulations and HPLC-ESI/HRMS led us to conclude that the electrooxidation of DCL on the BDDE involved two electrons and two protons, where the products are colorful and easily hydrolyzable dimers. Density functional theory calculations allowed to evaluate the stability of dimers A, B, and C, suggesting dimer C was more stable than the other two proposed structures, ca. 4 kcal mol(-1). The comparison of the dimers stabilities with the stabilities of the molecular ions observed in the MS, the compounds that showed retention time (RT) of 15.53, 21.44, and 22.39 min were identified as the dimers B, C, and A, respectively. Corroborating the observed chromatographic profile, dimer B had a dipole moment almost twice higher than that of dimers A and C. As expected, dimer B has really shorter RT than dimers A and C. The majority dimer was the A (71%) and the C (19.8%) should be the minority dimer. However, the minority was the dimer B, which was formed in the proportion of 9.2%. This inversion between the formation proportion of dimer B and dimer C can be explained by preferential conformation of the intermediaries (cation-radicals) on the surface.

Sensitive bi-enzymatic biosensor based on polyphenoloxidases-gold nanoparticles-chitosan hybrid film-graphene doped carbon paste electrode for carbamates detection.

A bi-enzymatic biosensor (LACC-TYR-AuNPs-CS/GPE) for carbamates was prepared in a single step by electrodeposition of a hybrid film onto a graphene doped carbon paste electrode (GPE). Graphene and the gold nanoparticles (AuNPs) were morphologically characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, dynamic light scattering and laser Doppler velocimetry. The electrodeposited hybrid film was composed of laccase (LACC), tyrosinase (TYR) and AuNPs entrapped in a chitosan (CS) polymeric matrix. Experimental parameters, namely graphene redox state, AuNPs:CS ratio, enzymes concentration, pH and inhibition time were evaluated. LACC-TYR-AuNPs-CS/GPE exhibited an improved Michaelis-Menten kinetic constant (26.9±0.5M) when compared with LACC-AuNPs-CS/GPE (37.8±0.2M) and TYR-AuNPs-CS/GPE (52.3±0.4M). Using 4-aminophenol as substrate at pH5.5, the device presented wide linear ranges, low detection limits (1.68×10(-9)±1.18×10(-10)-2.15×10(-7)±3.41×10(-9)M), high accuracy, sensitivity (1.13×10(6)±8.11×10(4)-2.19×10(8)±2.51×10(7)%inhibitionM(-1)), repeatability (1.2-5.8% RSD), reproducibility (3.2-6.5% RSD) and stability (ca. twenty days) to determine carbaryl, formetanate hydrochloride, propoxur and ziram in citrus fruits based on their inhibitory capacity on the polyphenoloxidases activity. Recoveries at two fortified levels ranged from 93.8±0.3% (lemon) to 97.8±0.3% (orange). Glucose, citric acid and ascorbic acid do not interfere significantly in the electroanalysis. The proposed electroanalytical procedure can be a promising tool for food safety control.

Simple laccase-based biosensor for formetanate hydrochloride quantification in fruits.

This work describes the development of an electrochemical enzymatic biosensor for quantification of the pesticide formetanate hydrochloride (FMT). It is based on a gold electrode modified with electrodeposited gold nanoparticles and laccase. The principle behind its development relies on FMT's capacity to inhibit the laccase catalytic reaction that occurs in the presence of phenolic substrates. The optimum values for the relevant experimental variables such as gold nanoparticles electrochemical deposition (at -0.2V for 100s), laccase immobilization (via glutaraldehyde cross-linking), laccase concentration (12.4mg/mL), substrate selection and concentration (5.83×10(-5)M of aminophenol), pH (5.0), buffer (Britton-Robinson), and square-wave voltammetric parameters were determined. The developed biosensor was successfully applied to FMT determination in mango and grapes. The attained limit of detection was 9.5×10(-8)±9.5×10(-10)M (0.02±2.6×10(-4)mg/kg on a fresh fruit weight basis). Recoveries for the five tested spiking levels ranged from 95.5±2.9 (grapes) to 108.6±2.5% (mango). The results indicated that the proposed device presents suitable characteristics in terms of sensitivity (20.58±0.49A/µM), linearity (9.43×10(-7) to 1.13×10(-5)M), accuracy, repeatability (RSD of 1.4%), reproducibility (RSD of 1.8%) and stability (19days) for testing of compliance with established maximum residue limits of FMT in fruits and vegetables.

Laccase-Prussian blue film-graphene doped carbon paste modified electrode for carbamate pesticides quantification.

A novel enzymatic biosensor for carbamate pesticides detection was developed through the direct immobilization of Trametes versicolor laccase on graphene doped carbon paste electrode functionalized with Prussian blue films (LACC/PB/GPE). Graphene was prepared by graphite sonication-assisted exfoliation and characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The Prussian blue film electrodeposited onto graphene doped carbon paste electrode allowed considerable reduction of the charge transfer resistance and of the capacitance of the device. The combined effects of pH, enzyme concentration and incubation time on biosensor response were optimized using a 2(3) full-factorial statistical design and response surface methodology. Based on the inhibition of laccase activity and using 4-aminophenol as redox mediator at pH 5.0, LACC/PB/GPE exhibited suitable characteristics in terms of sensitivity, intra- and inter-day repeatability (1.8-3.8% RSD), reproducibility (4.1 and 6.3% RSD), selectivity (13.2% bias at the higher interference:substrate ratios tested), accuracy and stability (ca. twenty days) for quantification of five carbamates widely applied on tomato and potato crops. The attained detection limits ranged between 5.2×10(-9)molL(-1) (0.002mgkg(-1) w/w for ziram) and 1.0×10(-7)molL(-1) (0.022mgkg(-1) w/w for carbofuran). Recovery values for the two tested spiking levels ranged from 90.2±0.1 (carbofuran) to 101.1±0.3% (ziram) for tomato and from 91.0±0.1% (formetanate) to 100.8±0.1% (ziram) for potato samples. The proposed methodology is appropriate to enable testing pesticide levels in food samples to fit with regulations and food inspections.

Biosensor based on multi-walled carbon nanotubes paste electrode modified with laccase for pirimicarb pesticide quantification.

This study focused on the development of a sensitive enzymatic biosensor for the determination of pirimicarb pesticide based on the immobilization of laccase on composite carbon paste electrodes. Multi-walled carbon nanotubes (MWCNTs) paste electrode modified by dispersion of laccase (3%, w/w) within the optimum composite matrix (60:40%, w/w, MWCNTs and paraffin binder) showed the best performance, with excellent electron transfer kinetic and catalytic effects related to the redox process of the substrate 4-aminophenol. No metal or anti-interference membrane was added. Based on the inhibition of laccase activity, pirimicarb can be determined in the range 9.90 × 10(-7) to 1.15 × 10(-5) mol L(-1) using 4-aminophenol as substrate at the optimum pH of 5.0, with acceptable repeatability and reproducibility (relative standard deviations lower than 5%). The limit of detection obtained was 1.8 × 10(-7) mol L(-1) (0.04 mg kg(-1) on a fresh weight vegetable basis). The high activity and catalytic properties of the laccase-based biosensor are retained during ca. one month. The optimized electroanalytical protocol coupled to the QuEChERS methodology were applied to tomato and lettuce samples spiked at three levels; recoveries ranging from 91.0 ± 0.1% to 101.0 ± 0.3% were attained. No significant effects in the pirimicarb electroanalysis were observed by the presence of pro-vitamin A, vitamins B1 and C, and glucose in the vegetable extracts. The proposed biosensor-based pesticide residue methodology fulfills all requisites to be used in implementation of food safety programs.

Square-wave adsorptive voltammetry of dexamethasone: redox mechanism, kinetic properties, and electroanalytical determinations in multicomponent formulations.

The electrochemical reduction behavior of dexamethasone at a hanging mercury drop electrode was investigated by cyclic and square-wave adsorptive voltammetries in a Britton-Robinson buffer at pH 2.0. The optimized experimental conditions consisted of a pulse potential frequency of 100 s(-1), a pulse amplitude of 15 mV, and a potential step height of 2 mV, with E(acc)=-0.60V and t(acc)=15s. From these parameters, it was also possible to develop a detailed study about the kinetic and mechanistic events involved in the reduction process. Two well-defined peaks were observed in the cathodic scan, and peak 2 was used to obtain analytical curves. A linear range between 4.98×10(-8) and 6.10×10(-7)mol L(-1), with a detection limit of 2.54×10(-9)mol L(-1) and a quantification limit of 8.47×10(-9)mol L(-1), was observed. Moreover, it was possible to achieve a simple, selective, and versatile methodology adaptable to the quantification of dexamethasone because common excipients used in multicomponent commercial formulations caused no interference. The satisfactory recoveries and the low relative standard deviation data reflected the high accuracy and precision of the proposed method for the determination of dexamethasone in injectable eye drops and elixir samples.

Square wave voltammetric determination of nitrofurantoin in pharmaceutical formulations on highly boron-doped diamond electrodes at different boron-doping contents.

The influence of the boron-doping levels in boron-doped diamond film electrodes on the electrochemical response of nitrofurantoin (NFT) and the development of an electroanalytical procedure for NFT determination were investigated. The investigations were carried out using the techniques of cyclic voltammetry and square wave voltammetry on diamond film electrodes with different boron-doping levels (i.e., 5000, 10,000 and 20,000 mg L(-1)). The level of boron-doping in the diamond film electrodes influenced the electrochemical reduction of NFT. The appropriate cyclic voltammetric response of NFT was obtained with Britton-Robinson buffer at pH 4 and for diamond films doped with 10,000 and 20,000 mg L(-1) of boron. These two films were selected for the development of the electroanalytical procedure. The use of square wave voltammetry with the optimized parameters demonstrated a good linear relationship between the peak current and the NFT concentration for a wide range of concentration. The lower limit of detection for the electrodes doped with 10,000 and 20,000 mg L(-1) of boron were 2.69 x 10(-8) mol L(-1) (6.40 microg L(-1)) and 8.15 x 10(-9) mol L(-1) (1.94 microg L(-1)), respectively, while the lower limits of quantification were 8.96 x 10(-8) mol L(-1) (21.33 microg L(-1)) and 2.72 x 10(-8) mol L(-1) (6.47 microg L(-1)), respectively. The applicability of the proposed procedure was tested using a commercial pharmaceutical formulation of NFT, and the results were compared with the procedure recommended by the British Pharmacopeia. The proposed procedure was sensitive, accurate and precise for analysis of NFT and did not require complex preparations or renovations of the electrode surface. This presents the advantage of eliminating mercury waste and minimizing the adsorptive problems related to the use of other electrodic solid surfaces.