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Contributing to the development of sustainable electroanalytical chemistry, electrochemically reduced graphene oxide (ERGO) films obtained from residual graphite of discharged Zn-C batteries are proposed in this work. Graphite from the cathode of discarded Zn-C batteries was recovered and used in the synthesis of graphene oxide (GO) by the modified Hummer's method. The quality of the synthesized GO was verified using different characterization methods (FT-IR, XRD, SEM, and TEM). GO films were deposited on a glassy carbon electrode (GCE) by the drop coating method and then electrochemically reduced by cathodic potential scanning using cyclic voltammetry. The electrochemical features of the ERGO films were investigated using the ferricyanide redox probe, as well as paracetamol (PAR) and hydroquinone (HQ) molecules as model analytes. From the cyclic voltammetry assays, enhanced heterogeneous electron transfer rate constants (k0) were observed for all redox systems studied. In analytical terms, the ERGO-based electrode showed higher analytical sensitivity than the bare and GO-modified GCE. Using differential pulse voltammetry, wide linear response ranges and limits of detection of 0.14 μmol L−1 and 0.65 μmol L−1 were achieved for PAR and HQ, respectively. Furthermore, the proposed sensor was successfully applied to the determination of PAR and HQ in synthetic urine and tap water samples (recoveries close to 100%). The outstanding electrochemical and analytical properties of the proposed ERGO films are added to the very low cost of the raw material, being presented as a green-based alternative for the development of electrochemical (bio)sensors with unsophisticated resources. [ABSTRACT FROM AUTHOR]

This work reports the construction of screen‐printed electrode (SPE) modified with carbon black (CB) and magnetic Fe3O4 nanoparticles coated with molecularly imprinted polymer (mag@MIP) based on an alternative low‐cost approach. The proposed device was used for the sensitive and selective voltammetric determination of the antibiotic ciprofloxacin. The results obtained from cyclic voltammetry pointed to the improvement of the SPE response toward the irreversible oxidation of ciprofloxacin after the modification of the electrode surface with CB‐based film and the magnetic preconcentration of mag@MIP containing adsorbed ciprofloxacin molecules. Compared to the non‐molecularly imprinted sensor (mag@NIP), the presence of cavities selective for ciprofloxacin recognition in the mag@MIP nanoparticles accounted for the improvement in analytical signal of the molecularly imprinted sensor. The application of differential pulse voltammetry for ciprofloxacin determination yielded a linear response in the concentration range of 0.5 to 7.0 μmol L−1. The repeatability and interference tests results showed that the proposed electrochemical sensor has good measurement accuracy and selectivity. The proposed device was applied for the voltammetric determination of ciprofloxacin in river water and synthetic urine samples, where recovery rates close to 100 % were recorded for all the samples. The quantification data obtained from the application of the proposed voltammetric method were quite consistent with those of the HPLC reference method. [ABSTRACT FROM AUTHOR]

A novel electrochemical method for determination of losartan using a glassy carbon electrode modified with carbon black nanoparticles immobilized within a crosslinked chitosan film is proposed. The electrochemical behavior of losartan was investigated using cyclic voltammetry, which presented an irreversible oxidation peak at a potential of + 1.28 V vs. Ag/AgCl (3.0 mol L−1 KCl). The electroactivity of losartan on the modified electrode was significantly improved in terms of peak potential and peak current intensity comparatively to bare working electrode. Using square-wave voltammetry technique under optimized conditions, the modified electrode showed a linear response in the concentration range of 4.97 to 47.6 μmol L−1 with a limit of detection of 0.479 μmol L−1. The developed electrochemical method was successfully applied for the determination of losartan in pharmaceutical formulation samples, with results consistent with those obtained by a comparative UV-Vis spectrophotometric method at 95% confidence level. In addition, losartan quantification was also achieved at synthetic biological fluid samples. [ABSTRACT FROM AUTHOR]

A disposable microfluidic electrochemical paper-based device for multiplexed analysis based on sixteen independent microfluidic channels with electrochemical detection is proposed. A major advantage of this work was the non-necessary use of a wax printer for devices manufacturing which has a high cost of operation. In addition, a commercial multiplexing module was used that has the multiplexing capability of 8–16 channels and, for the first time using this module, the strategy of multiplexing both the working and reference electrodes were used. These sixteen channels with the respective sensors can be operated employing one or multiple electrochemical techniques with good repeatability and reproducibility for high throughput analysis. As a proof of concept, the electrochemical performance of device was tested with ferrocenecarboxylic acid solution employing cyclic voltammetry, square-wave voltammetry, differential-pulse voltammetry and chronoamperometry. This innovative sensing platform presented capacity of production in large scale and application for clinical tests with safety and short time of assays. A biosensor was constructed using glucose oxidase on the platform for the glucose determination in urine as a non-invasive strategy. The analytical curve was linear in the glucose concentration range from 1.0 × 10−4 mol L−1 to 4 × 10−2 mol L−1, with a limit of detection of 3 × 10−5 mol L−1. Image 1 • The disposable low-cost microfluidic device proposed allows the high-throughput multiplexed analysis using a small sample volume of 60 μL. • Analytes of interest for clinical analysis can be detected with 16 independent microfluidic channels in multiplexed analysis. • Themicrofluidic device was successfully applied for the determination of glucose in non-invasive samples of urine. [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]

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]

η5-Monocyclopentadienyliron(II)/ruthenium(II) complexes of the general formula [M(η5-C5H5)(PP)(L 1)][PF6] {M = Fe, PP = dppe; M = Ru, PP = dppe or 2PPh3; L 1 = 5-[3-(thiophen-2-yl)benzo[ c]thiophenyl]thiophene-2-carbonitrile} have been synthesized and studied to evaluate their molecular quadratic hyperpolarizabilities. The compounds were fully characterized by NMR, FTIR and UV/Vis spectroscopy and their electrochemical behaviour studied by cyclic voltammetry. Quadratic hyperpolarizabilities ( β) were determined by hyper-Rayleigh scattering measurements at a fundamental wavelength of 1500 nm. Density functional theory calculations were employed to rationalize the second-order non-linear optical properties of these complexes. [ABSTRACT FROM AUTHOR]

Pindolol (PND), an antihypertensive agent indicated for patients in the treatment of angina, hypertension, cardiac arrhythmias and recently consumed as doping agent by athletes, is electrochemically determined in this research by using a cathodically pretreated boron-doped diamond (CPT-BDD) electrode. The electrochemical response of PND studied via cyclic voltammetry on the BDD surface, shows an irreversible oxidation process. From cyclic voltammetric assays carried out at different potential scan rates, the electrochemical parameters number of electrons transferred and the apparent heterogeneous electron transfer rate constant ( k 0 app ) were determined. Additionally, chronoamperometric measurements performed at different PND concentration levels yielded the apparent diffusion coefficient of this molecule ( D app ) in 0.2 mol L −1 phosphate buffer solution (pH = 6.0). After a number of optimization steps, a differential pulse voltammetric (DPV) procedure for the sensitive determination of PND using the CPT-BDD electrode was developed. Under the optimum experimental conditions, the obtained analytical curve was linear in the wide concentration range from 0.04 to 10.0 μmol L −1 and a limit of detection of 26 nmol L −1 was also determined. The viability of the proposed voltammetric procedure was checked out towards the quantification of PND in pharmaceutical formulation samples and biological fluids. The successfully application of the proposed voltammetric procedure suggest the potentiality of this approach for field applications, such as control of pharmaceutics and monitoring of PND in biological samples from athletes subjected to anti-doping exams. [ABSTRACT FROM AUTHOR]

A new family of eight ruthenium(II)-cyclopentadienyl bipyridine derivatives, bearing nitrogen, sulfur, phosphorous and carbonyl sigma bonded coligands, has been synthesized. Compounds bearing nitrogen bonded coligands were found to be unstable in aqueous solution, while the others presented appropriate stabilities for the biologic assays and pursued for determination of IC 50 values in ovarian (A2780) and breast (MCF7 and MDAMB231) human cancer cell lines. These studies were also carried out for the [ 5 : HSA] and [ 6 : HSA] adducts (HSA = human serum albumin) and a better performance was found for the first case. Spectroscopic, electrochemical studies by cyclic voltammetry and density functional theory calculations allowed us to get some understanding on the electronic flow directions within the molecules and to find a possible clue concerning the structural features of coligands that can activate bipyridyl ligands toward an increased cytotoxic effect. X-ray structure analysis of compound [Ru(η 5 -C 5 H 5 )(bipy)(PPh 3 )][PF 6 ] ( 7 ; bipy = bipyridine) showed crystallization on C2/c space group with two enantiomers of the [Ru(η 5 -C 5 H 5 )(bipy)(PPh 3 )] + cation complex in the racemic crystal packing. [ABSTRACT FROM AUTHOR]

Abstract: A series of new ruthenium(II) complexes of the general formula [Ru(η5-C5H5)(PP)(L)][PF6] (PP = DPPE or 2PPh3, L = 4-butoxybenzonitrile or N-(3-cyanophenyl)formamide) and the binuclear iron(II) complex [Fe(η5-C5H5)(PP)(μ-L)(PP)(η5-C5H5)Fe][PF6]2 (L = (E)-2-(3-(4-nitrophenyl)allylidene)malononitrile, that has been also newly synthesized) have been prepared and studied to evaluate their potential in the second harmonic generation property. All the new compounds were fully characterized by NMR, IR and UV–Vis spectroscopies and their electrochemistry behaviour was studied by cyclic voltammetry. Quadratic hyperpolarizabilities (β) of three of the complexes have been determined by hyper-Rayleigh scattering (HRS) measurements at fundamental wavelength of 1500 nm and the calculated static β 0 values are found to fall in the range 65–212 × 10−30 esu. Compound presenting β 0 = 212 × 10−30 esu has revealed to be 1.2 times more efficient than urea standard in the second harmonic generation (SHG) property, measured in the solid state by Kurtz powder technique, using a Nd:YAG laser (1064 nm). [Copyright &y& Elsevier]

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]