Sensitive and simple electroanalytical methods were developed for the determination of the loop diuretic furosemide (FUR) in pharmaceutical formulations and synthetic urine samples by coupling ...square-wave voltammetry (SWV) with polished basal-plane pyrolytic graphite (BPPG) or cathodically pretreated boron-doped diamond (BDD) and amorphous carbon nitride (a-CNx) as working electrodes. The analytical parameters obtained with the three methods were compared. With BPPG, best results were attained using 0.10molL−1 H2SO4 as supporting electrolyte, whereas with BDD and a-CNx, this was attained using a 0.040molL−1 BR buffer (pH 4.5). Cyclic voltammograms obtained for FUR evidenced an irreversible behavior (with two oxidation peaks), in agreement with the literature. On the BDD and a-CNx electrodes, the electrooxidation of FUR is a purely diffusion-controlled process, whereas on the BPPG electrode some degree of adsorption is also involved. The obtained linear response ranges (detection limits) for the BPPG, BDD, and a-CNx electrodes were 0.60–4.8 (0.47), 0.30–13 (0.30), and 0.50–99 (0.39) μmolL−1, respectively. The proposed methods were successfully applied in the determination of FUR in pharmaceutical formulations (tablets), with results similar to those obtained using a reference spectrophotometric method (at a confidence level of 95 %), and in the recovery of FUR in synthetic urine samples. The analytical conditions obtained with the novel SWV methods here reported are comparatively better than those for other electrochemical methods in the literature. As the pretreatment procedures are much simpler for BDD and a-CNx than for BPPG, one can conclude that the former two materials can be advantageously used to determine FUR with good sensitivity and selectivity.
A sensor based on glassy carbon electrode (GCE) modified within reduced graphene oxide (RGO) and carbon black (CB) in a chitosan film (CTS) is presented. The combination of the nanomaterials with CTS ...provided a stable dispersion and could be successfully used as electroactive layer. By using the Nicholson method and the results obtained by cyclic voltammetry with the proposed RGO-CB-CTS/GCE, the heterogeneous electron transfer rate constant (k0) of 5.6×10−3cms−1 was obtained. The proposed electrode was applied for the simultaneous determination of dopamine (DA) and paracetamol (PAR). Employing square-wave voltammetry, DA presented an anodic peak at 0.25V and PAR at 0.50V vs. Ag/AgCl (3.0molL−1 KCl). The analytical curves obtained were linear in the range from 3.2×10−6 to 3.2×10−5molL−1 and from 2.8×10−6 to 1.9×10−5molL−1 for DA and PAR, respectively, with detection limits of 2.0×10−7 for DA and 5.3×10−8molL−1 for PAR. The developed sensor presented advantages such as simple preparation, low cost of the nanomaterials employed and a fast response. Besides, it could successfully apply in the determination of DA and PAR in biological samples.
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•A thin film using reduced graphene oxide and carbon black in a chitosan film is proposed.•The proposed electrode is easy to prepare, presents low cost and fast response.•It was applied the simultaneous determination of dopamine and paracetamol.
A bare composite graphite-polyurethane electrode (EGPU) and two other modified with graphene (EGPU-GR) and functionalized multi-walled carbon nanotubes (EGPU-CNTs) were prepared and compared ...regarding their voltammetric response to escitalopran (EST). The modifiers were characterized by Raman spectroscopy and the resulting electrode materials by contact angle measurements with a hydrophilicity character in the ascending order for the composites: GPU > GPU-GR > GPU-CNTs and scanning electron microscopy (SEM). The electroactive areas of the EGPU, EGPU-GR, and EGPU-CNTs were 0.065, 0.080, and 0.092cm2, respectively, calculated from the chronocoulometry using K3Fe(CN)6 as a probe and the Cottrell equation. The cyclic voltammograms obtained for EST indicated irreversible electrochemical behavior, with an anodic peak at ca. +0.80V (νs. SCE). These measurements were carried out with the three electrodes, and comparison of the analytical responses led to the EGPU-GR electrode being selected for use in the subsequent experiments. Under optimal conditions, square wave and differential pulse voltammetry at EGPU-GR presented linear dynamic ranges between 1.5 × 10−6 and 1.2 × 10−5mol L−1, with a detection limit of 2.5 × 10−7molL−1 (SWV) and 1.5 × 10−6 and 1.2 × 10−5molL−1, with a detection limit of 3.2 × 10−7molL−1 (DPV) for EST. The proposed method was applied for the quantification of EST in synthetic urine and cerebrospinal fluid samples, offering advantages including simplicity of fabrication, no requirement for analyte preconcentration and surface renewal, fast response, and selectivity.
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•Graphite polyurethane electrodes modified with carbon nanotubes and graphene were prepared.•Performance of the resulting sensing devices were compared in the determination of Escitalopram.•Better analytical results were found in square wave voltammetry at graphene modified electrode.•This is the first time that graphene is used in EGPU modification and in escitalopram analysis.•The device was used in determination of escitalopram in urine and cerebrospinal synthetic fluids.
Gold nanoparticles (AuNP) were electrodeposited onto the surface of a graphite-polyurethane composite electrode (EGPU), followed by electrochemical treatment in NaOH medium using cyclic voltammetry. ...After characterization and optimization of the experimental conditions, the resulting device (EGPU-tAuNP) was used for voltammetric determination of tryptophan (TRP). Analyses using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) revealed a homogeneous covering of the electrode surface, with no alteration of the morphology due to the electrochemical treatment in NaOH. Electrochemical Impedance Spectroscopy (EIS) measurements showed that modification with AuNP and electrochemical treatment in basic media reduces the electron-transfer resistance and improves the electron-transfer rate. Chronocoulometric data and cyclic voltammograms obtained in the presence of 100.0μmolL−1 TRP revealed an increase in the peak current and a displacement of the peak potential to more negative values after the pretreatment in basic medium. A mechanism involving the Au0/Au3+ reaction on the electrode surface and TRP oxidation was proposed. Under optimized conditions, using differential pulse voltammetry (DPV), the EGPU-tAuNP presented a detection limit of 5.3×10−8molL−1 for the analysis of TRP. The device was used for the determination of TRP in synthetic urine and commercial poly-amino acids supplement. Tests of interference were carried out with biologically relevant compounds. The standard additions procedure could be used to overcome interferences in the analysis of synthetic urine containing creatinine.
•Graphite-polyurethane electrodes containing electrodeposited gold nanoparticles were prepared.•Electrochemical treatment was proposed for activation of gold nanoparticles.•Differential pulse voltammetry was used in the determination of tryptophan.•The device was used in the determination of tryptophan in biological and pharmaceutical samples.
Graphene is one of the most studied materials ever, owing to its exceptional electronic, mechanical and thermal properties, which allow for many different types of application. In this review, we ...shall concentrate on the use of graphene and derivatives for electrochemical sensors and biosensors, where emphasis is placed on the importance of surface functionalization as this permits synergistic combinations with other nanomaterials and biomolecules. In addition to describing recent advances in graphene‐based electroanalytical applications, we discuss a few examples of their use in detecting small biomolecules and in immunosensing for a few diseases using films and composites. Also discussed are the possible methods for mass production of graphene, which is key to low‐cost biosensors for implantable devices and portable systems in point‐of‐care diagnosis.
The envisaged ubiquitous sensing and biosensing for varied applications has motivated materials development toward low cost, biocompatible platforms. In this paper, we demonstrate that carbon ...nanodiamonds (NDs) can be combined with potato starch (PS) and be deposited on a glassy carbon electrode (GCE) in the form of a homogeneous, rough film, with electroanalytical performance tuned by varying the relative ND-PS concentration. As a proof of concept, the ND/PS film served as matrix to immobilize tyrosinase (Tyr) and the resulting Tyr-ND-PS/GCE biosensor was suitable to detect catechol using differential pulse voltammetry with detection limit of 3.9 × 10−7 mol L−1 in the range between 5.0 × 10−6 and 7.4 × 10−4 mol L−1. Catechol could also be detected in river and tap water samples. This high sensitivity, competitive with biosensors made with more sophisticated procedures and materials in the literature, is attributed to the large surface area and conductivity imparted by the small NDs (<5 nm). In addition, the ND-PS matrix may have its use extended to immobilize other enzymes and biomolecules, thus representing a potential biocompatible platform for ubiquitous biosensing.
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•Biosensor made with a biocompatible thin film containing nanodiamonds and potato starch, coated with tyrosinase.•The biosensor detected catechol with a low detection limit.•Catechol could also be detected in tap and river water samples.•Estimated cost per sensing unit of only US$ 0.04
•A new disposable bismuth film electrode is proposed.•The bismuth film electrode is easy to prepare.•Diquat and Paraquat pesticides are determined using the proposed electrode.
The development of a ...bismuth film on a disposable minisensor for electroanalytical determination of Diquat (DQ) and Paraquat (PQ) using voltammetric techniques as square-wave (SWV) and differential-pulse (DPV) is reported. The disposable minisensor consisted of a bismuth film-working electrode, a silver-pseudo-reference and copper-counter electrodes. Copper boards of a printed circuit were used as substrate and nail varnish was used as an electrical insulator to limit the electrode area. The disposable proposed minisensor was applied for the determination of DQ using SWV and PQ using DPV. Under optimal experimental conditions, the cathodic peak current was linear in the DQ concentration range of 0.19×10−6–9.3×10−6molL−1 with a detection limit of 8.9×10−8molL−1, and, for PQ the peak current was linear in the concentration range of 0.12×10−6–4.2×10−6molL−1 with a detection limit of 1.2×10−8molL−1. The proposed method was applied for the determination of both pesticides in natural water samples and the obtained results are in good agreement with those results obtained using a high-performance liquid chromatography at a 95% confidence level.
The electroanalytical detection of the neurotransmitter dopamine (DA) in the presence of uric acid (UA) is explored for the first time using commercially procured nanodiamonds (NDs). These are ...electrically wired via surface modification upon screen-printed graphite macroelectrodes (SPEs). The surface coverage of the NDs on the SPEs was explored in order to optimize electroanalytical outputs to result in well-resolved signals and in low limits of detection. The (electro)analytical outputs are observed to be more sensitive than those achieved at bare (unmodified) SPEs. Such responses, previously reported in the academic literature have been reported to be electrocatalytic and have been previously attributed to the presence of surface sp
2
carbon and oxygenated species on the surface of the NDs. However, XPS analysis reveals the commercial NDs to be solely composed of nonconductive sp
3
carbon. The low/negligible electroconductivity of the NDs was further confirmed when ND paste electrodes were fabricated and found to exhibit no electrochemical activity. The electroanalytical enhancement, when using NDs electronically wired upon SPEs, is attributed not to the NDs themselves being electrocatalytic, as reported previously, but rather changes in mass transport where the inert NDs block the underlying electroactive SPEs and create a random array of graphite microelectrodes. The electrode was applied to simultaneous sensing of DA and UA at pH 5.5. Figures of merit include (a) low working potentials of around 0.27 and 0.35 V (vs. Ag/AgCl); and (b) detection limits of 5.7 × 10
−7
and 8.9 × 10
−7
M for DA and UA, respectively.
Graphical abstract
The electroanalytical enhancement of screen-printed electrodes modified with inert/non-conductive nanodiamonds is due to a change in mass transfer where the inert nanodiamonds facilitate the production of a random microelectrode array.
In this paper, the electrochemical determination of the N-nitrosodiphenylamine was proposed comparing the voltammetric response of two non-modified carbon electrodes: a glassy carbon (GCE) and a ...solid graphite-polyurethane composite (GPUE). The surfaces of the electrodes were characterized by atomic force microscopy. The electroactive areas of GCE and GPUE were 0.040 and 0.068 cm2, respectively, calculated from chronocoulometry measurements using K4Fe(CN)6 as probe and the integrated form of Cottrell Equation. Cyclic voltammograms obtained for N-nitrosodiphenylamine using both electrodes indicated anodic and cathodic peaks (vs. Ag/AgCl (3.0 mol L−1 KCl), in agreement with the literature. At GCE, the electrochemical reduction of the molecule is a diffusion-controlled process, whereas at GPUE some degree of adsorption was also observed. Square wave and differential pulse voltammetry were explored in order to optimize the best analytical performance for the quantification of the molecule. Under optimal conditions, linear range (sensitivity and limit of detection) for GCE and GPUE of 8.02 to 46.6 μmol L−1 (1.09 μA L μmol−1 cm−2 and 4.54 μmol L−1) and of 2.51 to 17.5 μmol L−1 (5.50 μA L μmol−1 cm−2 and 0.270 μmol L−1) were obtained, respectively. Considering higher sensitivity and lower detection limits values, the GPUE was selected for the quantification of N-nitrosodiphenylamine in synthetic urine samples. The developed method presented a competitive detection limit compared to other sensors reported in the literature, considering the use of a non-modified electrode, with low cost of fabrication, easiness of surface renovation, and sustainability.
•GCE and GPUE were characterized by chronocoulometry, AFM, and EIS.•Voltammetric performances of the electrodes were compared in NDPhA determination.•Higher sensitivity and lower limit of detection were found in SWV using GPUE.•NDPhA was determinate for the first time in urine samples.
•Albendazole (ABZ) is determined by DP voltammetry with a diamond electrode.•A cathodically pretreated diamond electrode was used to develop the novel method.•The new method was used in the ...determination of ABZ in pharmaceutical formulations.•The attained detection limit is the best yet for a direct electroanalytical method.•The obtained results are in agreement with those of a comparative HPLC method.
A sensitive, simple, and rapid electrochemical method was developed for the determination of albendazole (ABZ) in anthelminthic pharmaceutical formulations using differential pulse voltammetry (DPV) with a cathodically pretreated boron-doped diamond (BDD) electrode and 0.05molL−1 H2SO4 as supporting electrolyte. The electrochemical behavior of ABZ obtained with cyclic voltammetry (CV) showed two oxidation peaks at 0.95 and 1.30V vs. Ag/AgCl (3.0molL−1 KCl). The total number of electrons (four) transferred during the oxidation process was estimated from the scan rate dependence of this CV response. The proposed method resulted in an analytical curve ranging from 0.0797 to 8.36μmolL−1, with a detection limit (based on 3-sigma) of 0.0625μmolL−1. This novel DPV method was successfully applied to determine ABZ in three pharmaceutical formulations (tablets), with results similar to those obtained using a reference HPLC method.
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