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© 2020 Wiley-VCH GmbH An electrochemical sensor using glassy carbon electrode modified with carbon black within a poly(allylamine hydrochloride) film is proposed in this work. The novel sensor was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry using the redox probe Fe(CN)63−/4−. The sensor was applied for the simultaneous determination of dopamine (DA), paracetamol (PAR), amlodipine (AML), and rosuvastatin (RSV). The quantification of all four analytes was carried out by linear sweep voltammetry and presented a linear concentration range for all analytes from 1.0 to 90 μmol L−1, with limit of detection of 0.55, 1.3, 5.7, and 3.0 μmol L−1 for DA, PAR, AML, and RSV, respectively. This sensor was successfully applied in the simultaneous determination of these analytes in environmental, pharmaceutical, and biological samples.

A photoelectrochemical biosensing strategy for the highly sensitive detection of the flavonoid rutin was developed by synergizing the photoelectrocatalytic properties of hematite (α-Fe2O3) decorated with palladium nanoparticles (PdNPs) and the biocatalysis towards laccase-based reactions. The integration of α-Fe2O3.PdNPs with a polyphenol oxidase as a biorecognition element yields a novel biosensing platform. Under visible light irradiation, the photoactive biocomposite can generate a stable photocurrent, which was found to be directly dependent upon the concentration of rutin. Under the optimal experimental conditions, the cathodic photocurrent, measured at 0.33 V vs. Ag/AgCl, from the square-wave voltammograms presented a linear dependence on the rutin concentration within the range of 0.008–30.0 × 10−8 mol L−1 (sensitivity: 1.7 μA·(× 10−8 M−1)·cm−2), with an experimental detection limit (S/N = 3) of 8.4 × 10−11 mol L−1. The proposed biosensor device presented good selectivity towards rutin in the presence of various organic compounds and inorganic ions, demonstrating the potential application of this biosensing platform in complex matrices. This bioanalytical device also exhibited excellent operational and analytical properties, such as intra-day (standard deviation, SD = 0.21%) and inter-day (SD = 1.30%) repeatability, and long storage stability (SD = 2.80% over 30 days). Graphical abstract

Laccase from Botryosphaeria rhodina MAMB-05 was covalently immobilized on carboxymethyl-botryosphaeran by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) in aqueous solution. This approach was employed to fabricate a novel laccase-based biosensor to electrochemically quantify quercetin (QCT), using a simple carbon black paste electrode as a transducer. The proposed biosensor was characterized by electrochemical impedance spectroscopy and Nyquist plots were used to evaluate the immobilization of the enzyme. For determining QCT, variables were optimized, that included experimental conditions for laccase immobilization, pH of the supporting electrolyte, and instrumental parameters of the electroanalytical technique. From square-wave-voltammograms, a linear dependence between the cathodic current peak and QCT concentration was observed within the range 4.98–50.0 × 10−8 mol L−1, with a theoretical detection limit of 2.6 × 10−8 mol L−1. The proposed method was successfully applied to determine QCT in beverages, pharmaceuticals, and biological samples. The proposed biosensor device presented good selectivity in the presence of uric acid, various inorganic ions, as well as other phenolic compounds, demonstrating the potential application of this biosensing platform in chemically complex solutions. Operational and analytical stability of the laccase-biosensor were evaluated, and good intra-day (SD = 1.23%) and inter-day (SD = 2.32%) repeatability, and long storage stability (SD = 3.47%) are presented.

In this work, we employed multiple linear regression analyses to satisfactorily determine cold symptoms treatment drugs paracetamol, phenylephrine hydrochloride, and loratadine in pharmaceutical formulations with combined dosage and spiked human urine sample. All the drugs are irreversibly oxidized on the boron-doped diamond electrode (BDDE) in diffusion-controlled oxidation processes with well-separated potentials in acidic media. A square-wave voltammetric (SWV) method was developed for their simultaneous determination in 0.1 mol L–1 H2SO4 and simple and multiple linear regression analyses were compared as calibration methods for SWV data. Precision and selectivity were also studied. The high concentration ratio between paracetamol and the other two drugs being minor components in the formulated dosage forms caused interference in their voltammetric responses. An assay based on multiple linear regression equations considering these multiple effects revealed statistically the same results as those obtained by a comparative HPLC-UV method at a 95% confidence level. We demonstrated that multiple linear regression provided adequate recovery for the determination of PAR, PHE, and LOR in spiked human urine sample. The developed SWV method is a very fast, low-cost, and environmentally friendly alternative to the routine simultaneous analysis of PAR, PHE, and LOR performed by HPLC-UV.

Laccase was immobilized on a glassy carbon electrode layered with multi-walled carbon nanotubes using a film of botryosphaeran, a fungal (1 → 3)(1 → 6)-β-D-glucan. This novel biosensing platform was characterized by electrochemical impedance spectroscopy and scanning electron microscopy, and applied for the determination of dopamine. Experimental variables such as enzyme concentration, pH value and operational parameters of the electroanalytical technique were optimized. Using square-wave voltammetry, there was a linear dependence of peak current and dopamine concentration within the range of 2.99–38.5 μmol L −1 with a limit of detection of 0.127 μmol L −1 . The biosensor was successfully applied in the determination of dopamine in pharmaceutical injection and synthetic biological samples, and presented good selectivity even in the presence of uric acid and ascorbic acid, as well as other phenolic compounds. The different aspects regarding the operational stability of the laccase biosensor were evaluated, demonstrating good intra-day and inter-day repeatability, and long-storage stability. Furthermore, this biosensor was evaluated in the indirect determination of spironolactone by using the analytical signal of dopamine, presenting a limit of detection of 0.94 μmol L −1 . The results obtained in the analysis of spironolactone in commercial pharmaceutical samples were satisfactory.

In this work, we explored the efficiency of the use of the pretreated boron-doped diamond electrode (BDDE) coupled to electroanalytical techniques for the individual determination of pravastatin (PRAV) and its association with acetylsalicylic acid (ASA). The voltammetric behavior of PRAV and ASA was investigated by cyclic voltammetry showing irreversible and diffusion-controlled oxidation processes for both analytes, regardless of the type of BDDE pretreatment. Under the optimized conditions (cathodically pretreated BDDE and phosphate buffer solution, pH 4.0), the analytical response for PRAV was linear over the range from 1.0 to 30 μmol L−1 for individual determination using amperometry, obtaining a limit of detection (LOD) of 0.102 μmol L−1. For simultaneous determination of PRAV and ASA, (using the anodically pretreated BDDE in 0.3 mol L−1 H2SO4 solution), the responses were linear over the range of 1.08–16.4 μmol L−1 for PRAV and 3.96–42.75 μmol L−1 for ASA using SWV, obtaining a LOD of 0.204 and 0.078 μmol L−1, respectively. The methods were successfully applied to pharmaceutical formulations, synthetic urine and tap water samples.