Electrochemical determination of metformin via a carbon paste electrode modified with an Ag NPs/Cu2O/CuO-decorated bacterial nanocellulose composite.

Metformin (MET) is widely used in the treatment of diabetes either alone or in combination with other drugs, in drug discovery to evaluate the anti-diabetic potential of other drugs, and usually as a comparison compound in pharmacokinetics/pharmacodynamics studies. Measuring the concentration of this substance is very important both pre-clinically in different species and clinically in the medical monitoring of diabetic patients to prevent toxicity and ensure adherence to described drugs. Therefore, it is very important to develop a sensitive and selective method to measure MET. In this work, a new electrochemical biosensor based on a carbon paste electrode, modified with bacterial nanocellulose, copper oxide, and silver nanoparticles (Ag NPs/Cu2O/CuO/BNC/CPE) was used for high-sensitivity MET determination. The morphology and structure of this bio-nanocomposite were characterized by ATR-IR, FE-SEM, EDS, mapping, XRD, and DRS techniques. Compared with the CPE electrode, the Ag NPs/Cu2O/CuO/BNC/CPE modified electrode showed much higher electrocatalytic activities toward the oxidation of MET. The measurements were carried out by the cyclic voltammetry technique. Surface conductance was evaluated using the impedance technique. The results showed an increase in surface conductivity. The detection limit was obtained at 42.3 nM and two linear ranges 0.1-76 and 76-1000.0 µM were observed. The developed sensor had good features such as high sensitivity, reproducibility and repeatability, low detection limit, and fast response time. The obtained results from the real sample (MET tablets) were completely satisfactory.

NiO hedgehog-like nanostructures/Au/polyaniline nanofibers/reduced graphene oxide nanocomposite with electrocatalytic activity for non-enzymatic detection of glucose.

A novel sensitive non-enzymatic glucose sensor was fabricated based on nickel oxide hedgehog-like nanostructures decorated ternary gold nanoparticles/polyaniline nanofibers/reduced graphene oxide nanocomposites (NiO/Au/PANI/rGO). The morphology and structure of NiO/Au/PANI/rGO nanocomposites were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FT-IR). Electrochemical impedance spectroscopy (EIS) data also indicated the charge transfer of each layer decreased compared to the underneath layer. Electrocatalytic and electrochemical behavior of the modified electrode for the detection and measurement of glucose determined by cyclic voltammetry and amperometric methods. The results revealed that the NiO/Au/PANI/rGO nanocomposite modified glassy carbon electrode exhibited remarkable electrocatalytic performance toward glucose oxidation, with a wide linear range of 0.09-6 mM and a low detection limit of 0.23 µM based on a signal to noise ratio of 3. This electrode can effectively analyse glucose concentration in human serum samples, avoiding interference, and compared to the spectrophotometry method. Using the Student's t-test and F-test, there was no significant difference between the compared methods. Also this electrode is a promising non-enzymatic glucose sensor due to its fast response, good selectivity and stability and low overpotential.

Flower-like ZnO decorated polyaniline/reduced graphene oxide nanocomposites for simultaneous determination of dopamine and uric acid.

A novel sensor was fabricated by electrochemical deposition of ZnO flower-like/polyaniline nanofiber/reduced graphene oxide nanocomposite (ZnO/PANI/RGO) on glassy carbon electrode (GCE) for direct detection of dopamine (DA) and uric acid (UA) in the presence of fixed concentration of ascorbic acid (AA). Surface morphology and characterization of the modified electrodes were confirmed by field emission scanning microscopy (FE-SEM), X-ray diffraction (XRD), Raman and FT-IR spectroscopies. For individual detection, the linear responses were in the two concentration ranges of 0.001-1 µM and 1-1000 µM with detection limit 0.8 nM (S/N = 3) for DA, and also 0.1-100 µM and 100-1000 µM with detection limit 0.042 µM (S/N = 3) for UA. Simultaneous determination of these species in their mixture solution showed the linear responses in the two concentration ranges of 0.1-90 µM and 90-1000 µM with detection limit 0.017 µM (S/N = 3) for DA and also showed two linear range of 0.5-90 µM and 100-1000 µM with detection limit 0.12 µM (S/N = 3) for UA, with coexistence of 1000 µM AA. The applicability of sensor for the analysis of DA, and UA in dopamine injection solution, human serum and human urine samples was successfully demonstrated.

Fabrication and characterization of non-enzymatic glucose sensor based on ternary NiO/CuO/polyaniline nanocomposite.

Novel nickel and copper oxide nanoparticle modified polyaniline (PANI) nanofibers (NiO/CuO/PANI) were fabricated and used as a non-enzymatic sensor for detecting glucose. PANI nanofibers were prepared through electrodeposition, whereas nickel and copper oxide nanoparticles were deposited on PANI nanofibers by electrodeposition and electrochemical oxidation in situ. The morphology and structure of NiO/CuO/PANI nanocomposites were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FT-IR). The as-prepared NiO/CuO/PANI electrode was employed for non-enzymatic glucose detection in alkaline electrolyte and showed better electrocatalytic activity compared with the PANI, CuO/PANI, and NiO/PANI electrodes. Consequently, an amperometric electrode of glucose was achieved under 0.6 V versus Ag/AgCl with a wide linear range from 20 to 2500 µM (R(2) = 0.9978) and a low detection limit of 2.0 µM (signal/noise [S/N] = 3). This electrode can effectively analyze glucose concentration in human serum samples, avoiding interference, and is a promising non-enzymatic glucose sensor due to its low overpotential, high sensitivity, good selectivity and stability, fast response, and low cost.

ZnO-CuxO/polypyrrole nanocomposite modified electrode for simultaneous determination of ascorbic acid, dopamine, and uric acid.

Novel zinc oxide (ZnO) nanosheets and copper oxide (CuxO, CuO, and Cu2O) decorated polypyrrole (PPy) nanofibers (ZnO-CuxO-PPy) have been successfully fabricated for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The morphology and structure of ZnO-CuxO-PPy nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Compared with the bare glassy carbon electrode (GCE), PPy/GCE, CuxO-PPy/GCE, and ZnO-PPy/GCE, ZnO-CuxO-PPy/GCE exhibits much higher electrocatalytic activities toward the oxidation of AA, DA, and UA with increasing peak currents and decreasing oxidation overpotentials. Cyclic voltammetry (CV) results show that AA, DA, and UA could be detected selectively and sensitively at ZnO-CuxO-PPy/GCE with peak-to-peak separation of 150 and 154 mV for AA-DA and DA-UA, respectively. The calibration curves for AA, DA, and UA were obtained in the ranges of 0.2 to 1.0 mM, 0.1 to 130.0 µM, and 0.5 to 70.0 µM, respectively. The lowest detection limits (signal/noise=3) were 25.0, 0.04, and 0.2 µM for AA, DA, and UA, respectively. With good selectivity and sensitivity, the current method was applied to the determination of DA in injectable medicine and UA in urine samples.

Electrochemically fabricated polypyrrole nanofiber-modified electrode as a new electrochemical DNA biosensor.

A new biosensor employing immobilized DNA on a nano-structured conductive polymer fixed onto a platinum electrode is presented. Upon optimization of synthesis parameters, polypyrrole nanofibers, 30-90 nm in diameter, were synthesized in an aqueous media by the electropolymerization of pyrrole using normal pulse voltammetry (NPV). The nanofiber film was investigated by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Double-stranded DNA was physisorbed onto the PPy nanofiber films. Various parameters, including the pH and DNA concentration, were optimized. The DNA immobilized on the nanofiber films was characterized using differential pulse voltammetry (DPV) and Fourier-transform infrared (FTIR) spectroscopy. Using DPV to study the interaction of spermidine with DNA, a binding constant (K) value of 4.08 x 10(5)+/-0.05 M(-1) was obtained. For the determination of spermidine, the proposed method exhibited a good dynamic range, correlation coefficient (0.05-1.0 microM and 0.9983, respectively) and a low detection limit (0.02 microM), although Ca(2+) ions were found to electrostatically bind to DNA and weaken the spermidine-DNA interaction.