Amperometric monoamine oxidase biosensors based on screen-printed graphite electrodes modified with nanostructured reduced graphene oxide (RGO) composites and cobalt nanoparticles (CoNPs) were ...developed to determine antidepressant drug substances (tianeptine, thioridazine, and fluoxetine). Carbon nanomaterials with metal nanoparticles (nanocomposites) allow individual components to retain their properties but also ensure better quality of devices owing to joint contribution of constituents. The nanomodifier was applied to the surface of screen-printed graphite electrodes via dropwise evaporation. The RGO fastening on the surface is due to electrostatic interaction between RGO carboxyl groups and amine groups of the amine derivative on the platform of polyester polyol (H20–NH
2
). Cobalt nanoparticles were obtained using the electrochemical chronoamperometry method at a potential
E
= –1.0 V and different times of their accumulation (50 and 60 s) on the electrode surface. According to atomic force microscopy data, the CoNP size varies with the time of electrochemical deposition of NPs, achieving predominately (40 ± 2) and (78 ± 8) nm. The electrochemical impedance spectroscopy reveals the lowest values of the charge transfer resistance for RGO-chitosan/CoNP nanocomposites and RGO-amine derivative on the polyester polyol (H20–NH
2
)/CoNPs platform. The use of these nanocomposites in the electrode surface modification was found to significantly improve the analytical characteristics of biosensors, extending the operating concentration range from 1 × 10
–4
to 5 × 10
–9
mol/L, increasing the sensitivity and correlation coefficients, and decreasing the detectable concentration limit. Biosensors were shown to be promising in the quality control of antidepressants upon the determination of the main active substance in medicinal drugs and biological fluids. The lower limit of detectable concentrations of (7–9) × 10
–10
mol/L is attained by using tyramine as a substrate for the determination of fluoxetine, thioridazine, and tianeptine.
Materials based on copolymers of isobornylacrylate (IBA) with methylmethacrylate (MMA) or acrylonitrile (AN) have been synthesized by radical copolymerization using monomeric mixtures with different ...composition. The copolymer compositions were determined and relative activities of monomers were calculated by different methods. All copolymers have transparency up to 80% in the ultraviolet region. The mechanical and thermophysical properties of the copolymers depend on composition. The best combination of optical transparency and tensile strength is achieved in the copolymers containing 13% and 49% units of IBA (in the case of MMA and AN, respectively. The prospects of application of the copolymers as a matrix for creating photoinduced nanocomposites containing CdS are shown. Using the specially selected compounds of cadmium, materials with new optical properties were obtained by UV irradiation.
A procedure was suggested for voltammetric determination of streptomycin from the catalytic current on a glassy carbon electrode with a composite based on reduced graphene oxide and gold–nickel ...binary system. The working conditions of the electrode modification (volume of the graphene oxide and chitosan suspension, duration of the electrolytic reduction of immobilized graphene oxide and electrodeposition of the gold–nickel binary system) and the conditions for recording the catalytic current in the flow injection system were determined. The procedure for streptomycin determination in a flow, compared to the determination under stationary conditions, is more sensitive, reproducible, and rapid. The streptomycin detection limit was 0.45 nmol, and the productive capacity of the analysis was 60 samples per hour. The streptomycin determination procedure passed trials in analysis of cow milk.
Biosensor devices that include hybrid nanostructures as transducer surface modifiers meet current requirements for methods of research and determination of drugs, including antidepressants. Here, we ...consider the features of amperometric monoamine oxidase biosensors based on screen-printed graphite electrodes modified with nanocomposite consisting of C
60
/cobalt nanoparticles/amino derivative of a second-generation polyether polyol/chitosan in the determination of the tricyclic antidepressant amitriptyline. The best modifier was selected using transmission electron microscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. In the biosensor development, the conditions for applying the composite based on cobalt nanoparticles/amino derivative of polyether polyol to the electrode surface were varied: electrochemical deposition, sequential deposition by the layer-on-layer method, and deposition of a mixture. As an analytical signal of the biosensor, we used the peak of the electrochemical oxidation of hydrogen peroxide, which is formed during the enzymatic oxidation of serotonin under the action of monoamine oxidase. The operating principle of the biosensor is based on the inhibitory effect of amitriptyline on the catalytic activity of immobilized monoamine oxidase. For the selected modifier, the determined concentration range of amitriptyline is 1 × 10
–4
–1 × 10
–8
mol/L and the lower limit of the determined contents is 5 × 10
–9
mol/L under optimal operating conditions. Comparison of the results of the amitriptyline determination in a pharmaceutical preparation and urine that were obtained using a monoamine oxidase biosensor and the method of fluorescence polarization immunoassay (dilution of the tracer of 1 : 32, dilution of antibodies of 1 : 128, range of working concentrations from 5 × 10
–8
to 5 × 10
–9
mol/L), which has proven itself in the determination of medicinal substances, confirmed the correctness of the developed method.
Acetylcholinesterase (ChE) sensor based on Prussian blue (PB) modified electrode was developed and tested for the detection of organophosphorus and carbamic pesticides. The signal of the sensor was ...generated in PB mediated oxidation of thiocholine recorded at+200 mv in DC mode. ChE from electric eel was immobilized by cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) on the surface of screen-printed carbon electrode covered with PB and Nafion. The content of the surface layer (specific enzyme activity, Nafion and BSA amounts) was optimized to establish high and reliable response toward the substrate and ChE inhibitors. The ChE/PB sensor makes it possible to detect Aldicarb, Paraoxon and Parathion-Methyl with limits of detection 30, 10 and 5 ppb, respectively (incubation 10 min). The feasibility of practical application of the ChE/PB sensor developed for the monitoring of degradation of the pesticides in wine fermentation was shown. To diminish matrix interferences, the electrolysis of the grape juice with Al anode and evaporation of ethanol were suggested, however the procedures decrease the sensitivity of pesticide detection and stability of the sample tested.
An inorganic film of ruthenium hexachlororuthenate (RuRuCl
6
), deposited on the surface of a glassy carbon electrode, exhibits electrocatalytic activity in the oxidation of purine nucleosides, such ...as guanosine and adenosine. Appropriate operating conditions are found for fabricating a polymer film on the surface of glassy carbon and for recording the maximum electrocatalytic current for the modified electrode. A method for the selective voltammetric determination of guanosine and adenosine in their simultaneous presence at an electrode modified by a RuRuCl
6
film is developed. A procedure is proposed for the amperometric detection of purine nucleosides with this modified electrode under the conditions of flow-injection analysis. The linear dependence of the analytical signal on the concentration of guanosine and adenosine is observed up to 5 × 10
–6
M in the stationary mode and up to 5 × 10
–7
M in the flow system. The proposed method for the selective determination of guanosine and adenosine was tested in the analysis of human urine.
The effect different types of bottom soil have on the acoustic signal produced by air bubbles passing through the soil into water is considered. The gas flux is calculated using data from recording ...of the acoustic signal produced by active bubbling methane seepages in Laspi Bay, allowing for the error introduced by the soil. The inconsistency in the intensity of the methane fluxes is demonstrated.
Surface modification of screen-printed graphite electrodes with nanostructured materials (multiwall carbon nanotubes, gold and silver nanoparticles) allow their application as supports of ...amperometric monoaminoxidase biosensors for the determination of antidepressant drugs (moclobemide, tianeptine, and amitriptyline). This approach improves analytical characteristics of the corresponding biosensors because of the inhibitory effect of antidepressants (two-parameter concerted inhibition) on the catalytic activity of an immobilized enzyme. The analytical capabilities of the developed biosensor types were compared. The range of working concentrations was from 5 × 10
–9
to 1 × 10
–4
M and the lower limit of the analytical range was of about 8 × 10
–10
M. Biosensors based on electrodes modified with nanostructured materials were tested in the control of the concentration of drugs in body fluids (urine) and dosage forms.
Structure vibration under the influence of unsteady hydrodynamic forces caused by the flow around their surfaces can adversely affect durability and rupture life. Reducing the adverse effects of ...hydrodynamic forces is currently possible with the help of linked
CFD
and vibration calculations. However, for an adequate description of the associated processes one should use calculation models and approaches specific to the hydro-vibration problem. To justify and validate such approaches, an experimental model was developed and a series of structure excitation tests in water flow was carried out.
The model comprises two cylinders installed sequentially in water crossflow. Vibration levels, pressure and velocity fluctuations were measured in the tests as a functions of the flow velocity. The application of different non-intrusive measurement techniques was possible due to relatively simple test model construction which may be used for cross-validation and experimental uncertainty quantification.
Flow-structure interaction, caused by synchronization effect of the flow separation frequency (or it’s spectral components) and eigenfrequency of cylinder, was analyzed based on simultaneously measured data. The tests performed gave the information about dynamical characteristics of the flow and vibration parameters of cantilevered cylinders. The experimental results are used for identification of required accuracy of hydrodynamic forces calculation by
CFD
and validation of oneand two-way linked methods for flow excitation frequency calculation.
The properties of hexarhenium chalcogenide nanoclusters (K
4
{Re
6
S
8
}(OH)
6
·8H
2
O and K
4
{Re
6
S
8
}(CN)
6
·8H
2
O) in combination with carbon nanomaterials (carbon nanotubes and graphene ...oxide) are studied by voltammetry, electrochemical impedance spectroscopy, atomic force microscopy, and spectrophotometry and their screening is performed for use as hybrid modifiers of screen-printed graphite electrodes in immunosensors in order to improve analytical characteristics. The high negative charge of nanoclusters can be considered the driving force of the adsorption of clusters in the formation of electrodes modified by hybrid nanomaterials. It was found that hexarhenium chalcogenide nanoclusters possess electrochemical activity, which was first used to register immunochemical interactions. The change in the resistance of electron transfer made it possible to choose the best hybrid nanomaterials. The parameters of the surface roughness of the modified electrodes associated with the height properties of the irregularities were estimated. The use of hexarhenium chalcogenide nanoclusters in combination with carbon nanomaterials as hybrid nanomodifiers has made it possible to develop highly sensitive and selective amperometric and impedimetric immunosensors for the determination of tricyclic antidepressants (amitriptyline, desipramine, and imipramine) in pharmaceuticals and urine. The limit of quantification (LOQ) is at the level (4–7) × 10
–11
M. The relative standard deviation does not exceed 5%.
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