The present work introduces nanocomposites based on carbon materials of various nature and hexarhenium chalcogenide clusters as surface modifiers of screen-printed graphite electrodes for ...amperometric immunosensing of the tricyclic antidepressant desipramine. The surface modification of the electrodes by chronoamperometric reduced graphene oxide in combination with chalcogenide hexarhenium clusters or nanodiamonds was developed for the determination of desipramine. The properties of the nanocomposites studied by voltammetry and electrochemical impedance spectroscopy (EIS) were correlated with the roughness parameters of their modified surface associated with the height properties of the irregularities estimated by atomic force microscopy. The composition of the hybrid nanostructures was optimized to provide the following analytical figures of merit for the immunosensors: the range of working concentrations from 1 × 10
−4
to 1 × 10
−9
М and the lower limit of the determined concentrations of (5-8) × 10
−10
М. The optimal parameters for sequential injection analysis were obtained at a flow rate of 25 µl s
−1
and the injected volume of 3125 µl of the supporting buffer at pH 7.5. It is possible to determine lower concentrations of desipramine equal to (7-9) × 10
−11
M using the proposed immunosensors in the flow mode. The testing of the developed immunosensors was characterized by the determination of the analyte in a pharmaceutical preparation and in urine. The relative standard deviation was less than 0.072.
•Model allowing synchronous measurement of flow and structure oscillations.•Experimental data used to validate the one-way and two-way FSI calculations.•Appearing harmonics of the vortex shedding and ...natural frequencies for lock-in mode.
This paper presents results of dynamic measurements of the flow and structure oscillations. We proposed a model consisting of two in-tandem flexible cylinders in the water cross-flow. During the studies, vibration acceleration amplitudes at the shedding frequency and at the cylinders natural frequency were obtained as a function of the flow velocity. The velocity pulsation and pressure pulsation spectra were determined in the flow. A relatively simple structure enabled the use of non-contact measurement systems for cross validation and uncertainty quantifications. The mutual influence of flow and structural dynamics induced by the lock-in effect between the vortex shedding frequency (or its harmonics) and the natural frequency was analyzed. These activities were conducted to generate representative data in order to validate the requirements for hydrodynamic force calculation accuracy and the methods of one-way and two-way coupled FSI calculations.
We propose two modified and rather "universal" methods for the quantitative evaluation of electrochemical noises registered in running voltammetric sensor systems in the presence of unremovable ...artefacts. One approach is based on the discrete geometrical invariant (DGI) method and another is based on the usage of modified Fourier transform. Both approaches did not use model suppositions and were free from the treatment errors. We discussed the reasons for the appearance of the artefacts and showed their applications for increasing the sensitivity and specificity in the detection of some complex organic fluids. As an example, we obtained olive oils from two different producers for their definite differentiation. The selected olive oils from two different countries (Italy and Spain) were placed in working tube electrode cells, and we realized the possibility for the extraction of some useful information from the large amount of nanocurrents. The obtained quantitative parameters allowed the differentiation of URA from possible random noises. These two treatment methods have been proven to be rather "universal" and can be used for the analysis of other URAs having different natures.
We propose two modified and rather "universal" methods for the quantitative evaluation of electrochemical noises registered in running voltammetric sensor systems in the presence of unremovable artefacts.
Contemporary small and medium enterprises, such as IT companies and legal, consulting, and logistic firms, use a variety of electronic tools for management purposes to provide their internal ...information exchange. However, there exist a number of problems (vacation registration, project reporting, professional literature issuance, etc.), which do not fit into the existing models of solutions. In similar cases, some IT companies create their own systems for the automation of homotypical procedures, but many firms have no software solutions for their automation. This paper presents the model and architecture of an open-code software for the staff appraisal service as one of the above mentioned unconventional problems. Such a system will enable the application of this flexible and simple solution at small and medium enterprises for frequently occurring management tasks.
The Au–Bi binary system electrodeposited on the surface of a glassy carbon electrode exhibits catalytic activity during the electrooxidation of phenylephrine, paracetamol, and caffeine that enhances ...the peak currents and decreases overvoltage in the oxidation of organic compounds. The potential difference between the peaks of oxidation on the modified electrode is 400 mV for phenylephrine and paracetamol and 300 mV for phenylephrine and caffeine, respectively. The possibility of simultaneous voltammetric determination of phenylephrine, paracetamol, and caffeine on the glassy carbon electrode modified by the Au–Bi binary system was established. The calibration curve is linear in the concentration range from 5·10–6 to 5·10–3 M. The developed method was tested in the analysis of combined drugs.
A significant proportion of publications related to the ionospheric disturbances that arise during earthquake preparation over the regions of their preparation refer to these disturbances as ...anomalies. In this case, the identification of the ionospheric precursor is actually based on an estimate of the amplitude of the deviation of the ionospheric parameters from the undisturbed value. We propose a completely different approach based on the physical mechanism of the generation of disturbances created by the interaction of the ionosphere with the lithosphere and atmosphere. At the same time, this interaction gives the observed variations unique properties that are typical only for earthquake precursors, based on which the precursors are identified with an intelligent algorithm. Another advantage of this approach is that the method, which we call “cognitive identification”, does not require large deviations from unperturbed values, since it is based on recognition of the “image” of the precursor. It is created in a way that considers morphological features of the precursors and can be effectively used even at low values of the signal/noise ratio.
It is found that mixed-valence iridium oxides electrodeposited on the surface of a glassy carbon electrode exhibit catalytic activity in the oxidation of caffeine. In this case, a more pronounced ...catalytic effect is obtained on an electrode modified with a composite based on a film of a perfluorinated sulfopolymer (Nafion) and mixed-valence iridium oxides. A selective voltammetric method for the determination of caffeine is developed. A linear logarithmic dependence of current on the caffeine concentration is observed in the range from 1 × 10
–8
to 5 × 10
–3
M. The developed method was used to determine caffeine in energy drinks.
The control of the precise concentration of steroid hormones and their synthetic analogs in biomedical objects is a relevant analytical task. A method for selective and highly sensitive simultaneous ...amperometric determination of adrenaline, melatonin, and cortisol with the use of a two-detector flow-injection system is developed. Screen-printed carbon electrodes (SPE) with one or two working electrodes modified with a gold–palladium binary system that exhibits catalytic activity upon electrooxidation of the organic compounds under consideration are used as detectors. The high sensitivity of determination is attributed to the catalytic properties of the metal modifier: the transition from the metal to the binary system leads to an increase in the catalytic oxidation current of hormones. The selectivity of determination of adrenaline in the presence of melatonin and cortisol is provided by the difference in the oxidation potentials of the hormones on the proposed electrode. For selective determination of melatonin and cortisol, the surface of the modified working electrode is coated with a Nafion film. The difference of potentials of the peaks of oxidation of adrenaline, melatonin, and cortisol on such an electrode is 300 mV. The proposed method is tested in the analysis of urine samples. The flow-injection scheme is supplemented with a dialyzer and a chromatographic minicolumn to eliminate the interfering effect of electrophilic compounds. The linear bilogarithmic dependence of the analytical signal on the concentration of adrenaline, melatonin, and cortisol is observed in the ranges of 5.0 × 10
–10
–5.0 × 10
–3
, 5.0 × 10
–11
–5.0 × 10
–3
, and 5.0 × 10
–12
–5.0 × 10
–3
mol/L, respectively. Amperometric determination of the hormones in the flow-injection system leads to an increase in the productivity of the analysis and a decrease in the consumption of the sample and makes it possible to automate the process.
Various nanostructured materials (graphene, fullerene C
60
, carbon nanotubes, and cobalt nanoparticles as a label) are used as nanocomposites to modify the surface of primary signal ...converters (screen-printed graphite electrode) in the development of amperometric immunosensors for the determination of tricyclic antidepressant amitriptyline. The use of nanomaterials improved the analytical characteristics of the corresponding immunosensors. The range of working concentrations of the immunosensor is 1 × 10
–9
–1 × 10
–4
M, the lower limit of the analytical range is at a level of 5 × 10
–10
M. The binding constants of antigen–antibody immune complexes are determined. Immunosensors are tested in the control of contents of medicinal preparations in urine.
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.
