Electrochemical determination of thiethylperazine using semi-graphitized carbon nanofibers-MnO nanocomposite.

A new voltammetric method is proposed for high sensitive thiethylperazine (THP) determination, using a glassy carbon electrode modified with semi-graphitized carbon nanofibers/MnO nanocomposite (eCNF/MnO/GC). To the best of our knowledge, this is the first electrochemical assay of THP  determination, and the first use of the eCNF/MnO as the electrode modifier. The proposed method using eCNF/MnO/GC is characterized by high repeatability and sensitivity of measurements, with the linearity of THP in the range from 0.05 to 2.2 µmol L-1. The lowest detection limit achieved on the eCNF/MnO/GC electrode for 30 s of preconcentration was 6.3 nmol L-1 THP in 0.05 mol L-1 acetate buffer of  pH 5.6. The proposed method was successfully applied to highly sensitive THP determination in complex matrices, such as tablets and plasma with good recovery (98-103%). The RSD value obtained for THP measurement at a concentration of 0.1 µmol L-1 was 1.3%. Amperometric measurements of THP under the flow injection conditions were also performed to indicate the possibility of its fast and accurate determination (103% and 95% for unmodified and modified electrode, respectively), with the duration of single analysis of approx. 30 s.

Exploring CVD Method for Synthesizing Carbon-Carbon Composites as Materials to Contact with Nerve Tissue.

The main purpose of these studies was to obtain carbon-carbon composites with a core built of carbon fibers and a matrix in the form of pyrolytic carbon (PyC), obtained by using the chemical vapor deposition (CVD) method with direct electrical heating of a bundle of carbon fibers as a potential electrode material for nerve tissue stimulation. The methods used for the synthesis of PyC proposed in this paper allow us, with the appropriate selection of parameters, to obtain reproducible composites in the form of rods with diameters of about 300 µm in 120 s (CF_PyC_120). To evaluate the materials, various methods such as scanning electron microscopy (SEM), scanning transmission electron microscope (STEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and tensiometer techniques were used to study their microstructural, structural, chemical composition, surface morphology, and surface wettability. Assessing their applicability for contact with nervous tissue cells, the evaluation of cytotoxicity and biocompatibility using the SH-SY5Y human neuroblastoma cell line was performed. Viability and cytotoxicity tests (WST-1 and LDH release) along with cell morphology examination demonstrated that the CF_PyC_120 composites showed high biocompatibility compared to the reference sample (Pt wire), and the best adhesion of cells to the surface among all tested materials.

Use of Hierarchical Carbon Nanofibers Decorated with NiCo Nanoparticles for Highly Sensitive Vortioxetine Determination.

A new voltammetry method for the highly sensitive antidepressant drug vortioxetine (VOR) is presented using glassy carbon electrodes modified with hierarchical carbon nanofibers with NiCo nanoparticles (eCNF/CNT/NiCo-GCE). The electrochemical behavior of VOR was investigated by cyclic voltammetry, which indicates that its oxidation is an adsorption-controlled process with the exchange of two electrons and one proton. The effects of various factors on the VOR peak, such as supporting electrolyte type, preconcentration time, and potential, or influence of interferents, were tested using the square wave voltammetry technique (SWV). The linear voltametric response for the analyte was obtained in the concentration range from 0.01·10-6 to 3.0·10-6 mol L-1 with the detection limit of 1.55·10-9 mol L-1 for a preconcentration time of 60 s. The proposed method was successfully applied for highly sensitive VOR determination in complex matrices such as tablets, urine, and plasma with good recovery parameter.

Hierarchical Nanocomposites Electrospun Carbon NanoFibers/Carbon Nanotubes as a Structural Element of Potentiometric Sensors.

This work proposes new carbon materials for intermediate layers in solid-contact electrodes sensitive for potassium ions. The group of tested materials includes electrospun carbon nanofibers, electrospun carbon nanofibers with incorporated cobalt nanoparticles and hierarchical nanocomposites composed of carbon nanotubes deposited on nanofibers with different metal nanoparticles (cobalt or nickel) and nanotube density (high or low). Materials were characterized using scanning electron microscopy and contact angle microscopy. Electrical parameters of ready-to-use electrodes were characterized using chronopotentiometry and electrochemical impedance spectroscopy. The best results were obtained for potassium electrodes with carbon nanofibers with nickel-cobalt nanoparticles and high density of nanotubes layer: the highest capacity value (330 µF), the lowest detection limit (10-6.3 M), the widest linear range (10-6-10-1) and the best reproducibility of normal potential (0.9 mV). On the other hand the best potential reversibility, the lowest potential drift (20 µV·h-1) in the long-term test and the best hydrophobicity (contact angle 168°) were obtained for electrode with carbon nanofibers with cobalt nanoparticles and high density of carbon nanotubes. The proposed electrodes can be used successfully in potassium analysis of real samples as shown in the example of tomato juices.

Influence of Heat Treatment of Electrospun Carbon Nanofibers on Biological Response.

The main aim of this study is to investigate the effect of fragmentation of electrospun carbon nanofibers (eCNFs) obtained at different temperatures, i.e., at 750 °C, 1000 °C, 1500 °C, 1750 °C and 2000 °C on the cellular response in vitro. In order to assess the influence of nanofibers on biological response, it was necessary to conduct physicochemical, microstructural and structural studies such as SEM, XPS, Raman spectroscopy, HRTEM and surface wettability of the obtained materials. During the in vitro study, all samples made contact with the human chondrocyte CHON-001 cell lines. The key study was to assess the genotoxicity of eCNFs using the comet test after 1 h or 24 h. Special attention was paid to the degree of crystallinity of the nanofibers, the dimensions of the degradation products and the presence of functional groups on their surface. A detailed analysis showed that the key determinant of the genotoxic effect is the surface chemistry. The presence of nitrogen-containing groups as a product of the decomposition of nitrile groups has an influence on the biological response, leading to mutations in the DNA. This effect was observed only for samples carbonized at lower temperatures, i.e., 750 °C and 1000 °C. These results are important with respect to selecting the temperature of thermal treatment of eCNFs dedicated for medical and environmental functions due to the minimization of the genotoxic effect of these materials.

New Electrochemical Sensor Based on Hierarchical Carbon Nanofibers with NiCo Nanoparticles and Its Application for Cetirizine Hydrochloride Determination.

A new electrochemical sensor based on hierarchical carbon nanofibers with Ni and Co nanoparticles (eCNF/CNT/NiCo-GCE) was developed. The presented sensor may be characterized by high sensitivity, good electrical conductivity, and electrocatalytic properties. Reproducibility of its preparation expressed as %RSD (relative standard deviation) was equal to 9.7% (n = 5). The repeatability of the signal register on eCNF/CNT/NiCo-GCE was equal to 3.4% (n = 9). The developed sensor was applied in the determination of the antihistamine drug-cetirizine hydrochloride (CTZ). Measurement conditions, such as DPV (differential pulse voltammetry) parameters, supporting electrolyte composition and concentration were optimized. CTZ exhibits a linear response in three concentration ranges: 0.05-6 µM (r = 0.988); 7-32 (r = 0.992); and 42-112 (r = 0.999). Based on the calibration performed, the limit of detection (LOD) and limit of quantification (LOQ) were calculated and were equal to 14 nM and 42 nM, respectively. The applicability of the optimized method for the determination of CTZ was proven by analysis of its concentration in real samples, such as pharmaceutical products and body fluids (urine and plasma). The results were satisfactory and the calculated recoveries (97-115%) suggest that the method may be considered accurate. The obtained results proved that the developed sensor and optimized method may be used in routine laboratory practice.

Surface Modification of Carbon Nanofibers to Improve Their Biocompatibility in Contact with Osteoblast and Chondrocytes Cell Lines.

The goal of this study is to investigate the influence of different types of modifiers, such as sodium hyaluronate (NaH), graphene oxide (GO), silica oxycarbide (SiOC) and oxidation process (ox) on physicochemical, morphological, and biological properties of electrospun carbon nanofibers (eCNFs). Scanning electron microscopy, X-ray photoelectron spectroscopy and infrared spectroscopy (FTIR) were used to evaluate the microstructure and chemistry of as-prepared and modified CNFs. The electrical properties of CNFs scaffolds were examined using a four-point probe method to evaluate the influence of modifiers on the volume conductivity and surface resistivity of the obtained samples. The wettability of the surfaces of modified and unmodified CNFs scaffolds was also tested by contact angle measurement. During the in vitro study all samples were put into direct contact with human chondrocyte CHON-001 cells and human osteosarcoma MG-63 cells. Their viability was analysed after 72 h in culture. Moreover, the cell morphology and cell area in contact with CNFs was observed by means of fluorescence microscopy. The obtained results show great potential for the modification of CNFs with polymer, ceramic and carbon modifiers, which do not change the fiber form of the substrate but significantly affect their surface and volume properties. Preliminary biological studies have shown that the type of modification of CNFs affects either the rate of increase in the number of cells or the degree of spreading in relation to the unmodified sample. More hydrophilic and low electrically conductive samples such as CNF_ox and CNF_NaH significantly increase cell proliferation, while other GO and SiOC modified samples have an effect on cell adhesion and thus cell spreading. From the point of view of further research and the possibility of combining the electrical properties of modified CNF scaffolds with electrical stimulation, where these scaffolds would be able to transport electrical signals to cells and thus affect cell adhesion, spreading, and consequently tissue regeneration, samples CNF_GO and CNF_SiOC would be the most desirable.

Effect of Secondary Carbon Nanofillers on the Electrical, Thermal, and Mechanical Properties of Conductive Hybrid Composites Based on Epoxy Resin and Graphite.

In this work, we present a comparative study of the impact of secondary carbon nanofillers on the electrical and thermal conductivity, thermal stability, and mechanical properties of hybrid conductive polymer composites (CPC) based on high loadings of synthetic graphite and epoxy resin. Two different carbon nanofillers were chosen for the investigation-low-cost multi-layered graphene nanoplatelets (GN) and carbon black (CB), which were aimed at improving the overall performance of composites. The samples were obtained by a simple, inexpensive, and effective compression molding technique, and were investigated by the means of, i.a., scanning electron microscopy, Raman spectroscopy, electrical conductivity measurements, laser flash analysis, and thermogravimetry. The tests performed revealed that, due to the exceptional electronic transport properties of GN, its relatively low specific surface area, good aspect ratio, and nanometric sizes of particles, a notable improvement in the overall characteristics of the composites (best results for 4 wt % of GN; σ = 266.7 S cm-1; λ = 40.6 W mK-1; fl. strength = 40.1 MPa). In turn, the addition of CB resulted in a limited improvement in mechanical properties, and a deterioration in electrical and thermal properties, mainly due to the too high specific surface area of this nanofiller. The results obtained were compared with US Department of Energy recommendations regarding properties of materials for bipolar plates in fuel cells. As shown, the materials developed significantly exceed the recommended values of the majority of the most important parameters, indicating high potential application of the composites obtained.

Structural and microstructural study of novel stacked toroidal carbon nanotubes.

The work presents a new carbon nanostructure in the form of stacked toroidal carbon nanotubes (STCNT) crystallized from the gas phase through a catalyst-free deposition process. Vapor-grown STCNT were obtained on a graphite substrate using methane as a source of carbon. The carbon structure was analyzed using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDX), Raman spectroscopy, X-ray Diffraction and X-ray photoelectron spectroscopy. The TEM images revealed that the nanostructured carbon phase consisted of a single toroidal element (toroid) that was composed of rolled multi-walled carbon nanotubes. The SEM/EDX study of different substrate sites showed the presence of the pure carbon structure. The average external diameter of a single toroid was 1000 nm, and the average distance between neighboring toroids was 100 nm. The space inside the toroids contained carbon spheres made of turbostratic crystallites.