A molecular approach on the ability of functionalized single walled carbon nanotube for cathinone sensing.

In this article, single walled carbon nanotube functionalized with COOH (NT1) and CONHCH3 (NT2) groups were used for detection of the cathinone (CT) molecule in the gas phase and the liquid phase from the theoretical point of view. Density functional theory (DFT) calculations indicate that the NT2 nanostructure is more sensitive to the cathinone molecule than to the NT1 nanostructure. Compared to the gas phase, in the liquid phase water increases the sensitivity of the nanostructures toward the cathinone molecules. DFT results show that the polarity of the solvent increases the stability of the complexes. Donor-acceptor orbital interactions reveal that the cathinone molecule has a more effective orbital interaction with the NT2 nanostructure, especially in a water solvent. Also, molecular dynamic (MD) simulations confirm that the interactions between the cathinone molecule and the nanostructures increase in the water solvent. Therefore, NT nanostructures are more sensitive toward the CT molecule in a water solvent.

A novel electrochemical imprinted sensor for ultrasensitive detection of the new psychoactive substance "Mephedrone".

Identification and quantitation of mephedrone as one of the popular new psychoactive substances (NPSs) in biological fluids is important. In this study, a novel electrochemical imprinted sensor was designed for ultrasensitive and selective measurement of mephedrone, based on sol-gel molecular imprinted polymer, polytyramine and functionalized multi-walled carbon nanotube@ gold nanoparticles (f-MWCNT@AuNPs) nanocomposite. The developed electrochemical sensor inherits characteristics of the gold and MWCNTs such as high electrical conductivity, large specific surface area and good biocompatibility. Also, tyramine as an additional monomer was used for fabrication of a strongly adhering film on the surface of the electrode. In the proposed method, the concentration of mephedrone was determined indirectly. The change in the current response of [Fe(CN)6]3-/4- redox probe in the presence and absence of mephedrone molecules was used for indirect measurement of mephedrone molecule in solution. Density functional theory (DFT) was applied to better understanding the interactions between the mephedrone, sol-gel polymer and tyramine from molecular viewpoint. Under the optimized experimental conditions, the calibration curve of the designed sensor was plotted and two dynamic linear ranges from 1 to 10 nM and 10-100 nM with a limit of detection (LOD) as low as 0.8 nM (142 pg ml-1) were obtained. Finally, the fabricated sensor was successfully used to detect the mephedrone in biological samples.

Voltammetric aptasensor for bisphenol A based on the use of a MWCNT/Fe3O4@gold nanocomposite.

The present study describes an electrochemical aptamer-based method for the determination of bisphenol A (BPA). It is making use of gold nanoparticles (AuNPs) immobilized on a conjugate between multiwalled carbon nanotubes and thiol-functionalized magnetic nanoparticles (MWCNT/Fe3O4-SH) that are modified with an aptamer. The nanocomposite was characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, elemental mapping analysis and energy dispersive X-ray diffraction. The aptasensor, typically operated at 0.20 V (vs. Ag/AgCl), has a linear response in the 0.1 to 8 nM BPA concentration range, a low detection limit (0.03 nM), and high sensitivity (86.43 µA nM-1 cm-2). Voltammetric experiments were performed by using the hexacyanoferrate redox system as an electrochemical probe. The results indicate that the presence of AuNPs, magnetic nanoparticles and MWCNTs results a synergistic electrochemical augmentation. The method is highly selective, sensitive, efficient and environmentally friendly. The method was successfully applied to the determination of BPA in spiked real samples. Graphical abstract Aptasensor fabricated by MWCNT/Fe3O4-SH@Au nanocomposite and anti-BPA aptamer. The conformation of aptamer change after BPA binding, triggering a decrease in the electron transfer of Fe(CN)63-/4- on the electrode surface. The observed decline was detectable as a function of BPA concentration.

New polypyrrole-carbon nanotubes-silicon dioxide solid-phase microextraction fiber for the preconcentration and determination of benzene, toluene, ethylbenzene, and o-xylene using gas liquid chromatography.

For the first time, a polypyrrole-carbon nanotubes-silicon dioxide composite film coated on a steel wire was prepared by an electrochemical method. Scanning electron microscopy images showed that this composite film was even and porous. The prepared fiber was used as an absorbent for the headspace solid-phase microextraction of benzene, toluene, ethylbenzene, and o-xylene, followed by gas chromatographic analysis. This method presented an excellent performance, which was much better than that of a polypyrrole-carbon nanotube fiber. It was found that under the optimized conditions, the linear ranges were 0.01-200 ng/mL with correlation coefficients >0.9953, the detection limits were 0.005-0.020 ng/mL, the relative standard deviations were 3.9-6.4% for five successive measurements with a single fiber, and the reproducibility was 5.5-8.5% (n = 3). Finally, the developed method was successfully applied to real water samples, and the relative recoveries obtained for the spiked water samples were from 91.0 to 106.7%.