Recent Advances in Electrochemical Sensors for Sulfur-Containing Antioxidants

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol-disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed.

Voltammetric Determination of Glutathionein Pharmaceutical and Biological Samples Using Multiwall Carbon Nanotubes Paste Electrode in the Presence of Rutin as a Mediator

A new sensitive and selective electrochemical sensor was developed for electrocatalytic determination of glutathione (GSH) in pharmaceutical and biological samples. GSH is a tripeptidethiol present in all eukaryotic and probiotic cells. A voltammetric study of GSH has been carried out at the surface of carbon paste electrode modified with multiwall carbon nanotubes in the presence of rutin as a mediator. The electrochemical oxidation of GSH was investigated by cyclic voltammetry, chronoamperometry and square wave voltammetry (SWV) techniques. Under the optimized conditions, the peak current was linear to GSH concentration over the concentration range of 0.3 to 180μmol L⁻¹ using SWV. The detection limit was 0.09μmol L⁻¹. The proposed method was successfully applied to the determination of GSH in the urine, tablet and hemolysed erythrocyte samples.

An innovative highly sensitive electrochemical sensor based on modified electrode with carbon quantum dots and multiwall carbon nanotubes for determination of methadone hydrochloride in real samples

In the present work, to enhance the properties of a pencil graphite electrode (PGE), highly functionalized carbon quantum dots (CQDs) were synthesized and mixed with multiwall carbon nanotubes (MWCNTs) as novel modifiers for the preparation of working electrodes. These modifiers exhibited unique characteristics owing to the fascinating and well-defined properties of the CQD-MWCNT nanocomposite, including high surface to volume ratio, high conductivity, high stability and excellent electrocatalytic activity. Consequently, a modified pencil graphite electrode based on poly (diallyldimethylammonium chloride) (PDDA)/MWCNT/CQD was used to monitor the oxidation signals of methadone hydrochloride. Notably, field emission scanning electron microscopy (FE-SEM) was used to characterize the morphology and features of the different modifiers on the electrode surface. The proposed sensor was characterized via electrochemical studies including differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under the optimum experimental conditions, the current response and concentration of methadone exhibited a linear relationship in the range of 0.1-225 μM with a detection limit of 0.03 μM. Furthermore, this sensor was successfully applied to determine methadone in human urine and plasma samples.

Effect of TTLL12 on tubulin tyrosine nitration as a novel target for screening anticancer drugs in vitro

Nitrotyrosine, a structural analogue of tyrosine, is present in cells in pathological conditions and is incorporated into tubulin to form tubulin tyrosine nitration, which disrupts the normal function of microtubules. There is limited research on the functional aspects of tubulin tyrosine nitration in different types of tumor. In the present study, the effect of tubulin tyrosine nitration and tubulin tyrosine ligase like 12 (TTLL12) on the proliferation of SCC-25 cells was investigated. TTLL12-overexpressing cell lines were constructed and used to assess the effect of tubulin tyrosine nitration and TTLL12 on the proliferation of SCC-25 cells via western blotting, immunofluorescent and MTT assays. An TTLL12-stably overexpressing SCC-25 cell line and the enzyme-linked immunosorbent assay were used to establish a novel experiment in vitro for screening anticancer drugs targeting tubulin tyrosine nitration by assessing its sensitivity, specificity and repeatability, and using it to find an effective drug. The results demonstrated that the proliferative rate of the control cells was notably inhibited in the presence of nitrotyrosine compared with that of TTLL12-overexpressing cells. The results of the MTT assay revealed that the proliferation of TTLL12-silenced cells was significantly inhibited compared with that of the control group. The sensitivity, specificity and repeatability of the experiment were positive. It was found that nocodazole could have better anticancer effect than paclitaxel. Taken together, the results of the present study suggest that TTLL12 enhances SCC-25 cell survival in the presence of nitrotyrosine by disrupting nitration of the tyrosine residues of tubulin, and tubulin tyrosine nitration may be developed for the basic research of anticancer drugs.

Fabrication of anl-glutathione sensor based on PEG-conjugated functionalized CNT nanocomposites: a real sample analysis

Three series of polyethylene glycol–carbon nanotube nanocomposites in the form of PEG/CNT_a–e, PEG/f-CNT.Oxi_a–e, and PEG/CNT.C_18a–ehave been fabricated using a dissolution stirring ultra-sonication method.

Synthesis and application of FePt/CNTs nanocomposite as a sensor and novel amide ligand as a mediator for simultaneous determination of glutathione, nicotinamide adenine dinucleotide and tryptophan

In this study, we report the synthesis and application of a FePt/CNTs nanocomposite as a highly sensitive sensor and novel amide ligand (9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximido)-4-ethylbenzene-1,2-diol as a mediator for the determination of glutathione (GSH), nicotinamide adenine dinucleotide (NADH) and tryptophan (Trp). The synthesized materials were characterized with different methods such as NMR, IR spectroscopy, TEM, XRD, FESEM, cyclic voltammetry, electrochemical impedance spectroscopy and square wave voltammetry (SWV). The modified electrode exhibited a potent and persistent electron mediating behavior followed by well-separated oxidation peaks of GSH, NADH and Trp. The peak currents were linearly dependent on GSH, NADH and Trp concentrations in the range of 0.08-220, 1.0-400 and 5.0-500 μmol L(-1), with detection limits of 0.05, 0.8 and 1.0 μmol L(-1), respectively. The modified electrode was used for the determination of these compounds in real samples.