Laser-induced graphene electrodes on polyimide membranes modified with gold nanoparticles for the simultaneous detection of dopamine and uric acid in human serum.

The level control of biological active molecules in human body fluids is important for the surveillance of several human diseases. Dopamine (DA) and uric acid (UA) are two important biomarkers of neurological and bone diseases, respectively. Design of sensitive and cost-effective sensors for their detection is an effervescent research field. We report on the straightforward design of laser-induced graphene electrodes (LIGEs) from the laser ablation of a polyimide substrate and their modification by electrochemical deposition of gold nanoparticles (AuNPs/LIGE) and their uses as chemosensors. Electrochemical investigations showed that the presence of gold nanoclusters onto the electrode surface improved the electrochemical surface area (ECSA) and the heterogenous electron transfer (HET) rate. Furthermore, the AuNPs/LIGEs can be used to detect simultaneously low concentrations of DA and UA in presence of ascorbic acid (AA) as an potentially interfering substance at redox potentials of 300 mV, 230 mV and 450 mV and 91 mV, respectively, compared with the Ag/AgCl (3 M KCl) reference electrode in cyclic voltametric. The method displayed linear ranges varying from 2 to 20 µM and 5 to 50 µM, led to limits of detection of 0.37 µM and 0.71 µM for DA and UA, respectively. The AuNPs/LIGE was applied to simultaneously detect both analytes in scarcely diluted human serum with good recoveries. The data show that the recovery percentages ranged from 94% ± 2.1 to 102 % ± 0.5 and from 94% ±0.3 to 112% ± 1.4 for dopamine and uric acid, respectively. Thus, the AuNPs/LIGEs are promising candidates for the detection of other biologically active molecules such as drugs, pesticides, and metabolites.

Sensitive Carbon Fiber Microelectrode for the Quantification of Diuron in Quality Control of a Commercialized Formulation.

Nickel(II) tetrasulfonated phthalocyanine (p-NiTSPc)-modified carbon fiber microelectrode (CFME) was used for the first time to investigate the electrochemical quantification of diuron in an agrochemical formulation. The surface morphology and elementary analysis of unmodified carbon fiber microelectrode (CFME) and p-NiTSPc-CFME were performed using atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX), respectively. Cyclic voltammetry (CV) was used to investigate the electrochemical behaviour of diuron, while square wave voltammetry (SWV) was used for quantitative analysis of diuron. Upon variation of some key analytical parameters, a calibration curve was plotted in the concentration range from 21.450 to 150.150 µM, leading to a detection limit (DL) of 8.030 µM mg/L (3.3σ/m) and a limit of quantification (LQ) of 20.647 µM mg/L. The fabricated p-NiTSPc-CFME was successfully applied for quality control in a commercialized formulation of diuron. The standard additional method was used, and the recovery rate of diuron was found to be 98.4%.

Phytochemical Screening and Antioxidant and Cytotoxic Effects of Acacia macrostachya.

Acacia macrostachya is used in Burkina Faso folk medicine for the treatment of inflammation and cancer. The purpose of this study was to evaluate the antioxidant and cytotoxic effects of this plant. The cytotoxic effects of root (dichloromethane B1 and methanol B2) and stem (dichloromethane B3 and methanol B4) bark extracts of A. macrostachya were assessed on chronic K562 and acute U937 myeloid leukemia cancer cells using trypan blue, Hoechst, and MitoTracker Red staining methods. The antioxidant content of extracts was evaluated using DPPH (2,2-diphenyl-1-picryl-hydrazyl) and FRAP (ferric reducing antioxidant power) methods. The root bark extracts B1 and B2 of A. macrostachya demonstrated higher cytotoxicity with IC50 values in a low µg/mL range on both U937 and K562 cells, while the stem bark B4 extract selectively affected U937 cells. Overall, healthy proliferating peripheral blood mononuclear cells (pPBMCs) were not or barely impacted in the range of concentrations cytotoxic to cancer cells. In addition, A. macrostachya exhibited significant antioxidant content with 646.06 and 428.08 µg ET/mg of extract for the B4 and B2 extracts, respectively. Phytochemical screening showed the presence of flavonoids, tannins, alkaloids, and terpenoids/steroids. The results of this study highlight the interest of A. macrostachya extracts for the isolation of anticancer molecules.

Photoluminescent nanoprobes based on thiols capped CdTe quantum dots for direct determination of thimerosal in vaccines.

CdTe quantum dots (CdTe QD) have been produced at different times of synthesis (1, 2, and 4 h) using thiols as capping agents: mercaptopropionic acid (MPA), mercaptosuccinic acid (MSA) and N-acetyl-l-cysteine (NAC) using water as a solvent. The produced CdTe QD were characterized by UV-vis and photoluminescence (PL) spectroscopy and showed a relationship among reflux time, size, and spectroscopic properties. CdTe QD were shown to interact with thimerosal (TM), an organic mercury compound, and the PL intensity was effectively quenched, characterizing an ON-OFF process. However, the NAC capped CdTe (CdTe-NAC) at 1 h presented the best sensitivity for TM determination. Under optimized conditions, a linear range from 0.1 to 1.0 µg mL-1 (0.25-2.5 µM) and a LOD of 26.6 µg L-1 (66.7 nM) were achieved. The influence of different mercuric species [Hg(II), methylmercury, ethylmercury, and phenylmercury], along with thiosalicylic acid (TSA), and other ionic species on the sensitivity of the method and the interaction mechanism between TM and CdTe-NAC have been discussed. The method was successfully applied for direct quantification of TM in vaccines, and the results were validated by cold vapor atomic fluorescence spectroscopy (CV AFS). Finally, the proposed method proved to be fast, sensitive, and simple for suitable use in vaccine quality control.

Targeting structural motifs of flavonoid diglycosides using collision-induced dissociation experiments on flavonoid/Pb2+ complexes.

Differentiation of flavonoid congeners remains a challenging analytical problem and confirming the structures of the different isomers is difficult, even when they can be adequately separated from mixtures. In the present report, in order to overcome the limits of our recently proposed method that relies on the distinctive CID behaviors of [(flavonoid - H(+)) + Cu(2+)] complexes to obtain direct structural evidences, we decided to investigate the possibility of using Pb(II) complexation to generate significant differences upon CID. We selected five flavonoid diglycosides with targeted structural features to estimate the applicability of this methodology. Electrospray ionization from methanol-not acetonitrile-solutions was advantageously used for preparing the [(flavonoid diglycoside - H(+)) + Pb(2)+](+) complexes. Upon collisional activation, [(flavonoid diglycoside- H(+)) + Pb(2+)](+) ions mainly dissociate by glycosidic bond cleavage. Nevertheless, specific cross-ring cleavages are also induced and lead to a clear-cut determination of (i) the nature of the disaccharide group, i.e. rutinose or neohesperidose, (ii) the nature of the aglycone part, flavanone or flavone and (iii) the relative position of the disaccharide substituent on the aglycone part, i.e. 3-O- vs 7-O positions.

Water-soluble, redox-active organometallic calcium chelators.

This paper describes a new series of organometallic water-soluble chelators combining a redox moiety (ferrocene) and a selective Ca2+ chelator (BAPTA) separated by an ethynyl bridge. We report the synthesis and characterization of organometallic derivatives of the BAPTA chelator featuring one (2a) and two ferrocenyl (2b) moieties. Single crystal X-ray structural analysis on these chelators revealed unexpected conformations for the ferrocenyl substituent with respect to the phenyl ring of the BAPTA unit. DFT calculations on a model system of the ferrocenyl-ethynyl-BAPTA molecule were carried out to evaluate the energy separation between the two limiting conformations observed experimentally in the solid state, and to check the effective electronic communication between the binding pocket and the redox probe. The binding affinity of 2a­b for Ca2+, as probed by UV-Vis and cyclic voltammetry, revealed distinct behaviors in the presence of a metal ion depending on whether BAPTA is substituted by one or two ferrocenyl groups.

An organometallic derivative of a BAPTA ligand: towards electrochemically controlled cation release in biocompatible media.

The combination of a ferrocenyl moiety with BAPTA provides a novel, water-soluble, redox-active chelator. This chelator behaving as a conformational sensor exhibits an unexpected electrochemical response with high affinity and selectivity for calcium.

Collision-induced dissociation of flavonoid 7-O-diglycoside cations: elucidation of important structural motifs by selection of the cationizing reaction.

Flavonoids are ubiquitous molecules in nature and are found in almost all plants, including fruits and vegetables. Although flavonoids are structurally similar, subtle differences in their structures lead to important changes in their biological activities. Over years, mass spectrometry has become an ideal tool for the characterization of those important molecules. In particular to overcome the challenge of structure assignment, tandem mass spectrometry was used in numerous studies. In the present study, we submitted selected flavonoid 7- O-diglycosides to electrospray ionization to prepare different kinds of flavonoid ions, i.e. protonated, sodium- cationized and copper-cationized molecules. Most of the investigated reactions are already described in the literature in several papers and the aim of the present study is to present concise and coherent relations between CID reactions, cationizing agents and flavonoid 7-O-diglycoside structures. Some insights in the reaction mechanisms and the role of the cationizing particles will also be attempted.

Finding out egyptian gods' secret using analytical chemistry: biomedical properties of egyptian black makeup revealed by amperometry at single cells.

Lead-based compounds were used during antiquity as both pigments and medicines in the formulation of makeup materials. Chemical analysis of cosmetics samples found in Egyptians tombs and the reconstitution of ancient recipes as reported by Greco-Roman authors have shown that two non-natural lead chlorides (laurionite Pb(OH)Cl and phosgenite Pb(2)Cl(2)CO(3)) were purposely synthesized and were used as fine powders in makeup and eye lotions. According to ancient Egyptian manuscripts, these were essential remedies for treating eye illness and skin ailments. This conclusion seems amazing because today we focus only on the well-recognized toxicity of lead salts. Here, using ultramicroelectrodes, we obtain new insights into the biochemical interactions between lead(II) ions and cells, which support the ancient medical use of sparingly soluble lead compounds. Submicromolar concentrations of Pb(2+) ions are shown to be sufficient for eliciting specific oxidative stress responses of keratinocytes. These consist essentially of an overproduction of nitrogen monoxide (NO degrees ). Owing to the biological role of NO degrees in stimulating nonspecific immunological defenses, one may argue that these lead compounds were deliberately manufactured and used in ancient Egyptian formulations to prevent and treat eye illnesses by promoting the action of immune cells.

Ex vivo activities of beta-lapachone and alpha-lapachone on macrophages: a quantitative pharmacological analysis based on amperometric monitoring of oxidative bursts by single cells.

ARTIFICIAL SYNAPSES FOR FEMTOMOLAR DETECTION: Amperometry at platinized carbon fibre electrodes has been used to unravel the complexity of beta-lapachone's effects on cellular oxidative stress. Alpha-lapachone, the pharmacologically inactive para-quinone isomer, did not display such characteristics, but over longer incubation periods both quinones induced apoptosis. The observed effects were interpreted in terms of two mechanisms involving opposite reactivities of quinones in living cells. Beta-lapachone (1) has been widely used for its pharmacological activity, particularly against cancer. However, its mechanism of action at the cellular level remains unclear, although a common major hypothesis involves its prooxidant properties. Electrochemical measurements with microelectrodes were taken in order to quantitatively investigate the activity of 1 at different concentrations and several incubation times, on the oxidative bursts released by single macrophages. The exact natures of the electroactive reactive oxygen species (ROS) and reactive nitrogen species (RNS) released by macrophages under the effect of 1 were characterized, and their fluxes were measured quantitatively. This allowed the reconstruction of the primary O2*- and NO production by the cells. In the first hour, at 10 microM, the decrease in the oxidative burst involved mainly RNS, while the amount of H(2)O(2) was found to be higher than in controls. After a longer incubation time-that is, 4 h-at 1 microM, the total amount of ROS and RNS had increased, with significant enhancements of H(2)O(2) and NO. In contrast, alpha-lapachone, the pharmacologically inactive para-quinone isomer, was unable to increase the production of RONS by macrophages significantly. Over much longer incubation periods (about one day), however, each quinone induced cell death by apoptosis. All these effects were interpreted by consideration of two different mechanisms involving opposite reactivities of quinones in living cells.

Angeli's salt (Na2N2O3) is a precursor of HNO and NO: a voltammetric study of the reactive intermediates released by Angeli's salt decomposition.

Under physiological conditions, it is usually accepted that the aerobic decomposition of Angeli's salt produces nitrite (NO(2)(-)) and nitroxyl (HNO), which dimerizes and leads to N(2)O. No consensus has yet been established on the formation of nitric oxide (NO) and/or peroxynitrite (ONOO(-)) by Angeli's salt. Because this salt has recently been shown to have pharmacological properties for the treatment of cardiovascular diseases, identification of its follow-up reactive intermediates is of increasing importance. In this work, we investigated the decomposition mechanism of Angeli's salt by voltammetry performed at platinized carbon fiber microelectrodes. By following the decomposition process of Angeli's salt, we showed that the mechanism depends on the experimental conditions. Under aerobic neutral and slightly alkaline conditions, the formation of HNO, NO(2)(-), but also of nitric oxide NO was demonstrated. In strongly alkaline buffer (pH>10), we observed the formation of peroxynitrite ONOO(-) in the presence of oxygen. These electrochemical results are supported by comparison with UV spectrophotometry data.

Electrochemical detection in a microfluidic device of oxidative stress generated by macrophage cells.

The release of reactive oxygen species (ROS) or reactive nitrogen species (RNS), i.e., the initial phase of oxidative stress, by macrophage cells has been studied by electrochemistry within a microfluidic device. Macrophages were first cultured into a detection chamber containing the three electrodes system and were subsequently stimulated by the microinjection of a calcium ionophore (A23187). Their production of ROS and RNS was then measured by amperometry at the surface of a platinized microelectrode. The fabricated microfluidic device provides an accurate measurement of oxidative release kinetics with an excellent reproducibility. We believe that such a method is simple and versatile for a number of advanced applications based on the detection of biological processes of secretion by a few or even a single living cell.