Jacques Devynck

Electrochemical nitric oxide microsensors: sensitivity and selectivity characterisation

In this study, we have prepared two nitric oxide (NO) microsensors using two combinations of nickel tetrasulfonated phthalocyanine (NiTSPc), o-phenylenediamine (o-PD) and Nafion® based layers to modify the surface of 8 μm diameter carbon fiber electrodes. We have compared the performances of the obtained composite microsensors (carbon/NiTSPc/Nafion®, and carbon/Nafion®/o-PD, respectively) in our home made operating conditions. We have developed the sessile drop contact angle measurement technique as well as the use of the electrochemical quartz crystal microbalance (EQCM), differential normal pulse voltammetry (DNPV) and differential normal pulse amperometry (DNPA) to correlate the hydrophobicity, mass deposit of the polymer coatings and the sensitivity of the examined microsensors. By comparing the permeability of the microsensors to various interfering analytes, such as L-arginine, ascorbate, nitrite, serotonine, dopamine, acetamidophenol, 4-met-catechol, epinephrine, norepinephrine, dopac and 5-hydroxyindol, we have discussed the molecular sieving exclusion of the deposited membranes in term of molecular weight cutoff (MWCO).

Nitric oxide production by endothelial cells: Comparison of three methods of quantification

Vascular endothelial cells have been found to produce a relaxant mediator, identified as nitric oxide (NO) and implicated in numerous physiological functions. Subsequently, there has been an intensive search for accurate and specific detection methods to measure biological NO production. In the present study, we compared three approaches to evaluate NO production, based respectively on the Griess reaction (that quantifies nitrites and nitrates after their reduction), on the hemoglobin reaction (that quantifies oxyhemoglobin to methemoglobin transformation by NO), and on the electrochemical NO detection with a porphyrinic micro-probe. Comparison was made both under standard conditions and biological conditions, through calibration curves and measurements of histamine-induced NO production by cultured human endothelial cells and its modulation by L-arginine and N(omega)-monomethyl-L-arginine. We demonstrated that these three methods differ in terms of sensitivity and selectivity. The hemoglobin reaction and nitrate measurements suffer from a lack of specificity. Nitrite determination by the Griess reaction was hardly suitable for kinetic studies but it remains useful for the evaluation of basal NO production. The electrochemical technique, although it does not allow measurement of basal NO production, is the only one to exhibit great sensitivity and specificity and to allow instantaneous and non destructive measurements. This study brings up the potential hazards and pitfalls that may be associated with the various methods.

The use of gold electrodes in the electrochemical detection of nitric oxide in aqueous solution

It was recently discovered that vascular endothelial cells could synthesize the free-radical gas nitric oxide (NO) [1,2] and since that discovery, it has been possible to demonstrate the considerable physiological importance of NO as for example in the control of human blood flow and pressure. Several works are now dealing with the understanding of the mechanism by which NO is synthesized [3]. As a matter of fact, it has appeared that measuring NO in biological models is very difficult because of its low stability and high fugacity. In a recent review Archer [4] has summarized the different NO measurement strategies reported in the literature. The most widely used techniques involve the ex-situ detection of NO by (i) electron paramagnetic resonance, (ii) spectrophotometry and (iii) chemiluminescence. New amperometric microelectrode probes are now developed to detect NO and the use of electrochemistry, as a potential way to do so is very promising. Indeed, ultramicroelectrode design and elaboration are now reaching very high levels of sophistication [5] contributing very actively to the promotion of the use of the electrochemical techniques for in vivo NO detection in intact tissues and from single cells. There are two amperometric methods reported in the literature for measuring NO in vitro and from tissues and single cells. The first method is based on the direct oxidation of NO on platinum electrode. Shibuki [6] reported the detection of NO by using a miniature Clark-type electrode. The electrode was designed by introducing a platinum wire within a pipette with a fire-polished 150-250 pm tip (with a thin chloroprene rubber seal) filled with an aqueous solution of 30 mM NaCl and 0.3 mM HCI. The platinum indicator electrode was placed as close as possible to

Electrochemistry of conducting polypyrrole films containing cobalt porphyrin: Part 2. New developments and inclusion of metallic aggregates in the coordination polymer

The electrochemical polymerization of a pyrrole-substituted cobalt porphyrin complex (i.e. 5-(3-(4-(1-pyrrolyl)butyl)phenoxy)-10,15,20-tritolylporphine cobalt) has been performed in acetonitrile + tetrabutylammonium tetrafluoroborate solution. The redox properties of the film were examined by cyclic voltammetry and chronoamperometry. The voltammograms of these films exhibited a reversible process for the Co(II)/Co(I) reaction at a formal potential of −0.90 V (vs. SCE). Using chronoamperometry, quantitative analysis of the curves allowed us to extract the diffusion coefficient D for the Co(II)/Co(I) step of the cobalt porphyrin film, D = 1.46×10−11cm2 s−1. The cobalt porphyrin content was estimated by cyclic voltammetry, and this shows that thick polymers act as insulators in the low potential range E < −1 V (vs. SCE). Electroreductive inclusion of Pt and Ag aggregates in these coordination polymers from K2PtCl4, H2PtCl6 and AgClO4 solutions was concluded. Evidence that metallic particles were included in the polymer films was provided by scanning electron microscopy coupled with X-ray fluorescence analysis.

Electrochemical and spectrophotometric study of the behavior of electropolymerized nickel porphyrin films in the determination of nitric oxide in solution

We describe in this paper an electrochemical and spectrophotometric study of the behavior of an electropolymerized nickel porphyrin film as a sensor for the determination of nitric oxide (NO) in aqueous solution. Our results show that the anodic oxidation of NO at the modified electrode may not be the result of a catalytic effect induced by the porphyrinic complex. However, the current (measured by differential pulse amperometry) and calculated NO concentration showed a linear relationship in the range 15 nM-6 muM in aerobic phosphate buffer solution (pH 7.4). These results provide a fruitful example of calibration of such electrochemical sensors for the selective detection of NO with a calculated detection limit, at a signal-to-noise ratio of three, equal to 1.5 nM.

ELECTROCHEMISTRY OF CONDUCTING POLYPYRROLE FILMS CONTAINING COBALT PORPHYRIN

The electrochemical polymerisation of pyrrole-substituted cobalt tetraphenylporphine complex on a vitreous carbon electrode has been performed in acetonitrile+tetrabutylammonium tetrafluoroborate solution. The redox properties of the film have been examined by cyclic voltammetry and compared to those of cobalt-porphyrin monomer in solution. Voltammograms of these films exhibit a reversible process for the Co(II)/Co(I) reaction at a formal potential of −0.87 V/SCE. The cobalt-porphyrin content of the films has been estimated by cyclic voltammetry, and the conductivity of the polymers has been assessed by studying well-known electrochemical processes in solution at these modified electrodes. Thus, it appears that thick polyporphyrin films act as insulators in low potential range E < −1 V/SCE. Copolymerisation of the pyrrole-substituted cobalt porphyrin with pyrrole and 3-(pyrrol-1-ylmethyl)pyridine has been achieved. No improvement of the electrochemical properties has been noted for the copolymers obtained. We have also proved that interchain complexation reaction of the cobalt(III) sites occurs by the pyridine moieties of the copolymer films.

Design and characterization of chemically modified electrodes with iron(III) porphyrinic-based polymers: study of their reactivity toward nitrites and nitric oxide in aqueous solution

Abstract This study gives new examples of iron porphyrin film electrodes prepared either by electrochemical polymerization or by incorporation in pre-electropolymerized pyrrole derivatives. It shows also the different kinds of interactions between nitric oxide, nitrites and the supported iron porphyrins in acidic and neutral aqueous solutions. It gives clear indications, by cyclic voltammetry and UV-visible spectrophotometry of the formation of the suggested iron-nitrosyl intermediate, [Fe(III)(NO)]+, in supported films.

Metalloporphyrin-polypyrrole film electrode: characterization and catalytic application

Abstract The visible electroreflectance (ER) technique, coupled to capacitive and voltammetric measurements, has been used to characterize the redox properties of polypyrrole-modified electrodes, doped with meso -tetrakis (4-carboxyphenyl) porphine cobalt, iron and manganese (PP/TCPPM). The ER spectra give direct evidence for the location of a reversible electron/transfer reaction and allow us to determine the redox potential of the TCPPM(III)/M(II) process in the polypyrrole film (in 0.1 M CH10 4 solution). The values obtained ( + 0.200 V vs SCE for TCPPCo(III)/Co(II); −0.100 V for TCPPFe(III)/Fe(II) and −0.200 V for TCPPMn(III)/Mn(II) are compared to those determined by ER for the same species. TCPPM, adsorbed on gold electrodes. The catalytic application of 2,6-diterbutylphenol oxidation by molecular oxygen in acetonitrile with PP/TCPPMn(III) is tested. The catalytic species TCPPMn(II) is obtained by electrolysis of the modified electrode PP/TCPPMn at −0.300 V. The results show that the entire heterogeneous catalytic oxidation process of phenol, with a Mnoxygen adduct as intermediate, can be developed without damaging the PP/TCPPMn film.

Electrooxidative polymerization of cobalt, nickel and manganese salen complexes in acetonitrile solution

We report in this study a new extension of the electrochemical polymerisation approach to the preparation of metal Schiff-base complex (cobalt-, nickel- and manganese-salen) polymers as new materials for modified electrodes. This approach is based on the electro-oxidation of the salen ligand in acetonitrile solution which can allow quick polymerisation of the units into an electroactive polymer, and offers the advantage of using «simple» ligands without any chemical derivatization

Electrochemistry of zeolite-encapsulated complexes: Part 3. Characterization of iron and manganese SALEN entrapped in Y faujasite type zeolite☆

Abstract [Mn III SALEN] + and [Fe III SALEN] + complexes have been entrapped in the supercages of zeolite Y. The redox properties of these zeolite-encapsulated complexes are investigated by cyclic voltammetry in acetonitrile and dimethyl sulphoxide solutions. The results show the existence of two kinds of entrapped [Fe III SALEN] + forms within the zeolite. Their existence is related to the mechanism of their preparation and depends on the electrolytic media. The electroactivity of encapsulated Mn-SALEN towards the biomimetic activation of molecular oxygen is discussed.