Simultaneous determination of ascorbic acid, dopamine, uric acid and xanthine using a nanostructured polymer film modified electrode

This paper describes the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and xanthine (XN) using an ultrathin electropolymerized film of 2-amino-1,3,4-thiadiazole (p-ATD) modified glassy carbon (GC) electrode in 0.20 M phosphate buffer solution (pH 5.0). Bare GC electrode failed to resolve the voltammetric signals of AA, DA, UA and XN in a mixture. On the other hand, the p-ATD modified electrode separated the voltammetric signals of AA, DA, UA and XN with potential differences of 110, 152 and 392 mV between AA-DA, DA-UA and UA-XN, respectively and also enhanced their oxidation peak currents. The modified electrode could sense 5 μM DA and 10 μM each UA and XN even in the presence of 200 μM AA. The oxidation currents were increased from 30 to 300 μM for AA, 5 to 50 μM for DA and 10 to 100 μM for each UA and XN, and the lowest detection limit was found to be 2.01, 0.33, 0.19 and 0.59 μM for AA, DA, UA and XN, respectively (S/N = 3). The practical application of the present modified electrode was demonstrated by the determination of AA, UA and XN in human urine samples.     

Electrochemical elaboration of adherent poly(3,4-ethylene-dioxythiophene) films and hybride nanowires on nickel

In the line of elaboration of conducting polymer on oxidizable metal, electropolymerization of 3,4-ethylene-dioxythiophene (PEDOT) was performed in ammonium oxalate aqueous solution on nickel. The advantageous effect of the oxalate ions on the electropolymerization process as well as on the physical characteristics of the resulting polymer film has been evidenced. Among these properties, adhesion has been drastically improved. Hybride nanowires nickel/PEDOT have been elaborated to highlight the nickel-PEDOT adhesion. The protective effect of the PEDOT film against corrosion in NaCl is nevertheless very slight.     

Synthesis and characterization of a Schiff base derived from 2-aminobenzylamine and its Cu(II) complex: electropolymerization of the complex on a platinum electrode

A precursor (H₃A) was synthesized by the mono condensation of 2-aminobenzylamine with salicylaldehyde and then a tetradentade Schiff-base ligand (H₂L) prepared by using H₃A and 3-methoxysalicylaldehyde. The copper(II) complex of this new ligand was prepared and characterized by elemental analysis, electronic absorption, Fourier transform infrared (FT-IR), and magnetic susceptibility. For the ligand, ¹H- and ¹³C-NMR and liquid chromatography mass spectrometry (LC–MS) spectra were obtained. The tetradentate ligand is coordinated to Cu(II) through the phenolic oxygen and azomethine nitrogen. The use of this metal complex in the preparation of a modified electrode is also described. CuL was electropolymerized on a platinum electrode surface in a 0.1 mol dm^?3 solution of lithium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.6 V versus Ag/Ag⁺. Electrochemical properties of the electroactive polymeric film have been investigated and a surface confined polymerization mechanism was proposed.     

Simple Fabrication of Amperometric Nitric Oxide Microsensors Based on Electropolymerized Membrane Films

Demand for highly sensitive, selective, and practically reliable sensors which could be easily fabricated is increasing for various applications in biological and biomedical systems. Thus, here we present a novel and simple amperometric NO microsensor based on electropolymerized polymeric films. The sensor consists of a platinized Pt disk anode (25‐μm diameter) which surface is modified with electropolymerized polymer films and a Ag/AgCl wire cathode coiled around the anode. Three different electropolymerized films prepared from m‐phenylenediamine (m‐PD), 2,3‐diaminonaphthalene (2,3‐DAN), and 5‐amino‐1‐naphthol (5A1N) are compared in terms of their permselectivity for NO over major biological interferents such as anionic nitrite, ascorbic acid, uric acid; neutral acetaminophen; and cationic dopamine. Poly‐5A1N film layer among the three different polymers shows the best anti‐interference characteristics for all the electroactive interferents examined. Indeed, single polymer film of electropolymerized 5A1N without any additional modification as a NO selective membrane is confirmed to be sufficient to reject anionic, neutral, as well as cationic interferents while allowing relatively high permeation of NO through it. Other analytical performance of the NO microsensor fabricated with poly‐5A1N is evaluated: reliable linear dynamic range (a few tens nM to μM); sensitivity of 122.0±2.5 pA/μM; detection limit of <5.8 nM (S/N=3); response time, t_90%<5 s, which are excellent when considering the small sensor size. Another sensor design which has both an anode (poly‐5A1N modified platinized Pt) and a cathode (Ag/AgCl disk) embedded in a single sensor body is also presented.     

MIP‐esterase/Tyrosinase Combinations for Paracetamol and Phenacetin

A new electrochemical MIP sensor for the most frequently used drug paracetamol (PAR) was prepared by electropolymerization of mixtures containing the template molecule and the functional monomers o‐phenylenediamine, resorcinol and aniline. The imprinting factor of 12 reflects the effective target binding to the MIP as compared with the non‐imprinted electropolymer. Combination of the MIP with a nonspecific esterase allows the measurement of phenacetin – another analgesic drug. In the second approach the PAR containing sample solution was pretreated with tyrosinase in order to prevent electrochemical interferences by ascorbic acid and uric acid. Interference‐free indication at a very low electrode potential without fouling of the electrode surface was achieved with the o‐phenylenediamine: resorcinol‐based MIP.     

Electrochemical Aptasensor Based on Poly(Neutral Red) and Carboxylated Pillar[5]arene for Sensitive Determination of Aflatoxin M1

Aptasensor for highly sensitive determination of aflatoxin M1 (AFM1) was developed on the base of glassy carbon electrode (GCE) covered with polymeric Neutral red (NR) dye obtained by electropolymerization in the presence of polycarboxylated pillar[5]arene derivative. Aptamer against AFM1 and NR label were then covalently linked to the carboxylic groups of the carrier by carbodiimide binding. At presence of AFM1 the cathodic peak current related to the NR conversion decreases. AFM1 induced also an increase of the charge transfer resistance measured by electrochemical impedance spectroscopy. In optimal conditions, this make it possible to determine from 5 to 120 ng/L AFM1 in standard solutions with limit of detection (LOD) of 0.5 ng/L. The aptasensor was validated on the spiked samples of cow and sheep milk as well as in kefir after their methanol dilution. Reliable detection of the 40–160 ng/kg of mycotoxins was reached. This is below limited threshold value (50 μg/kg) established in EC.     

Synthesis and characterization of porphyrin electrochromic and photovoltaic electropolymers

New asymmetric porphyrins, with electroactive functionalities were synthesized. 5,15-Bis[4(-N,N-diphenylamino)phenyl]-10,20-bis[3-(N-ethylcarbazoyl)]porphyrin and its Zn(II) derivative allow the electrochemical formation of conjugated, conducting and stable polymeric films over semitransparent indium-tin oxide surface. The spectral changes observed upon oxidation of the films produced different colorations. The polymeric materials showed the generation of photoinduced charge separation states and charge migration upon porphyrin excitation, making them promising candidates for application in optoelectronics devices.     

Phthalocyanine-cored conductive polymer design: effect of substitution pattern and chalcogen nature on optical and electrical properties of Zn(II)-phthalocyanine–cored polycarbazoles

Phthalocyanines are one of the important candidates of tetrapyrrolic macrocycles having a π-conjugated system, and conductive polymers (CPs) have recently attracted an increasing interest as designing of new molecular materials. A smart combination of these two unique structures can produce materials with the desired properties to design various organic-molecular devices. However, fundamental principles of the design engineering for synthesis of phthalocyanine-cored CP with unique optoelectronic properties has not been investigated yet. For this purpose, tetrasubstituted peripheral or non-peripheral Zn(II)-phthalocyanine containing thioalkyl- or alkoxy-group–linked carbazoles have been synthesized. Electropolymerization of the materials under potentiodynamic conditions yielded a series of analogous donor?acceptor CPs in which the only difference was the nature of the chalcogen (O or S) and substitution pattern (peripheral or non-peripheral) on the phthalocyanine core. This was shown to have a significant impact on the optical and electrochemical properties of the CPs because of the difference in electronegativity of chalcogen and inductive effect of the substitution pattern. Here, a comprehensive investigation of the design of phthalocyanine-cored CP has been concluded to reveal structure–property relationship.     

Amperometric cholesterol biosensors based on the electropolymerization of pyrrole and the electrocatalytic effect of Prussian-Blue layers helped with self-assembled monolayers

Three cholesterol biosensor configurations based on the formation of a layer of Prussian-Blue (PB) on a Pt electrode for the electrocatalytic detection of the H₂O₂ generated during the enzymatic reaction of cholesterol with cholesterol oxidase (ChOx) were constructed. The enzyme was entrapped within a polypyrrole (PPy) layer electropolymerized onto the PB film. The influence of the formation of self-assembled monolayers (SAMs) on the Pt surface on the adherence and stability of the PB layer and the formation of an outer layer of nafion (Nf) as a means of improving selectivity were both studied. A comparative study was made of the analytical properties of the biosensors corresponding to the three configurations named: Pt/PB/PPy-ChOx, Pt/SAM/PB/PPy-ChOx and Pt/SAM/PB/PPy-ChOx/Nf. The sensitivity (from 600 to 8500 nA mM⁻¹ cm⁻²) and selectivity of the developed biosensors permitted the determination of the cholesterol content in reference and synthetic serum samples. The detection limit for the Pt/SAM/PB/PPy-ChOx/Nf biosensor was 8 μM. Formation of the SAM on the electrode surface and covering with a Nf film considerably improved the stability and lifetime of the biosensor based on the catalytic effect of the PB layer (as the PB layer was retained longer on the electrode), and the Nf layer protects the enzyme from the external flowing solutions. Lifetime is up to 25 days of use. The formation of the SAM also has an effect on the charge transfer and the formation of the PB layer.