Dependence of redox-kinetic parameters at poly(o-phenylenediamine)-modified electrodes upon the oxidation and protonation levels of the polymer

Effects of applied potential on the mass of non-conducting poly(ortho-phenylenediamine) electro-deposited on EQCM electrodes: comparison with biosensor selectivity parameters

An electrochemical quartz-crystal microbalance (EQCM) was used to determine the mass of poly-(o-phenylenediamine) (PoPD) layers electro-deposited at different applied potentials in neutral buffered monomer solution, conditions that produce the insulating form of the polymer used as a permselective membrane in biosensor applications. There was a systematic increase in the total, steady state PoPD mass deposited for fixed applied potentials from 0.05 to 0.6 V vs. SCE, followed by a plateau up to 0.8 V. Comparison of PoPD mass and permselectivity parameters indicates that the ability of the passivating form of PoPD to block interference species in biosensor applications is not related in a simple way to the mass of material deposited on the surface. Instead, effects of the applied electropolymerisation potential in driving the electro-oxidation of oPD dimers and oligomers formed during the electro-deposition process are likely to have a more direct impact on the selectivity characteristics of the PoPD layer. The results highlight the usefulness of apparent permeabilities, especially of ascorbic acid, in revealing differences between PoPD layers electro-deposited under different conditions.

Optimization for the Chemical Synthesis of Conducting Poly (m-aminophenol) in HCl using Ammonium Persulfate

Poly ( m-aminophenol) (PmAP) was synthesized from m-aminophenol (mAP) by ammonium persulfate (APS) as an oxidizing agent in aqueous HCl. Polymerization conditions were optimized by varying HCl concentration, amount of mAP and APS, temperature and time. The synthesized polymers were insoluble in organic solvents even after dedoping. The polymers were characterized by UV-VIS and Fourier transform infrared spectroscopy, thermogravimetric and elemental (CHNS) analyses. Four-probe DC electrical conductivity of the pelletized polymer was measured. The spectral results clearly indicated that the ladder structure was formed during the chemical polymerization of mAP in aqueous HCl. This structure was supported by elemental analysis. Thermal stability of the undoped and in-situ HCl doped polymers was measured. The highest conductivity of the synthesized polymer pellet was 1.0 × 10-7 S cm -1. A polymerization mechanism was proposed.

Surface plasmon resonance spectroscopy and electrochemistry study of 4-nitro-1,2-phenylenediamine: a switchable redox polymer with nitro functional groups

Electrochemistry and electrochemical surface plasmon resonance (SPR) spectroscopy have been applied to study the electrochemical deposition and the redox transition of poly(4-nitro-1,2-phenylenediamine) (P4NoPD) on gold disk. It was shown that SPR can be the signal transducer for the different redox states of P4NoPD. Using a model biomolecular system, involving streptavidin, biotinylated DNA, and its complementary target DNA, it was found that the presence of nitro groups in P4NoPD allows the biorecognition events to be modulated by voltages. There is minimal nonspecific binding of biomolecules on oxidized (+0.2 V) or as-prepared P4NoPD, and binding occurs more significantly on the reduced P4NoPD (-0.2 to -0.6 V) with the presence of amine groups. The electrochemical deposition of P4NoPD film was also conducted on boron-doped diamond (BDD) electrode. The stability of the reduced P4NoPD film on gold and BDD was comparatively evaluated by electrochemical impedance spectroscopy (EIS). The result showed that BDD allows the electrochemical reduction of the P4NoPD film at wider cathodic limits than gold.

Simultaneous measurement of dopamine and ascorbate at their physiological levels using voltammetric microprobe based on overoxidized poly(1,2-phenylenediamine)-coated carbon fiber

Overoxidized poly-(1,2-phenylenediamine) (OPPD)-coated carbon fiber microelectrodes (CFMEs) exhibit, in combination with square-wave voltammetry (SWV) detection mode, the attractive ability to simultaneously measure low nM dopamine (DA) and mM ascorbate (AA) in a pH 7.4 medium. The PPD polymer film is electrodeposited onto a carbon fiber at a constant potential of 0.8 V versus Ag/AgCl using a solution containing sodium dodecylsulfate as the dopant. After overoxidation using cyclic voltammetry (CV) in the potential range from 0 to 2.2 V at a scan rate of 10 V/s, the resulting OPPD-CFME displays a high SWV current response to cationic DA at approximately 0.2 V and has a favorably low response to anionic AA at approximately 0.0 V vs Ag/AgCl. The preparation of the new OPPD-sensing film has been carefully studied and optimized. The OPPD properties and behavior were characterized using CV and SWV under various conditions and are discussed with respect to DA and AA detection. The linear calibration range for DA in the presence of 0.3 mM AA is 50 nM to 10 microM, with a correlation coefficient of 0.998 and a detection limit of 10 nM using 45-s accumulation. The detection limit for DA in the absence of AA was estimated to be 2 nM (S/N = 3). The linear range for AA in the presence of 100 nM DA is 0.2-2 mM, with a correlation coefficient of 0.999 and a detection limit of 80 microM. The reproducibilities of SWV measurements at OPPD-CFCMEs are 1.6% and 2.5% for 100 nM DA and 0.3 mM AA, respectively. Potential interfering agents, such as 3,4-dihydroxyphenylacetic acid, uric acid, oxalate, human serum proteins, and glucose, at their physiologically relevant or higher concentrations did not have any effect. These favorable features offer great promise for in vitro and in vivo application of the proposed OPPD-coated microprobe.

Uricase-catalyzed oxidation of uric acid using an artificial electron acceptor and fabrication of amperometric uric acid sensors with use of a redox ladder polymer

Electrochemical oxidation of uric acid catalyzed by uricase (uric acid oxidase, UOx; EC 1.7.3.3) was studied using several redox compounds including 5-methylphenazinium (MP) and 1-methoxy-5-methylphenazinium (MMP) as electron acceptors for UOx, which does not contain any redox cofactor. It was found that MP and MMP were useful to mediate electrons from UOx to an electrode in the enzymatic oxidation of uric acid. A novel redox polymer, poly(N-methyl-o-phenylenediamine)(poly-MPD), containing the MP units was also found to possess the mediation ability for UOx, and poly-MPD was immobilized together with UOx onto an electrode substrate covered with a self-assembled monolayer of 2-aminoethanethiolate with use of glutaraldehyde as a binding agent. The resulting electrode (poly-MPD/UOx/Au) exhibited amperometric responses to uric acid with very fast response of approximately 30 s, allowing reagentless amperometric determination in a concentration range covering that in the blood of a healthy human being. Kinetic parameters of the apparent Michaelis constant and the maximum current response obtained at the poly-MPD/UOx/Au suggested that electrochemical oxidation of uric acid was controlled by diffusion of uric acid into the enzyme film and that the redox polymer worked well in mediating between active sites of UOx molecules and the electrode substrate.