In vivo measurements of changes in pH triggered by oxalic acid in leaf tissue of transgenic oilseed rape

Oxalic acid (OA), a non-host-specific toxin secreted by Sclerotinia sclerotiorum during pathogenesis, has been demonstrated to be a major phytotoxic and pathogenic factor. Oxalate oxidase (OXO) is an enzyme associated with the detoxification of OA, and hence the introduction of an OXO gene into oilseed rape (Brassica napus L.) to break down OA may be an alternative way of increasing the resistance of the plant to Sclerotinia sclerotiorum. In order to investigate the activation of OXO in transgenic oilseed rape, a convenient and accessible method was used to monitor changes in pH in response to stress induced by OA. The pH sensor, a platinum microcylinder electrode modified using polyaniline film, exhibited a linear response within the pH range from 3 to 7, with a Nernst response slope of 70 mV/pH at room temperature. The linear correlation coefficient was 0.9979. Changes induced by OA in the pH values of leaf tissue of different oilseed rape species from Brassica napus L. were monitored in real time in vivo using this electrode. The results clearly showed that the transgenic oilseed rape was more resistant to OA than non-transgenic oilseed rape.     

Electrocatalytic activity of core/shell magnetic nanocomposite

Electrically active magnetic nanocomposites (EAMNCs), Au nanoparticles/self-doped polyaniline@Fe₃O₄ (AuNPs/SPAN@Fe₃O₄) with well-defined core/shell structure, were first synthesized by a simple method. The morphology and composition of the as-synthesized AuNPs/SPAN@Fe₃O₄ nanocomposite have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT–IR), ultraviolet–visible (UV–Vis), X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA). Horseradish peroxidase (HRP)–AuNPs/SPAN@Fe₃O₄ biocomposites were immobilized onto the surface of indium tin oxide (ITO) electrode to construct an amperometric hydrogen peroxide (H₂O₂) biosensor. The effects of HRP dosage, solution pH, and the working potential on the current response toward H₂O₂ reduction were optimized to obtain the maximal sensitivity. Under the optimal conditions, the proposed biosensor exhibited a linear calibration response in the range of 0.05 to 0.35 mM and 0.35 to 1.85 mM, with a detection limit of 0.01 mM (signal-to-noise ratio = 3). The modified electrode could virtually eliminate the interference of ascorbic acid (AA) and uric acid (UA) during the detection of H₂O₂. Furthermore, the biosensor was applied to detect H₂O₂ concentration in real samples, which showed acceptable accuracy with the traditional potassium permanganate titration.     

Polyaniline/carbon nanotubes platform for sexually transmitted disease detection

Polyaniline/carbon nanotubes composite (PANI‐CNT) electrochemically deposited onto indium‐tin‐oxide (ITO) coated glass plate has been utilized for Neisseria gonorrhoeae detection by immobilizing 5′‐amino‐labeled Neisseria gonorrhoeae probe (aDNA) using glutaraldehyde as a cross‐linker. PANI‐CNT/ITO and aDNA‐Glu‐PANI‐CNT/ITO electrodes have been characterized using scanning electron microscopy (SEM), Fourier Transform Infrared (FT‐IR) spectroscopy, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). This bioelectrode can be used to detect N. gonorrhoeae using methylene blue (MB) as redox indicator with response time of 60 s and stability of about 75 days when stored under refrigerated conditions. DPV studies reveal that this bioelectrode can detect complementary DNA concentration from 1 × 10^?6 M to 1 × 10^?17 M with detection limit of 1.2 × 10^?17 M. Further, this bioelectrode (aDNA‐Glu‐PANI‐CNT/ITO) exhibits specificity toward N. gonorrhoeae species and shows negative response with non‐Neisseria gonorrhoeae Neisseria species (NgNS) and other gram negative bacteria (GNB). Copyright © 2010 John Wiley & Sons, Ltd.     

Glucose biosensor based on polyaniline synthesized in ionic liquid

The use of good electro-active polyaniline at high pH for immobilizing glucose oxidase is reported. The response current increased with increasing potential from 0.35 to 0.70 V. The maximum response current occurred at about pH 7.0. The relationship between response current and the glucose concentration was linear from 0.005 to 10.0 mmol dm^?3. The Michaelis–Menten constant K_m', maximum response current i_max and the apparent activation energy (E_a) were 31.59 mmol dm^?3, 21.28 µA and 32.58 kJ mol^?1, respectively. The response currents of the biosensor increased with increasing temperature. The biosensor was characterized by FTIR, UV-Vis spectra and AC impedance.     

Preparation and chiro-optical characterization of polyaniline doped with (+) or (-)-2-pyrrolidone-5-carboxylic acid (PCA)

Optically active polyaniline (PANI) salts were readily generated in solution via the enantioselective acid doping of neutral emeraldine base (EB) form of PANI with either (+) or (-)-2-pyrrolidone-5-carboxylic acid (PCA) in dimethylsulfoxide (DMSO) and dimethylformamide (DMF) solvents. Strong mirror imaged circular dichroism (CD) spectra were obtained for the deep green polymer solutions obtained with (+) or (-) PCA, suggesting that the acid doping is enantioselective, with one helical screw of the polymer chain being preferentially produced depending on the nature of enantiomer. It was observed that molar concentration of PCA as well as nature of solvent plays a very important role in the generation of optically active PANI. The generated optically active PANI did not show any loss of optical activity up to 200 h.     

Nucleic acid sensor for insecticide detection

Nucleic acid sensor based on polyaniline (PANI) has been fabricated by covalently immobilizing double stranded calf thymus (dsCT) DNA onto perchlorate (ClO(-) (4))-doped PANI film deposited onto indium-tin-oxide (ITO) glass plate using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) chemistry. These dsCT-DNA-PANI-ClO(4)/ITO and PANI-ClO(4)/ITO electrodes have been characterized using square wave voltammetry, electrochemical impedance, scanning electron microscopy (SEM) and Fourier-transform-infrared (FTIR) measurements. This disposable dsCT-DNA-PANI-ClO(4)/ITO bioelectrode, stable for about 4 months, can be used to detect cypermethrin (0.005 ppm) and trichlorfon (0.01 ppm) in 30 and 60 s, respectively.     

Femtomol SPR detection of DNA-PNA hybridization with the assistance of DNA-guided polyaniline deposition

The inability of surface plasmon resonance (SPR) spectroscopy to detect extremely small refractive index changes has hindered its applications in ultrasensitive DNA analysis. In this study we report a signal amplification strategy that uses DNA-templated polyaniline deposition, suitable for DNA hybridization analysis with charge neutral peptide nucleic acid (PNA) being probes. Under acidic conditions, protonated aniline monomers are adsorbed on DNA backbones through electrostatic interaction. The microenvironment provided by the DNA facilitates oxidative aniline polymerization initialized by H₂O₂ in the presence of horseradish peroxide. Under optimal conditions, the detection limit is lowered from 5 nM for conventional SPR detection to 0.1 pM. The significant sensitivity improvement is attributed to the in-situ polymer chain growth along DNA strands, which introduces drastic refractive index increases. This signal amplification approach does not involve secondary hybridization processes. The detection sensitivity obtained is much better than that of gold nanoparticle-based amplification involving a secondary hybridization process and labeled DNA detection probes.     

Green synthesis of conductive polyaniline by Trametes versicolor laccase using a DNA template

The green synthesis of highly conductive polyaniline by using two biological macromolecules, i.e laccase as biocatalyst, and DNA as template/dopant, was achieved in this work. Trametes versicolor laccase B (TvB) was found effective in oxidizing both aniline and its less toxic/mutagenic dimer N‐phenyl‐p‐phenylenediamine (DANI) to conductive polyaniline. Reaction conditions for synthesis of conductive polyanilines were set‐up, and structural and electrochemical properties of the two polymers were extensively investigated. When the less toxic aniline dimer was used as substrate, the polymerization reaction was faster and gave less‐branched polymer. DNA was proven to work as hard template for both enzymatically synthesized polymers, conferring them a semi‐ordered morphology. Moreover, DNA also acts as dopant leading to polymers with extraordinary conductive properties (～6 S/cm). It can be envisaged that polymer properties are magnified by the concomitant action of DNA as template and dopant. Herein, the developed combination of laccase and DNA represents a breakthrough in the green synthesis of conductive materials.