Molecularly imprinted polyaniline film for ascorbic acid detection

Molecularly imprinted polyaniline (PANI) film (～ 100 nm thick) has been electrochemically fabricated onto indium-tin-oxide (ITO) coated glass plate using ascorbic acid (AA) as template molecule. Fourier transform infra-red spectroscopy, scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV) studies indicate the presence of AA in PANI matrix, which also acts as a dopant for PANI. Further, the AA selective molecularly imprinted PANI electrode (AA-MI-PANI/ITO) has been developed via over-oxidation of AA doped PANI electrode which leads to the removal of AA moieties from PANI film. The response studies using DPV technique have revealed that this molecularly imprinted AA-MI-PANI/ITO electrode can detect AA in the range of 0.05-0.4 mM with detection limit of 0.018 mM and sensitivity of 1.2 × 10(-5) AmM(-1). Interestingly, this AA-MI-PANI/ITO electrode shows excellent reusability, selectivity and stability.     

Omp85 genosensor for detection of human brain bacterial meningitis

The 5′-thiolated DNA probe based on specific virulence gene, Omp85, was immobilized onto a screen-printed gold electrode followed by hybridization with 6–100 ng/6 μl (5.9 × 10⁵–9.3 × 10⁶ c.f.u.) of Neisseria meningitidis single stranded genomic DNA (ssG-DNA) for 10 min at 25 °C from the cerebrospinal fluid (CSF) of a meningitis patient. The Omp85 genosensor can detect as little as 6 ng ssG-DNA in 6 μl CSF of a human brain meningitis patient in 30 min including a response time of 1 min by cyclic voltammetry, differential pulse voltammetry (DPV) and electrochemical impedance. The sensitivity of the genosensor electrode was 2.6(μA/cm²)/ng using DPV with regression coefficient (R²) 0.954. The genosensor was characterized using Fourier transform infrared spectroscopy and atomic force microscopy. Omp85 genosensor was stable for 12 months at 4 °C with 12 % loss in DPV current.     

Polyaniline-carbon nanotube composite film for cholesterol biosensor

Nanocomposite film composed of polyaniline (PANI) and multiwalled carbon nanotubes (MWCNT), prepared electrophoretically onto indium tin oxide (ITO)-coated glass plate, was used for covalent immobilization of cholesterol oxidase (ChOx) via N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) chemistry. Results of linear sweep voltammetric measurements reveal that ChOx/PANI-MWCNT/ITO bioelectrode can detect cholesterol in the range of 1.29 to 12.93 mM with high sensitivity of 6800 nA mM⁻¹ and a fast response time of 10 s. Photometric studies for ChOx/PANI-MWCNT/ITO bioelectrode indicate that it is thermally stable up to 45 °C and has a shelf life of approximately 12 weeks when stored at 4 °C. The results of these studies have implications for the application of this interesting matrix (PANI-MWCNT) toward the development of other biosensors.     

Preparation of co‐Co3O4/carbon nanotube/carbon foam for glucose sensor

Co‐Co₃O₄/carbon nanotube/carbon foam (Co‐Co₃O₄/CNT/CF) nanocomposites were prepared by soaking melamine foam into a solution of Co(NO₃)₂·6H₂O, followed by calcination in N₂ and air in sequence. The obtained Co‐Co₃O₄/CNT/CF nanocomposites were characterized with scanning electron microscopy and cyclic voltammetry. It was found that Co₃O₄ nanoparticles were grown on the external of CF successfully, while CNTs were grown on the surfaces of CF in a large amount, which further improved the electrical conductivity of the. The prepared Co‐Co₃O₄/CNT/CF nanocomposites were then used to construct nonenzymatic sensor to detect glucose in alkaline solution. The sensor showed detection range from 1.2 μM to 2.29 mM with a detection limit of 0.4 μM (S/N =3) and a high sensitivity of 637.5 μA^?1 cm^?2. The developed sensor also showed an instant response, favorable reproducibility, and high selectivity. The results attest that Co‐Co₃O₄/CNT/CF composites have great potential in the development of nonenzymatic sensors for glucose.     

Three‐dimensional (3‐D) fluorescence spectroscopy analysis of the fluorescent dissolved organic matter released by the marine toxic dinoflagellate Alexandrium catenella exposed to metal stress by zinc or lead

We investigated the effects of zinc or lead on growth and on exudation of fluorescent dissolved organic matter (FDOM) by the marine toxic dinoflagellate Alexandrium catenella (Whedon & Kofoid) Balech. The species was exposed to increasing free zinc (1.34 × 10^?7 M–3.98 × 10^?6 M) or lead (5.13 × 10^?9 M–1.82 × 10^?7 M) concentra‐tions. Low metal levels ([Zn²⁺] = 1.34 × 10^?7 M; [Pb²⁺] = 5.13 × 10^?9 M) had no effect on cell growth. Toxic effects were observed from higher metal contamination ([Zn²⁺] = 3.98 × 10^?6 M; [Pb²⁺] = 6.54 × 10^?8 M), as a conversion of vegetative cells into cysts. Analysis of the released FDOM by three‐dimensional (3‐D) fluorescence spectroscopy was achieved, using the parallel factor analysis (PARAFAC). The PARAFAC modeling revealed four components associated with two contributions: one related to the biological activity; the other linked to the organic matter decomposition in the culture medium. The C1 component combined a tryptophan peak and characteristics of humic substances, whereas the C2 component was considered as a tryptophan protein fluorophore. The two others C3 and C4 components were associated with marine organic matter production. Relea‐sed fluorescent substances were induced by low ([Zn²⁺]= 1.34 × 10^?7 M; [Pb²⁺] = 5.13 × 10^?9 M) and moderate ([Zn²⁺] = 6.21 × 10^?7 M; [Pb²⁺] = 2.64× 10^?9 M) metal concentrations, suggesting the activation of cellular mechanisms in response to metal stress, to exudate FDOM that could complex metal cations and reduce their toxicity toward A. catenella cells.     

Molecularly imprinted polyaniline molecular receptor–based chemical sensor for the electrochemical determination of melamine

Molecularly imprinted polymer‐modified glassy carbon electrode (GCE)‐based electrochemical sensor is prepared using the electropolymerization of aniline in the presence of melamine (MA) as a template. In this work, the advantages of molecularly imprinted conducting polymers (MICPs) and electroanalytical methods were combined to obtain an electronic device with better performances. The sensor performance was evaluated by cyclic voltammetry (CV) and square wave voltammetry (SWV) with the linear range of 0.6‐16 × 10^?9M, quantification limit of 14.9 × 10^?10M, and detection limit of 4.47 × 10^?10M (S/N = 3). The selectivity of the sensor was tested in the presence of acetoguanamine (AGA), diaminomethylatrazine (DMT), casein, histidine, and glycine interfering molecules taken at the triple concentration with MA that demonstrated too small current response compared with that of the analyte indicating high specificity of the sensor towards the template. The sensor was successfully applied to determine MA in infant formula samples with significant recovery greater than 96% and relative standard deviation (RSD) less than 4.8%. Moreover, the good repeatability, recyclability, and stability make this sensor device promising for the real‐time monitoring of MA in different food stuffs.     

Revealing binding interaction between seven drugs and immobilized β2‐adrenoceptor by high‐performance affinity chromatography using frontal analysis

The development of new approaches to study the affinity between ligands and G‐protein‐coupled receptors proves to be of growing interest for pharmacologists, chemists, and biologists. The aim of this work was to determine the binding of seven drugs to β₂‐adrenoceptors by frontal analysis using immobilized receptor stationary phase. The dissociation constants (K_d) were determined to be (3.16 ± 0.09) × 10^?4 M for salbutamol, (4.29 ± 0.12) × 10^?4 M for terbutaline, (6.19 ± 0.16) × 10^?4 M for methoxyphenamine, (2.11 ± 0.07) × 10^?4 M for tulobuterol, (1.82 ± 0.11) × 10^?4 M for fenoterol, (9.75 ± 0.24) × 10^?6 M formoterol, and (9.84 ± 0.26) × 10^?5 M for clenbuterol. These results showed a good correlation with the data determined by radioligand binding assay. Further investigations revealed that the dissociation constant mainly attributed to the number of hydrogen bonds in the structures of ligands. This study indicates that affinity chromatography using immobilized receptor stationary phase can be used for the direct determination of drug‐receptor binding interactions and has the potential to become a reliable alternative for quantitative studies of ligand–receptor interactions. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

A new polyaniline–catalase–glutaraldehyde-modified biosensor for hydrogen peroxide detection

A new biosensor based on catalase enzyme immobilized on electrochemically constructed polyaniline (PANI) film modified with glutaraldehyde has been developed for the determination of hydrogen peroxide (H₂O₂) in milk samples. Assembly processes of polyaniline and immobilization of the enzyme were monitored with the help of electrochemical impedance spectroscopy. Amperometric measurements have been performed at cathodic peak (?0.3?V vs. Ag/AgCI) which was attributed to reduction of PANI. Hydrogen peroxide was determined by using amperometric method at ?0.3?V. The biosensor responses were correlated linearly with the hydrogen peroxide concentrations between 5.0?×?10^?6 and 1.0?×?10^?4?M by amperometric method. Detection limit of the biosensor is 2.18?×?10^?6?M for H₂O₂. In the optimization studies of the biosensor, some parameters such as optimum pH, temperature, concentration of aniline, amount of enzyme, and number of scans during electropolymerization were investigated.     

Induction of deflagellation by various local anesthetics in Chlamydomonas reinhardtii Dangeard (Chlamydomonadales,Chlorophyceae)

Dibucaine, a local anesthetic, is known to induce flagellar excision in Chlamydomonas reinhardtii. Herein, we investigate whether other local anesthetics have similar effects. Tetracaine, bupivacaine, procaine, and lidocaine also caused flagellar excision, although their potencies were lower than that of dibucaine. Bupivacaine, procaine, and lidocaine induced a morphological change in flagella from a rod‐like shape to a disk‐like shape before flagellar excision. Except for lidocaine, these local anesthetics caused cell‐wall shedding in addition to flagellar excision. The anesthetics in order of their median effective concentration (1‐h EC₅₀) for flagellar excision are as follows: dibucaine (1.37 × 10^?5 M) < tetracaine (3.16 × 10^?5 M) < bupivacaine (4.25 × 10^?4 M) < procaine (2.02 × 10^?3 M) < lidocaine (3.61 × 10^?3 M). In all cases, Ca²⁺ depletion from the solution inhibited flagellar excision. However, Ca²⁺‐channel blockers, IP3 receptor antagonists, and inhibitors of phospholipase C did not prevent excision. We suggest that the local anesthetics induce flagellar excision by increasing the fluidity of the flagellar/cell membrane, thereby allowing extracellular Ca²⁺ to flow into the cell and cause flagellar excision.     

Chiral single‐walled carbon nanotubes as chiral selectors in multimode enantioselective sensors

Single‐walled carbon nanotube‐(7,6) chirality was used for the design of multimode enantioselective sensors using different carbon matrices such as graphene paste, graphite paste, and carbon nanopowder‐based paste. l ‐ and d ‐malic acids were used as model analytes. The responses of the multimode sensors were evaluated for potentiometric and differential pulse voltammetry (DPV) modes. When carbon nanopowder was used as matrix, the multimode sensor was enantioselective for d ‐malic acid in the concentration range 10^?3 to 10^?15 mol/L for the potentiometric mode and 10^?5 to 10^?8 mol/L for the DPV mode. The graphite paste‐based sensor was enantioselective for l ‐malic acid in the ranges: 10^?10 to 10^?13 for the potentiometric mode and 10^?4 to 10^?7 mol/L for the DPV mode. The sensors based on graphene and chiral single‐walled carbon nanotubes were enantioselective for d ‐malic acid, and a response was obtained only in the DPV mode. Accordingly, the matrix influenced both the enantioselectivity and the sensitivity of the measurements. The application of the sensors was for the enantioanalysis of malic acid in wines and apple juice samples. The proposed method is fast and reliable and allows the quantification of l ‐ and d ‐malic acids using electrochemical methods based on different principles, from the real samples after a buffering of the samples. The enantioanalysis of malic acid in wine and juice samples was performed with high recoveries (higher than 90.00%) and low relative standard deviation (RSD) (%) values (lower than 1.00%).     

New Phytotoxic Metabolites from Pestalotiopsis sp. HC02, a Fungus Residing in Chondracris rosee Gut

Two new phytotoxic γ‐lactones, pestalotines A and B ( 1 and 2 , resp.), along with 4‐oxo‐4H‐pyran‐3‐acetic acid ( 3 ) and 6‐hydroxyramulosin (=3,4,4a,5,6,7‐hexahydro‐6,8‐dihydroxy‐3‐methyl‐1H‐2‐benzopyran‐1‐one; 4 ), were isolateded from the culture of Pestalotiopsis sp. HC02, a fungus residing in the Chondracris rosee gut. Structures of the new metabolites were elucidated on the basis of their IR, NMR, and MS data. Pestalotines A and B ( 1 and 2 , resp.) significantly inhibited the radical growth of Echinochloa crusgalli with IC₅₀ values of 1.85×10^?4 and 2.50×10^?4 M , respectively, comparable to that of 2‐(2,4‐dichlorophenoxy)acetic acid (0.94×10^?4 M ) used as a positive control.     

Determination of bergenin based on the electrochemiluminescence quenching of tris(2,2′‐bipyridine)‐ruthenium(II)

Quenching effects of bergenin, based on the electrochemiluminescence (ECL) of the tris(2,2′‐bipyridyl)‐ruthenium(II) (Ru(bpy)₃²⁺)/tri‐n‐propylamine (TPrA) system in aqueous solution, is been described. The quenching behavior can be observed with a 100‐fold excess of bergenin over Ru(bpy)₃²⁺. In the presence of 0.1 m TPrA, the Stern–Volmer constant (K_SV) of the ECL quenching is as high as 1.16 × 10⁴ M^?1 for bergenin. The logarithmic plot of the inhibited ECL versus logarithmic plot of the concentration of bergenin was linear over the range 3.0 × 10^?6–1.0 × 10^?4 mol/L. The corresponding limit of detection was 6.0 × 10^?7 mol/L for bergenin (S/N = 3). In the mechanism of quenching it is believed that the competition of the active free radicals between Ru(bpy)₃²⁺/TPrA and bergenin was the key factor for the ECL inhibition of the system. Photoluminescence, cyclic voltammetry, coupled with bulk electrolysis, supports the supposition mechanism of the Ru(bpy)₃²⁺/TPrA–bergenin system. Copyright © 2015 John Wiley & Sons, Ltd.     

Differential in vitro inhibition of polyphenoloxidase from a wild edible mushroom Lactarius salmonicolor

The polyphenol oxidase (LsPPO) from a wild edible mushroom Lactarius salmonicolor was purified using a Sepharose 4B-L-tyrosine-p-amino benzoic acid affinity column. At the optimum pH and temperature, the K_M and V_Max values of LsPPO towards catechol, 4-methylcatechol and pyrogallol were determined as 0.025 M & 0.748 EU/mL, 1.809 × 10^{? 3} M & 0.723 EU/mL and 9.465 × 10^{? 3} M & 0.722 EU/mL, respectively.

Optimum pH and temperature values of LsPPO for the three substrates above ranged between the pH 4.5–11.0 and 5–50°C. Enzyme activity decreased due to heat denaturation with increasing temperature. Effects of a variety of classical PPO inhibitors were investigated opon the activity of LsPPO using catechol as the substrate. IC₅₀ values for glutathione, p-aminobenzenesulfonamide, L-cysteine, L-tyrosine, oxalic acid, β-mercaptoethanol and syringic acid were determined as 9.1 × 10^{? 4}, 2.3 × 10^{? 4} M, 1.5 × 10^{? 4} M, 3.8 × 10^{? 7} M, 1.2 × 10^{? 4} M, 4.9 × 10^{? 4} M, and 4 × 10^{? 4} M respectively. Thus L-tyrosine was by far the most effective inhibitor. Interestingly, sulfosalicylic acid behaved as an activator of LsPPO in this study.     

Synthesis,Chemical Characterization,DNA Binding,Antioxidant, Antibacterial,and Antifungal Activities of Ferrocence Incorporated Selenoureas

Ferrocene‐incorporated selenoureas 1‐(4‐methoxybenzoyl)‐3‐(4‐ferrocenylphenyl)selenourea (P4Me), 1‐(3‐methoxybenzoyl)‐3‐(4‐ferrocenylphenyl)selenourea (P3Me), and 1‐(2‐methoxybenzoyl)‐3‐(4‐ferrocenylphenyl)selenourea (P2Me) were synthesized and characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, atomic absorption spectroscopy, CHNS, and single‐crystal X‐ray diffraction. DNA interaction of the compounds was investigated with cyclic voltammetry, UV–visible spectroscopy, and viscometry, which is a prerequisite for anticancer agents. Drug‐DNA binding constant was found to vary in the sequence: K_P4Me (4.9000 × 10⁴ M^?1) > K_P2Me (2.318 × 10⁴ M^?1) > K_P3Me (1.296 × 10⁴ M^?1). Antioxidant (1,1‐diphenyl‐2‐picrylhydrazyl), antifungal (against Faussarium solani and Helmentosporium sativum), and antibacterial (against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis) activities have also been reported in addition.     

Electrophoresis–chemiluminescence detection of phenols catalyzed by hemin

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis–chemiluminescence (CE‐CL) detection method for phenols using a hemin–luminol–hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br^? and F^? could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE‐CL detection system because of the self‐polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin–luminol afforded a stable CE‐CL baseline. The indirect CE‐CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10^?8 mol/L (o‐sec‐butylphenol), 4.9 × 10^?8 mol/L (o‐cresol), 5.4 × 10^?8 mol/L (m‐cresol), 5.3 × 10^?8 mol/L (2,4‐dichlorophenol) and 7.1 × 10^?8 mol/L (phenol). Copyright © 2013 John Wiley & Sons, Ltd.     

N‐butylamine functionalized graphene oxide for detection of iron(III) by photoluminescence quenching

An N‐butylamine functionalized graphene oxide nanolayer was synthesized and characterized by ultraviolet (UV)–visible spectrometry, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and transmission electron microscopy. Detection of iron(III) based on photoluminescence spectroscopy was investigated. The N‐butylamine functionalized graphene oxide was shown to specifically interact with iron (III), compared with other cationic trace elements including potassium (I), sodium (I), calcium (II), chromium (III), zinc (II), cobalt (II), copper (II), magnesium (II), manganese (II), and molybdenum (VI). The quenching effect of iron (III) on the luminescence emission of N‐butylamine functionalized graphene oxide layer was used to detect iron (III). The limit of detection (2.8 × 10^?6 M) and limit of quantitation (2.9 × 10^?5 M) were obtained under optimal conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrophoretic fabrication of chitosan-zirconium-oxide nanobiocomposite platform for nucleic acid detection

The present work describes electrophoretic fabrication of nanostructured chitosan-zirconium-oxide composite (CHIT-NanoZrO(2)) film (180 nm) onto indium-tin-oxide (ITO)-coated glass plate. This nanobiocomposite film has been explored as immobilization platform for probe DNA specific to M. Tuberculosis as model biomolecule to investigate its sensing characteristics. It is revealed that pH-responsive behavior of CHIT and its cationic skeleton is responsible for the movement of CHIT-NanoZrO(2) colloids toward cathode during electrophoretic deposition. The FT-IR, SEM, TEM, and EDX techniques have been employed for the structural, morphological, and composition analysis of the fabricated electrodes. The morphological studies clearly reveal uniform inter-linking and dispersion of hexagonal nanograins of ZrO(2) (30-50 nm) into the chitosan matrix, resulting in homogeneous nanobiocomposite formation. Electrochemical response measurements of DNA/CHIT-NanoZrO(2)/ITO bioelectrode, carried out using cyclic voltammetry and differential pulse voltammetry, reveal that this bioelectrode can specifically detect complementary target DNA up to 0.00078 μM with sensitivity of 6.38 × 10(-6) AμM(-1).     

Highly sensitive and selective uric acid biosensor based on a three-dimensional graphene foam/indium tin oxide glass electrode

A three-dimensional (3D) continuous and interconnected network graphene foam (GF) was synthesized by chemical vapor deposition using nickel foam as a template. The morphologies of the GF were observed by scanning electron microscopy. X-ray diffraction and Raman spectroscopy were used to investigate the structure of GF. The graphene with few layers and defect free was closely coated on the backbone of the 3D nickel foam. After etching nickel, the GF was transferred onto indium tin oxide (ITO) glass, which acted as an electrode to detect uric acid using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The GF/ITO electrode showed a high sensitivity for the detection of uric acid: approximately 9.44 mA mM⁻¹ in the range of 25 nM–0.1 μM and 1.85 mA mM⁻¹ in the range of 0.1–60 μM. The limit of detection of GF/ITO electrode for uric acid is 3 nM. The GF/ITO electrode also showed a high selectivity for the detection of uric acid in the presence of ascorbic acid. This electrode will have a wide range of potential application prospects in electrochemical detection.     

Resonance light scattering technique for determination of polychlorinated biphenyls with silver nanoparticles

In this paper, a simple and novel method for the determination of polychlorinated biphenyls (PCBs), using silver nanoparticles (AgNPs) as a resonance light scattering (RLS) probe, is proposed. Under optimized conditions, there existed linear relationships between the enhancing RLS intensity of the system and the concentrations of PCBs in the range 8.0 × 10^?8?1.0 × 10^?6 g mL^?1 for 2,4,4′‐trichlorbiphenyl (PCB28), 9.0 × 10^?8?1.0 × 10^?6 g mL^?1 for 2,2′,5,5′‐tetrachlorbiphenyl (PCB52) and 4.0 × 10^?8?1.0 × 10^?6 g mL^?1 for 3,3′,4,4′‐tetrachlorobiphenyl (PCB77). The corresponding detection limits (S/N = 3) were 2.6 × 10^?8 g mL^?1 for PCB28, 3.3 × 10^?8 g mL^?1 for PCB52 and 6.3 × 10^?9 g mL^?1 for PCB77, respectively. Finally, the mechanism of RLS enhancement was also studied. The results indicated that PCBs were adsorbed on the surface of AgNPs to form larger AgNP–PCB aggregates, resulting in the RLS enhancement of the system. Copyright © 2011 John Wiley & Sons, Ltd.