Microwave Gas Sensors Based on Electrodeposited Polypyrrole-Nickel Phthalocyanine Hybrid Films.

Previous studies have shown that the incorporation of sulfonated metallophthalocyanines into sensitive sensor materials can improve electron transfer and thus species detection. Herein, we propose a simple and easy alternative to the use of generally expensive sulfonated phthalocyanines by electropolymerizing polypyrrole together with nickel phthalocyanine in the presence of an anionic surfactant. The addition of the surfactant not only helps the incorporation of the water-insoluble pigment into the polypyrrole film, but the obtained structure has increased hydrophobicity, which is a key property for developing efficient gas sensors with low sensitivity to water. The obtained results show the effectiveness of the materials tested for the detection of ammonia in the range of 100 to 400 ppm. It is shown by comparing the microwave sensor responses that the film without nickel phthalocyanine (hydrophilic) produces greater variations than the film with nickel phthalocyanine (hydrophobic). These results are consistent with the expected results since the hydrophobic film is not very sensitive to residual ambient water and therefore does not interfere with the microwave response. However, although this excess response is usually a handicap, as it is a source of drift, in these experiments the microwave response shows great stability in both cases.

From the solution processing of hydrophilic molecules to polymer-phthalocyanine hybrid materials for ammonia sensing in high humidity atmospheres.

We have prepared different hybrid polymer-phthalocyanine materials by solution processing, starting from two sulfonated phthalocyanines, s-CoPc and CuTsPc, and polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), poly(acrylic acid-co-acrylamide) (PAA-AM), poly(diallyldimethylammonium chloride) (PDDA) and polyaniline (PANI) as polymers. We also studied the response to ammonia (NH3) of resistors prepared from these sensing materials. The solvent casted films, prepared from s-CoPc and PVP, PEG and PAA-AM, were highly insulating and very sensitive to the relative humidity (RH) variation. The incorporation of s-CoPc in PDDA by means of layer-by-layer (LBL) technique allowed to stabilize the film, but was too insulating to be interesting. We also prepared PANI-CuTsPc hybrid films by LBL technique. It allowed a regular deposition as evidenced by the linear increase of the absorbance at 688 nm as a function of the number of bilayers. The sensitivity to ammonia (NH3) of PANi-CuTsPc resistors was very high compared to that of individual materials, giving up to 80% of current decrease when exposed to 30 ppm NH3. Contrarily to what happens with neutral polymers, in PANI, CuTsPc was stabilized by strong electrostatic interactions, leading to a stable response to NH3, whatever the relative humidity in the range 10%-70%. Thus, the synergy of PANI with ionic macrocycles used as counteranions combined with their simple aqueous solution processing opens the way to the development of new gas sensors capable of operating in real world conditions.

Development of amperometric biosensors based on nanostructured tyrosinase-conducting polymer composite electrodes.

Bio-composite coatings consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and tyrosinase (Ty) were successfully electrodeposited on conventional size gold (Au) disk electrodes and microelectrode arrays using sinusoidal voltages. Electrochemical polymerization of the corresponding monomer was carried out in the presence of various Ty amounts in aqueous buffered solutions. The bio-composite coatings prepared using sinusoidal voltages and potentiostatic electrodeposition methods were compared in terms of morphology, electrochemical properties, and biocatalytic activity towards various analytes. The amperometric biosensors were tested in dopamine (DA) and catechol (CT) electroanalysis in aqueous buffered solutions. The analytical performance of the developed biosensors was investigated in terms of linear response range, detection limit, sensitivity, and repeatability. A semi-quantitative multi-analyte procedure for simultaneous determination of DA and CT was developed. The amperometric biosensor prepared using sinusoidal voltages showed much better analytical performance. The Au disk biosensor obtained by 50 mV alternating voltage amplitude displayed a linear response for DA concentrations ranging from 10 to 300 µM, with a detection limit of 4.18 µM.

Electropolymerization of Pyrrole-Tailed Imidazolium Ionic Liquid for the Elaboration of Antibacterial Surfaces.

A strategy was developed to prepare antibacterial surfaces by electropolymerization of a pyrrole-functionalized imidazolium ionic liquid bearing an halometallate anion. The objective was to combine the antibacterial efficiency of polypyrrole (PPy) with those of the ionic liquid's components (cation and anion). For this, N-(1-methyl-3-octylimidazolium)pyrrole bromide monomer [PyC8MIm]Br was synthesized and coordinated to ZnCl2 affording [PyC8MIm]Br-ZnCl2. The antibacterial properties of [PyC8MIm]Br-ZnCl2 monomer were evaluated against Escherichia coli and Staphylococcus aureus by measurement of the minimum inhibitory concentration (MIC) values. This monomer presents higher activity against S. aureus (MIC = 0.098 µmol·mL-1) than against E. coli (MIC = 2.10 µmol·mL-1). Mixtures of pyrrole and the pyrrole-functionalized ionic liquid [PyC8MIm]Br-ZnCl2 were then used for the electrodeposition of PPy films on Fluorine-doped tin oxide (FTO) substrates. The concentration of pyrrole was fixed to 50 mM, while the concentration of [PyC8MIm]Br-ZnCl2 was varied from 5 to 100 mM. The efficient incorporation of the imidazolium cation and zinc halometallate anion into the films was confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements confirmed the homogeneity of the different films with structures that depend on the [PyC8MIm]Br-ZnCl2 concentration. The films' thickness determined by profilometry varies only slightly with the [PyC8MIm]Br-ZnCl2 concentration from 7.4 µm at 5 mM to 8.9 µM at 100 mM. The films become more hydrophilic with an increase of [PyC8MIm]Br-ZnCl2 concentration with water contact angles varying from 47° at the lowest concentration to 32° at the highest concentration. The antibacterial activities of the different PPy films were determined both by the halo inhibition method and by the colony forming units (CFUs) counting method over time against Gram-positive S. aureus and Gram-negative E. coli bacteria. Films obtained by incorporation of [PyC8MIm]Br-ZnCl2 showed excellent antibacterial properties, at least two times higher than those of neat PPy, validating our strategy. Furthermore, a comparison of the antibacterial properties of the films obtained using the same [PyC8MIm]Br-ZnCl2 concentration (50 mM) evidenced much better activity against Gram-positive (no bacterial survival within 5 min) than against Gram-negative bacteria (no bacterial survival within 3 h). Finally, the antibacterial performances over time could be tuned by the concentration of the employed pyrrole-functionalized ionic liquid monomer. Against E. coli, using 100 mM of [PyC8MIm]Br-ZnCl2, the bacteria were totally killed within a few minutes, using 50 mM, they were killed after 2 h while using 10 mM, about 20% of bacteria survived even after 6 h.

Electrochemical Biosensing of Dopamine Neurotransmitter: A Review.

Neurotransmitters are biochemical molecules that transmit a signal from a neuron across the synapse to a target cell, thus being essential to the function of the central and peripheral nervous system. Dopamine is one of the most important catecholamine neurotransmitters since it is involved in many functions of the human central nervous system, including motor control, reward, or reinforcement. It is of utmost importance to quantify the amount of dopamine since abnormal levels can cause a variety of medical and behavioral problems. For instance, Parkinson's disease is partially caused by the death of dopamine-secreting neurons. To date, various methods have been developed to measure dopamine levels, and electrochemical biosensing seems to be the most viable due to its robustness, selectivity, sensitivity, and the possibility to achieve real-time measurements. Even if the electrochemical detection is not facile due to the presence of electroactive interfering species with similar redox potentials in real biological samples, numerous strategies have been employed to resolve this issue. The objective of this paper is to review the materials (metals and metal oxides, carbon materials, polymers) that are frequently used for the electrochemical biosensing of dopamine and point out their respective advantages and drawbacks. Different types of dopamine biosensors, including (micro)electrodes, biosensing platforms, or field-effect transistors, are also described.

In vitro induction of differentiation by retinoic acid in an immortalized olfactory neuronal cell line.

In this study, we used a neuronal cell line generated by transfection of rat olfactory epithelium with immortalizing recombinant oncogene E1A of adenovirus-2. The resulting 13.S.1.24 line of transformed cells expressed an antigenic phenotype of olfactory neuronal progenitors. Time-dependency assessments over 1 week of treatment indicated that apoptosis and differentiation induced by retinoic acid (RA) were concomitant. Indeed, RA altered the cell proliferation rate, but it also stimulated differentiation of surviving 13.S.1.24 cells into bipolar olfactory marker protein-immunoreactive neurons. To characterize the nature of the cells we used immunocytochemistry, optical imaging, scanning electron microscopy and atomic force microscopy.

Synthesis and characterization of polyaniline-silica composites: Raspberry vs core-shell structures. Where do we stand?

The synthesis of polyaniline-silica composites has been reinvestigated in view of the opposing results found in the literature. Firstly, we synthesized silica particles with tunable size using the Stöber process. These silica particles have been fully characterized before being used as solid support for the polymerization of aniline. This polymerization was performed according to a published procedure where the pH of the reaction mixture was below the pKa of aniline but at a value where the silica particles surface was still slightly negatively charged. The objective of this procedure was to favor electrostatic interactions between anilinium cations and the silica surface to lead to the formation of silica-polyaniline core-shell particles. Several sets of nanocomposites were prepared under different experimental conditions (oxidant/aniline ratio, silica concentration, temperature, silica particles diameters). The study evidenced that under all the conditions used the formation of core-shell nanoparticles is impossible. However, using different particle sizes, noticeable morphological differences were observed. The use of large silica particles led to the formation of non-uniform polyaniline-silica composites whereas the use of smaller particles always led to raspberry-like morphology as reported by other groups in highly acidic media. The difference in morphology led to different electrical properties with electrical conductivities measured at room temperature ranging from 1.6×10-3 to 2.5×10-5S cm-1.

Quantitative self-powered electrochromic biosensors.

Self-powered sensors are analytical devices able to generate their own energy, either from the sample itself or from their surroundings. The conventional approaches rely heavily on silicon-based electronics, which results in increased complexity and cost, and prevents the broader use of these smart systems. Here we show that electrochromic materials can overcome the existing limitations by simplifying device construction and avoiding the need for silicon-based electronics entirely. Electrochromic displays can be built into compact self-powered electrochemical sensors that give quantitative information readable by the naked eye, simply controlling the current path inside them through a combination of specially arranged materials. The concept is validated by a glucose biosensor coupled horizontally to a Prussian blue display designed as a distance-meter proportional to (glucose) concentration. This approach represents a breakthrough for self-powered sensors, and extends the application of electrochromic materials beyond smart windows and displays, into sensing and quantification.

Urea potentiometric biosensor based on modified electrodes with urease immobilized on polyethylenimine films.

The development of a new electrochemical sensor consisting in a glass-sealed metal microelectrode coated by a polyethylenimine film is described. The use of polymers as the entrapping matrix for enzymes fulfils all the requirements expected for these materials without damaging the biological material. Since enzyme immobilization plays a fundamental role in the performance characteristics of enzymatic biosensors, we have tested four different protocols for enzyme immobilization to determine the most reliable one. Thus the characteristics of the potentiometric biosensors assembled were studied and compared and it appeared that the immobilization method leading to the most efficient biosensors was the one consisting in a physical adsorption followed by reticulation with dilute aqueous glutaraldehyde solutions. Indeed, the glutaraldehyde immobilized urease sensor provides many advantages, compared to the other types of sensors, since this type of urea biosensor exhibits short response times (15-30s), sigmoidal responses for the urea concentration working range from 1 x 10(-2.5) to 1 x 10(-1.5) M and a lifetime of 4 weeks.

Miniaturized pH biosensors based on electrochemically modified electrodes with biocompatible polymers.

Potentiometric pH sensors based on linear polyethylenimine (L-PEI) and linear polypropylenimine(L-PPI), two synthetic enzymes and biocompatible polymers, films were prepared by electropolymerization of three different monomers: ethylenediamine (EDA), 1,3-diaminopropane (1,3-DAP) and diethylenetriamine (DETA) in order to be used in clinical, dermatological and biological applications, such as in vivo analysis. In a first step a biosensor was tested which consisted in a platinum wire protruded from glass sheath. The polymer film coated on these platinum electrodes showed good linear potentiometric responses to pH changes from pH 3 to 10. Resulting electrodes present both good reversibility and good stability versus time. The effect of the different polymer film thicknesses to potentiometric responses was also studied. This study allowed us to develop a miniaturized pH biosensor in the second step. This sensor was fabricated using photo-lithography, followed by sputtering and lift-off processes, and it included an electronic detection system. We have also successfully studied the potentiometric responses to pH changes of this device over a period of 1 month, and so we propose this new pH micro-biosensor as an alternative to classical pH sensors currently used in dermatology.

Elaboration of ammonia gas sensors based on electrodeposited polypyrrole--cobalt phthalocyanine hybrid films.

The electrochemical incorporation of a sulfonated cobalt phthalocyanine (sCoPc) in conducting polypyrrole (PPy) was done, in the presence or absence of LiClO4, in order to use the resulting hybrid material for the sensing of ammonia. After electrochemical deposition, the morphological features and structural properties of polypyrrole/phthalocyanine hybrid films were investigated and compared to those of polypyrrole films. A gas sensor consisting in platinum microelectrodes arrays was fabricated using silicon microtechnologies, and the polypyrrole and polypyrrole/phthalocyanine films were electrochemically deposited on the platinum microelectrodes arrays of this gas sensor. When exposed to ammonia, polymer-based gas sensors exhibited a decrease in conductance due to the electron exchange between ammonia and sensitive polymer-based layer. The characteristics of the gas sensors (response time, response amplitude, reversibility) were studied for ammonia concentrations varying from 1 ppm to 100 ppm. Polypyrrole/phthalocyanine films exhibited a high sensitivity and low detection limit to ammonia as well as a fast and reproducible response at room temperature. The response to ammonia exposition of polypyrrole films was found to be strongly enhanced thanks to the incorporation of the phthalocyanine in the polypyrrole matrix.

Adsorption of Ni(II) ions on colloidal hybrid organic-inorganic silica composites.

Two new silica-based composites were prepared as adsorbents for the capture of Ni(II) ions. The first strategy consists in coating chitosan on colloidal fumed silica after acidic treatment yielding the composite SiO(2)+CS. The second route involves in a first step surface condensation of triethoxysilylbutyronitrile, followed by acidic hydrolysis of the surface-bound nitrile groups affording silica particles covered by carboxylic group. In a third step, chitosan has been grafted on the surface-bound C(=O)OH groups yielding the composite SiO(2)(CO(2)H)+CS. The novel hybrid materials were characterized by IR spectroscopy, scanning electron and AFM microscopy, and zeta potential measurements. Batch experiments were conducted to study the sorption performance of these composites for Ni(II) removal from aqueous NiCl(2) solution at different pH. Both Langmuir, Freundlich, and Temkin isotherm models provide good fits with the experimental data. It was shown that these low-cost materials present a promising capacity to adsorb Ni(II) ions. At pH 7, the maximum adsorption capacity q(max)of Ni(II) on the adsorbent, is found to be 182 mg g(-1) for SiO(2)+CS, and 210 mg g(-1) for SiO(2)(CO(2)H)+CS.

Urea potentiometric enzymatic biosensor based on charged biopolymers and electrodeposited polyaniline.

A potentiometric biosensor based on urease was developed for the quantitative determination of urea concentration in aqueous solutions for biomedical applications. The urease was either physisorbed onto an electrodeposited polyaniline film (PANI), or immobilized on a layer-by-layer film (LbL) assembled over the PANI film, that was obtained by the alternate deposition of charged polysaccharides (carboxymethylpullulan (CMP) and chitosan (CHI)). In the latter case, the urease (Urs) enzyme was either physically adsorbed or covalently grafted to the LbL film using carbodiimide coupling reaction. Potentiometric responses of the enzymatic biosensors were measured as a function of the urea concentration in aqueous solutions (from 10(-6) to 10(-1) mol L(-1) urea). Very high sensitivity and short response time were observed for the present biosensor. Moreover, a stability study showed a higher stability over time for the potentiometric response of the sensor with the enzyme-grafted LbL film, testifying for the protective nature of the polysaccharide coating and the interest of covalent grafting.

Charge properties of membranes modified by multilayer polyelectrolyte adsorption.

Alternate adsorption of polyanions and polycations on a polyethersulfone (PES) membrane was studied by the tangential streaming potential method using a parallel-plate channel to investigate the properties of the outer surface of the membrane. These streaming potential data were complemented by diffusion experiments and by membrane potential measurements in order to characterize the inner surface of the membrane. Tangential streaming potential measurements demonstrated that after completing a bilayer of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS), periodic variations in the zeta potential between positive and negative values appeared for multilayer films obtained from membrane dipped in polyelectrolyte (PE) solutions at 10 g/L. On the contrary, the zeta potential was always positive when multilayer films were obtained from 1 and 5 g/L polyelectrolyte concentration solutions. Diffusion experiments carried out with unmodified and modified membranes showed a decrease in the solute flux after functionalization of the membrane by several polyelectrolyte bilayers, indicating that the diffusional resistance of the PE layers contributes significantly to the overall resistance to diffusion of the modified membrane. By means of membrane potential measurements the pore walls of the membrane were functionalized since the charge of its pore walls was modified even if it is difficult to discriminate between the contribution of the membrane and that of the multilayer buildup.

Ammonia gas sensor based on electrosynthesized polypyrrole films.

In this work, design and fabrication of micro-gas-sensors, polymerization and deposition of poly(pyrrole) thin films as sensitive layer for the micro-gas-sensors by electrochemical processing, and characterization of the polymer films by FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), are reported. The change in conductance of thin polymer layers is used as a sensor signal. The behaviours, including sensitivity, reproducibility and reversibility, to various ammonia gas concentrations ranging from 8 ppm to 1000 ppm are investigated. The influence of the temperature on the electrical response of the sensors is also studied. The experimental results show that these ammonia gas sensors are efficient since they are sensitive to ammonia, reversible and reproducible at room temperature.

Development of miniaturized pH biosensors based on electrosynthesized polymer films.

A new type of pH biosensor was developed for biological applications. This biosensor was fabricated using silicon microsystem technology and consists in two platinum microelectrodes. The first microelectrode was coated by an electrosynthesized polymer and acted as the pH sensitive electrode when the second one was coated by a silver layer and was used as the reference electrode. Then, this potentiometric pH miniaturized biosensor based on electrosynthesized polypyrrole or electrosynthesized linear polyethylenimine films was tested. The potentiometric responses appeared reversible and linear to pH changes in the range from pH 4 to 9. More, the responses were fast (less than 1 min for all sensors), they were stable in time since PPy/PEI films were stable during more than 30 days, and no interference was observed. The influence of the polymer thickness was also studied.

Ab initio study of the electronic and structural properties of the crystalline polyethyleneimine polymer.

Polyethyleneimine is a very interesting polymer, not only for its extensive use in biological applications, but also for its crystal structure as a double-stranded helix in the anhydrous state. In order to elucidate the electronic bulk properties of the crystalline (or linear) polyethyleneimine built from ethylenediamine molecules in anhydrous conditions, we performed ab initio density functional theory calculations on water-free molecular crystal structures. The resulting polymer is a semiconductor with a small band gap: Eg = 0.40 eV.