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.

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.

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.

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.

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.