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Ammonia (NH3) gas is an important chemical in many industries. Employees working in such industrial areas may exposed to a certain concentration of NH3 which could cause various symptoms such as irritation of skin and eyes and problems in respiratory system. The development of new NH3 sensing material has attracted great attention. In this study, porous tin dioxide nanofibers (SnO2 NFs) were successfully fabricated by electrospinning. The SnO2 NFs was composited with polyaniline (PANI), conducting polymer. The tin dioxide nanofibers@polyaniline nanocomposite (SnO2 NFs@PANI) was examined and showed improving and desirable sensing for NH3 gas, which includes high sensitivity, quick response and fast recovery times at room temperature. HIGHLIGHTS Ammonia (NH3) gas has been used in many industries. For worker safety in those industrial area, a reliable NH3 gas sensor is necessary A new tin dioxide nanofibers@polyaniline nanocomposite (SnO2 NFs@PANI) had successfully developed for a selectively ammonia gas sensor Excellent analytical performance in team of stability, repeatability and widely response for NH3 concentration was achieved GRAPHICAL ABSTRACT

Novel 1,4-dihydropyridine (DHP) derivatives containing 3 carboxylic acid units are synthesized via cyclotrimerization of N -substituted β-aminoacrylates followed by basic hydrolysis of the triester. These DHP derivatives are readily soluble in aqueous media buffered at pH 8.0 and the solutions give blue fluorescent signals with quantum yields of 7–23%. One of these compounds, bearing a p -methoxyphenyl N -substituted group, shows specific fluorescent quenching with the mercuric ion (Hg 2+ ). The fluorescent signal of the DHP derivative decays over a period of minutes to hours depending on the Hg 2+ concentration, which implies that the sensing mechanism involves chemical reaction between the Hg 2+ ion and the DHP compound. The 1 H NMR and MS data suggest that Hg 2+ mediates the oxidation of the DHP ring into a pyridinium ring. The event is useful for fluorescent detection of Hg 2+ at the micromolar level within 30 min, with a detection limit of 0.2 μM in aqueous medium.

A new method has been developed for the determination of carbaryl pesticides, , in water and fruit samples using gold nanoparticles electrode conductivity detection. The effects of pH on the binding between carbaryl and humic acid (HA) and number of layer coated electrode were investigated and optimized. HA modified the polyelectrolyte multilayer thin films (PEMs) coating electrode was used to detect carbaryl. The current was decreased 4.75% after dipping in HA for 10 minutes. The current was decreased around 7.28% from the initial value after HA binding with carbaryl. The results demonstrated that the newly developed method was an efficient procedure for the detection of carbamate pesticides in water.

A new method for the surface modification of the surface of fruits based on the Layer-by-Layer (LbL) deposition of polyelectrolyte multilayers (PEM) is presented. Mangoes fruits were coated by sequential dipping in solutions of either Poly(diallyldimethylammonium chloride), (PDADMAC) or Poly(styrene sulfonate sodium salt) (PSS). After the deposition of only few polyelectrolyte layers, the skin of the fruits was changed from hydrophobic to hydrophilic as shown by contact angles measurements decreasing from 90 to 10. Fourier transform infrared spectroscopy (FTIR) was used to confirm the deposition of the PEM coating on the fruit which was then used as a matrix to load curcumin as model compound. Ultraviolet Visible (UV-Vis) spectroscopy was used to evaluate the amount of a curcumin loaded on the fruit surface as a function of the thickness of the film by indirect leaching in ethanol. This coating method provides a new approach to dope active compound on the fruit surface such as anti-oxidant, fragrance, color and other nutriment which could increase the market value of fruits.

Microelectrodes to be used in microfluidic devices were prepared from the layer-by-layer flow deposition of gold nanoparticles. Pre-designed microfluidic channels were used as templates for the flow driven deposition of the nanoparticles in sequence with poly (diallyldimethyl amonium chloride) (PDADMAC). The electrical resistivity of the gold nanoparticle assembly was found to be strongly dependant on the concentration of sodium citrate used in the gold nanoparticle synthesis. As the electrical properties of the film changed from insulating to conducting when decreasing the citrate concentration, a 4 point probe setup was used to measure the resistivity of the film. Near bulk conductivity (5.42 × 10−6 Ω cm) was achieved with only 10 layers of film. The thickness and morphology of the flow-printed multilayer microelectrode was characterized using atomic force microscopy (AFM) and a field emission scanning electron microscope (FE-SEM). To demonstrate its usefulness, the microelectrode assembly was then tested toward the detection of KCl in solution, having a concentration ranging from 1 to 20 mM using AC current detection in a simple setup. Good linearity and stability of the electrode confirmed that this method could be very convenient for the fabrication of microelectrodes for lab-on-chip applications.

The layer-by-layer (LbL) deposition technique was used to coat and protect poly(methyl methacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) substrate from organic solvent. PMMA and PDMS substrates were protected by polyelectrolyte multilayers (PEM) thin films of either poly(diallydimethiyl ammonium chloride) and Poly(styrene sulfonate) PDADMAC/PSS or chitosan/alginate. The PEM depositited on the PMMA and PDMS substrates improved the organic solvent resistance with the best results obtained from the chitosan/alginate over the PDADMAC/PSS pair. The more hydrophilic character of the chitosan/alginate and the PDADMAC/PSS film caused a significant decreasing rate of organic solvent pentration into the PMMA substrate which retain transparent optical properties for up to 30 dipping in acetonitrile. A 20 layers chitosan alginate film also decreased PDMS substrate swelling when exposed to chloroform vapor. The PEMs coating could protect the PMMA and PDMS sample against organic solvent and vapor which could make them useful in microfluidic systems even in agressive environment.

A novel dimethylglyoxime (DMG)/poly(caprolactone) (PCL) blend was electrospun into fibers to serve as an optical sensor for the nickel detection based on the formation of a red Ni(DMG) 2 complex. DMG was mixed with PCL at 10, 20 and 30% (w/w) in a mixture of N, N-dimethylformamide (DMF) and dichloromethane (DCM) (50/50, v/v) prior electrospunning process. The best fibers were prepared under an electric field of 20 kV and a distance between needle and collector of 20 cm. From scanning electron microscopy (SEM), the average diameter of the fibers remained nearly constant with increasing amount of DMG. The optimum mass ratio of DMG and PCL was found to be 20:80 as it produced fibers with the smallest diameter distribution and the best sensing property. The formation of the Ni(DMG) 2 complex was confirmed by Fourier transform infrared spectroscopy (FT-IR). The colorimetric response of the PCL/DMG electrospun fibers were then tested against the nickel ions over a concentration range of 1–10 ppm using reflectance spectroscopy. Good linearity between the reflectance values at 547 nm and the concentrations was obtained (R 2 = 0.9925). These proposed DMG and PCL fibers could be used as the naked-eye sensor for nickel in waste water.