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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.