Gold nanoparticles for sensing Mn2+ in water

Abstract: Gold nanoparticles coated with polymers like chitosan, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and poly acrylic acid (PAA) can effectively be used to detect the presence of Mn2+ ions in water. A shift in the optical absorbance peak of the Au colloid is observed in the presence of Mn2+ ions. The shift in the absorbance peak wavelength is directly proportional to the concentration of Mn2+ ions in water. Chitosan capping was found to give the maximum shift and as such was selected for the development of a sensor for detecting Mn2+ ions in water. The variation in photo-energy of the photons after passing through the colloidal dispersion of chitosan coated Au nanoparticles varies the conductivity of the detector and this can be related to the concentration of the Mn2+ ions in water. Two different detectors were tested, a nanosensor and a light dependent resistor, with the latter demonstrating better response.

Developments of Nanoporous AAO Based Capacitive-Type Sensors for Heavy Metal Ion (Arsenic) Sensing Application

In this work the evolution of a capacitive type sensor based on nanoporous anodic aluminum oxide (AAO) fabricated by a two-step anodization process using a low-cost customized setup designed in-house is reported. The parallel plate capacitors were fabricated using aluminum (Al) as base electrode and gold as top electrode, where the porous AAO was used as the dielectric material. This demonstrated the clear dependence of the capacitance values of the as prepared different sensors on the dielectric material’s thickness. The as developed sensors were tested for the detection of arsenic (As) ions.An increase in the capacitance was observed while increasing the concentration of the As ion in aqueous solutions. The presence of As ion was confirmed through EDS (Energy dispersive X-ray spectroscopy) mapping carried out in a FESEM. This change in capacitance can be attributed to the change in dielectric constant of the active material with the incorporation of metal ions