Table of Contents

Abstract: A reference electrode fabricated by means of thick-film technique is deposited onto a silicon substrate and combined with a thin-film pH sensor to a “hybrid” chip system. To evaluate the suitability of this combination, first investigations were carried out. The characteristics of the thin-film pH sensor were studied towards the thick-film Ag/AgCl reference electrode. Measurements were performed in the capacitance/voltage (C/V) and constant capacitance (Concap) mode for different pH values keeping the concentration of chloride ions constant. No difference of the sensor behaviour could be found when comparing the results to measurements, obtained versus a conventional macroscopic Ag/AgCl reference electrode.

Abstract: A carbon dioxide (CO₂) sensor is fabricated by depositing a thin layer of a multiwall carbon nanotube (MWNT) – silicon dioxide (SiO₂) composite upon a planar inductorcapacitor resonant circuit. By tracking the resonant frequency of the sensor the complex permittivity of the coating material can be determined. It is shown that the permittivity of MWNTs changes linearly in response to CO₂ concentration, enabling monitoring of ambient CO₂ levels. The passive sensor is remotely monitored with a loop antenna, enabling measurements from within opaque, sealed containers. Experimental results show the response of the sensor is linear, reversible with no hysteresis between increasing and decreasing CO₂ concentrations, and with a response time of approximately 45 s. An array of three such sensors, comprised of an uncoated, SiO₂ coated, and a MWNT-SiO₂ coated sensors is used to self-calibrate the measurement for operation in a variable humidity and temperature environment. Using the sensor array CO₂ levels can be measured in a variable humidity and temperature environment to a ± 3% accuracy.

Abstract: The electrochemical polymerization of 2-aminobenzenesulfonic acid with and without aniline has been carried by cyclic potencial sweep in sulfuric acid solution at the glassy carbon electrode. The polymer and copolymer formed have been characterized voltammetrically. The sulfonated polyaniline coated mercury thin-film electrodes have been evaluated for use with anodic stripping voltammetry. The electrodes were tested and compared with a conventional thin-film mercury electrode. Calibration plots showed linearity up to 10^-7 mol L^-1. Detection limits for zinc, lead and cadmium test species are very similar at around 12 nmol L^-1. Applications to analysis of waters samples are demonstrated.