“Enhancement of Sensitivity and Selectivity of Chemical Sensors Through Thin Film Coatings and Surface Modifications

Chemical sensors have become major analytical tools for how we monitor
and obtain information about the chemical nature of ourselves and our
surroundings. Two characteristics of chemical sensors that are under constant
development and improvement are their selectivity and their sensitivity.
Selectivity is a concern of any chemical sensor, without it the signal obtained by
a chemical sensor cannot be related to the target species concentration with any
confidence. With chemical sensors the selectivity is generally created by the
used of a chemical recognition layer such as a permeable membrane, or a thin
chemical film. The sensitivity of a chemical sensor is a concern, as with any
quantitative analytical method, so that small differences in analyte concentration
are distinguishable and trace analysis can be performed. In this work the
selectivity and sensitivity of two distinctly different devices used as chemical
sensors are investigated. The first device combines a scintillation fiber with a
selective polymer coating to create a chemical sensor selective for 137Cs. Both
the selectivity and sensitivity of the scintillation fiber are improved with the
addition of the chemical recognition layer. The second device investigated is a
microcantilever sensor. Microcantilevers have been used to monitor chemicals
present in both air and liquid environments. However, in moving from
measurements made in air to measurements made in liquids, a great deal of
sensitivity is lost due to differences in the interfacial energies of the
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microcantilevers in these two different environments. To overcome this limitation
surface modification of the microcantilevers was investigated to improve the
sensitivity of these devices. Surfaces of the microcantilevers were modified by
several different methods, the binding of gold nanobeads to the surface, creation
of a roughened dealloyed surface, and the physical milling and chemical etching
of grooves into the surface of the microcantilevers, each of these surface
modifications was shown to enhance the sensitivity of microcantilever chemical
senors over microcantilever chemical sensors with smooth surfaces.