Advanced microfabrication strategies for functional microcantilever probes

Abstract

The goal of the thesis was to add to the available microfabrication technologies and strategies for microcantilever-based sensors, with particular emphasis on polymeric microcantilever sensors and solid-state, ion-selective electrodes (ISEs) on microcantilevers. The cornerstone of the thesis was the development of a highly versatile microcantilever patterning strategy by so-called dry film photoresist lithography. Reliable spin-coating of already free-standing microstructures is known to be demanding, and the dry film photoresist-based technique now opens up for exploring new, and potentially more efficient microfabrication protocols toward microcantilever-based sensors. The possibilities within dry film photoresist lithography for microcantilever fabrication and patterning were thoroughly examined in this work. Emphasis was placed on employing mainly well-known, high-throughput microfabrication strategies within the dry film photoresist protocols. This ensures the usefulness of dry film photoresist lithography for other researchers as well as for the commercial market, and sets the stage toward high-volume microcantilever sensor manufacturing by dry film photoresist-based protocols. Some examples of microcantilever sensor designs enabled by dry film photoresist lithography were already demonstrated in this work, applying cantilevers made either from silicon nitride, or from polymeric, dry film photoresists. Within the latter, dry film photoresist lithography was used to expand on the already existing fabrication strategies for polymeric microcantilevers, but without need for any of the potentially damaging probe release strategies employed so far in the state-of-the-art. The experimental part concludes with work on microcantilever probes equipped with solid-state, potassium-selective micro-ISEs. Here the cantilever design readies the ISE sensors’ applicability toward localized ion-concentration measurements on cells, for instance in combination with an atomic force microscope. ISEs were so far rarely realized by microfabrication strategies, relying instead on pulled glass micropipettes as starting point for the sensor fabrication. The fabrication strategy shown here should therefore serve as a valuable contribution toward high throughput micro-ISE fabrication, while simultaneously expanding on the potential applications for microcantilever- and probe based sensors.