1 Nanoprobes Group, NanoSystemsEngineering Section, Department of Micro- and Nanotechnology, Technical University of Denmark2 NanoSystemsEngineering Section, Department of Micro- and Nanotechnology, Technical University of Denmark3 Department of Micro- and Nanotechnology, Technical University of Denmark4 Center for Intelligent Drug Delivery and Sensing Using Microcontainers and Nanomechanics, Center, Technical University of Denmark5 DTU Danchip, Technical University of Denmark
This thesis presents a novel read-out method developed for cantilever-based sensors. Cantilevers are thin beams clamped at one end and during the last 10 years they have emerged as an interesting new type of bio/chemical sensor. The specific recognition of a chemical manifests itself as a bending of the cantilever from the generated surface stress. Conventionally the read-out used for this type of sensors is external and thereby very bulky. It is beneficial to fabricate a miniaturised system. Moreover, improved sensitivity is obtained by fabricating the cantilever in a polymeric material that has a low Young’s modulus instead of the conventional materials Si and Si3N4. Here, a novel read-out method is presented where optical waveguides are used to integrate the light into the cantilever. It is an all-polymer device where both the cantilever and the waveguides are fabricated in the negative resist SU-8. Waveguides are structured on either side of the cantilever that is free-hanging in a microfluidic channel. Light is guided into the system and is either transmitted through the cantilever or reflected off the cantilever front-end, depending on the mode of operation. This work shows that waveguides, only supporting the fundamental mode at 1 310 nm and with a propagation loss of only 1.2 dB/cm can be fabricated and integrated with free-hanging cantilevers. A theoretical model is developed to analyse the read-out sensitivity of the two different read-out modes. From calibration experiments the minimum detectable cantilever deflection in the transmission mode is measured as 45 nm, which compares well with the calculated value of 30 nm. Proof-of-principle is shown for the reflection mode as well but no conclusive value can be determined for the read-out sensitivity. It is believed both these novel principles present interesting alternatives for integrated read-out for cantilever based sensors to enable to fabrication of point-of-care analysis systems.