Nanoplasmonic sensing: from biology to catalysis

Doctoral thesis, 2009

Our continuously increasing concerns about our health, safety, environment and climate has brought about a need for more sophisticated sensors that enable reliable detection of a variety of events. Sensors are today omnipresent in daily life. They are used in many diverse applications such as pollution control, medical diagnostics, food quality control, chemical industry process control and touch buttons on electric appliances. Although sensors have been developed for a large variety of applications they often suffer from problems such as low sensitivity and selectivity, long response time, short lifetime and/or large size. Nanotechnology has been suggested as one solution to many of these problems because of the unique properties of nanoscale materials. One nanotechnology subarea of particular interest for sensing applications is the plasmon (optical) resonances (LSPRs) in metal nanoparticles, since they offer the possibility for highly sensitive, label-free, real-time and remote detection of molecular events occurring in the close surrounding of the nanoparticles. In this thesis, LSPRs are first explored for their application in biosensing. The sensitivity of a new nanostructure, a gold nanoring, with respect to biomolecular binding events is investigated. Nanorings are found to exhibit a higher sensitivity to the adsorption of molecular layers than most other structures. Subsequently, the plasmonic properties of single nanorings and two nanorings (one concentric and one non-concentric) in a stack are investigated in more detail. The plasmonic sensing scheme is then brought into a completely new field, namely catalysis. We show that using nanoplasmonic sensing it is possible to monitor changes in the adsorbate coverage on platinum clusters of a size comparable to that used in many commercial catalysts. This technique is judged to have the potential of becoming a new valuable tool in catalysis research. Finally, a novel experimental chamber is developed for simultaneous measurements on the same surface using quartz crystal microbalance with dissipation monitoring (QCM-D) and LSPR sensing. The combination of these two techniques offer several advantages including more in depth information about adsorbed layers and surface processes.