The present Ph.D. dissertation concerns the application of surface plasmon resonance (SPR) spectroscopy, which is a surface-based biosensor technology, for studies of adsorption dynamics. The thesis contains both experimental and theoretical work. In the theoretical part we develop the theory for convection, diffusion, and adsorption in surface-based biosensors in general. In particular, we study the transport dynamics in a model geometry of a Biacore SPR sensor. An approximate quasi-steady theory, which has been widely adopted in the SPR literature to capture convective and diffusive mass transport, is reviewed, and an analytical solution is provided. The important nondimensional Damk¨ohler number, inherent in the quasi-steady theory, is derived in terms of the nondimensional adsorption coefficient (Biot number), the nondimensional flow rate (P´eclet number), and the model geometry. Also, a two-component theoretical model, designed to capture competitive adsorption dynamics of two adsorbing species, is developed and presented. Transient dynamics is investigated numerically, and we quantify the error of using the quasi-steady theory for experimental data fitting in both kinetically limited and convection-diffusion-limited regimes. The results clarify the conditions under which the quasi-steady theory is reliable or not. In extension to the well known fact that the range of validity is limited under convection-diffusionlimited conditions, we also show how the ratio of the inlet concentration to the maximum surface capacity is critical for reliable use of the quasi-steady theory. Our theoretical results provide users of surface-based biosensors with a tool of correcting experimentally obtained adsorption rate constants, based on the quasisteady theory. Finally, the consequence of adsorption on all surfaces present in the flow cell of the surface-based biosensor, in addition to the sensor surface, is investigated. In the experimental part of the thesis we use a Biacore SPR sensor to study lipase adsorption on model substrate surfaces, as well as competitive adsorption of lipase and surfactants. A part of the experimental data obtained during the project is presented and discussed. In particular, this part provides apparent kinetic adsorption/desorption rate constants, and gives an overview of the major challenges of basing theoretical modeling on this data. We emphasize the importance of some conditions, which necessarily have to be fulfilled in order to attain a comprehensive link between the experimental data and the theoretical modeling.
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Bruus, Henrik, Callisen, Thomas H,, Hassager, Ole
Technical University of Denmark, Department of Chemical Engineering, 2012