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Towards ultrasensitive SPR-based sensing: self-referencing and detection of single nanoparticles
(2018)
Surface plasmon resonance (SPR) and its extensions, surface plasmon resonance imaging (SPRi) and surface plasmon resonance microscopy (SPRM) both enabling visualization of the sensor surface, belong to classical, indispensable highly sensitive and robust optical (bio)analytical techniques to study affinity processes on a surface. Nevertheless, SPR and SPRi/SPRM undergo a continuous development in regard to the improvement of sensitivity. The main challenge in this direction is attributed to the separation of signals due to the binding of analytes and those due to the bulk effect. The main task of the present thesis was to apply different strategies to improve the performance of SPR sensing. Within this scope, two main objectives were pursued: (1) implementation and realization of a so-called internal referencing towards suppression of the bulk effect leading to an improvement and optimization of the signal-to-noise ratio (SNR) and (2) application of wide-field (WF)-SPRM to detect, to visualize and to characterize single nanoparticles adsorbed to modified surfaces. The first objective of this thesis comprises the realization of three different internal-referencing approaches. In the first approach, a self-referencing effect based on arbitrarily distributed micro-patterned self-assembled monolayer (SAM) containing sensing and referencing spots was realized. Measurements of classical antigen-antibody-interaction resulted in a 10-fold improvement of the SNR by suppression of the bulk effect and the corresponding microfluctuations of the bulk temperature. The application of the second internal-referencing-approach, ionic referencing, acting as an assessment of patterned SAM was realized using electrolytes with a high molar refraction of either anions or cations to micro-patterned SAM combined with WF-SPRM as detecting technology. As a result, successful, unobtrusive visualization and spatial distinction of micro-patterned surfaces was shown. Unlike visualization of micro-scaled surface areas, the application of spatio-temporal referencing in WF-SPRM, as a third type of internal referencing, enables to detect, moreover to visualize and localize, smallest changes in refractive index near/on the sensor surface. In that sense, the second objective of this thesis was dedicated to the application of the WF-SPRM technology combined with spatio-temporal referencing to detect, to visualize, to quantify and to characterize single nanoparticles adsorbed to the sensor surface; here, nanoparticles act as analyte species. Based on a sophisticated image analysis, successful detection and characterization of single nanoparticles in complex media such as wine, juice and sun cream was performed. Besides being a powerful solution for nanoparticles analytics, the WF-SPRM technology represents a base to develop novel, ultra-sensitive and fast (bio)sensing platforms. Within this scope, enzyme-assisted generation of nanoparticles was studied.