| dc.description.abstract | The guided mode resonance (GMR) device is developed to be a low-cost, label-free and high sensitivity biosensor. Typically, the GMR is an optical filter which reflects a specific light wave according to its sub-wavelength waveguide grating structures. As biomolecules attach on GMR surface, it changes the boundary conditions of GMR and results in a shift of characteristic spectrum. This presented work includes the theoretical study of GMR sensitivity for biosensing, a mutated high sensitive GMR structure (metal-assisted guided mode resonance, MaGMR), constructions of the related sensing platform and in vitro bioanalytical application. In experimental part, a nano-imprint method is developed for low-cost and high uniformity chip processes. A surface modification for antifouling and aptamer immobilized chip which specific binds to thrombin is also demonstrated. Finally, spectrum-resolved and intensity-resolved sensor platforms based on MaGMR and GMR are individually demonstrated.
In theoretical study of the GMR sensitivity, a simplified waveguide model for predicting the sensitivity of surface-relief GMR biosensors is presented. The proposed model is a convenient and rapid calculation method compared to those current optical simulation tools such as the rigorous couple wave analysis (RCWA) or finite-difference time domain (FDTD). Thus, by using this proposed model, a systematic and theoretical discussion on the GMR geometric structure and its sensitivity is also presented. Calculations of sensitivity between the proposed model and the RCWA method show a good agreement.
For the high sensitive mutation type of GMR section, a novel metal layer assisted guide mode resonance (MaGMR) device is proposed for bioanalytical applications and its performances are experimentally proved. Compare to the typical GMR, the sensitivity is one fold enhanced. We find the reflection spectra show a unique inversed response and the resonance mechanism is discussed as well. Numerical calculation results indicate that the high sensitivity performance of MaGMR comes from the strongly asymmetric resonance modal profile and low propagation angle inside the waveguide. There is a one-fold enhancement of the evanescent wave in the analytes region compared to typical GMR. In addition, a nano-imprint method for high uniformity and low cost MaGMR chip is developed. Furthermore, the surface to bulk sensitivity is also enhanced through the nano-imprint method.
In construction of sensing platforms, two sensing systems for MaGMR and GMR are individually demonstrated. One is a spectrum-resolved method for MaGMR sensors, and the other is a polarization-control setup for intensity-resolved GMR sensors. The spectrum-resolved system is performed under a low éntendue design which makes the measurement much easier and totally reduces the spectrum fringe noises from substrate. On the other hand, the intensity-resolved setup transfers polarization ellipses into linear polarization state and then suppresses the signals to a dark signal by an analyzer. Hence, any changes in the refractive index results in an increase in the intensity signals.
Finally, an aptamer based MaGMR sensor (aptasensor) for label-free and real-time detection is demonstrated. Two strains of thrombin binding aptamer (TBA) are immobilized on the surface of MaGMR chips as a recognizing ligand for thrombin. The MaGMR aptasensors also passed the nonspecific antifouling tests. The sensitivity of 15 and 29-mer TBA MaGMR aptasensor is 0.55 and 0.44 nm/μM and the limit of detection (LOD) is achieved 190 and 230 nM, respectively. | en_US |