Novel Fiber Optic Biosensors Based on Nanoplasmonic and Interferometric Modalities
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New and improved monitoring of complex multivariable environments often relies on the diversity and implementation of new sensor technologies. Before and after the worldwide recession, the sensor market showed to have a growth around 10% per year. This suggests that there is a substantial need of tools for realtime detection of various chemical compounds and biochemical entities in various applications. These application areas may be as diverse as monitoring of energy storing or energy production processes, monitoring of biohazard or human-made chemical contaminants, or monitoring of biomarkers for medical diagnostics and treatments. Different types of sensors are often made for specific applications in mind such as to work in high temperatures, in corrosive environments, or with the possibility for miniaturization. Biochemical sensor development is often driven by certain functionalities such as label-free, selective and high sensitivity sensing with possibilities for miniaturization to obtain fast diffusion times and sensor response. Optical fiber (OF) based waveguide sensors have shown to be a popular platform for miniaturization with possibility for sensor insertion into small volumes, tissues or vessels. Also, the sensing with OFs can be multiplexed by using the free-variables of light properties of frequency, amplitude, phase, and polarization. This thesis presents novel fiber optic (FO) sensor architectures based on interferometric or localized surface plasmon resonance (LSPR) modalities for multianalyte label-free sensing at a single point. The sensor consists of a stimuli-responsive hydrogel that represents a low-finesse Fabry-Perot (FP) cavity embedded with noble metal nanoparticles (NMNP) that exhibit LSPR. The sensing modalities were interrogated in reflection by spectroscopic measurements in visible (VIS) and infrared (IR) light frequencies. The interferometric sensing was performed by detecting chemically induced length changes of the FP cavity from the phase change measurements of the sinusoidal spectra in IR light frequencies. The LSPR sensing was performed by detecting the change in the local refractive index (RI) on the NMNP surfaces from the resonance frequency change measurements of the Lorentzian spectra in VIS-IR light frequencies. Proof-of-concept demonstrations of the FO sensor system show that the LSPR wavelength changes of the NMNP for deswelling hydrogels were dominated by local RI variations for low number densities (ND), while for high NDs, the LSPR wavelength changes for deswelling hydrogels were dominated by plasmon coupling. The interferometric sensor was negligibly influenced by the NDs used with a signal and a response comparable to previous work. At optimized NDs, the LSPR wavelength changes were small for gold nanorods (GNR) in different hydrogel swelling equilibriums, whereas for receptor-analyte recombinations on the GNR surface significant LSPR changes were observed. The proof-of-concept sensor systems presented in this thesis introduces some general aspects for obtaining multiparameter sensing in a single point as well as models for understanding the response of the sensing modalities. With further optimization, the FO designs may prove to be a highly selective, sensitive and a fast label-free monitoring device of specific biomarkers for biological or medical applications.