Improvements in self-assembled optical fiber-based biosensors

This paper describes improvements that have been made in optical fiber biosensors based on thin films deposited onto the ends of optical fiber waveguides using molecular-level self-assembly processes. The properties of the sensor films may be varied by controlling both the chemistry and the morphology and ordering of the films during their fabrication. For example, multilayer segments of films having different indices of refraction may be deposited to form quarter wavelength stack filters whose reflection properties change as a function of concentration of target chemical that modifies the index of the outermost layer or layers. Prior work has shown that by using different chemicals in the self-assembled layers, correspondingly different target chemicals may be detected. These have included water vapor, ammonia, dichloromethane and others. Improvements have been made in the range of index of refraction that may be achieved in the individual layer segments, specifically over the range of 1.2 to 1.8 at visible and near-infrared wavelengths. This paper shows how such an improvement in index difference influences the minimum detectable chemical concentration difference detectable using this approach.