Highly Sensitive Fiber Bragg Grating Biosensors

Abstract

Fiber Bragg grating sensors are highly sensitive, cost-effective solutions in chemical and biological sensing. By reducing the resolution of the optical interrogation set-up and enhancing the fiber's evanescent field, etched fiber Bragg gratings (FBG) can detect minimal refractive index shifts. Etched FBG Fabry Perot sensors decrease detectable index shifts (~2x10-9 riu) by introducing extremely narrow spectral resonances to single FBG spectra. Furthermore, we describe the fabrication of ultrahigh finesse fiber cavities and a temperature-compensated mount that will be implemented in future chemical testing. With highly sensitive refractive index sensors, we developed procedures for investigating complex surface chemistry. Chemical species are immobilized on the sensor's silica surface in order to study protein conjugation with Concanavalin A, 21-mer DNA hybridization, monolayer adsorption, and silanization. Sensor results with homogeneous or multilayer environments demonstrate good agreement with theoretical Bragg shifts calculated using the beam propagation method of determining the effective modal index.