Label-free fiber-optic interferometric immunosensors based on waist-enlarged fusion taper

Label-free, all-fiber immunosensors based separately on Mach-Zehnder interferometry (MZI) and Michelson interferometery (MI) implemented using only single mode fiber (SMF) are proposed and experimentally demonstrated. The proposed SMF-MZI and SMF-MI sensors rely on intermodal interference between the core mode and cladding modes to detect ambient refractive index changes due to protein absorption on the cladding-ambient interface. The fiber surfaces were functionalized with self-assembled polyelectrolyte layers (chitosan (CS)/polysodium styrene sulfonate (PSS)). Immunoglobulin G (IgG) was immobilized on the polyelectrolyte layer and anti-immunoglobulin G (anti-IgG) molecular binding events were monitored through measurement of wavelength shifts. The proposed immunosensors exhibit anti-IgG detection sensitivities of 27.37 nm/(ng/mm(2)) and 5.91 nm/(ng/mm(2)) with concentration detection limits of 0.181 nM and 4.941 nM for MZI and MI sensor respectively. The specificities of the sensors were investigated using correlated/non-correlated anti-IgG-IgG pairs. These results demonstrate the feasibility of these sensors for various bio/chemical applications such as DNA hybridization detection and immunosensing. (c) 2012 Elsevier B.V. All rights reserved.