Immunoassays using tilted fiber Bragg gratings: an overview

Biosensors are expected to provide fast, sensitive, and robust detection at low cost. Despite all these constraints which weigh on the development of emerging technologies and conception of new prototypes, the major challenge is still to carry out measurements in complex matrices and hard-to-reach environments. Optical fibers are perfectly suited to fulfill these requirements. In this paper, we investigate the use of tilted fiber Bragg gratings (TFBGs) photo-inscribed in the core of telecommunication-grade optical fibers as biosensors Thanks to their high refractive index sensitivity, they are able to track molecular interactions happening on their surface. We present different strategies to use them for label-free immunoassays. Bare, gold-sputtered, gold electroless-plated (ELP), and hybrid configurations were functionalized with antibodies, aiming at the detection of cancer biomarkers. We discuss the relative performances of these four configurations and show that each leads to singular key features, driving their own selection as a function of the target application. The optrodes were tested in laboratory settings but also in gelled phantoms and in human resected lung tissues to study the surface plasmon excitation inside complex media, and to discriminate the nature of the tissue through biomarkers detection.