Abstract

This work aims to investigate the application of exposed core optical fibre (ECF) sensing platforms to uses such as in field detection of plant pathogens. Presented here is the investigation into the multimode nature of an ECF to form an interferometric sensing platform by splicing the ECF with lead-in and lead-out single mode fibers (SMF). Since guided modes in the ECF propagate with different propagation constants, an interference pattern can be formed in the transmission spectrum. These fringes will shift w.r.t. to a change in the refractive index (RI) of the ambient environment, including localised RI change on the fiber core as result of a biochemical binding event. The interference pattern is complex because there are typically more than two modes involved. Therefore the interference is first analysed by a Fast Fourier Transform (FFT) and the strongest FFT frequency component, corresponding to the interference between the two most dominantly excited modes, is filtered and chosen as the sensor indicator. As expected, the fringes exhibit corresponding red-shift w.r.t increasing the RI of the ambient solution. To demonstrate the biosensing capability of the proposed platform, biotin was chosen as the bio-probe and streptavidin was used as the sensing target due to the known strong binding affinity between these two [1]. The “fuzzy nanoassembly” process using polyelectrolyte coating [2] was use to interface the fiber surface with biotin. For convenience we monitored the phase change at the strongest frequency component in the spatial frequency spectrum instead of the fringe shifts during the functionalization process. Clear phase change was obtained when streptavidin binds to biotin functionalised on the fiber surface, indicating in a localised increase of the RI on the fibre surface. On the other hand, a control fibre without functionalised biotin shows no significant phase change when the sensor were subjected to buffer solution containing Streptavidin, indicating no binding event or non-specific binding having taken place. Further work will include the functionalisation of the fibre surface with pathogen-specific detectors. With its all-fibre configuration, this novel biosensing platform is highly stable and therefore very attractive for applications of a portable detection device.

© 2015 IEEE