Optical Chemical Sensors Based on Waveguides with a Core of Molecularly Imprinted Polymer

An innovative extrinsic optical fiber sensor was developed and tested to detect a specific analyte. More specifically, plastic optical fibers (POFs) are coupled to a sensitive chip based on an FR4 substrate in which a trench is achieved by a numerical control machine. The latter is filled by a molecularly imprinted polymer (MIP) which acts as an optical waveguide. The optical-chemical chip is monitored through two POFs integrated into the sensor chip, one coupled with a white light source and another with a spectrometer. As a proof of concept, the optical-chemical chip is realized using a MIP specific for furfural (2-FAL) detection in water. In such a way, when the binding between the analyte (furfural) and the receptor (MIP) occurs, the MIP-filled channel, acting as the waveguide core, presents a variable refractive index since the furfural concentration modulates it. Therefore, when the binding occurs, the core's refractive index changes by efficiently changing the light propagation and the transmission spectrum. The preliminary results denoted good performance in terms of a low detection limit equal to 2.5 μg L-1, comparable to more complex and expensive techniques, paving the way to the applicability of this sensing approach in real scenarios.