Optical Waveguides Based on a Core of Molecularly Imprinted Polymers: An Efficient Approach for Chemical Sensing

This work presents an innovative optical chemical sensing approach, which considers a molecularly imprinted polymer (MIP) as the core of an optical waveguide. More specifically, a channel was achieved into an FR4 substrate through a CNC machine. As proof of concept, a MIP prepolymeric mixture for furfural (2-FAL) detection was poured into the channel and then polymerized to obtain the waveguide’s core. The optical-chemical platform was interrogated through two plastic optical fibers (POFs) integrated into the system itself. The idea was to create a core with a refractive index (RI) variable as a function of the analyte-receptor binding interaction. First, the optical chemical sensor response was numerically evaluated by finite element method (FEM) simulations. Then, the sensor platform was tested by using two different experimental setups, both including two channels: the sensor channel consisting of the MIP-core based waveguide and the reference channel, consisting of another waveguide having a core of not imprinted polymer (NIP). The introduction of a reference channel in the experimental setup allowed to eliminate several factors of irreproducibility and noise, due to external conditions (e.g., temperature) or light source fluctuations. Moreover, selectivity tests were carried out to confirm the good selectivity of the proposed optical-chemical sensor system. The results obtained by the two experimental setups are comparable in terms of the limit of detection (LOD), which is equal to around 0.003 mg L−1. The achieved results paved the way for this innovative, low-cost, and selective sensing methodology.