Two sensors based on molecularly imprinted polymers and plastic optical fibers for fast and cost-effective MCPA herbicide detection in environmental monitoring

Molecularly imprinted polymers (MIPs) can be exploited to develop low-cost optical-chemical sensor configurations with several advantages via different sensing principles. In this work, two MIP-based plastic optical fiber (POF) sensors have been designed, realized, and tested for the selective detection of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide in environmental monitoring, aiming to achieve two different detectable concentration ranges. In the first case, the MIPs pre-polymeric mixture was spun onto the surface plasmon resonance (SPR) area of D-shaped POF probes to achieve the detection of MCPA in a nano-to micromolar concentration range (7 nM–1 μM). A second type of POF-MIP sensor for detecting MCPA has been developed to demonstrate the capabilities of the MIP as the core of optical waveguides, enabling highly sensitive sensors with an intensity-based configuration. In particular, an extrinsic POF sensor scheme has been implemented via an optical-chemical chip based on two POFs connected via a MIP waveguide. The optical-chemical chip was achieved by filling a trench with two POFs at the end with the pre-polymeric mixture, followed by thermal polymerization. This intensity-based POF-MIP sensor can detect MCPA in a pico-to nanomolar concentration range (80 pM–10 nM). Moreover, the same experimental setup can be used to monitor both POF-MIP chips, allowing for the detection of MCPA over an ultra-wide concentration range from 80 pM to 1 μM.