Development of a mid-infrared fiber sensor for molecular monitoring

Mid-infrared (mid-IR) optical fiber sensors offer highly specific and sensitive detection and analysis of various chemical species due to many molecular vibrations and fundamental absorption bands in this range. In this paper, we present a novel optical fiber probe design allowing for controlled optical pathlength. The optical fiber probe was fabricated using a silver halide polycrystalline fiber, a gold-coated short fiber as a mirror, and a connector to align the two parts to face each other. The outer diameter of the connector, 1.59 mm, dictates the overall probe diameter. To demonstrate the sensing performance, a quantum cascade laser (QCL) was coupled to the optical fiber probe to measure glucose solutions at physiological concentration levels by monitoring the C-O stretching vibration at 1,035 cm^-1. A detection limit of 8.91 mM for glucose was achieved. The results highlight the potential of the proposed optical fiber probe for molecular detection and analysis, offering a promising solution for chemical and biomedical applications.