Microstructured Optical Sensors: Design, Fabrication, and Applications

Microstructured optical sensors (MOS) have emerged as transformative photonic devices offering unprecedented sensitivity, miniaturization, and multiplexing capability. This review synthesizes the state of the field for specialists in photonics and optics, covering principal design architectures—photonic crystal fibers, microresonators, plasmonic nanostructures, and integrated waveguide platforms—alongside the fabrication methodologies underpinning their realization. We examine four high-impact application domains: environmental monitoring, biomedical diagnostics, structural health monitoring, and food safety. A central argument runs through the review: the dominant bottleneck constraining MOS adoption has shifted from sensitivity—where many platforms now approach the physical detection limit—to the engineering triad of packaging difficulty, calibration drift, and manufacturing reproducibility. Against this backdrop, we provide frank comparative assessments of platform readiness for each application domain, distinguishing proof-of-concept demonstrations from deployable systems. A dedicated Critical Perspective section addresses the translation of laboratory sensitivity figures to field performance, the genuine and overstated contributions of machine learning, and a commercialization-readiness assessment for principal MOS platform families.