Evolution of Photonic Crystal Fiber Based Smart Sensors with Emphasis on Biomedical Applications: A Review

Photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensors have emerged as powerful groundbreaking platforms for smart biomedical sensing due to their exceptional light–matter interaction, structural tunability, and high sensitivity. This review presents a concise and critical overview of recent advances in PCF SPR sensing technologies with a primary focus on biomedical applications, including disease biomarkers, proteins, DNA, glucose, and pathogenic microorganisms’ detection. Smart sensing capabilities such as real-time monitoring, miniaturization, multiplexed detection, and enhanced sensor selectivity have been systematically analyzed. Key sensor performance parameters, including sensitivity, resolution, limit of detection (LOD), specificity, response time, refractive index (RI) based detection, internal metal deposition (IMD), external metal deposition (EMD), biocompatibility, and hybrid models in sensor optimization are comprehensively discussed. Across recent reports, wavelength sensitivity reaches up to 130,000 nm/RIU, sensor resolution is reported on the order of 10^-7 RIU, detection limits (LOD) can be as low as 1.19 × 10^-5 RIU, and figures of merit (FOM) up to 6000 have been demonstrated. Additionally, the review briefly addresses temperature, chemical, and pressure sensing to provide a broader perspective. This work further highlights current challenges, research gaps, hybrid techniques, use of artificial intelligence (AI) and future opportunities in the development of next-generation smart PCF–SPR biomedical sensors.