Simultaneous detection of inflammatory process indicators via <i>operando</i> dual lossy mode resonance-based biosensor

Detecting multiple analytes simultaneously, crucial in disease diagnosis and treatment prognosis, remains challenging. While planar sensing platforms demonstrate this capability, optical fiber sensors still lag behind. An <italic>operando</italic> dual lossy mode resonance (LMR) biosensor fabricated on a D-shaped single-mode fiber (SMF) is proposed for quantification of clinical indicators of inflammatory process, like in COVID-19 infection. Dual LMRs, created via two-step deposition process, yield a nanostructure with distinct SnO₂ thicknesses on the flat surface of the fiber. Theoretical and experimental analyses confirm its feasibility, showing a sensitivity around <styled-content style-type="number">4500</styled-content> nm/RIU for both LMRs. A novel insight in spatially-separated biofunctionalization of the sensitive fiber regions is validated through fluorescence assays, showcasing selectivity for different immunoglobulins. Real-time and label-free detection of two inflammatory markers, C-reactive protein and D-dimer, empowers the platform capability with a minimum detectable concentration below 1 μg/mL for both biomolecules, which is of clinical interest. This proof-of-concept work provides an important leap in fiber-based biosensing for effective and reliable multi-analyte detection, presenting a novel, compact and multi-functional analytical tool.