OICC Press International Journal of Nano Dimension 2228-5059 17 3 2026 07 10 Label-free Sensing of Thiamine, Pantothenic Acid and Pyridoxine Hydrosoluble Vitamins Using a Symmetric Photonic Heterostructure Resonator 10.57647/ijnd.2026.1703.07 EN Hadi Rahimi Department of Physics, Shab.C., Islamic Azad University, Shabestar, Iran https://orcid.org/0000-0003-4723-6953 Journal Article 2026 07 10 This study presents a label-free biosensor based on a symmetric one-dimensional photonic heterostructure resonator for the refractometric detection of three water-soluble B-complex vitamins. By filling the defect cavity with vitamin solutions, the sensor generated distinct resonance shifts proportional to refractive-index changes, enabling precise molecular discrimination. Optimal performance was achieved at a 60° incidence angle under transverse-electric polarization, yielding ultra-high sensitivity (nearly 280 nm/RIU), a sharp resonance quality factor exceeding 2000, and a detection limit as low as 1.21×10⁻³ RIU, accompanied by a figure of merit greater than 800 surpassing conventional 1D photonic crystal biosensors. A strong polarization-dependent response was observed, with transverse-magnetic (TM) mode performance degrading at high angles due to Brewster’s effect, confirming TE polarization as the superior sensing configuration.