UV label-free detection of fat-soluble A/D/E/K Vitamins using 1D multilayer composed of silver-doped nanocomposite

This work introduces a UV photonic crystal biosensor incorporating Ag–SiO₂ nanocomposite layers and a vitamin-based defect for the label-free detection of fat-soluble vitamins A, D, E, and K. The platform enables precise refractive-index detection with enhanced spectral resolution. Using the transfer matrix method, the device exhibits sharp defect resonances located near each vitamin’s intrinsic UV absorption peak centered around 325 nm (A), 270 nm (D), 300 nm (E), and 250 nm (K). The spectral response is strongly influenced by incident angle, nanoparticle filling fraction, and structural periodicity, enabling tunable control of the resonance features. The biosensor demonstrates high performance with quality factors exceeding 17,000, stable sensitivity of about 18 nm/RIU, and a detection limit on the order of 10⁻⁴ RIU. These results show that combining nanocomposite layers with a vitamin defect layer creates a highly selective and accurate platform for UV biosensing, providing a frame for biochemical analysis and diagnostics.