<![CDATA[Gelatine is commonly found in food, pharmaceutical, health, and cosmetic products. However, its use has generated significant debate due to concerns about the numerous sources, particularly for religious reasons. For Muslims and Jews, gelatine derived from porcine sources must be avoided, as it is strictly prohibited by religious laws. The detection in these products is important, and this led to the design of an optical biosensor based on a one-dimensional (1D) photonic crystal (PhC) with a defect layer. The aim was to detect the distinctive characteristics of gelatine with high sensitivity. Additionally, the defect layer was placed in the center of the structure, where the gelatine solution was introduced. The designed PhC structure consisted of N layers of (ZnO/SiO₂)ᴺ/defect/(ZnO/SiO₂)ᴺ. The reflectance and transmittance characteristics of the PhC were calculated by using the transfer matrix method (TMM), performed with the MATLAB software. For simplicity, the normal incidence of light on the PhC was assumed to avoid the complexities of oblique angles. Sensor performance was evaluated by calculating sensitivity (S), quality factor (Q), figure of merit (FOM), resolution (RS), and detection limit (LOD). The biosensor achieved an average S, Q, FOM, RS, and LOD of 225.7694 nm/RIU, 2249.413, 806.3185, 0.1332, and 4.13 × 10⁻⁵, respectively. These metrics showed the simple PhC design was a highly sensitive, non-invasive detection platform for monitoring and identifying gelatine-based products that did not meet Halal and Kosher requirements. The novelty of the study centered on the application of a simple 1D PhC with a defect cavity to detect gelatine concentrations in both aqueous and oily solutions, a problem that had not been addressed in detail.]]>
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