<p>Here, we introduce a new pH-responsive optical nanosensor designed for precise detection and selective uptake of Pd²⁺ ions from wastewater and urban mining sites. Our approach focuses on creating silica nano-sphere mesostructure-based nanosensor (MSNS-OYS) through a simple and reproducible synthesis method by directly immobilizing disodium 6-hydroxy-5-[(4-sulfonatophenyl)diazenyl]naphthalene-2-sulfonate (orange yellow S; OYS) chelate onto mesoporous silica nano-spheres (MSNS) carriers. We exploited the inherent surface properties and active acid sites of silica to facilitate stable interactions with the OYS chelate [OYS-Pd]ⁿ⁺, ensuring the integrity of the sensor during Pd²⁺ sensing assays as evidenced by N₂ adsorption/desorption, FT-IR, SEM, HR-TEM, XPS, and elemental analyses. The nano-sized MSNS-OYS has large surface-to-volume ratios with a surface area of 686 m²/g and a pore volume of 0.0925 cm³/g. Adsorption capacity reaches 70.8 mg/g at pH 2. Fast mass transfer properties allow the equilibrium to be reached within 30 min. This method yields a sensitive sensor capable of detecting Pd²⁺ ions down to a limit of detection (LOD) of 11.6 µg/L and a limit of quantification (LOQ) of 38.6 µg/L, offering stability, selectivity, and sensitivity. Additionally, the sensor can be easily regenerated by treatment with thiourea acidified with 0.05 M HNO₃.</p>