Highly sensitive and selective colorimetric tin optode based on rhodamine B-cysteine immobilized on agarose membrane

An eco-friendly agarose-based optode was developed for the selective and sensitive detection of tin ions in aquatic and biological environments using UV-Vis spectroscopy. For this purpose, in a green synthesis method, cysteine was attached to rhodamine B and immobilized on an agarose membrane to prepare an optical sensor. For the first time, the agarose membranes were prepared using a specially designed homemade mold, which ensured uniform surface and dimensions, thereby significantly enhancing the reproducibility of the assays. The developed optode showed superior selectivity for tin ions over various interfering cations in an aqueous environment. The absorption studies indicated that the optode achieved its best performance at pH 4, enabling direct detection of Sn²⁺ ions within a concentration range of 0.5-25×10² ng mL^-1. Colorimetric analysis revealed a detection limit of 4.96 ng mL⁻¹ for the optode, with intra-day and inter-day relative standard deviations (RSD %) of 1.01% and 1.04%, respectively. This optode successfully determined Sn²⁺ in environmental and biological samples without matrix separation.