Thymine-capped mesoporous silica nanoparticles as ion-responsive release system: A paper-based colorimetric sensing platform for rapid and selective mercuric identification

In this study, a convenient method was proposed for the synthesis of thymine-capped mesoporous silica nanoparticles (MSN) using strong hydrogen bonding in non-protonic solvent. Furthermore, application of the functionalized MSN for the recognition of mercuric ion (Hg²⁺) based on a paper-based platform with smartphone-assisted colorimetric detection was developed. The synthesized materials were characterized by techniques including X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), N₂ adsorption-desorption, particle size analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Through the specific and robust interaction between thymine and Hg²⁺, thymine molecules were uncapped in the presence of Hg²⁺, leading to the substantial release of Rhodamine B and the rapid production of a purple color on paper-based analytical devices within 30 s. The results were captured using a smartphone and subsequently analyzed using Photoshop software or a smartphone App developed by us. The RGB value increased linearly in the 0.74-44.2 mM Hg²⁺ concentration range (R = 0.9920), with a detection limit of 73.7 nM. Interference deviations of metal ions and anions to Hg²⁺ were in the range of -5% to +5%. The method was applied to determine Hg²⁺ in five Chinese herbal medicines, showing a recovery between 98.3% and 101.5% and demonstrating its superior reliability. The work highlights the potential of the method to detect Hg²⁺ in real samples with low cost and high efficency.