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 (Hg) 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), N 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 Hg, thymine molecules were uncapped in the presence of Hg, 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 Hg concentration range (R = 0.9920), with a detection limit of 73.7 nM. Interference deviations of metal ions and anions to Hg were in the range of -5% to +5%. The method was applied to determine Hg 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 Hg in real samples with low cost and high efficency.