Ultrasensitive colorimetric detection of manganese(II) ions based on anti-aggregation of unmodified silver nanoparticles

We report a facile, selective, and sensitive colorimetric assay for Mn 2+ ions based on the anti-aggregation of unmodified silver nanoparticles (AgNPs). In the absence of Mn 2+ ions, the addition of l -arginine to the AgNPs dispersion caused the aggregation of AgNPs via Ag–N covalent interaction, and the color of the solution changed from yellow to colorless. While the presence of Mn 2+ ions can prevent the aggregation of AgNPs due to the formation of the complex between Mn 2+ ions and l -arginine, accompanying with a distinct color change from colorless to yellow with the increase of Mn 2+ ions. Under the optimal experimental conditions, the absorbance at 390   nm was linearly proportional to the Mn 2+ ions concentration in the ranges from 0 to 700   nM, and from 5   μM to 70   μM, with a detection limit of 20   nM. Also, it was successfully used for the detection of Mn 2+ ions in environmental water samples.