Colorimetric detection of Mn2+ using silver nanoparticles cofunctionalized with 4-mercaptobenzoic acid and melamine as a probe

A facile, selective and highly sensitive method is proposed for colorimetric detection of manganese ions using 4-mercaptobenzoic acid (4-MBA) and melamine (MA) modified silver nanoparticles (AgNPs). The presence of Mn2+ induces the aggregation of AgNPs through cooperative metal–ligand interaction, resulting in a color change from bright yellow to purple. The cofunctionalized AgNPs showed obvious advantages over the ones functionalized only by 4-MBA or MA in terms of selectivity. Mn2+ could be monitored by colorimetric response of AgNPs by a UV–vis spectrophotometer or even naked eyes. The absorbance ratio (A550 nm/A408 nm) is linear with the concentration of Mn2+ ranging from 5×10−7 mol/L to 1×10−5 mol/L with a correlation coefficient of 0.993, and the detection limit is as low as 5×10−8 mol/L. Particularly, this cost-effective process also allowed rapid and simple determination of the Mn2+ in drinking water.