A simple and rapid colorimetric method for the determination of Mn2+ based on pyrophosphate modified silver nanoparticles

A simple, and reliable colorimetric detection method for manganese ion (Mn 2+ ) based on pyrophosphate capped silver nanoparticles (P 2 O 7 4− -AgNPs) is developed. The P 2 O 7 4− -AgNPs was synthesized by wet chemical method. The P 2 O 7 4− -AgNPs solution shows a yellow color and the maximum absorption at 403   nm can be observed. After the addition of Mn 2+ , the absorption intensity of the P 2 O 7 4− -AgNPs solution decreased drastically, which associated with the changes of solution color from yellow to purple. The observed changes can be attributed to the aggregation of AgNPs induced by Mn 2+ because of the ion-templated chelating reaction. The absorption intensity of P 2 O 7 4− -AgNPs at 403   nm is found to be proportional to the concentration of Mn 2+ in the range of 0.03–20   μM, and the detection limit for Mn 2+ is as low as 0.03   μM (S/N   =   3). Due to high affinity toward Mn 2+ , the P 2 O 7 4− -AgNPs as a colorimetric sensor displays an excellent selectivity for Mn 2+ detection. More important, the proposed method was successfully applied in the determination of Mn 2+ in real environmental samples.