A new rapid colorimetric detection method of Mn2+ based on tripolyphosphate modified silver nanoparticles

A new facile and rapid colorimetric method is proposed for detection of manganese ion (Mn2+) with high sensitivity and excellent selectivity using tripolyphosphate stabilized silver nanoparticles (P3O105−–AgNPs). The silver nanoparticles (AgNPs) were prepared by reducing silver nitrate with sodium borohydride in the presence of sodium tripolyphosphate. Energy dispersive X-ray spectrum (EDS) and infrared spectra (IR) indicate that tripolyphosphates anions (P3O105−) are capped on the surfaces of AgNPs. The P3O105−–AgNPs aggregate quickly in the presence of Mn2+, which leads to color change of the nanoparticle dispersion from yellow to reddish brown and decrease of the surface plasmon absorption intensity. The Mn2+ can form a six-coordinated structure with P3O105− coating on the AgNPs and leads to formation of large particles aggregation. The selectivity of P3O105−–AgNPs detection system for Mn2+ is excellent comparing with other ions and mixture of the above ions except Mn2+. Furthermore, this Mn2+ detection method based on surface plasmon resonance (SPR) absorption by ultraviolet and visible spectrophotometer (UV–vis) offers a wide linear detection range from 0.05 μM to 20 μM. The lowest detection concentration by the naked eyes is 0.1 μM, which is also lower than the national table-water standard (1.8 μM). The results of Mn2+ detection in real water samples reinforce that our P3O105−–AgNPs detection system is applicable for Mn2+ detection in the real environmental water samples.