Colorimetric detection of Cr3+ using tripolyphosphate modified gold nanoparticles in aqueous solutions

A sensitive and selective colorimetric assay method for the detection of Cr3+ has been developed using tripolyphosphate functionalized gold nanoparticles (P3O105−–AuNPs). Infrared (IR) spectra and energy dispersive X-ray spectroscopy (EDS) confirmed that tripolyphosphates capped on the surfaces of gold nanoparticles (AuNPs). Gold nanoparticles were prepared by reducing HAuCl4 with sodium borohydride (NaBH4) in the presence of sodium tripolyphosphate (Na5P3O10). Upon exposure to Cr3+, the color of the gold nanoparticle solution changed from red to violet, which was in response to the surface plasmon absorption of dispersed and aggregated nanoparticles. The P3O105−–AuNPs were bound by Cr3+ and showed excellent selectivity compared to other ions (Hg2+, Fe3+, Cr6+, Mn2+, Cd2+, Ni2+, Pb2+, Ba2+, Co2+, Cu2+, Ca2+, Mg2+, Zn2+, Al3+, Na+, Cl−, SO42−, PO43−, CO32−, NO3−, and all of the above interfering ions with the exception of Cr3+) and had a detection limit of 10−7 M by the naked eye in this way. Most importantly, the P3O105−–AuNPs can be stored at room temperature over half a year. In addition, the P3O105−–AuNPs were also used to detect Cr3+ in real environmental water samples, with low interference.