Colorimetric detection of Fe3+ ions using pyrophosphate functionalized gold nanoparticles

Abstract

A sensitive, selective colorimetric Fe³⁺ detection method has been developed by using pyrophosphate functionalized gold nanoparticles (P₂O₇⁴⁻–AuNPs). Gold nanoparticles were prepared by reducing HAuCl₄ with sodium borohydride, in the presence of Na₄P₂O₇. IR spectra suggested that pyrophosphates were capped on the surface of the gold nanoparticles. Aggregation of P₂O₇⁴⁻–AuNPs was induced immediately in the presence of Fe³⁺ ions, yielding a color change from pink to violet. This Fe³⁺-induced aggregation of P₂O₇⁴⁻–AuNPs was monitored using first the naked eye and then UV-vis spectroscopy with a detection limit of 5.6 μM. The P₂O₇⁴⁻–AuNPs bound by Fe³⁺ showed excellent selectivity compared to other metal ions (Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, and Zn²⁺). The best detection of Fe³⁺ was achieved in a pH range from 3 to 9. In addition, the P₂O₇⁴⁻–AuNPs were also used to detect Fe³⁺ in lake water samples, with low interference.