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

Abstract

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.