Sensitive and selective detection of trivalent chromium using Hyper Rayleigh Scattering with...

Hyper Rayleigh Scattering (HRS) and absorption spectral assays using surface-modified gold nanoparticles (AuNP) have been developed for sensitive and selective detection of trivalent chromium (Cr³⁺) from other metal ions including hexavalent chromium (as Cr₂O₇^2-). Gold nanoparticles of 13 nm, covalently attached with 5,5'-dithio-bis-(2-nitrobenzoic acid) (AuNP-DTNBA), is used as a probe for both the absorption and HRS assays. AuNP-DTNBA is able to detect Cr³⁺ at 20 ppb level at pH 6.0 using absorption spectral change of the AuNP-DTNBA. Visible color change can be observed when mixed with 250 ppb of Cr³⁺, while there is no color change when mixed with 2 ppm level of some of the most common metal ions such as Cr₂O₇^2-, Hg²⁺, Ba²⁺, Fe³⁺, Pb²⁺, Na⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Ca²⁺, and Ni²⁺. However, a color change is observed when mixed with Ni²⁺, Zn²⁺, and Cd²⁺ at a concentration higher than 2 ppm. The detection limit for the HRS assay is on a remarkable 25 ppt level, and there is no detectable HRS signal at 2 ppm level for Cr₂O₇^2-, Hg²⁺, Ba²⁺, Fe³⁺, Pb²⁺, Na⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Ca²⁺, and Ni²⁺.