Water dispersible glycylglycine functionalized gold nanoparticles: application in colorimetric sensing of Hg(II), Pb(II) and Cr(III) in aqueous media

Glycylglycine functionalized water-dispersible gold nanoparticles (AuNPs) were prepared and characterized on the basis of ultraviolet and visible spectroscopy (UV-vis), Fourier transform infrared (FTIR), dynamic light scattering (DLS), transmission electron microscope (TEM) and energy dispersive X-ray (EDX) analysis. The AuNPs exhibited a strong SPR band at 522 nm, which after functionalization with glycylglycine, appeared at 525 nm. This SPR band of the functionalized nanoparticles is used as a tool for the detection of toxic metal ions in water. A large number of metal ions were tested, among which Hg²⁺, Pb²⁺, and Cr³⁺ exhibited distinct colour change, detectable with bare eye, and substantial UV-vis spectral change. TEM images and EDX analysis suggested that the colour change is due to metal-induced aggregation of the functionalized nanoparticles due to inter-particle plasmon coupling. The aggregation, which resulted in an increase in particle size, is further confirmed by DLS measurement. A mechanism of metal-induced aggregation is also proposed. The present study is an example of a simple methodology to prepare water-dispersible functionalized nanoparticle for colorimetric detection of toxic heavy metal ions such as Cr³⁺, Pb^2+, and Hg²⁺ with high sensitivity.

Graphical abstract

Synopsis Glycylglycine functionalized water dispersible gold nanoaprticles were prepared, characterized and its metal-ion sensing property was evaluated with the aid of spectroscopic, microscopic and energy dispersive X-ray analysis. These nanoparticles detect Hg²⁺, Pb²⁺ and Cr³⁺ with colour change due to inter particle plasmon coupling because of metal-induced aggregation of the nanoparticles.