Figure 3.

(a) Absorption profile of modified gold nanoparticles before and after addition of different concentrations of Hg(II) ions. (b) Photographic images of color of MPA–PDCA-modified gold nanoparticles (13 nM) in presence of different concentration of Hg (II) ion, (1) 3 ppm, (2) 6 ppm, (3) 10 ppm, (4) 50 ppm.