systemThe colorimetric assay and UV–vis spectra are both used to esti-mate the sensitivity of our Hg2+detection system. Fig. 5 shows thephotographic image of the AuNPs-based detection systems incu-bated with various concentrations of Hg2+ranging from 0.08 to2.08 M. It is found that the color of the AuNPs-based detectionsystems stepwise changes from blue to red with the increase ofHg2+concentration. Compared with the control (without Hg2+incu-bation), the color change of the AuNPs-based detection systemsincubated with Hg2+higher than 0.1 M can be readily read out,but that with 0.08 M of Hg2+is not. Therefore, the limit of detec-tion (LOD) of our Hg2+detection system is 0.1 M by the nakedeyes