As the concentration of iodide was calculated by the silver TNPs concentration, lower concentration of silver TNPs can be used for detecting lower concentrations of iodide. We found that very low concentration of silver TNPs beyond the sensitivity of a common spectrophotometer can interact with very low concentration ofiodide. The spectrophotometer used in our experiment can dis-tinguish the UV–vis absorption of a solution whose absorbance is larger than 0.0002. In our experiment condition, silver TNPs with maximum absorbance about 0.0007 can be distinguished from ablank sample and the spectral transformation in the presence of iodide can be measured (see Supporting Information, Fig. S16). The lowest detectable iodide concentration can be measured as 8.8 nM. However, in our opinion, the sensitivity can be further improved,if advanced spectral technologies, for example single nanoparticles UV–vis absorption spectrophotometer [59,60] are used for detection of silver TNPs detection.