Figure 2: (a) The UV-Vis spectra of gold NPs of different size. The absorbance was normalized for better comparison. (b) The change of maximum absorbance of 17 to 80nm gold NPs over 4 weeks. The concentrations were 0.083mM for 17nm, 0.040mM for 30nm, 0.015mM for 40nm, 0.017mM for 50nm, 0.019mM for 60nm, and 0.028mM for 80nm.