Fig. 2

Optimization of divalent ions. From 0 to 800 mM of NaCl were mixed with constant GNP (1 O.D.). After 15 min, scanned at the wavelength from 400 to 800 nm. Photographs were taken by the digital camera as in figure inset. The spectrum and color changes are indicated by the aggregation of GNP with 100 mM NaCl. Peaks were indicated with the respective colored spheres