The evolution of the optical absorption spectrum of three samples. With different volume ratios of HAuCl4 and Na2S2O3 during the reactions: (a) 5 ml HAuCl4 + 2.2 ml Na2S2O3, (b) 5 ml HAuCl4 + 1.4 ml Na2S2O3, and (c) 5 ml HAuCl4 + 0.8 ml Na2S2O3. Samples were taken during the reaction and diluted five times with DI water then immediately measured by UV–vis-NIR spectrophotometer.
Zhang et al. Nanoscale Research Letters 2012 7:337 doi:10.1186/1556-276X-7-337