Fig. 3

a Photographs of Au⁺-complex solution taken 1 min after the addition of THPC-Au seeds (final ratio in solution: [Au⁺]/[Au seed] = 152). Final [Au⁺] and [Au seed] in solution were 1 and 6.6 nM, respectively; b TEM image of resulting lager Au NPs after mixing Au⁺-complex solution and THPC-Au NPs for 1 min; c Size distribution histograms of LBA-Au NPs; d Absorption spectrum of the resulting lager Au NPs in Fig. 2b; e Evolution of the absorption spectrum of the solution after mixing Au⁺-complex solution and THPC-Au NPs, where the spectra were recorded at intervals of 10 s. Experimental conditions were the same as in Fig. 2a