Fig. 1.

Characterization of gold nanoparticles. a, b Transmission electron microscopic images (TEM), c asymmetric field flow fractionation (AFFF) results, and d surface plasmon extinction spectra of PEGylated gold nanospheres (a and black solid line) and nanoflowers (b and red solid line). The TEM images show the narrow size distribution and regular shape of the small gold nanospheres (a) and the polydisperse large gold nanoflowers (b). The AFFF results in part (c) confirm the difference in size and polydispersity of PEGylated small gold nanospheres and nanoflowers. d Small gold nanospheres possess a well-defined absorption peak at 518 nm, which contrasts the broad and lower energy absorption of gold nanoflowers