Fig. 1. Characterization of Au–Gd NCs. (A) The hydrodynamic size of Au–Gd NCs. (B) TEM image of Au–Gd NCs. Scale bar = 10 nm. (C) Zeta potential of Au–Gd NCs. (D) UV-Vis absorption and fluorescence emission spectra of Au–Gd NCs. The inset: NIR-II FL image of Au–Gd NCs. (E) r1 values of Gd-DTPA and Au–Gd NCs as a function of the molar concentration of Gd in the solution. The insets: MR T1 weighted images of Gd-DTPA and Au–Gd NCs at equivalent concentrations of Gd. (F) The circular dichroism spectra of BSA and Au–Gd NCs.