Fig. 1

Structural characterization of Au₂₅ clusters. a Schematic illustration of noninvasive TBI treatment with gold clusters via a catalytic system. b TEM image of MPA-protected Au₂₅, Au₂₄Cu₁ and Au₂₄Cd₁ clusters. Scale bar: 20 nm. c Size distribution of MPA-protected Au₂₅ nanocluster measured by analyzing 100 nanodots from TEM images. d Hydrodynamic diameters of MPA-protected Au₂₅, Au₂₄Cu₁ and Au₂₄Cd₁ in PBS buffer, and the mean sizes of Au₂₅, Au₂₄Cu₁ and Au₂₄Cd₁ were 1.98, 1.92 and 2.58 nm respectively. e Stability of Au₂₅ nanocluster in H₂O after 24 and 48 h at room temperature, and the slightly increase of hydrodynamic diameter revealed satisfying stability. Additionally, the zeta potentials of the clusters f were around -35 mV, indicative of good colloid stability (n=3 independent experiments, data are presented as mean ± SD)