Fig. 1.

(A) TEM image and size distribution histogram of GPG. (B) High-resolution TEM (HR-TEM) image of GPG. (C) AFM topography image of GPG on a 300 nm SiO₂/Si substrate. Inset: height profile analysis along the line shown in the image. (D) XPS survey spectrum of GPG. (E) High-resolution XPS C 1s, O 1s, and Gd 4d spectra of GPG. (F) Raman spectrum of GPG. Two intense defect-related D and G peaks are found, centered at 1345.2 and 1597.0 cm^–1, respectively. (G) Zeta potentials of GPG, Ab, and GPG-Ab. (H) T₁s measured during the conjugation between GPG and Ab. T₁ acquired at 0 min is measured from the pure GPG solution. Error bars indicate standard deviation (SD).