Fig. 6. Total amounts of Gd element in the main organs and tumors of mice at 1 h (a) and 24 h (b) post-injection of NaGdF₄@bp-peptide NPs or NaGdF₄@CPP NPs, respectively. Error bars mean standard deviations (n = 3, **P < 0.01 or ***P < 0.001 from an analysis of variance with Tukey's post-test).