As shown in Fig. 3i, j, both Gd-NTs and free Mb could barely influence tumor hypoxia status, while Mb@Gd-NTs significantly relieved tumor hypoxia at 24 h post-injection, which resulted from the largely enhanced tumor uptake (Fig. 3g) and obviously prolonged blood circulation of Mb@Gd-NTs proven by pharmacokinetics studies (Fig. 3h). Here, MB is linked to neoplasm.