Size‐Dependent Cascade Enhancement of T1‐T2 Dual‐Modal MRI in Tumors

Abstract Currently, there is no conclusive evidence indicating that in situ self‐assembled Gd nanostructures of varying sizes demonstrate distinct T 1 and T 2 signal enhancement capabilities. Furthermore, it remains uncertain whether size adjustment can effectively achieve enhanced T 1 ‐T 2 dual‐modal MRI. To address these uncertainties, a two‐step in situ self‐assembly strategy is developed. This approach began with a small‐sized nanoprobe, Gd‐TCO‐P, with a hydrodynamic diameter (dH) of 16 ± 3 nm. This nanoprobe underwent alkaline phosphatase (ALP) cleavage and self‐assembled intracellularly into short nanofibers termed Gd‐NFs (dH: 200 ± 51 nm). The subsequent introduction of tetrazine‐tetrazine crosslinked these Gd‐NFs, leading to the formation of larger two‐stage dendritic nanofibers known as Gd‐TS‐NFs (dH: 4371 ± 236 nm). This process achieves size‐dependent enhancement of both T 1 and T 2 signals, which is validated through both in vitro and in vivo experiments, enabling precise long‐term imaging of ALP‐overexpressing tumors. This study not only provides valuable insights into the relationship between the size of in situ formed Gd nanostructures and T 1 /T 2 MRI contrast enhancement, but also suggests a promising strategy for clinical applications of T 1 ‐T 2 dual‐modal MRI.