This article highlights our recent achievements on the development and upgrade of new potential tumor-specific contrast agents for magnetic resonance imaging (MRI) based on gadolinium complexes and peptides, assemblied in amphiphilic supramolecular aggregates. The physico-chemical characterization of these aggregates provides novel and interesting opportunities to investigate surfactant aggregation properties, that may be exploited in several applications such as in medical diagnostics or in drug and gene delivery.