The challenge of imaging is to combine resolution and sensitivity in order to gain accuracy in diagnosis. No single modality can provide comprehensive information. Then, the solution is to design probes that are able to gather on a single platform the best features of the different imaging modalities. To achieve this objective, we have combined two types of probes, one associated with photoacoustic imaging (PAI) and the other with magnetic resonance imaging (MRI), within polysaccharide-based nanohydrogels. For that, chitosan (CS) which is a cationic polysaccharide was grafted with the photoacoustic probe ZW800-1. The synthesis of the corresponding CS-ZW800 and the purification conditions that allow to overcome ZW800 aggregation on the course of the protocol were carefully analyzed. Nanohydrogels that encapsulated gadolinium chelates as MRI probes were further obtained by ionic gelation between CS-ZW800 and the anionic hyaluronic acid (HA) in the presence of tripolyphosphate (TPP) as an ionogenic cross-linker. The bimodal nanohydrogels were then subjected to MSOT and MRI experiments. Upon excitation at 770 nm the nanoparticles were then able to produce a significant MSOT signal while in MRI at 3T, a significant positive contrast was obtained with low Gd doses.< Leer menos