Self-assembled, biocompatible and biodegradable TEMPO-conjugated nanoparticles enable folate-targeted tumor magnetic resonance imaging

•A new application for chitosan-TEMPO (CS-TEMPO) is uncovered for the first time.•Carefully selecting starting materials obviated the conventional use of metal-based catalysts for similar synthesis•Compartmentalization of TEMPO in CS greatly reduced its ease of in vivo reduction.•Folic acid-decorated CS-TEMPO (CS-TEMPO-FA) can be taken up by various tumor cells.•The totally metal-free CS-TEMPO-FA provides safe and commensurate tumor-targeted MRI.