Nanostructures formed from the self‐assembly of amino acids are promising materials in many fields, especially for biomedical applications. However, their low stability resulting from the weak noncovalent interactions between the amino acid building blocks limits their use. In this work, nanoparticles co‐assembled by fluorenylmethoxycarbonyl (Fmoc)‐protected tyrosine (Fmoc‐Tyr‐OH) and tryptophan (Fmoc‐Trp‐OH) are crosslinked by ultraviolet (UV) light irradiation. Two methods are investigated to induce the dimerization of tyrosine, irradiating at 254 nm or at 365 nm in the presence of riboflavin as a photo‐initiator. For the crosslinking performed at 254 nm, both Fmoc‐Tyr‐OH and Fmoc‐Trp‐OH generate dimers. In contrast, only Fmoc‐Tyr‐OH participates in the riboflavin‐mediated dimerization under irradiation at 365 nm. The participation of both amino acids in forming the dimers leads to more stable crosslinked nanoparticles, allowing also to perform further chemical modifications for cancer applications. The anticancer drug doxorubicin (Dox) is adsorbed onto the crosslinked nanoparticles, subsequently coated by a tannic acid‐iron complex, endowing the nanoparticles with glutathione‐responsiveness and photothermal properties, allowing to control the release of Dox. A remarkable anticancer efficiency is obtained in vitro and in vivo in tumor‐bearing mice thanks to the combined chemo‐ and photothermal treatment.