A highly bright red-light chemiluminescent probe for inflammation imaging

Both red-light chemiluminescence (CL) emission and high CL efficiency are desirable highly favorable for deep-tissue imaging, however, it was usually achieved by transferring the energy from a CL donor to a fluorophore acceptor based on the CL resonance energy transfer (CRET), which is significantly affected by the spectral overlap range and distance between them. Herein, a red-light CL emitter (L-ISN) was synthesized by conjugating the isoindole BODIPY with the phthaloyl hydrazine moiety (a luminol derivative). When the phthaloyl hydrazine moiety was initiated by ¹O₂, the released reaction energy can be transferred to the whole molecule through intramolecular energy transfer, showing an astonishingly improved CL efficiency by 13 times than luminol. Besides, the CL of L-ISN can penetrate tissues thicker than 2.0 cm, and the limit of detection (LOD) was calculated to be about 52.87 nmol L^{−1 1}O₂. When L-ISN nanoparticles (NPs) were prepared by using F127 as the surfactant, L-ISN NPs successfully detected intracellular ¹O₂ and distinguished inflammation tissue in vivo. We believe this study will provide a novel idea for the design of red-light CL emission probe with higher brightness in the field of detection ¹O₂.