Anionic Solid Solution MXene for Low‐Dosage NIR‐II Tumor Photothermal Therapy

Abstract Due to the deep biological penetrability and therapeutic depth, the photothermal therapy over second near‐infrared region (NIR‐II) is booming against deep‐seated tumors. Intensive endeavors are committed to looking for suitable photothermal agents (PTAs), but the progress seems not so satisfied toward the choice of PTA dosage. Herein, a comprehensive parameter, incident photon‐to‐thermal conversion coefficient (IPTCE), is used to evaluate the overall conversion of PTAs at different dosage, which will benefit for determining the optimized dosage of PTAs in pursuit of complete healing together with reduced long‐term damages of nanodrugs. To prove the possibility, a series of anionic solid solution MXenes are chosen as hosts due to their versatile chemical compositions and correspondingly tunable light response. By deconvoluting fundamental structure–composition–property relationships, anionic regulation with extra electron injection leads to tunable free carrier densities and enhanced NIR‐II harvesting. Ti 3 C 1.23 N 0.77 with high‐level nitrogen exhibits extraordinary extinction coefficient (43.5 L g −1 cm −1 ) than other MXenes. The parameter of IPTCE can guide the choice of PTA concentration for complete photothermal healing in vitro and vivo. This proof‐of‐principle demonstration highlights synthetically tailoring of the light harvesting over NIR‐II biowindow for a given host material by anionic regulation and further optimizes tumor photothermal therapy at low dose.