Highly efficient lanthanide‐doped theranostic nanoplatform for real‐time monitoring of direct triplet‐sensitized photodynamic therapy

Abstract Photodynamic therapy (PDT) is widely used in cancer treatment because of its noninvasiveness and minimal side effects. However, low therapeutic efficiency and the challenge of treatment visualization limit its development. Herein, we constructed a simple yet efficient lanthanide‐doped theranostic nanoplatform termed as LiLuF 4 :Yb,Er,Ce@ LiYF 4 @LiLuF 4 : Nd‐chlorine 6 (TNPs‐Ce6) that enables real‐time monitoring of the therapeutic effects of PDT. Upon orthogonal excitation by near‐infrared (NIR) light, the Nd 3+ ‐doped TNPs activated the triplets of Ce6 photosensitizers via a direct lanthanide‐triplet energy transfer process, which allowed to directly active the low‐lying triplet state of the photosensitizer without undergoing singlet–triplet intersystem crossing (ISC) process, thereby significantly enhancing the efficiency of the photodynamic process. Meanwhile, the incorporation of Er 3+ ions within the core endowed the nanoplatform with NIR‐IIb imaging capabilities, allowing convenient real‐time monitoring of the photodynamic treatment process. Characterization tests revealed that the TNPs‐Ce6 nanoplatform, exhibiting an NIR quantum yield of 21.7% at an ultralow excitation power density of 0.1 W cm −2 , provides a real‐time imaging resolution as low as 75 μm in the NIR‐IIb range and achieves a tumor suppression rate of 94%. Therefore, this highly efficient theranostic nanoplatform, with real‐time treatment monitoring capability, demonstrates significant potential in cancer therapy.