Self-Assembled Nanobody-Albumin Platform with Dye Encapsulation for NIR-II Imaging-Guided Photodynamic Therapy

Nanobodies have emerged as a promising alternative to full-length immunoglobulin G (IgG) in a wide range of biomedical applications. However, the low molecular weight of nanobodies causes a limited drug-loading capacity and rapid renal clearance in vivo, leading to diminished delivery efficiency. Here, we describe a tumor-targeted nanobody platform that employs albumin binding and dye encapsulation for NIR-II imaging-guided photodynamic therapy. The nanobody is genetically engineered for human serum albumin (HSA) binding to form a monodisperse delivery carrier. The albumin encapsulates cyanine dyes in its cavity, leading to enhanced NIR-II fluorescence and singlet oxygen generation under 808-nm laser excitation. This affinity-driven self-assembling yields a homogeneous nanobody-albumin platform for targeted tumor delivery. Particularly, the albumin binding significantly improved nanobody pharmacokinetics, enabling substantially enhanced tumor accumulation that exceeded the nanobody retention in clearance organs. Consequently, we demonstrated high-contrast NIR-II imaging and effective photodynamic therapy in colorectal cancer xenograft models with a low NIR light dose of 420 J/cm². Our findings highlight the bioderived feature and superior therapeutic outcome of the self-assembled nanobody platform, providing a viable strategy for the design of precision theranostic agents.