Self‐Calibrated Identification of Metastatic Lymph Nodes Using Full‐NIR‐II Tunable Ag ₂ Se Quantum Dots Engineered by Short‐Chain Phosphines

Ratiometric fluorescence imaging in the second near-infrared (NIR-II) region holds great promise for the accurate identification of metastatic lymph nodes (MLNs), but faces challenges in biocompatible probe design with simplified composition and broad spectral tunability. Here, a minimalist, self-calibrating ratiometric probe based on homologous Ag₂Se quantum dots (QDs) is developed. Through rational redesign of tributylphosphine-mediated coordination kinetics, continuous size-dependent emission tuning across 935-1710 nm, with the synthetic mechanism and structure-property relationships systematically elucidated, is achieved. The inherently low-toxicity Ag₂Se core, combined with poly(amino acid) coating, ensures excellent biosafety, as validated by in vitro cytotoxicity and in vivo biochemical assays. Two spectrally distinct QDs (emitting at 1040 and 1305 nm, with full width at half maximum of 176 and 119 nm) enable multiplexed anatomical imaging, allowing both real-time intraoperative detection and postoperative assessment of MLNs, with a diagnostic threshold ratio of ≈0.9. This work presents a scalable strategy for full-NIR-II monochromatic QD synthesis and establishes a minimal-component biocompatible platform for precision ratiometric diagnostics.