A NIR-II fluorescent probe for articular cartilage degeneration imaging and osteoarthritis detectionElectronic supplementary information (ESI) available: Synthesis steps, toxicity of CH1055-WL, MS spectra of compounds. See DOI: 10.1039/c8bm01440j

Articular cartilage (AC) is a complex water-bearing tissue consisting of chondrocytes, proteoglycans, and collagen. AC degeneration, which occurs in the early stage and throughout the entire course of osteoarthritis (OA), is one of the main pathological changes of OA. However, current clinical approaches are unable to detect AC degradation during the early stage of OA. Herein, a novel NIR-II probe, CH1055-WL, was developed with an organic fluorophore (CH1055) and type II collagen-binding peptide (WYRGRL) for AC targeting and degeneration imaging. In vitroand in vivoimaging studies demonstrated that CH1055-WLspecifically bound to AC and permitted sensitive detection of age-related or surgically induced AC degeneration in living mice. In vitroimaging of cartilage samples from pig knee joint and in vivoimaging of live mice with the probe administered vialocal injection in joint cavities demonstrated that CH1055-WLspecifically and efficiently bound to AC. Further evaluation of CH1055-WLrevealed sensitive detection of age-related AC degeneration and surgically induced AC degeneration in living mice. Our results indicated that the cartilage-targeting probe CH1055-WLallowed visual monitoring of AC degeneration in living subjects, thus displaying promise for early OA detection.