Self‐Aggregated Carbon Dots Enable High‐Contrast NIR‐II In Vivo Bioimaging

Abstract Carbon dots (CDs), particularly those with dimensions below 5 nm, exhibit unique tissue‐penetrating capabilities, enabling them to traverse subcellular compartments and cross microbial membranes. However, they suffer from rapid renal clearance via glomerular filtration, which results in limited retention in target tissues and diminished bioavailability. Considering the superior tissue penetration and enhanced imaging resolution of the second near‐infrared (NIR‐II, 900–1700 nm) window, this study presents a novel cyanine dye‐derived NIR‐II CDs (Cy‐CDs, λ em = 1044 nm) with a relative fluorescence quantum yield of 3.75% through a facile solvothermal method, which is applied for in vivo deep NIR‐II fluorescence imaging. More importantly, Cy‐CDs (2.5 nm) can spontaneously aggregate in aqueous solution to form large‐sized CDs (A‐CDs, 30–40 nm) through specific hydrogen bonding interactions, thereby exhibiting excellent tumor‐targeting ability and strong acid/base resistance. By taking advantage of these unique properties, high‐resolution vascular imaging, tumor imaging, and real‐time dynamic monitoring of intestinal peristalsis have been successfully achieved in vivo. These applications not only underscore the potential of Cy‐CDs in imaging‐guided disease diagnosis but also highlight the strategic importance of the aggregation behavior of CDs in aqueous environments.