Bright NIR-II fluorescence from biocompatible gel-coated carbon nanotubes for in vivo imaging

Near-infrared light in the second region (NIR-II, similar to 1000-1400 nm) can penetrate biological tissues with minimal absorption and scattering, making it ideal for in vivo diagnostic imaging. However, most NIR-II-fluorescent materials lack adequate brightness and biocompatibility. One such example is single-walled carbon nanotube (SWCNT). In this study, we improved fluorescence brightness and biocompatibility of SWCNTs by coating them with gel of polyethylene glycol (PEG)-based cross-linked polymers, which was prepared by a one-pot method called "carbon nanotube micelle polymerization (CMP)". The PEG confers SWCNT biocompatibility, and structural defects of SWCNT induced by CMP enhanced NIR-II fluorescence intensity. Due to these improvements, the gel-coated SWCNTs clearly imaged vasculatures in mice at a low dose of 8.4 mu g/mouse, proving the potential use of gel-coated SWCNTs as high-quality bio-imaging agents.