A route to brightly fluorescent carbon nanotubes for near-infrared imaging in mice

The near-infrared photoluminescence intrinsic to semiconducting single-walled carbon nanotubes is ideal for biological imaging owing to the low autofluorescence and deep tissue penetration in the near-infrared region beyond 1 µm. However, biocompatible single-walled carbon nanotubes with high quantum yield have been elusive. Here, we show that sonicating single-walled carbon nanotubes with sodium cholate, followed by surfactant exchange to form phospholipid–polyethylene glycol coated nanotubes, produces in vivo imaging agents that are both bright and biocompatible. The exchange procedure is better than directly sonicating the tubes with the phospholipid–polyethylene glycol, because it results in less damage to the nanotubes and improves the quantum yield. We show whole-animal in vivo imaging using an InGaAs camera in the 1–1.7 µm spectral range by detecting the intrinsic near-infrared photoluminescence of the ‘exchange’ single-walled carbon nanotubes at a low dose (17 mg l−1 injected dose). The deep tissue penetration and low autofluorescence background allowed high-resolution intravital microscopy imaging of tumour vessels beneath thick skin. Single-walled carbon nanotubes can be modified into bright and biocompatible agents for high resolution whole-animal imaging at wavelengths in the 1100–1700 nm region.