Shortwave Infrared in Vivo Imaging with Gold Nanoclusters

The use of visible/NIR-emitting gold nano clusters (Au NCs), previously proposed for in vivo imaging, has been limited to some extent by low quantum yields (QYs) and the limited penetration of visible light in tissue. Here we report short wavelength infrared (SWIR, lambda = 1-2 mu m) emitting Au NCs with a good photoluminescence QY for this wavelength range (0.6% to 3.8% for lambda(em) = 1000 to 900 nm) and excellent stability under physiological conditions. We show that surface ligand chemistry is critical to achieving these properties. We demonstrate the potential of these SWIR-emitting Au NCs for in vivo imaging in mice. The Au NCs have a hydrodynamic diameter that is small (similar to 5 nm) enough that they exhibit a rapid renal clearance, and images taken in the SWIR region show better resolution of the blood vessels than in the NIR region.