Gold nanoclusters (Au NCs) are an emerging type of theranostic agents combining therapeutic and imaging features with reduced toxicity. Au NCs stabilized by a zwitterion ligand with a fine control of the metal core size and the ligand coverage were synthesized by wet chemistry. Intense fluorescence signal is reported for the highest ligand coverage, whereas photoacoustic signal is stronger for the largest metal core. The best Au NC candidate with an average molecular weight of 17 kDa could be detected with high sensitivity on a 2D-near-infrared imaging instrument (limit of detection (LOD) = 2.3 μM
) and by photoacoustic imaging. In vitro and in vivo experiments demonstrate an efficient cell uptake in U87 cell lines, a fast renal clearance (t 1/2α
= 6.5 ± 1.3 min), and a good correlation between near infrared fluorescence and photoacoustic measurements to follow the early uptake of Au NCs in liver.