Abstract: The present invention relates to gold nanocluster compounds, especially gold nanoparticles, having a reduced toxicity, especially cytotoxicity, which are preferably appropriate for use in medical diagnostics such as medical imaging (e.g. X-ray, CT etc.), said gold nanocluster compounds comprising a core of at least one gold atom and at least one ligand bound to said core, wherein the reduction of toxicity, especially cytotoxicity, of said gold nanocluster compound is controlled and/or adjusted via its ligand structure and/or its ligand chemistry.