The invention relates to a ligand compound having a structure A-B-C, wherein (a) A represents a mono- or polyphosphorylated amino acid linked to part B by its amino group to form an amide bond B represents (i) a carboxylic acid, and (ii) an amino acid or peptidyl group of 2-10 amino acids, an alkyl or alkenyl group comprising 1-26 carbon atoms, a polyethylene glycol group comprising 1-26 carbon atoms or a combination thereof covalently linked to the carboxylic acid and C represents a hydrophilic group covalently linked to the group of B (ii) or (b) A represents a mono-or polyphosphorylated amino acid linked to B by its carboxylic acid to form an amide bond B represents an amino acid or peptidyl group of 2-10 amino acids, an amino substituted alkyl or alkenyl group comprising 1-26 carbon atoms, an amino substituted polyethylene glycol group comprising 1-26 carbon atoms or a combination thereof covalently linked to A by their amino group C represents a hydrophilic group covalently linked to the group of B. The invention further relates to a coated metal nanoparticle such as super paramagnetic iron oxide nanoparticle (SPIONs) coated with a plurality of the aforementioned ligands and a method of producing thereof.
