A metal nanostructure is described. Such a metal nanostructure may comprise a nanometric metal core comprising gold, silver or an assembly or alloy of gold and silver, and one or more molecules attached to one or more surfaces of the nanometric metal core, where each of the molecules has the structural formula W-X-Y-Z, where W is an atom or a chemical group bound to the nanometric metal core, X is a hydrophobic spacer, Y is a hydrophilic spacer and Z is either hydrogen or a reactive group able to bind a reactive substrate or biomolecule. Such a metal nanostructure may be useful in making pharmaceutical compositions.