A new type of strategically designed functional ligands was used to cap gold nanocrystals and form robust colloidal nanoparticles, resistant to pH changes, temperature, and ionic strength variations as well as ligand-exchange reactions. The nanoparticles are coated with ligands that polymerize upon UV-irradiation, consequently embedding the particles in a stable organic shell. The ligand consists of an anchoring thiol group, which binds directly to the nanocrystal surface and two units, one hydrophobic and one hydrophilic. The hydrophobic alkyl unit contains a diacetylene group, which undergoes a 1,4-topochemical polymerization leading to a poly(enyne) structure during UV-irradiation. The hydrophilic unit contains an oligo-ethylene glycol chain, which ensures water solubility, and a terminal carboxylic group. Derived particles were characterized by transmission electron microscopy, surface enhanced Raman spectroscopy, and visible spectroscopy. Their stability was investigated and compared to particles capped with nonpolymerized ligands.