Synthesis of fluorescent, triangular gold nanoplates through surface capping by a cationic diacetylene

In this work triangular gold nanoplates (AuNTPs) are prepared by spontaneous conversion of spherical-like gold precursors induced by the shape-directing properties of the diacetylene N,N,N-trimethylpentacosa-10,12-diyn-1-ammonium bromide (PCD_ABr), employed as capping agent. In detail, thin AuNTPs with edge length below 200 nm are obtained by incubating premade isotropic gold nanoparticles protected with chitosan (Chit@AuNPs) in PCD_ABr solutions through a standard ligand-exchange reaction (LER) carried out in water at room temperature. Control of the AuNTPs size as well as the reaction shape-yield up to 65% is achieved by simply varying the reagents ratio in the incubation mixture. Because of the high anisotropy of the flat nanoparticles, the AuNTPs-containing hydrosols show intense, well-defined absorptions in the NIR spectral region, which make them excellent candidates as biosensors also for in vivo assays with biological tissues and fluids. When subjected to UV light, both triangular and nearly spherical PCD_ABr-coated gold nanoparticles exhibit fluorescent properties and Raman features typical of disordered, sp2-based carbon nanostructures. The photogeneration of graphite-like moieties within the diacetylene shell instead of expected polydiacetylene skeleton is most likely due to poor alignment of the monomer chains on the gold surfaces and seems to be favored on isotropic nanoparticles.