Femtosecond Laser Ablation Synthesis of Aryl Functional Group Substituted Gold Nanoparticles

Femtosecond laser ablation synthesis of gold-aryl nanoparticles in solution was explored. Laser irradiation of the yellow solution of diazonium tetrachloroaurate(III) salt [C₈F₁₇-4-C₆H₄N≡N]AuCl₄ in acetonitrile formed ruby red color of gold-aryl nanoparticles without the need for external chemical reducing agent. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and nanodrop UV-Vis spectroscopy were used in the nanoparticles characterization. XPS showed the presence of the core–shell and the formation of gold(0) oxidation state only. The nanoparticles size distribution estimated by TEM is dependent on the duration of laser irradiation. Longer irradiation time resulted in decreasing the nanoparticles size. UV-Vis studies in acetonitrile showed that the absorption of gold(III) at 310 nm vanished with a concomitant formation of a plasmon absorbance at 532 nm due to the formation of “embryonic” gold-aryl nanoparticles. The novelty of this work is the in situ conjugation of core–shell structure without the need for adjusting the conjugate/gold ratio, chemicals-free synthesis from reducing agents and surfactants, synthesis of nanoparticles using gold salts unlike the common ablation of flat metal surfaces, and the use of reactive [AuCl₄]⁻ counter-ion that permits the co-deposition of gold and conjugates. Released solvated electrons and hydrogen radicals are believed to induce the reduction reaction of the gold salts. Isolation of pure nanoparticles is important for further biomedical applications including cellular uptake.