Pulsed nanosecond laser ablation of gold in deionized water and aqueous chitosan solution

• Produced gold nanoparticles (AuNP) via 1064 nm laser ablation and 532 nm irradiation.
• Nanosecond laser ablation of Au in chitosan yields free, sub-13 nm diameter NP.
• Irradiation of gold nanoparticles yields free, sub-6 nm diameter nanoparticles.
• Chitosan prevents coalescence and agglomeration.
• AuNP prepared in chitosan exhibited lamellar structures without oxidation.

Gold nanoparticles (AuNP) are produced using a Nd:YAG laser in deionized water and aqueous chitosan solutions via 1064 nm nanosecond laser ablation and subsequent 532 nm nanosecond laser irradiation. AuNP produced in deionized water under single laser ablation and subsequent irradiation for 20–40 min time exhibited coalescence and the formation of nano-chains, with average particle diameters ranging from 34.3 to 18.8 nm and 37.2 to 27.3 nm, respectively. The introduction of chitosan as a bio-compatible surfactant yielded lesser average diameters and tighter size-distributions with a narrow range of UV-Vis absorption spectra values (514–525 nm). For instance, at 20 and 40 min, the single laser ablation and subsequent irradiation produced the average diameters of 12.3 and 5.3 nm and 5.7 and 4.3 nm, respectively. Increases in ablation and irradiation time decrease AuNP size. As time increased, the size-distributions of the AuNP produced in chitosan solution narrowed and the particle size monotonically decreased. Chitosan functionalized the AuNP surface, promoting hydrophobicity, preventing electrostatic attraction of the Au nanoparticles, thus inhibiting coalescence and agglomeration. UV-Vis absorption spectra, TEM and HR-TEM images are used to verify AuNP size distributions. X-ray diffraction measurements of AuNP produced in chitosan confirmed crystallite size and the absence of gold-oxide despite the high-energy laser ablation. Furthermore, samples prepared in chitosan solution showed minimal agglomeration after 24 months.