Synthesis of Size-Tunable Polymer-Protected Gold Nanoparticles by Femtosecond Laser-Based Ablation and Seed Growth

A femtosecond laser-assisted method has been developed to produce stable, size-tunable (3 to similar to 80 nm) and low dispersed gold nanoparticles. The method implies the formation of initial nanosized seeds (<10 nm) by laser ablation from a gold target in aqueous solutions of biopolymers. Those seeds are then irradiated by a femtosecond laser-induced white-light supercontinuum to initiate a controlled growth of larger nanoparticles. The use of biopolymers (chitosan, alpha,omega-dithiol poly(N-isopropylacrylamide), poly(ethylene glycol), and dextran) of different concentrations enables in situ surface functionalization and size control during the process. We discuss mechanisms of nanoparticle growth and demonstrate an example of their application in biosensing, using a model of nanoparticle aggregation via specific binding of the gold-dextran bioconjugate to concanavalin A.