Highly Efficient and Controllable PEGylation of Gold Nanoparticles Prepared by Femtosecond Laser Ablation in Water

This paper demonstrates a new method for fabrication of stable gold nanoparticle–poly(ethylene glycol) (PEG) conjugates bearing a defined number of one or multiple types of PEG molecules. The PEG molecules are directly bound to the surface of gold nanoparticles with almost 100% conjugation efficiency, and the PEG surface coverage is tunable to be any percent value between 0 and 100%. The method comprises preparation of a colloidal suspension of naturally negative charged pure gold nanoparticles with a bare surface via a novel approach of femtosecond laser ablation of gold bulk target in deionized water first, and then the surface modification with PEG is carried out by adding PEG molecules containing thiol groups. It is revealed that because of their unique bare surface very efficient and controlled conjugation of PEG molecules to these gold nanoparticles could be achieved. The PEGylation process described in this paper just serves as one example to testify that the bare surface of gold nanoparticles provides significant benefits for their further surface modifications. The discussed strategies are of a general nature and could be readily applied in the same way to construct a mixed monolayer composed of other biologically important molecules onto the surface of a gold nanoparticle to form a multifunctional composite nanoparticle for offering improved performance in biomedical applications.