Preparation of near-infrared light absorbing gold nanoparticles using polyethylene glycol-attached dendrimers

The photochemical properties of gold nanoparticles (Au NPs) are largely influenced by their size and morphology. Stably dispersed Au NPs that absorb near-infrared (NIR) light are useful for biomedical applications. We prepared well-dispersed NIR-absorbing Au NPs using seeding growth from Au NPs encapsulated in polyethylene glycol (PEG)-attached dendrimers. Formaldehyde was used as a reductant to prepare gold nanoparticles with convex–concave surfaces. Low pH and an appropriate amount of gold ion were required to prepare Au NPs that absorbed NIR-light. Interestingly, the encapsulation of Au NPs within the PEGylated dendrimers was important for preparation of NIR-absorbing Au NPs. Transmission electron microscope (TEM) analysis showed that these Au NPs had convex–concave surfaces and large diameters. This paper presents a novel preparation method for NIR-responsive Au NPs by reduction with formaldehyde.