PEG-Attached PAMAM Dendrimers Encapsulating Gold Nanoparticles: Growing Gold Nanoparticles in the Dendrimers for Improvement of Their Photothermal Properties

Abstract

Recently, we demonstrated that loading of HAuCl(4) in poly(ethylene glycol) (PEG)-attached poly(amidoamine) (PAMAM) G4 dendrimers and subsequent reduction with NaBH(4) yield dendrimers encapsulating gold nanoparticles (Au NPs), which have photoinduced heat-generating properties. This study was undertaken to enhance photothermal properties of the Au NP-incorporated PEG-attached dendrimers by growing Au NPs in the dendrimers. Repeated loading of HAuCl(4) in the PEG-attached dendrimers and subsequent reduction with NaBH(4) enhanced the surface plasmon resonance, indicating that Au NPs were grown in the PEG-attached dendrimers using that procedure. Transmission electron microscopy (TEM) analysis revealed that the size of Au NPs formed in the dendrimers increased with the number of repetitions of HAuCl(4) loading and subsequent reduction in the dendrimers, although the size distribution of the Au NPs remained narrow. The photoinduced-heat generation capability of the Au NPs-encapsulating dendrimers increased as the Au NPs grew. These dendrimers with Au NPs exhibited strong cytotoxicity against HeLa cells under visible light irradiation. The result demonstrates that PEG-attached dendrimers encapsulating the grown Au NPs might be useful as devices for target-specific therapy when used with light irradiation.

Applications of Gold Nanoparticle-Loaded Thermosensitive Elastin-Mimetic Dendrimer to Photothermal Therapy

“…The cells were irradiated by green laser light (532 nm, 50 mW,  6.9 µm) at 37°C using a Thermo Plate (TR-110R05, Tokai Hit Co. Ltd., Shizuoka, Japan) for 1 min, and with a fluorescence microscope (IX71, Olympus Co., Tokyo, Japan) equipped with a laser irradiation system (SIGMA KOKI Co., Ltd., Tokyo, Japan) [23]. The live or dead assay was performed according to our previous reports [16,23].…”

“…The cells treated with AuNP-loaded dendrimer were photo-irradiated for 1 min using our single cell photo-irradiation system. A live/dead assay was performed using calcein-AM (green) and PI (red) to stain live and dead cells, respectively [16,23]. Photo-irradiated cells treated with AuNP-loaded ELP-den at 37 °C became red.…”

“…Previously, polyethylene glycol (PEG)-conjugated dendrimers (PEG-den) have been used as a carrier for AuNPs. We prepared AuNP-loaded PEG-den and demonstrated the photothermal properties and the photo-induced cytotoxicity [15,16]. However, seeded growth of AuNPs in the dendrimer is necessary for effective photocytotoxicity, because AuNP-loaded PEG-den does not associate with cells efficiently owing to the excluded volume effect of PEG chains [16].…”

Dendrimer-based bionanomaterials produced by surface modification, assembly and hybrid formation

“…84 Considering their applications to bionanomaterials, PEG-modified PAMAM dendrimers have been used for complex formation with Au NPs. [85][86][87] As is the case of unmodified PAMAM dendrimers, PEG-modified PAMAM dendrimers are useful as a template for the formation of Au NPs. When AuCl 4 À ions were reduced within the PEG-modified PAMAM G4 dendrimer, Au NPs with average diameters of approximately 2 nm were generated within the dendrimer.…”

“…Indeed, the heat-generating ability under light irradiation increases with the increasing size of the Au NPs, not only because of the increased amount of Au NPs in the dendrimer but also because of the more efficient surface plasmon resonance of the well-grown Au NPs. 87 When cells were incubated with these PEG-modified dendrimer-Au NP hybrids, these hybrid particles are taken up by cells through endocytosis. After treatment with the hybrids, the cells were killed by light irradiation.…”