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Vials containing samples of hairy nanoparticles. (Credit: Rob Felt, Georgia Tech)

"Hairy" nanoparticles made with light-sensitive materials that assemble themselves could one day become "nanocarriers," providing doctors a new way to simultaneously introduce both therapeutic drugs and cancer-fighting heat into tumors. That's one potential application for a new technology that combines water-repelling yet light-sensitive and water-absorbing materials into polymeric nanoreactors for creating photoresponsive gold nanoparticles.

Light of specific wavelengths causes the nanoparticles to assemble and disassemble on demand, allowing the dynamic organization of the nanoparticles for smart in vitro drug release. By including chemotherapy molecules in the nanoparticle structures when they are assembled, the molecules could be drawn into tumors - and then released with the application of a light at a shorter wavelength that triggers disassembly through photo-cleavage.

In addition to such a dynamic self-assembly and disassembly, the encapsulation and release of chemotherapy molecules could also be achieved by reversible covalent bonding of anticancer drugs to the polymeric "hairs" situated on the surface of nanoparticles. And by absorbing the same light that triggers the drug release, the gold nanoparticles could also heat the cancer cells, providing a double punch.

Under light, the assemblies of photosensitive nanoparticles separate over a period of hours at a rate that can be controlled by the intensity and wavelength of the light. The hairy nanoparticles are fabricated around a tiny core of beta-cyclodextrin from which polymer chains of poly(acrylicacid)-block-poly(7-methylacryloyloxy-4-methylcoumarin) (PAA-b-PMAMC) are grown. That material attracts water-soluble metal precursors, which use the space within the polymer hairs as nanoreactors to form gold nanoparticles.

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