Reduction-responsive diblock copolymer-modified gold nanorods for enhanced cellular uptake

Reduction-responsive polymer micelles are highly promising drug carriers with better tumor therapeutic effect, which can be achieved by controlled drug release under stimulation. Gold nanorods (AuNRs) have attracted considerable attention due to their unique optical and electronic properties when used for biomedical applications. Herein, the lipoic-acid-functionalized reduction-responsive amphiphilic copolymer poly(epsilon-caprolactone)-b-poly[(oligoethylene glycol) acrylate] (LA-PCL-SS-POEGA) with a disulfide group between the two blocks was prepared to modify AuNRs via Au-S bonds. The size and morphology of AuNRs@LA-PCL-SS-POEGA were measured by dynamic laser light scattering (DLS) and transmission electron microscopy (TEM) methods. The stabilities of AuNRs@LA-PCL-SS-POEGA in different types of media were studied by UV/vis spectroscopy and DLS techniques. The results show that AuNRs@LA-PCL-SS-POEGA gradually aggregate in a concentrated salt solution containing 150 mM dithiothreitol (DTT), but exhibit high stability in a non-reducing environment. Near infrared (NIR)-induced heating of AuNRs@LA-PCL-SS-POEGA was investigated in an aqueous solution under NIR laser irradiation (808 nm), revealing that AuNRs@LA-PCL-R-POEGA maintain excellent photothermal conversion efficiency after modification. When compared with non-reduction responsive AuNRs@LA-PCL-CC-POEGA, the in vitro internalization of AuNRs@LA-PCL-SS-POEGA demonstrates that the reduction-responsive polymer could enhance the cellular uptake of nanoparticles measured by inductively coupled plasma mass spectrometry (ICP-MS) and TEM.