Targeted drug delivery has become important, attractive and challenging in biomedical science and applications. Anti-HER2 antibody-conjugated poly-L-lysine functionalized reduced graphene oxide (antiHER2-rGO-PLL) nanocarriers were prepared to efficiently deliver doxorubicin targeting at the nucleus of HER2 over-expressing cancer cells. The polycationic PLL was first covalently grafted to graphene oxide (GO) nanosheets followed by reduction to obtain rGO-PLL with high drug loading and good colloidal stability. The anti-HER2 antibodies were subsequently conjugated to the amino groups of PLL to achieve excellent cell uptake capability. Cellular uptake of anti-HER2-rGO-PLL into MCF7/HER2 cells is significantly higher than that of rGO-PLL due to the specific targeting of anti-HER2 to HER2 overexpressing breast cancer cells. Additionally the anti-HER2-rGO-PLL enables a fast accumulation of DOX inside the nucleus, its subcellular site of action. In vitro cytotoxicity measurements clearly reveal a seven fold improvement in the anticancer efficacy for anti-HER2-rGO-PLL/DOX in comparison to rGO-PLL/DOX. The enhanced anticancer efficacy could be ascribed to the different intracellular DOX distributions resulted from the different internalization routes that are energy-dependent macropinocytosis and energy-independent direct penetration by anti-HER2-rGO-PLL and rGO-PLL, respectively. The results demonstrate that anti-HER2 conjugated rGO-PLL developed is a promising vehicle for efficient nuclear delivery of chemotherapeutic agents to HER2 over-expressing tumours. (C) 2016 Elsevier Inc. All rights reserved.