Over the past 10 years, polyvalent DNA-gold nanoparticle (DNA-GNP) conjugate has been demonstrated as an efficient, universal nanocarrier for drug and gene delivery with high uptake by over 50 different types of primary and cancer cell lines. A barrier limiting its in vivo effectiveness is limited resistance to nuclease degradation and non-specific interaction with blood serum contents. Herein we show that terminal PEGylation of the complementary DNA strand hybridized to a polyvalent DNA-GNP conjugate can eliminate non-specific adsorption of serum proteins and greatly increases its resistance against DNase I based degradation. The PEGylated DNA-GNP conjugate still retains high cell uptake property, making it an attractive intracellular delivery nanocarrier for DNA binding reagents. We show it can be used for successful intracellular delivery of doxorubicin, a widely used clinical cancer chemotherapeutic drug. Moreover, it can be used for efficient delivery of some cell-membrane impermeable reagents such as propidium iodide (a DNA intercalating fluorescent dye currently limited to the use of staining dead cells only) and a di-ruthenium complex (a DNA groove binder), for successful staining of live cells.