Limiting the protein corona: A successful strategy for in vivo active targeting of anti-HER2 nanobody-functionalized nanostars

Gold nanoparticles hold great promise as anti-cancer theranostic agents against cancer by actively tar- geting the tumor cells. As this potential has been supported numerously during in vitro experiments; the effective application is hampered by our limited understanding and control of the interactions within complex in vivo biological systems. When these nanoparticles are exposed to a biological environment; their surfaces become covered with proteins and biomolecules; referred to as the protein corona; reducing the active targeting capabilities.We demonstrate a chemical strategy to overcome this issue by reducing the protein corona's thickness by blocking the active groups of the self-assembled monolayer on gold nanostars. An optimal blocking agent; 2-mercapto ethanol; has been selected based on charge and length of the carbon chain. By using a nanobody as a biological ligand of the human epidermal growth factor 2 receptor (HER2); the active targeting is demonstrated in vitro and in vivo in an experi- mental tumor model by using darkfield microscopy and photoacoustic imaging. In this study; we have established gold nanostars as a conceivable theranostic agent with a specificity for HER2-positive tumors.