Multibranched gold nanoparticles coated with serum proteins fit for photothermal tumor ablation

Photothermal tumor ablation might be carried out with multibranched gold nanoparticles (MBAuNPs) having maximum absorbance (Amax) in the infrared region and functionalized with ligands that would bind them to the target tumor markers. However, in nanomedicine applications, the nanostructures must reach their target tissues to be effective, but the corona of serum proteins they instantaneously acquire when administered by intravenous injection may affect their activity; for this reason, we decided to analyze the effect that exposing MBAuNPs to bovine serum albumin (BSA) and human serum (HS) have on their protein corona and physical properties. The synthesized spherical Au seeds stoichiometrically generate piñata-like MBAuNPs of 8–20 peaks potentially useful for photothermal tumor ablation since they induce hyperthermia of more than 4 °C in phantom gels mimicking the skin irradiated with an 808 nm laser at 0.75 W/cm2. The calculated surface area of MBAuNPs ranges from 24 984 nm2 to 40 669 nm2, depending on the number of peaks we use for modeling the NPs. When MBAuNPs are exposed to BSA, they acquire a protein corona with an internal “hard” portion composed by one or two layers of BSA containing ∼1000–4000 molecules covalently bound to their surface, and an external “soft” portion formed by agglomerated BSA molecules linked by non-covalent bonds. Functionalization with BSA decreases the tendency of MBAuNPs to agglomerate and increases their size dispersion. MBAuNPs and MBAuNPs–BSA exposed to HS bind HS albumin and other HS proteins ranging from 25 kDa to 180 kDa that increase their hydrodynamic diameter and decrease their stability. We conclude that MBAuNPs exposed to serum albumin and HS instantaneously acquire a hard and soft protein corona that may affect prior or subsequent functionalization aiming to direct them to specific cell or tissue targets.