Bio-inspired NIR responsive Au-pDA@pDA sandwich nanostructures with excellent photo-thermal performance and stability

Recently, bottom-up assembly of plasmonic core-shell nanostructures have attracted the great attention of scientists for effective/efficient photothermal applications. In this study, a novel systematic layer-by-layer strategy was used to fabricate Au-pDA(core)@pDA(shell) sandwich morphologies based on three main steps: 1) the reactive functional groups onto pDA demonstrated zwitterionicity behavior due to the protonation of amino groups at low pH value and the change in the surface charge provided electrostatic immobilization of citrate capped gold nanoparticle (Au NP) colloidal solution. 2) A fixation process was carried out to eliminate the removal of Au NPs using an electrodeless chemical plating technique. 3) Finally, a thin layer (⁓ 5 nm) of polydopamine (pDA) was coated onto the Au-pDA nanostructures which remarkably enhanced the photothermal performance of nanostructures with good NIR responsivity. No severe agglomeration and good dispersion stability of the nanostructures in aqueous medium provided sensible heating curves that reached up to 41.1, 48.2, and 58.4 °C for Au-pDA@pDA aqueous dispersions having 0.025, 0.05, and 0.1 mg/mL concentration, respectively, after 10 min of irradiation at 1.5 W/cm2 power density. Furthermore, efficient plasmon oscillation, completely wrapping of pDA shell layer, reasonable reusability/stability, good cytocompatibility, as well as good NIR responsivity in Au-pDA@pDA nanostructures led to a noteworthy power conversion efficiency (PCE = 55.2 %) which is higher than that of pDA colloids.