Poly(-caprolactone)-b-poly(L-lysine) (PCL-b-PLys) that was synthesized by ring-opening polymerization

self-assembled into spherical micelles with PCL core and PLys shell in aqueous solution

and the intensity-averaged diameter was about 287 nm.Using the micelle as template

HAuCl4 was reduced by HCHO in basic solution (i.e.

pH 10) and with ultrasonication for 4 min

the coordination of the primary amines of PLys with gold resulted in the growth and accumulation of gold in the micellar shell

and finally led to the formation of the micelle@gold nanoshell.To the best of our knowledge

the micelle@gold nanoshell was prepared for the first time

and then fully characterized by UV-Vis

XPS

WXRD

TEM

DLS

TGA

photothermal conversion and in vitro tumor cell-killing experiment.The average diameter of the micelle@gold nanoshell was about 380 nm

which was about 30%~40% bigger than the original micelle

and the mass fraction of gold accounted for about 2/3.Moreover

it showed strong surface plasmon resonance absorption in the near infrared region

and gave a high photothermal conversion efficiency of 63%.After near-infrared laser irradiation for 10 min

about 60% of Hela cells were killed

while the gold nanoshells had low cytotoxicity.Collectively

the micelle@gold nanoshells demonstrated good biocompatibility

and could efficiently kill tumor cells in vitro

making them potential for photothermal tumor therapy.