Understanding the Collective Optical Properties of Complex Plasmonic Vesicles

Abstract Vesicular assembly of small plasmonic nanoparticles, or plasmonic vesicle, is a promising multifunctional theranostic platform for photothermal therapy, near infrared (NIR) light‐responsive drug release, and rapid clearance of small inorganic particles from the body. Wide ranges of optical properties are reported including characteristic absorption peak in the visible or NIR ranges, or broadband absorption. It is unclear how the complex interaction among a large number of small gold nanoparticles contribute to the collective optical property of a plasmonic vesicle. In this study, the collective optical properties of plasmonic vesicles are examined and four characteristic regimes, namely the isolated nanoparticle regime, Coulomb interaction regime, black gold regime, and nanoshell regime, are revealed. Small plasmonic nanoparticles need to be very close or weakly overlap to give a broadband absorption (i.e., black gold regime) or form a NIR plasmon peak. Furthermore, smaller gold nanoparticle or larger core size leads to higher NIR peak shift and photothermal conversion efficiency. It is anticipated that this study provides design guidelines and thus have a significant impact on further design and development of complex plasmonic nanostructures and vesicles for biomedical applications.