Synthesis of nanoporous gold nano-shell structure by simple plasma treatment

A nanoporous gold nanoparticle can have an advantage of plasmonic nanoporous structure, such as a large surface area and multiple hot-spots, together with a benefit of a small overall size in nanoscale. Its plasmonic property... [ view full abstract ]

A nanoporous gold nanoparticle can have an advantage of plasmonic nanoporous structure, such as a large surface area and multiple hot-spots, together with a benefit of a small overall size in nanoscale. Its plasmonic property can be determined by a size of an overall structure as well as its ligaments. Therefore, its size tunability can be critical for the desired optical property. Here, a simple way to synthesize a nanoporous gold nano-shell (NPGNS) structure having a near-IR localized surface plasmon resonance (LSPR) peak will be provided.

Citrate-stabilized gold nanoparticles (AuNP) with a size of 15 nm were mixed with positively functionalized polystyrene (PS) microspheres with a size of 1 μm in aqueous solution. AuNP were attached to the surface of microspheres by the electrostatic interaction. A monolayer of microspheres with attached AuNPs was formed on the glass substrate, and then it was treated by oxygen plasma. A plasma treatment reduces the size of PS microspheres, which makes inter-particle distance between attached AuNPs to be reduced. Finally, AuNPs contact each other on the microsphere surface to make a nanoporous gold frame. Further plasma treatment completely removes a polystyrene core part to leave only a NPGNS structure.

A fabricated NPGNS structure has a diameter of approximately 300 nm and ligaments of a size similar to used AuNPs. It shows a LSPR peak in the near-IR range. By using different sizes of AuNPs and microspheres, a diameter and a ligament size of a NPGNS can be controlled and the corresponding LSPR peak can be shifted quite well. Because a connection point between AuNPs in a NPGNS is not very smooth and there are many pores with rough ligaments, there can exist many hot-spots in a NPGNS. A simple post plasma treatment combined with the well-established chemical synthesis of colloid AuNP and polymer microsphere can provide a new synthetic route for nanoporous gold nanoparticle structure with a tunable LSPR peak in the near-IR range.