When the light is scattered by the asymmetric plasmonic nanoparticle, its polarization can be partially rotated from original polarization, which is called depolarized light scattering (dPLS). Since dPLS is very sensitive to the nanoparticle asymmetry, it can be a very sensitive technique in monitoring early aggregation of spherical gold nanoparticles (AuNPs) in the solution compared to the traditional optical monitoring methods such as the extinction or the polarized light scattering intensity. Furthermore, since the asymmetric plasmonic nanoparticle can induce much greater dPLS than the asymmetric dielectric particle having similar aspect ratio due to its plasmonic resonance at two wavelengths, the dPLS can be very useful for selectively monitoring AuNP aggregation among other dielectric particles by suppressing the background signal contributed from dielectric particles. All these characteristics of dPLS can suggest the possibility of its application in the fields of highly sensitive bio/chemical sensing.

A Nanoporous gold (NPG) structure consists of many interconnected continuous nano-sized gold ligaments and pores. Due to its large surface area with many low-coordinated gold atoms and multiple hot-spots for electromagnetic field enhancement that can be induced by its localized surface plasmon resonance (LSPR), it has been intensively studied for various optical and catalytic applications. Especially, NPG nanoparticles having nanoscale overall sizes can have additional merits in light-coupling efficiency compared to the NPG film. 

We develop a unique fabrication technique for the hollow porous gold nanoshell (HPAuNS) structure based on the plasma etching of polymer colloid templates. This method can provide high structural tunability of HPAuNSs such as the oversize, the ligament & pore sizes, and the sharpness of ligament junctions. By tuning the structure of HPAuNSs, we can greatly change their LSPR property for the specific application. Furthermore, our method is much more environmental-friendly than the traditional dealloying method using corrosive chemicals. We are studying on the applications of HPAuNSs in the fields of the surface-enhanced sensing (ex, Surface-enhanced Raman scattering, SERS) as well as the plasmonic catalysis. 

Semiconductor-based photocatalysts can absorb photons to generate electron-hole pairs that can be used for oxidation or reduction of materials on the photocatalyst surface. Among others, TiO2 has been the most studied material owing to its abundance, low price, non-toxicity, high chemical stability, and high photoactivity. However, one significant drawback of TiO2 is its large bandgap energy, owing to which it can absorb only UV light, a very minor portion of the solar spectrum. 

A Plasmonic photocatalyst is based on a combination of TiO2 and plasmonic metal nanoparticles which can strongly absorb visible light due to the LSPR (Localized Surface Plasmon Resonance). Due to highly energetic electrons (hot electrons) induced by LSPR, plasmonic photocatalysts can catalyze oxidation and reduction reaction in response to the visible light as well as the UV light. We work on developing the efficient plasmonic photocatalyst based on the metal/oxide hybrid nanoparticles.

A film of colloid particles having a size from sub-micron to micron has been widely used as the template for the fabrication of unique metal nanostructures. However, the traditional brigh-field microscopic imaging technique have a difficulty in providing sufficient contrast for defects and domain structures of the film, especially for the sub-micron size colloid particles. We try to develop various ways to enhance contrast without using labels such as fluorophores for imaging of a colloidal film, compared to the traditional bright-field imaging.