Yonghwi Kim

Grating-based surface plasmon resonance detection of core-shell nanoparticle mediated DNA hybridization

In this report, we have investigated enhanced surface plasmon resonance (SPR) detection of DNA hybridization using gold core - silica shell nanoparticles in localized plasmonic fields. The plasmonic fields were localized by periodic linear gratings. Experimental results measured for hybridization of 24-mer single-stranded DNA oligomers suggest that core-shell nanoparticles (CSNPs) on gratings of 400 nm period provide enhanced optical signatures by 36 times over conventional thin film-based SPR detection. CSNP-mediated DNA hybridization produced 3 times larger angular shift compared to gold nanoparticles of the same core size. We have also analyzed the effect of structural variation. The enhancement using CSNPs was associated with increased surface area and index contrast that is combined by improved plasmon coupling with localized fields on gratings. The combined approach for conjugated measurement of a biomolecular interaction on grating structures is expected to lower the limit of detection to the order of a few tens of fg/mm(2).

Self-aligned colocalization of 3D plasmonic nanogap arrays for ultra-sensitive surface plasmon resonance detection

We report extremely sensitive plasmonic detection that was performed label-free based on the colocalization of target DNA molecules and electromagnetic hot spots excited at 3D nanogap arrays. The colocalization was self-aligned by oblique evaporation of a dielectric mask over the 3D nanopatterns, which creates nanogaps for spatially selective target binding. The feasibility was experimentally confirmed by measuring hybridization of 24-mer single-stranded DNA oligonucleotides on triangular and circular 3D nanogap arrays. We were able to achieve significantly amplified optical signatures that lead to sensitivity enhancement in terms of detectable binding capacity in reference to conventional thin film-based surface plasmon resonance detection on the order of 1 fg/mm(2).

Nanogap-based dielectric-specific colocalization for highly sensitive surface plasmon resonance detection of biotin-streptavidin interactions

We have performed highly sensitive surface plasmon resonance (SPR) detection by colocalizing the evanescent near-fields and target molecular distribution. The colocalization is based on oblique metal evaporation to form nanogaps of a size under 100 nm without using electron-beam lithography. The concept was demonstrated by detecting siloxane-based biotin/streptavidin interactions. 50-nm nanogaps produced the largest amplification of optical signatures and two orders of magnitude enhancement of sensitivity over conventional thin film-based measurements. The enhancement is associated with efficient overlap of localized near-fields and target. Colocalized detection scheme is expected to provide clues to molecular sensitivity for SPR biosensing.

Ethylene Epoxidation Catalyzed by Ag Nanoparticles on Ag-LSX Zeolites formed by Pressure- and Temperature-Induced Auto-Reduction

Ag+ -Exchanged LSX (Ag-LSX: Ag96 Al96 Si96 O384 ⋅n H2 O), a large pore low silica analogue (Si/Al=1.0) of faujasite, was prepared and post-synthetically modified using pressure and temperature in the presence of various pore-penetrating fluids. Using high-resolution synchrotron X-ray powder and single crystal diffraction we derive structural models of the as-prepared and post-synthetically modified Ag-LSX materials. In the as-prepared Ag-LSX model, we located 96 silver cations and 245 H2 O molecules distributed over seven and five distinctive sites, respectively. At 1.4(1) GPa pressure and 150 °C in ethanol the number of silver cations within the pores of Ag-LSX is reduced by ca. 47.4 %, whereas the number of H2 O molecules is increased by ca. 40.8 %. The formation of zero-valent silver nanoparticles deposited on Ag-LSX crystallites depends on the fluid present during pressurization. Ag-nanoparticle-Ag-zeolite hybrid materials are recovered after pressure release and shown to have different chemical reactivity when used as catalysts for ethylene epoxidation.

Structuration under pressure: Spatial separation of inserted water during pressure-induced hydration in mesolite

Abstract In situ high-pressure single-crystal X-ray diffraction studies of mesolite, an aluminosilicate composed of stacks of Na+ -containing natrolite and Ca2+-containing scolecite layers in the ratio of 1:2, showed two discrete steps of pressure-induced hydration (PIH): first H2O molecules are inserted into the natrolite layers between ∼0.5 and ∼1.5 GPa and subsequently into the scolecite layers. During the PIH in the natrolite layers, the coordination environment of Na+ changes from six to seven, the same as that of Ca2+ in the scolecite layers. While the natrolite layers behave as in the mineral natrolite, the scolecite layers show a different behavior from the mineral scolecite by adopting the super-hydrated natrolite-type structure at higher pressure, as a larger distortion is not favorable in the 1:2 layered framework. This spatial separation of inserted H2O during PIH and the growing structural similarity of the two layers result in a weakening of k ≠ 3n reflections maintaining the 1:2 layer configuration. Our study of this unique behavior of mesolite provides a simple model of structuration under pressure, and the implications of our experimental findings are discussed.

Nanoplasmonic co-localization for highly sensitive surface plasmon resonance detection of molecular interactions

Surface plasmon resonance (SPR) has been applied to sensing biomolecular and drug interactions because it allows real-time monitoring and label-free detection. Traditional thin film based SPR biosensing suffers from moderate detection sensitivity. In this research, we investigate sensitivity enhancement by target colocalized SPR using various subwavelength nanostructures. The nanostructures were designed by calculating near-field distribution based on rigorous coupled-wave analysis. Experimentally, angled shadow evaporation was performed to fabricate the nanostructures for target colocalization and measured resonance shifts using angle scanning SPR. The feasibility was tested by measuring DNA hybridization. Experimental results confirm significantly enhanced detection sensitivity over traditional SPR techniques to be feasible. The results are expected to open a new approach to biomolecular detection based on SPR.