Young-Jae Oh

Glass Nanopillar Arrays with Nanogap‐Rich Silver Nanoislands for Highly Intense Surface Enhanced Raman Scattering

The enhancement of surface enhanced Raman scattering (SERS) with nanogap-rich silver nanoislands surrounding glass nanopillars at wafer level is reported. High-density hot spots are generated by increasing the number of nanogap-rich nanoislands within a detection volume. The SERS substrate shows a high enhancement factor of over 10(7) with excellent signal uniformity (∼7.8%) and it enables the label-free detection of aqueous DNA base molecules at nanomolar level.

Terahertz photoconductive antenna with metal nanoislands

This work presents a nanoplasmonic photoconductive antenna (PCA) with metal nanoislands for enhancing terahertz (THz) pulse emission. The whole photoconductive area was fully covered with metal nanoislands by using thermal dewetting of thin metal film at relatively low temperature. The metal nanoislands serve as plasmonic nanoantennas to locally enhance the electric field of an ultrashort pulsed pump beam for higher photocarrier generation. The plasmon resonance of metal nanoislands was achieved at an excitation laser wavelength by changing the initial thickness of metal film. This nanoplasmonic PCA shows two times higher enhancement for THz pulse emission power than a conventional PCA. This work opens up a new opportunity for plasmon enhanced large-aperture THz photoconductive antennas.

Beyond the SERS: Raman Enhancement of Small Molecules Using Nanofluidic Channels with Localized Surface Plasmon Resonance

This work was supported by KRIBB (Korea Research Institute of Bioscience & Biotechnology) and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2010–0017693).

Reduction of nonspecific surface-particle interactions in optoelectronic tweezers

We demonstrate three-dimensional optoelectronic tweezers (3D OET) for the adsorption-free manipulation of microparticles. In typical OET, nonspecific interactions between the manipulated particles and the device surfaces, such as hydrophobic, Van der Waals, and electrostatic interactions, interfere with the effective microparticle manipulation. Here, by using the 3D OET device, which is composed of two photoconductive layers, we succeeded in three-dimensional focusing and manipulating polystyrene microbeads in a channel-less microenvironment without the particle adsorption. The 3D OET with the light-induced negative dielectrophoresis also shows a higher particle trapping efficiency and less particle adsorption rate than typical OET.

Biologically Inspired Biophotonic Surfaces with Self-Antireflection

with interstitial medium can be considered as single-layer ARS. Based on the Maxwell Garnett model, [ 5 ] the self-antirefl ection can be realized by using the spontaneous index modulation of ARS, i.e., medium-fi lled GNA with ∼0.5 FF, at both air-substrate ( n air and n sub ) and solution-substrate ( n sol and n sub ) interfaces, where a surrounding medium with an index ranging from 1.0 to 1.8 completely fi lls the interstitial gaps between the nanopillars. As a result, the effective index naturally meets an antirefl ection condition (Supporting Information Figure S2). The biophotonic surfaces exhibit diverse examples such as antirefl ective substrates with single-side GNA (SS-GNA) and double-side GNA (DS-GNA) or nanoplasmonic surfaces for highly sensitive fl uorescence sensing or surface enhanced Raman scattering (SERS) as well as high contrast imaging (Figure 1 c). A wafer-level nanofabrication of GNA with self-antirefl ection was done by using thin silver fi lm annealing and reactive ion etching (RIE) on a borosilicate glass substrate (n≈1.47). Thermal annealing transforms thin silver fi lm into size-controllable silver nanoislands, which serve as an etching mask for nanopillar formation during the RIE process. Note that the FF of GNA was precisely controlled with the density of Ag nanoislands depending on the initial thickness of thin silver fi lm. This method was applied on both sides of the glass wafer, where the top-side GNA can also be further functionalized as plasmonic nanostructures by evaporating thin silver or gold fi lm ( Figure 2 a). The GNA were etched down by a quarter-wavelength to suppress specular refl ection at air-substrate interface. The effective index for 0.5 ± 0.01 FF GNA with 130 nm in nanopillar height naturally varies from 1.22 to 1.64 for 1.0 to 1.8 in surrounding index, close to the geometric mean of substrate and surrounding indices, i.e., an ideal antirefl ection condition at the interface (Supporting Information Figure S2). In experiment, the maximum transmission through the SS-GNA is clearly shown at 130 nm in nanopillar height, which improves transmission by ∼3.8 percent at air-substrate interface, compared with the fl at surface (Figure 2 b). The DS-GNA remarkably double the transmission improvement, which shows transmittance over 99 percent. In particular, the size distribution of GNA offers broadband antirefl ection in a visible range from 485 nm to 655 nm. The optical images show specular refl ections from fl at surfaces, SS-GNA, and DS-GNA on 4-inch glass wafers, respectively (Figure 2 b). The DS-GNA provides a clear image of the letters whereas those behind the fl at surfaces are visually unreadable due to the substantial specular refl ection. DOI: 10.1002/smll.201303876 Biophotonic Surfaces

Electrokinetic preconcentration of small molecules within volumetric electromagnetic hotspots in surface enhanced Raman scattering.

The on-chip integration of a preconcentration chamber for ultrasensitive surface-enhanced Raman scattering (SERS) is shown. Small molecules are preconcentrated using 3D volumetric electromagnetic hotspots. The experimental results demonstrate an enhancement of the SERS signals of over two orders of magnitude, which allows the fingerprinting of neurotransmitter molecules at the nanomolar level and furthers the selective detection of oppositely charged molecules. This on-chip integration will provide new directions for ultrasensitive SERS applications.

Nanoplasmonic biopatch for in vivo surface enhanced raman spectroscopy

Surfaced enhanced Raman scattering (SERS) has been extensively exploited for label-free and non-destructive biochemical detections. Recently diverse SERS substrates have been reported to improve sensitivity of SERS. However, the current platforms still have technical limitation for in vivo applications. Here, we report a nanoplasmonic biopatch of plasmonic nanoparticles physically embedded in highly biocompatible and Raman inactive agarose hydrogel. Molecular diffusion of small molecules such as neurotransmitter through nanoplasmonic biopatch was quantitatively visualized without labeling by using real-time microscopic SERS. In particular, the nano/micro porous structures within agarose hydrogel allow the SERS detection of macromolecules such as amyloid fibrils. This soft SERS platform opens up new opportunities for in vivo SERS applications.

Engineering Hot Spots on Plasmonic Nanopillar Arrays for SERS: A Review

Nanopillar arrays have provided unique optical properties due to their multi-dimensional architectures with large surface area. Recently, surface enhanced Raman spectroscopy (SERS) has taken full benefits of nanopillar arrays for highly sensitive chemical and biosensing. This article gives an overview of hot spot engineering on nanopillar arrays for SERS. Nanopillar arrays are very beneficial for providing high density plasmonic nanostructures, which induce the oscillation of free electrons to create highly localized electric fields, i.e., electromagnetic hot spots, for highly intense SERS detection. The diverse methods have successfully demonstrated the nanofabrication of hotspot-rich nanopillar arrays on silicon or glass substrates. Tailoring hot spots enables ultrasensitive detection of biomolecules at low concentrations and even allows single-molecule level detections. This review overviews the nanofabrication methods for nanopillar array construction, the design strategies for electromagnetic hot spot generation on nanopillar arrays, and their SERS applications.

High intensity plasmon enhanced photoacoustic generation from polymeric absorber with 3D plasmonic nanostructures

Photoacoustic effect has been emerging as the ultrasound generation mechanism to overcome frequency limits of ultrasound generation from piezoelectric material. This work presents the effect of the plasmonic nanostructures in photoacoustic generation. The plasmonic nanoparticles are implemented to enhance the photoacoustic generation in polymeric optical absorber. The plasmonic structures are fabricated in three dimensional formation to give volumetric electromagnetic field enhancement.

A Real-time Interactive Control System for Optical Manipulation of Microparticles using Liquid Crystal Display

This paper describes a control system for realtime interactive manipulation of microparticles using optoelectronic tweezers (OET) on a liquid crystal display. The OET is a powerful tool for trapping and manipulation of microparticles via image-induced dielectrophoresis (DEP). We develop a new control system for the real-time interactive manipulation of microparticles using OET. Our control system is successfully demonstrated to the real-time interactive manipulation of 75 mum polystyrene beads using a liquid crystal display. The velocity of 75 mum polystyrene particle is measured to be 25 mum/s. The microparticles trapped by a virtual DEP cage are formed a single particle array within only a few minutes. This interactive OET system can be utilized to several biological and medical applications including cell patterning and bead-based protein assays.