Youngjin Oh

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).

Colocalization of gold nanoparticle-conjugated DNA hybridization for enhanced surface plasmon detection using nanograting antennas

We have investigated enhanced surface plasmon resonance detection through colocalization of gold nanoparticle (GNP)-conjugated target molecules and near-fields established by nanograting-based antennas. The target colocalization was implemented by angled dielectric thin-film deposition on the nanograting structure. The concept was tested by detecting DNA hybridization and shows that the colocalization produces an additional 60%-80% increase of resonance shifts. The colocalization involves a much smaller number of target molecules, so that the measured enhancement per molecule by the colocalization of GNP-conjugated DNA oligomers was estimated to be by more than 2 orders of magnitude relative to that of thin-film-based conventional detection.

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).

Surface-enhanced localized surface plasmon resonance biosensing of avian influenza DNA hybridization using subwavelength metallic nanoarrays

We demonstrated enhanced localized surface plasmon resonance (SPR) biosensing based on subwavelength gold nanoarrays built on a thin gold film. Arrays of nanogratings (1D) and nanoholes (2D) with a period of 200 nm were fabricated by electron-beam lithography and used for the detection of avian influenza DNA hybridization. Experimental results showed that both nanoarrays provided significant sensitivity improvement and, especially, 1D nanogratings exhibited higher SPR signal amplification compared with 2D nanohole arrays. The sensitivity enhancement is associated with changes in surface-limited reaction area and strong interactions between bound molecules and localized plasmon fields. Our approach is expected to improve both the sensitivity and sensing resolution and can be applicable to label-free detection of DNA without amplification by polymerase chain reaction.

Plasmonics-based spatially activated light microscopy for super-resolution imaging of molecular fluorescence

In this Letter, we explore plasmonics-based spatially activated light microscopy (PSALM) for sub-diffraction-limited imaging of biomolecules. PSALM is based on the spatially switched activation of local amplified electromagnetic hot spots under multiple light incidence conditions. The hot spots are associated with surface plasmons that are excited and localized by surface nanostructures. The feasibility of the concept was demonstrated by imaging fluorescent nanobeads on a two-dimensional gold nanograting of a 100-nm-wide grating ridge, the size of which is the measure of the imaging resolution. The result confirms the performance of PSALM for imaging nanobeads at a resolution below the conventional diffraction limit.

Surface plasmon-enhanced nanoscopy of intracellular cytoskeletal actin filaments using random nanodot arrays

The feasibility of super-resolution microscopy has been investigated based on random localization of surface plasmon using blocked random nanodot arrays. The resolution is mainly determined by the size of localized fields in the range of 100-150 nm. The concept was validated by imaging FITC-conjugated phalloidin that binds to cellular actin filaments. The experimental results confirm improved resolution in reconstructed images. Effect of far-field registration on image reconstruction was also analyzed. Correlation between reconstructed images was maintained to be above 81% after registration. Nanodot arrays are synthesized by temperature-annealing without sophisticated lithography and thus can be mass-produced in an extremely large substrate. The results suggest a super-resolution imaging technique that can be accessible and available in large amounts.

Three-Dimensional Superlocalization Imaging of Gliding Mycoplasma mobile by Extraordinary Light Transmission through Arrayed Nanoholes.

In this paper, we describe super-resolved sampling of live bacteria based on extraordinary optical transmission (EOT) of light. EOT is produced by surface plasmon confinement and coupling with nanostructures. Bacterial fluorescence is excited by the localized fields for subdiffraction-limited sampling. The concept was applied to elucidating bacterial dynamics of gliding Mycoplasma mobile (M. mobile). The results analyzed with multiple M. mobile bacteria show individual characters and reveal that M. mobile undergoes a significant axial variation at 94 nm. The sampling error of the method is estimated to be much smaller than 1/10 of the diffraction limit both in the lateral and depth axis. The method provides a powerful tool for investigation of biomolecular dynamics at subwavelength precision.

Plasmon-enhanced total-internal-reflection fluorescence by momentum-mismatched surface nanostructures

We investigate optimum plasmon-enhanced total-internal-reflection fluorescence imaging by metallic thin films and nanostructures. The enhancement is based on the mismatch between the conditions of plasmon resonance and maximal near-field intensity. We have calculated plasmon-associated near-field and far-field characteristics using rigorous coupled-wave analysis. Near-field intensity was experimentally measured with fluorescent beads on silver thin films, nanogratings, and nanoislands. The results for nanostructure-based plasmon excitation confirm that momentum mismatching when exciting plasmons can increase the consequent emission of fluorescence substantially. The improvement can be critical depending on the specific structure.

T-jet: a novel thermal inkjet printhead with monolithically fabricated nozzle plate on SOI wafer

A novel thermal inkjet printhead with monolithically fabricated nickel nozzle plate on SOI wafer has been proposed for the first time. A chamber and a restrictor are implemented on the 40 /spl mu/m thick top-silicon layer, and a nozzle plate covering heater layers are monolithically fabricated on them. Unlike the general back-shooters, the inkjet printhead reported here is a kind of back-shooter, which has a chamber and a restrictor with arbitrary shape by utilizing the silicon dioxide etch-stop layers in the bottom and sidewalls of chamber. Moreover, nozzle plating mold process, followed by placing the chamber underneath the heater layer, is performed on a planar surface, resulting in more uniform and reliable control of nozzle size. The new design was applied for monochrome inkjet printhead, which has 56 nozzles in 2 columns with real 600NPI(nozzle per inch), and showed good performances such as a drop velocity of 12 m/s, a drop volume of 30 pl, and a maximum firing frequency of 12 kHz for single nozzle ejection. From nozzle by nozzle inspection, we observed the uniformity variation of less than 4% in drop speed as well as drop volume. The monolithic fabrication process resulted in a good uniformity and is expected to have superior manufacturing yield to the nozzle assembly process.

Molecular overlap with optical near-fields based on plasmonic nanolithography for ultrasensitive label-free detection by light-matter colocalization

In this work, we investigate the detection sensitivity of surface plasmon resonance (SPR) biosensors by engineering spatial distribution of electromagnetic near-fields for colocalization with molecular distribution. The light-matter colocalization was based on plasmonic nanolithography, the concept of which was confirmed by detecting streptavidin biotin interactions on triangular nanoaperture arrays after the structure of the aperture arrays was optimized for colocalization efficiency. The colocalization was shown to amplify optical signature significantly and thereby to achieve detection on the order of 100 streptavidin molecules with a binding capacity below 1fg/mm2, an enhancement by more than three orders of magnitude over conventional SPR detection.