Wonju Lee

Vision-Based Vehicle Detection System With Consideration of the Detecting Location

In this paper, we propose a vision-based vehicle detection system. We use a method composed of a hypothesis generation (HG) step and a hypothesis verification (HV) step, following the general approach to vision-based vehicle detection systems. In the HG step, the system extracts hypotheses using shadow regions that appear under vehicles. In the HV step, the system classifies feature vectors extracted from hypotheses to determine whether those hypotheses are vehicles. Along with the histogram of oriented gradients (HOG), we propose and implement a new type of feature vector, i.e., HOG symmetry vectors, in this paper. We also propose a new classification method that uses data importance in the HV step. The data importance value is based on the locations of hypotheses to prioritize hypotheses that have greater risks of accident. Experimental results show the strong performance of our proposed system.

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).

Enhanced detection of virus particles by nanoisland-based localized surface plasmon resonance

In this paper, we investigate localized surface plasmon resonance (SPR) detection based on nanoislands. Theoretical calculation performed with rigorous coupled-wave analysis and analytical transfer matrix method using effective medium theory suggests improvement on nanoislands in the limit of detection and sensitivity over conventional thin film-based SPR detection. Experimental results obtained with non-specific detection of ambient adenovirus confirm the improvement by more than one order of magnitude increase in the limit of detection. The enhancement achieved with nanoislands was explored in connection with efficient overlap between target and near-field distribution produced by nanoislands.

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.

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.

Field-matter integral overlap to estimate the sensitivity of surface plasmon resonance biosensors

We have analyzed the effectiveness of field-matter integral overlap between target index distribution and local near-fields to assess detection sensitivity of surface plasmon resonance (SPR) biosensors. The correlation of the overlap with sensitivity was clear. An overlap integral defined with lateral electric field intensity produced the highest correlation due to tangential continuity across a boundary. Among the three detection scenarios considered, the correlation for localized SPR sensing was slightly lower than that of thin film-based detection and improved with an increased fill factor in the structure. The results will be useful to maximize the optical signature created by target interactions and to produce highest sensitivity of SPR detection to variations when target or field distribution is not uniform.

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.

Electromagnetic Near-Field Nanoantennas for Subdiffraction-Limited Surface Plasmon-Enhanced Light Microscopy

We investigate electromagnetically amplified local fields or hot spots created by surface nanoantennas for subdiffraction-limited plasmon-enhanced microscopy under total internal reflection at angled light incidence. Different shapes of near-field hot spots were calculated by varying geometrical parameters of nanoantenna structures. An inverse relationship between full-width-at-half-maximum (FWHM) and ellipticity of a hot spot was found. Among the three patterns considered, square nanoantenna patterns provided the smallest FWHM ellipticity product with a spot size of approximately 53 × 110 nm2 due to efficient plasmon localization. The size of a nanopattern affects FWHM significantly by producing a smaller hot spot if the size decreases. The effects of other parameters are also discussed.