Kyujung Kim

Nanowire-based enhancement of localized surface plasmon resonance for highly sensitive detection: a theoretical study

A nanowire-based localized surface plasmon resonance (LSPR) biosensor has been investigated to evaluate the impact of design parameters of nanowires on the excitation of localized surface plasmons (LSPs) and the sensitivity enhancement of a LSPR biosensor. The results based on rigorous coupled wave analysis and finite difference time domain method indicate that significant sensitivity increase is associated with LSP excitation mediated by nanowires and that resonant coupling of LSPs through a nanogroove achieves larger field enhancement and sensitivity improvement than LSP excitation in a single nanowire. A specific optimization provided a nanowire-based structure with the sensitivity increase by more than 23 times as well as good linear detection properties.

Target-Localized Nanograting-Based Surface Plasmon Resonance Detection toward Label-free Molecular Biosensing

We explore the sensitivity enhancement of label-free detection based on localized surface plasmon resonance using surface-relief nanograting structures. A nanograting structure was modeled, so that target molecular interactions are localized in hot spots of the near fields. The nanograting structure was optimized numerically for the highest enhancement of sensitivity with hybridization between complementary strands of DNA as the model target interaction. Experimentally, angled evaporation was performed to fabricate the target-localized nanograting samples. Measured data confirm the numerical results that sensitivity enhancement by an order of magnitude may be feasible on a per-unit-volume basis through target localization.

Localized surface plasmon resonance detection of layered biointeractions on metallic subwavelength nanogratings

Enhanced detection of multiple targets such as self-assembled monolayer (SAM) formation, DNA hybridization, and ethanol ambient changes was explored using localized surface plasmon resonance (LSPR) excited by metallic surface nanogratings. The sensitivity enhancement depends on the target as well as the nanostructure with a maximum at 242% over a conventional structure when detecting an 11-mercaptoundecanoic acid SAM with an LSPR structure of 200 nm period. The measured enhancement shows smaller target-dependent variance when detecting various layered biointeractions, while structure-dependent variance was much larger. The result suggests the feasibility of the efficient detection of multiple biointeractions at enhanced sensitivity and extends the applicability of a nanostructured LSPR biosensor for diverse biomolecular events.

Surface-enhanced plasmon resonance detection of nanoparticle-conjugated DNA hybridization.

We have investigated surface-enhanced plasmon resonance detection of DNA hybridization. Surface enhancement was based on the excitation of localized surface plasmon using subwavelength nanogratings, at a 300 nm period, coated with 24-mer ssDNA oligonucleotide, while optical signatures of DNA were amplified at the same time by gold nanoparticles conjugated with complementary ssDNA strands. When using nanoparticles of different sizes, maximum sensitivity enhancement, of more than 18 times, was obtained with nanoparticles of 20 nm diameter. This enhancement is mainly due to nanoparticle-associated signal amplification. Additional surface enhancement boosted the detection sensitivity by 57%. We have also confirmed the sensitivity enhancement to be linearly related to nanoparticle volume.

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.

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.

Microfluidic assay-based optical measurement techniques for cell analysis: A review of recent progress.

Since the early 2000s, microfluidic cell culture systems have attracted significant attention as a promising alternative to conventional cell culture methods and the importance of designing an efficient detection system to analyze cell behavior on a chip in real time is raised. For this reason, various measurement techniques for microfluidic devices have been developed with the development of microfluidic assays for high-throughput screening and mimicking of in vivo conditions. In this review, we discuss optical measurement techniques for microfluidic assays. First of all, the recent development of fluorescence- and absorbance-based optical measurement systems is described. Next, advanced optical detection systems are introduced with respect to three emphases: 1) optimization for long-term, real-time, and in situ measurements; 2) performance improvements; and 3) multimodal analysis conjugations. Moreover, we explore presents future prospects for the establishment of optical detection systems following the development of complex, multi-dimensional microfluidic cell culture assays to mimic in vivo tissue, organ, and human systems.

Nanograting-based plasmon enhancement for total internal reflection fluorescence microscopy of live cells

We investigated evanescent field enhancement based on subwavelength nanogratings for improved sensitivity in total internal reflection microscopy of live cells. The field enhancement is associated with subwavelength-grating-coupled plasmon excitation. An optimum sample employed a silver grating on a silver film and an SF10 glass substrate. Field intensity was enhanced by approximately 90% when measured by fluorescent excitation of microbeads relative to that on a bare prism as a control, which is in good agreement with numerical results. The subwavelength-grating-mediated field enhancement was also applied to live cell imaging of quantum dots, which confirmed the sensitivity enhancement qualitatively.

A Localized Surface Plasmon Resonance Sensor Using Double-Metal-Complex Nanostructures and a Review of Recent Approaches

From active developments and applications of various devices to acquire outside and inside information and to operate based on feedback from that information, the sensor market is growing rapidly. In accordance to this trend, the surface plasmon resonance (SPR) sensor, an optical sensor, has been actively developed for high-sensitivity real-time detection. In this study, the fundamentals of SPR sensors and recent approaches for enhancing sensing performance are reported. In the section on the fundamentals of SPR sensors, a brief description of surface plasmon phenomena, SPR, SPR-based sensing applications, and several configuration types of SPR sensors are introduced. In addition, advanced nanotechnology- and nanofabrication-based techniques for improving the sensing performance of SPR sensors are proposed: (1) localized SPR (LSPR) using nanostructures or nanoparticles; (2) long-range SPR (LRSPR); and (3) double-metal-layer SPR sensors for additional performance improvements. Consequently, a high-sensitivity, high-biocompatibility SPR sensor method is suggested. Moreover, we briefly describe issues (miniaturization and communication technology integration) for future SPR sensors.