Soon Joon Yoon

Experimental study of sensitivity enhancement in surface plasmon resonance biosensors by use of periodic metallic nanowires

We have experimentally confirmed sensitivity enhancement of a nanowire-based surface plasmon resonance (SPR) sensor structure. Gold nanowires with periods of 200 and 500 nm were fabricated, respectively, by electron-beam and interference lithography on a gold/SF10 substrate. Sensitivity enhancement was measured to be 44% compared with a conventional thin-film-based SPR structure for nanowires of 200 nm period and 31% for 500 nm when evaluated using ethanol at a varied concentration. This result is consistent with numerical data. Surface roughness is responsible for sensitivity reduction by more than 10%. More significant sensitivity improvement can be achieved by inducing strong localized plasmon coupling with finer nanowires.

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.

Sensitivity Enhancement of Surface Plasmon Resonance Imaging Using Periodic Metallic Nanowires

A nanowire-mediated surface plasmon resonance (SPR) imaging is numerically investigated for enhanced sensitivity. The results calculated by rigorous coupled-wave analysis present that interplays between localized surface plasmons and surface plasmon polaritons contribute to sensitivity enhancement. Compared to conventional thin film-based SPR imaging measurement, an optimal nanowire structure can provide sensitivity enhancement by 3.44 times as well as highly linear detection property for quantification of surface reactions of interests. This paper demonstrates the potential and limitation for a highly sensitive, label-free, and real-time SPR imaging sensor based on periodic metallic nanowires.

Target dependence of the sensitivity in periodic nanowire-based localized surface plasmon resonance biosensors

We investigate the target dependence of the sensitivity in a localized surface plasmon resonance (LSPR) biosensor and compare it with that of a conventional thin-film-based plasmon resonance structure. An LSPR biosensor was modeled as subwavelength periodic nanowires on a metal/dielectric substrate and targets either as bulk refractive index changes or as a biomolecular interaction that forms a monolayer. The results found that significant target-dependent variation arises in sensitivity and sensitivity enhancement by LSPR. The variation is attributed to the nonlinearity in the plasmon dispersion relation as well as the effective permittivity due to strong LSPR signals. The target dependence suggests that an LSPR structure be designed based on estimated index changes induced by target interactions. Associated broadening of resonance width can be controlled by way of profile engineering, which is discussed in connection with experimental data.

Sensitivity analysis of a nanowire-based surface plasmon resonance biosensor in the presence of surface roughness

We have investigated the effect of surface roughness on the sensitivity of conventional and nanowire-based surface plasmon resonance (SPR) biosensors. The theoretical research was conducted using rigorous coupled-wave analysis with Gaussian surface profiles of gold films determined by atomic force microscopy. The results suggest that, when surface roughness ranges near 1 nm, the sensitivity of a conventional SPR system is not significantly affected regardless of the correlation length. For a nanowire-based SPR biosensor, however, we have found that the sensitivity degrades substantially with decreasing correlation length. In particular, at a correlation length smaller than 100 nm, a random rough surface may induce destructive coupling between excited localized surface plasmons, which can lead to prominent reduction of sensitivity enhancement.

Thin-film-based field penetration engineering for surface plasmon resonance biosensing

Penetration depth defines the measurable range in evanescent-wave-based sensing techniques such as surface plasmon resonance (SPR). We investigate penetration depth variation implemented with dielectric layers in a SPR sensing structure. The results show that the penetration depth can be controlled to increase or decrease depending on a specific configuration. Effective medium theory was introduced to describe the field penetration in dielectric multilayer designs. Comparison was made with the field penetration of a localized SPR structure based on periodic nanowires. The penetration depth variation in response to environmental changes was also explored.

Effective medium-based analysis of nanowire-mediated localized surface plasmon resonance

We explore a nanowire-based localized surface plasmon resonance (LSPR) sensor system using an effective medium for the nanowire layer. The effective medium is obtained based on the far-field characteristics of the nanowire-based LSPR system. Near-field properties as well as the sensitivity performance of the effective medium-based SPR structure are compared to exact results of the nanowire-based LSPR system. The results indicate that an effective medium can reproduce the far-field and near-field characteristics of nanowires fairly well, while it represents the nanowire-based LSPR on a limited basis in terms of sensitivity characteristics, particularly when the LSPR is significantly enhanced.

Effect of surface roughness on the extinction-based localized surface plasmon resonance biosensors

We investigated the effect of surface roughness on the sensor performance of extinction-based localized surface plasmon resonance (LSPR) biosensors. The sensor measures resonance wavelength shifts in transmittance caused by biomolecular interactions that are amplified by periodic nanostructures. The numerical computation was conducted using rigorous coupled-wave analysis with Gaussian random surface profiles. The results suggest that, when a surface has a roughness smaller than 2 nm in height deviation, the sensitivity of a LSPR biosensor is not significantly influenced regardless of correlation length (CL). However, we found that the extinction peak amplitude and curve width are affected substantially by a decrease in CL. At a less than 100 nm CL, surface roughness can induce interference between localized surface plasmons excited by the surface and nanowires, which can lead to major degradation of sensor performance.

Influence of surface roughness on the polarimetric characteristics of a wire-grid grating polarizer

The influence of surface roughness on the polarimetric performance of a wire-grid polarizer (WGP) is numerically investigated using rigorous coupled-wave analysis over 100 random surface realizations. Surface roughness is modeled with a Gaussian surface, represented by two independent parameters: surface height deviation and correlation length of a profile. The results show that WGP performance can suffer from significant degradation as well as increased deviation with surface roughness, although the extent varies with specific parameters. The influence of roughness was also examined with respect to grating period as a WGP parameter and incident light properties, such as wavelength and angle.

Performance analysis of extinction-based localized surface plasmon resonance biosensors in the presence of surface roughness

We investigated the effect of rough surface on the performance of extinction-based localized surface plasmon resonance (LSPR) biosensors. The sensor measures resonance wavelength shifts in transmittance due to biomolecular interactions amplified by periodic nanostructures. The numerical calculation was conducted using rigorous coupled-wave analysis with Gaussian random profiles. The results suggest that, when a surface has a roughness smaller than 2 nm, the sensitivity of an LSPR biosensor is not significantly affected regardless of correlation length (CL). However, we found that extinction peak amplitude and curve width are affected substantially with a decrease in CL. At CL less than 100 nm, surface roughness may induce interference between localized surface plasmons excited by the surface and nanowires, which can lead to significant degradation of sensor performance.