Numerical study on an application of subwavelength dielectric gratings for high-sensitivity plasmonic detection

Biosensors based on Bloch surface waves in one-dimensional photonic crystal with graphene nanolayers

In biosensors research, much effort has been made to achieve high sensitivity to detect lower concentrations of analyte in a solution by testing different kinds of materials. In this paper, we present a biosensor based on Bloch surface waves made of photonic crystal (PhC) including graphene nanolayers under the Kretschmann configuration. The band structures, surface modes, reflectivity, and sensitivity of the PhC biosensor are calculated by the transfer matrix method and results are compared with those of the structure without graphene layers. Our investigations show that the angular sensitivity of the biosensor considerably increases in the presence of the graphene layers. Moreover, we study the effect of the number of the graphene layers placed on the surface of the biosensor on the performance of our proposed biosensor. The results reveal that the sensitivity of the biosensor is enhanced by increasing the number of graphene layers on the surface due to the π-stacking interactions between graphene's honeycomb cells and the carbon rings in biomolecules. Furthermore, our results show that the phase sensitivity is higher than the angular sensitivity, which can promote the accuracy of the calculations.

Grating surface plasmon resonance sensor: angular sensitivity, metal oxidization effect of Al-based device in optimal structure

We present the wavelength (λ)-independent ultimate and maximum angular sensitivity of a grating surface plasmon resonance sensor, as long as the grating of metal has much higher permittivity than analyte (na2). For 1.32≤n(a)≤1.36, the maximum angular sensitivity reaches 493.7 (535.9)°/RIU by the single (double)-dip method. The real Al-based sensor in an optimal structure for a high figure of merit exhibits higher sensitivity but narrower reflection dip when working at a longer wavelength, and the real sensitivity increases from 292.5 (344.5) to 338.0 (396.3)°/RIU at respective λ=0.85 and 1.55 μm before the metal oxidation. After the oxidization, the sensitivity is degraded by ≤3.2% (2.8%), and the detection error of δn(a)≤1.3e-3 (1.1e-3) is introduced to the sensor working at near-infrared wavelengths of interest.

Investigation of subwavelength grating structure for enhanced surface plasmon resonance detection

A metallic subwavelength grating structure built on a thin gold film is studied for surface plasmon resonance (SPR) detection of refractive index variations of biological buffer solutions. By employing finite element analysis as a numerical method, characteristics of the angle interrogated SPR sensor were calculated and discussed in a broad operating wavelength varying from visible to near-infrared (NIR). The effects of grating structural parameters such as grating depth, grating period, and grating fill factor in different operating wavelengths have been evaluated on the sensor performance parameters of sensitivity, full width at half-minimum, minimum reflectance at resonance, and resonance angle. Numerical results indicate that adjusting grating geometrical parameters can enhance the performance parameters of the sensor especially in the NIR wavelengths. The enhanced sensor performance parameters for optimizing grating geometry have been explored in detail for visible and NIR wavelengths of 633 and 984 nm, respectively. These findings are important for developing localized surface plasmon sensors with enhanced performance.

Design study of nanograting-based surface plasmon resonance biosensor in the near-infrared wavelength

A key issue with surface plasmon resonance (SPR) biosensors, which are the focus of many researchers, is improving their sensitivity to detect lower amounts of analyte in a solution. Most SPR developments have focused on the grating-based sensitivity-enhancement approach. In addition to sensitivity, a substantial enhancement of other sensor characteristics such as resolution and signal-to-noise ratio (SNR) is desired for designing a practical sensor. So, in this paper, the characteristics of surface plasmon polaritons sustained by 1D subwavelength metallic gratings on a thin metal slab (under the Krestchmann configuration) have been investigated numerically for the analyte-ligand interactions detection. Effects of different structural parameters, such as grating period, grating depth, metal film thickness, and fill factor have been evaluated on the sensor sensitivity as well as resolution and SNR. Numerical results indicate that the sensor working in the near-infrared wavelength has a better performance than that in the visible one. The result of numerical investigation has been used to design an optimized sensor with the best figure of merit.