Essam M. A. Elkaramany

Label-Free Highly Sensitive Hybrid Plasmonic Biosensor for the Detection of DNA Hybridization

A highly sensitive hybrid plasmonic slot-waveguide (HPSW) biosensor based on silicon-on-insulator is proposed and analyzed for DNA hybridization detection. The reported design is based on increasing the light interaction with the sensing region by using slot waveguide with plasmonic material. Due to the high index contrast and plasmonic effect, an ultrahigh optical confinement is achieved in the low-index regions, which enables the detection of the smallest change in the analyte refractive index with high sensitivity. The normalized power confinement, power density, and effective index of the supported modes by the HPSW are analyzed to achieve high-power confinement through the suggested biosensor and hence high sensitivity can be obtained. The HPSW is also incorporated with straight slotted resonator to calculate the sensitivity of the proposed design. The simulation results are calculated using full vectorial finite element method. The reported biosensor has high sensitivity of 1890.4 nm/RIU (refractive index unit), which is the highest in the literature to the best of our knowledge with a detection limit of 2.65 × 10 –6 RIU.

Two Dimensional Long Transmission Line-Frequency Domain (Ltl-Fd) Treatment of Waveguides

In this paper, two dimensional transmission line circuits are used to determine cutoff wavenumbers of homogeneous arbitrarily shaped cylindrical waveguides. The derived circuits depend mainly on long transmission line (LTL) circuits. The resonance frequencies of these circuits are the required cutoff frequencies of the guide. The problem is reduced to a simple eigenvalue problem, which is solved to get the required solution. Numerical results are given to compare results with available analytical solutions and results given by other reported methods.

Two Dimensional Long Transmission Line-Frequency Domain (Ltl-Fd) Treatment of Dielectric Loaded Waveguides

In this paper, two dimensional long transmission line-frequency domain (LTL-FD) circuits [1] are used to determine cutoff wavenumbers of slab loaded arbitrarily shaped cylindrical waveguides. Treatment of interfaces between different media is given. The resonance frequencies of the resulting circuits are the required cutoff frequencies of the guide. The problem is reduced to an eigenvalue problem, which is solved to get the required solution. Numerical results are given to compare results with available analytical solutions and results given by other reported methods.

Circuit Models for 2-Dimensional EM Absorption by Biological Bodies

In this paper, new circuit models are used to calculate the induced fields in biological media exposed to an incident plane wave in the two-dimensional cases. These models represent the induced fields in the medium using the lossy long transmission line model [1]. The voltages and currents in the circuit model simulate the electric and magnetic fields in the medium. The response of the medium to the incident wave is represented by equivalent conduction and polarization current sources in the medium. These currents are used as the excitation sources in the circuit model from which the required induced fields are obtained. An accurate absorbing impedance boundary condition for open boundaries is used which considerably reduces the matrix dimensions. The validity of these models is tested in the problem of absorption of Eand H-waves by biological multilayered cylinders. Results are compared with available analytical and numerical solutions.

Analysis of Microwave Cavities Using LTD-FD Method

In this paper, improved three dimensional long transmission line-frequency domain (LTL-FD) circuits are used to determine cutoff wavenumbers of microwave resonators. The II-form of long transmission line representation [1] is used to construct the model. Consequently, treatment of boundaries and interfaces between different media is shown to be a simple procedure. The resonance frequencies of the resulting circuits are the required cutoff frequencies of the resonator. The problem is reduced to an eigenvalue problem, which gives the required solution. The models ensure the satisfaction of field divergence equations and, so, results are free from spurious modes. Results for homogeneous cavities and partially dielectric-filled cavities are given and are compared with available analytical solutions as well as those given by other methods.

Detection of DNA hybridization by hybrid alternative plasmonic biosensor

In order to detect DNA hybridization with label free and high sensitivity, a hybrid alternative plasmonic slot waveguide (HAPSW) biosensor based on silicon-on-insulator (SOI) is proposed and analyzed. The reported design increases the light interaction with the sensing region by using a slot-waveguide along with titanium nitride as an alternative plasmonic material. The suggested biosensor can detect the slightest change in the analyte refractive index with high sensitivity due to an ultra-high optical confinement in the low-index regions caused by the high index contrast and plasmonic enhancement. The effective index, normalized power confinement, and sensitivity are analyzed for the detection of the DNA hybridization. The simulation results are obtained using full vectorial finite element method (FVFEM). The suggested biosensor has high sensitivity of 1190 nm/RIU (refractive index unit) for DNA hybridization detection, which is very high relative to those reported in the literature to the best of our knowledge.

Introduction to Silicon Photonics

This chapter reviews the fundamentals of the silicon on insulator (SOI) technology due to its advantages. The chapter starts with an introduction to the SOI followed by the different waveguides based on the SOI technology and their advantages. Further, the novel platforms that have been recently emerging beside the SOI are also presented. Finally, various fabrication processes for performing the SOI wafer are introduced in more detail.

Introduction to Optical Waveguides

This chapter presents an introduction to the optical waveguides including planar and nonplanar structures. Additionally, an analysis of planner waveguides based on ray-optical approach and Maxwell’s equations approach is investigated. In this context, types of modes, dispersion, cutoff frequency, and effective thickness of the optical waveguides are discussed thoroughly. Further, the different numerical techniques and their based mode solvers which are used to analyze optical waveguides are summarized in brief. Finally, the coupling mechanisms to the optical waveguide are introduced including transversal coupling techniques and the longitudinal coupling techniques.

Basic Principles of Biosensing

Recently, optical sensors have been improved extensively due to the rising need of sensing applications in different specialties such as, medicine, military, environment, food quality control. The improvement of the photonic technologies based on the CMOS compatible silicon-on-insulator (SOI) and photonic crystal structures improves the sensing performance significantly. This chapter presents the basic principles of the sensing process. Additionally, it introduces the different configurations of optical sensors based on working principle, sensor design, and detection purpose.

Silicon Nanowires for DNA Sensing

Highly sensitive hybrid plasmonic slot waveguide (HPSW) biosensors based on silicon on insulator (SOI) are proposed and analyzed for DNA hybridization detection. The reported designs are based on increasing the light interaction with the sensing region by using slot waveguide with plasmonic material. Due to the high index contrast and plasmonic effect, an ultrahigh optical confinement is achieved in the low-index regions which enables the detection of the smallest change in the analyte refractive index with high sensitivity. The normalized power confinement, power density, effective index of the supported modes by the HPSWs are analyzed to achieve high power confinement through the suggested biosensors, and hence, high sensitivity can be obtained. The HPSWs are also incorporated with straight slotted resonator to calculate the sensitivity of the proposed design. In this study, two different plasmonic materials (gold and titanium nitride) are used for the proposed designs. The simulation results are calculated using full vectorial finite element method (FVFEM). The reported biosensors have high sensitivity of 1890.4 nm/RIU (refractive index unit) with a detection limit of 2.65 × 10−6 RIU with gold material and 1190 nm/RIU with a detection limit of 4.2 × 10−6 RIU based on titanium nitride material, which are the highest in the literature to the best of our knowledge.