研究目的
To numerically investigate a nanoscale plasmonic biosensor based on Mach-Zehnder interferometry, examining its operation through two methods: intensity measurement method (IMM) and wavelength interrogation method (WIM), to evaluate transmission, sensitivity, figure of merit (FOM), and quality factor (Q-factor) under various geometric conditions and refractive index changes.
研究成果
The numerical simulations demonstrate that the plasmonic MZI biosensor exhibits high sensitivity and performance, with transmission changes up to 56.6% for specific geometries. Increasing the thickness or length of the gold layer enhances Q-factor and FOM, and adding additional gold layers further improves sensitivity and FOM. These findings are consistent with existing literature and suggest potential for highly sensitive biosensing applications, though experimental verification is needed.
研究不足
The study is purely numerical and based on simulations, which may not fully capture real-world experimental conditions such as fabrication imperfections, environmental factors, or biological variability. The sensitivity and performance metrics are dependent on the specific geometric parameters and material properties assumed, and may require experimental validation for practical applications.
1：Experimental Design and Method Selection:
The study uses numerical simulations based on the finite difference time domain (FDTD) method to model surface plasmon polariton (SPP) propagation in a Mach-Zehnder interferometer (MZI) structure. The Drude model is employed to describe the complex refractive index of gold. Two methods are used: intensity measurement method (IMM) for fixed wavelength and varying refractive indices, and wavelength interrogation method (WIM) for fixed refractive index and varying wavelengths.
2：Sample Selection and Data Sources:
The simulations involve a silicon-on-insulator (SOI) configuration with a gold layer. The sample medium's refractive index is varied between 1.18 and 1.48 for IMM, and fixed at specific values (e.g., 1.33 and 1.3325) for WIM. Data is generated through numerical simulations.
3：18 and 48 for IMM, and fixed at specific values (e.g., 33 and 3325) for WIM. Data is generated through numerical simulations.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: The primary material is a gold layer with varying lengths and thicknesses, embedded in a silicon membrane on a silica substrate. Software used is OptiFDTD8.0 from Optiwave Corporation for simulations.
4：0 from Optiwave Corporation for simulations.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: For IMM, a Gaussian input wave is used with specified half-widths, and transmission is calculated as the ratio of output to input Poynting vectors for different refractive indices. For WIM, a broadband input wave is used, and spectral minima in transmission are monitored for wavelength shifts. Simulations are performed for various geometries (e.g., different lengths and thicknesses of the gold layer).
5：Data Analysis Methods:
Transmission data is fitted using equations (e.g., Eq. 3) via Origin software. Sensitivity is calculated as the shift in resonance wavelength per refractive index unit (nm/RIU), Q-factor as resonance wavelength divided by full width at half maximum (FWHM), and FOM as sensitivity divided by FWHM.
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