Long-range surface plasmons supported by a bilayer metallic structure for sensing applications

Area of Science:

• Plasmonics
• Nanophotonics
• Optical Sensing

Background:

• Surface plasmon resonance (SPR) sensors are crucial for detecting analytes.
• Conventional SPR sensors often face limitations in sensitivity and resolution.
• Long-range surface plasmons (LRSPs) offer potential for improved sensing performance.

Purpose of the Study:

• To theoretically and experimentally investigate LRSPs in a novel asymmetric bimetallic structure.
• To optimize the geometrical parameters of the structure for efficient LRSP excitation.
• To compare the performance of the bimetallic asymmetric structure with monometallic and conventional SPR sensors.

Main Methods:

• Utilized the transfer matrix method based on Fresnel reflection for theoretical optimization.
• Employed a custom-made automated optical setup for experimental excitation of LRSPs.
• Performed angular interrogation with a precision of 0.01° to analyze reflectivity.

Main Results:

• Demonstrated that the asymmetric bimetallic structure (silver/gold bilayer with MgF2 buffer) supports LRSPs.
• Optimized geometrical parameters for efficient LRSP excitation.
• The bimetallic asymmetric structure achieved superior minimum reflectivity resolution compared to monometallic structures.

Conclusions:

• The bimetallic asymmetric structure significantly enhances LRSP excitation and sensing capabilities.
• Achieved a figure of merit more than double that of monometallic LRSP configurations.
• The proposed sensor design offers an 8-fold improvement in figure of merit over conventional SPR sensors.