Surface Plasmon Resonance of Two-Dimensional Gold Colloidal Crystals Formed on Gold Plates

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Surface Plasmon Resonance (SPR) sensors utilize the oscillation of free electrons in metals like gold when exposed to electromagnetic waves.
• SPR sensors are crucial in biosensing for drug discovery, biomarker screening, virus detection, and food safety analysis.
• The resonance frequency of SPR is sensitive to the surrounding medium's permittivity, enabling sensing applications.

Purpose of the Study:

• To fabricate and characterize a novel metal-insulator-metal (MIM) SPR sensor.
• To investigate the sensing performance of the MIM structure using ethylene glycol solutions.
• To evaluate the potential of the MIM sensor for highly sensitive detection in pharmaceutical sciences.

Main Methods:

• Fabrication of a MIM SPR sensor using a two-dimensional (2D) array of gold (Au) colloidal particles on an insulator layer over a thin Au film.
• Formation of 2D colloidal crystals via electrostatic adsorption of 3D crystals onto a positively charged insulator.
• Measurement of plasmon peaks/dips in aqueous solutions of varying ethylene glycol (EG) concentrations.

Main Results:

• Observation of multiple plasmon peaks/dips attributed to localized SPR (LSPR) and Fano resonance.
• Significant shift of plasmon peaks/dips to higher wavelengths with increasing EG concentration due to refractive index changes.
• The observed peak/dip shift was approximately double that of LSPR from an isolated Au particle, indicating enhanced sensitivity.

Conclusions:

• The fabricated MIM SPR sensor exhibits enhanced sensitivity compared to traditional LSPR sensors.
• The sensor's performance is strongly correlated with the refractive index of the surrounding medium.
• The developed MIM substrate holds promise as a highly sensitive sensing platform for pharmaceutical applications.