Plasmonic amplification for bioassays with epi-fluorescence readout.

Area of Science:

• Plasmonics
• Biophotonics
• Surface Chemistry

Background:

• Fluorescence bioassays are crucial for diagnostics.
• Signal amplification is needed to improve sensitivity and detect low analyte concentrations.
• Surface plasmon resonance (SPR) offers a pathway for signal enhancement.

Purpose of the Study:

• To design and investigate corrugated metallic surfaces for enhanced fluorescence bioassay signal amplification.
• To improve the sensitivity of immunoassays using epi-fluorescence readout.
• To explore the use of crossed gold gratings for combined excitation rate increase and directional fluorescence emission.

Main Methods:

• Theoretical simulation and experimental investigation of crossed gold gratings.
• Utilizing near-field coupling between surface plasmons and fluorophore labels (Alexa Fluor 647).
• Application to a sandwich interleukin-6 immunoassay with epi-fluorescence detection.

Main Results:

• Simulated and experimentally measured enhancement factor (EF) of approximately 10^2 for Alexa Fluor 647.
• Observed surface-selective enhancement in a sandwich interleukin-6 immunoassay.
• Demonstrated a two-orders-of-magnitude increase in measured fluorescence signal for surface-bound molecules.

Conclusions:

• Corrugated metallic surfaces, specifically crossed gold gratings, effectively enhance fluorescence bioassay signals.
• The plasmonic structure significantly improves immunoassay sensitivity and enables kinetic measurements by reducing background noise.
• This approach holds promise for sensitive and quantitative analysis of molecular binding events.