Quantitative analysis of enhanced light irradiance in waveguide-based fluorescent microarrays

Area of Science:

• Optoelectronics
• Biophotonics
• Surface Science

Background:

• Microarray assays provide hybridization kinetics data but suffer from high supernatant background noise in common detection methods.
• Evanescent field excitation of microarray surfaces is a known method to improve signal specificity.
• Planar optical waveguides can significantly enhance excitation irradiance at the interface.

Purpose of the Study:

• To theoretically and experimentally compare guided excitation using planar optical waveguides with classical external excitation for microarray assays.
• To quantify the irradiance enhancement provided by tailored waveguides.
• To discuss the implications of this enhancement for biochip reader design.

Main Methods:

• Full electromagnetic analysis to predict irradiance enhancement.
• Theoretical comparison of guided versus external excitation.
• Experimental deposition of high-index TiO(2) sol-gel waveguides on glass substrates.
• Quantitative analysis using biological fluorescent spots to confirm enhancement.

Main Results:

• Electromagnetic analysis predicted irradiance increases greater than 10^4 for tailored waveguides.
• Experimental results with TiO(2) waveguides confirmed significant irradiance amplification.
• The enhancement was validated using actual biological fluorescent spots.

Conclusions:

• Planar optical waveguides offer a dramatic excitation irradiance enhancement at the waveguide/surrounding matter interface.
• This amplification significantly improves signal-to-background ratio in microarray assays.
• The findings facilitate the design of simpler, low-cost biochip readers and sensor systems.