Lambda Theta Reflectometry: A New Technique for Measuring Optical Film Thickness in Planar Protein Arrays

Area of Science:

• Biomolecular interaction analysis
• Label-free biosensing
• Optical metrology

Background:

• Quantitative protein measurements are crucial for understanding biological processes and diseases.
• Label-free methods are preferred for preserving native protein interactions.
• Existing reflectometry techniques face limitations in complexity, sensitivity, and manufacturing.

Purpose of the Study:

• Introduce Lambda Theta Reflectometry (LTR), a novel reflectometric technique.
• Address limitations of current label-free protein detection methods.
• Demonstrate LTR's capability for precise film thickness and biosensing measurements.

Main Methods:

• Developed Lambda Theta Reflectometry (LTR), measuring film thickness via null reflectivity.
• Simultaneously illuminated substrate with a range of wavelengths and angles.
• Resolved reflected light both angularly and spectrally.
• Utilized a prototype LTR reflectometer for measurements.

Main Results:

• Achieved milli-Ångström precision in SiO₂ layer thickness measurements.
• LTR measurements of Si/SiO₂ films showed excellent agreement with spectroscopic ellipsometry.
• Enabled label-free biosensing of biological analytes from 0.5 ng/mL to μg/mL concentrations.

Conclusions:

• LTR is a sensitive and precise label-free technique for biomolecular analysis.
• The method overcomes limitations of existing reflectometry, simplifying biosensing.
• LTR offers a robust platform for quantitative protein measurements and diagnostics.