Modelling of diffraction grating based optical filters for fluorescence detection of biomolecules

Area of Science:

• Optics and Photonics
• Biomedical Engineering
• Materials Science

Background:

• Fluorescence measurements are crucial for genetic, proteomic, and cellular analysis.
• Conventional optical filters (absorbing and interference) limit diagnostic performance due to low rejection ratios or complex fabrication.
• Specific challenges exist for fluorophores with small Stokes' shifts, like green fluorescent protein (GFP).

Purpose of the Study:

• To explore dielectric diffraction gratings as an alternative to conventional optical filters for fluorescence detection.
• To investigate three distinct grating-based filter designs using optical modeling.
• To assess the efficiency, rejection ratios, and manufacturing feasibility of these novel filters.

Main Methods:

• Finite Element Method (FEM)-based optical modeling was employed for design optimization.
• Three filtering concepts were simulated: surface grating on an absorbing filter, embedded grating, and a combined approach.
• Performance was evaluated based on rejection ratios, particularly for GFP (λexc = 480 nm, λem = 510 nm).

Main Results:

• Embedded grating concepts demonstrated high rejection ratios (>100,000) for GFP.
• These designs showed sensitivity to manufacturing errors and incident angle variations.
• An optimized embedded grating on an absorbing filter achieved a 60-fold improvement in rejection ratio over conventional filters.

Conclusions:

• Dielectric diffraction gratings present a highly efficient and manufacturable alternative for optical filtering in fluorescence applications.
• Optimized grating designs can overcome limitations of conventional filters, significantly enhancing diagnostic capabilities.
• Further research may focus on mitigating sensitivity to manufacturing variations for practical implementation.