Surface orientation ambiguity for single molecules at dielectric interfaces.

Area of Science:

• Optical Biophysics
• Surface Science
• Computational Modeling

Background:

• Fluorescent molecules emit light in a dipole radiation pattern.
• Defocused fluorescence microscopy infers molecular orientation from this pattern.
• Accurate orientation measurement relies on precise mathematical modeling.

Purpose of the Study:

• To identify and address an ambiguity in common calculations of dipole radiation patterns.
• To investigate the impact of dielectric surfaces on measured molecular orientation.
• To provide a method for correcting orientation measurements for molecules near interfaces.

Main Methods:

• Analysis of mathematical models for dipole radiation patterns near dielectric surfaces.
• Comparison of theoretical predictions with experimental data.
• Application of finite-element modeling to simulate on-surface emitters between dielectric media.

Main Results:

• An ambiguity in standard calculations leads to erroneous dipole rotation towards dielectric surfaces.
• This rotation can be misinterpreted as preferential horizontal molecular orientation.
• Finite-element modeling successfully resolves the theoretical ambiguity.

Conclusions:

• Common orientation calculations are compromised for molecules near dielectric interfaces.
• A new theoretical treatment considering finite current elements is required.
• A prescription for correcting measured orientations at arbitrary interfaces is provided.