The Origin of Single-Molecule Sensitivity in Label-Free Solution-Phase Optical Microcavity Detection

Area of Science:

• Optics and Photonics
• Biophysics
• Analytical Chemistry

Background:

• Fiber Fabry-Perot microcavities (FFPCs) enhance light-matter interactions.
• Photothermal nonlinearities and Pound-Drever-Hall frequency locking are key to sensitive detection.

Purpose of the Study:

• To elucidate the quantitative mechanism behind single-molecule sensitivity in FFPCs.
• To achieve quantitative agreement between experimental observations and theoretical models.

Main Methods:

• Utilizing a combination of experimental techniques and computational simulations.
• Operating FFPCs in an unstable regime to exploit photothermal nonlinearities.
• Employing Pound-Drever-Hall frequency locking for precise control.

Main Results:

• Demonstrated a mechanism where rapid shifts between photothermal equilibria amplify responses to molecular perturbations.
• Identified a 'molecular velocity filter window' for selective and amplified detection.
• Achieved quantitative agreement between the model and experimental data.

Conclusions:

• The developed model quantitatively explains single-molecule detection sensitivity.
• The FFPC system can detect resonance fluctuations smaller than the microcavity line width.
• The model provides a predictive tool for exploring single-molecule hydrodynamic behavior detection.