Universal axial fluctuations in optical tweezers

Area of Science:

• Biophysics
• Nanotechnology
• Molecular dynamics

Background:

• Optical tweezers (OTs) are vital for nanoscale measurements, particularly single-molecule end-to-end distance fluctuations.
• Experimental data from OTs can be compromised by instrumental artifacts, such as axial fluctuations.
• Axial fluctuations share timescales with molecular conformational changes, risking data misinterpretation.

Purpose of the Study:

• To identify and characterize instrumental axial fluctuations in optical tweezers experiments.
• To develop a method for distinguishing axial fluctuations from genuine molecular conformational transitions.
• To provide a general strategy for accurate analysis of single-molecule fluctuation data.

Main Methods:

• Analyzing the force-dependent behavior of both axial and conformational fluctuations.
• Developing a general formula to describe axial fluctuations across different OT setups.
• Comparing fluctuation spectra to differentiate instrumental from biological signals.

Main Results:

• Axial fluctuations, bead movements along the light propagation axis, were identified as a key instrumental artifact.
• A characteristic timescale of axial fluctuations mimics that of molecular folding transitions.
• A precise force-dependent analysis allows for the effective disentanglement of axial and conformational fluctuations.

Conclusions:

• Accurate interpretation of single-molecule experiments requires distinguishing instrumental axial fluctuations from conformational changes.
• A general formula and strategy are provided to help researchers identify and mitigate the impact of axial fluctuations.
• This work enhances the reliability of optical tweezers in studying molecular dynamics and biophysical processes.