A single-molecule stretching method for lateral and normal AFM lever calibration.

Area of Science:

• Atomic Force Microscopy (AFM)
• Single-Molecule Spectroscopy
• Nanomechanics

Background:

• Accurate calibration of atomic force microscope (AFM) cantilevers is crucial for quantitative measurements.
• Traditional methods for lateral force measurement (LFM) calibration can be complex and may require tip modifications.
• Developing efficient and reliable calibration techniques is essential for advancing nanoscale force analysis.

Purpose of the Study:

• To introduce a novel, tip-modification-free method for quantitative lateral force measurement (LFM) calibration.
• To calibrate both lateral and normal spring constants of AFM levers simultaneously using a single scan.
• To validate the developed method using dextran single-molecule stretching events.

Main Methods:

• Utilized a single-molecule spectroscopy approach combined with a non-standard (tilted) AFM scanning geometry.
• Employed dextran molecules, chosen for their distinct force-elongation curve plateau, to identify single-molecule stretching.
• Analyzed both normal and lateral force signals to extract calibration parameters.

Main Results:

• Achieved simultaneous calibration of lateral and normal spring constants with a single image scan.
• Demonstrated good agreement between the determined normal spring constant and values obtained via the energy equipartition theorem.
• Reported reproducible lateral sensitivity results with a relative standard deviation below 15%.

Conclusions:

• The developed single-molecule spectroscopy method offers an effective and accurate approach for LFM calibration.
• The technique eliminates the need for tip modifications, simplifying the calibration process.
• This novel method provides reproducible and reliable calibration of AFM levers for nanoscale force measurements.