Improved Force Spectroscopy Using Focused-Ion-Beam-Modified Cantilevers

Area of Science:

• Biophysics
• Materials Science
• Nanotechnology

Background:

• Atomic force microscopy (AFM) is essential for biophysical research, particularly in force-spectroscopy studies of protein folding and ligand interactions.
• Current AFM data quality is often limited by the mechanical properties of commercial cantilevers, presenting a tradeoff between force stability and precision.
• Existing limitations hinder the accuracy and resolution of AFM-based measurements in sensitive biological applications.

Purpose of the Study:

• To present a novel method for enhancing AFM cantilever performance through focused-ion-beam (FIB) modification.
• To overcome the inherent limitations of commercial cantilevers, improving both force precision and stability without sacrificing temporal resolution.
• To provide an accessible and customizable protocol for fabricating improved AFM cantilevers for diverse biophysical applications.

Main Methods:

• Focused-ion-beam (FIB) modification of commercially available AFM cantilevers.
• Reduction of cantilever hydrodynamic drag and stiffness through controlled FIB milling.
• Selective retention of gold coating at the cantilever's free end to enhance stability.

Main Results:

• Achieved sub-pN force precision over five decades of bandwidth (0.01–1000 Hz) using modified short cantilevers (L=40μm), with minimal impact on temporal resolution (~75μs).
• Demonstrated improved force precision and stability in ultrashort cantilevers (L=9μm), maintaining 1-μs-scale temporal resolution.
• Eliminated underdamped high-frequency motion in ultrashort cantilevers, preventing unwanted force oscillations on molecules.

Conclusions:

• FIB modification offers a viable method to significantly enhance AFM cantilever performance, addressing critical limitations in force precision and stability.
• The protocol is accessible to researchers, with undergraduate students capable of fabricating modified cantilevers efficiently.
• FIB-modified cantilevers are expected to advance a wide range of AFM-based biophysical research by providing higher quality data.