Wearing a single DNA molecule with an AFM tip

TL;DR

This paper introduces an in situ method for characterizing AFM tip radius and monitoring tip wear during experiments, enabling more accurate nanoscale measurements of biomolecules like DNA.

Contribution

The authors develop a real-time, in situ technique to measure AFM tip radius and wear, improving the accuracy of nanoscale biomolecular imaging.

Findings

Able to detect tip radius variations as small as one nanometer

Demonstrated monitoring of DNA molecules with simultaneous height and width measurements

Showed that sharp tips can exceed yield stress at typical operating amplitudes

Abstract

While the fundamental limit on the resolution achieved in an atomic force microscope (AFM) is clearly related to the tip radius, the fact that the tip can creep and/or wear during an experiment is often ignored. This is mainly due to the difficulty in characterizing the tip, and in particular a lack of reliable methods that can achieve this in situ. Here, we provide an in situ method to characterize the tip radius and monitor tip creep and/or wear and biomolecular sample wear in ambient dynamic AFM. This is achieved by monitoring the dynamics of the cantilever and the critical free amplitude to observe a switch from the attractive to the repulsive regime. The method is exemplified on the mechanically heterogeneous sample of single DNA molecules bound to mica mineral surfaces. Simultaneous monitoring of apparent height and width of single DNA molecules while detecting variations in the tip radius R as small as one nanometer are demonstrated. The yield stress can be readily exceeded for sharp tips (R<10 nm) at typical operating amplitudes (A>10nm). The ability to know the AFM tip radius in situ and in real-time opens up the future for quantitative nanoscale materials properties determination at the highest possible spatial resolution.