Carbon nanotubes as AFM tips: measuring DNA molecules at the liquid/solid interface

High-resolution imaging of soft and weakly adsorbed biomolecules on surfaces within buffer solutions presents a big challenge in research. Here we demonstrate that a single carbon nanotube could be used as a tip for probing biomolecules in solution using atomic force microscopy (AFM). Combining the unique properties of carbon nanotube tips with the newly developed magnetically driven oscillating AFM technique, we were able to obtain molecular-level, high-resolution images of DNA molecules adsorbed on the mica surface in solution. The length and the buckling force of the single nanotube tip can be derived directly from the force–distance curve. These measurements indicate that the nanotube tip is quite resilient, and it can quickly recover to its full length after repeatedly being crashed on the surface with excess force. The well-defined tip geometry provides extraordinary resolution in AFM imaging. The application of carbon nanotubes as AFM tips could lead to breakthroughs in biological studies.