Viscoelasticity of living cells allows high resolution imaging by tapping mode atomic force microscopy

Abstract

Application of atomic force microscopy (AFM) to biological objects and processes under physiological conditions has been hampered so far by the deformation and destruction of the soft biological materials invoked. Here we describe a new mode of operation in which the standard V-shaped silicon nitride cantilever is oscillated under liquid and damped by the interaction between AFM tip and sample surface. Because of the viscoelastic behavior of the cellular surface, cells effectively "harden" under such a tapping motion at high frequencies and become less susceptible to deformation. Images obtained in this way primarily reveal the surface structure of the cell. It is now possible to study physiological processes, such as cell growth, with a minimal level of perturbation and high spatial resolution (approximately 20 nm).

Molecular Resolution Imaging of Protein Molecules in Liquid Using Frequency Modulation Atomic Force Microscopy

“…3(d) presents the one with a single molecular defect. The images obtained here are still not as fine as those obtained by the contact-mode AFM 2) , however, it is comparable to those obtained by the AM-AFM 8,9) and we believe that the resolution of the images can be improved by the further optimization of the imaging parameters. We also measured the frequency shift versus tip-sample distance curves as shown in Fig.…”

“…Amplitude-modulation AFM (AM-AFM) has been successfully applied for imaging biological samples 2) . On the other hand, a large number of true atomic and molecular resolution AFM images have been presented by the use of the frequency modulation (FM) method 3) in vacuum environments 4) .…”

Atomic Force Microscopy in Detection of Viruses

“…This method overcomes problems associated with friction, adhesion, electrostatic forces, and other difficulties that conventional AFM scanning methods by alternately placing the tip in contact with the surface to provide high resolution and then lifting the tip off the surface to avoid dragging the tip across the surface, avoiding sample damage by compressing, and tearing. The cantilever vibrates at its resonant frequency under an external electrical excitation, the feedback loop adjusts the oscillation amplitude to restore the original set point value, and a height image can be recorded (Putman, van der Werf et al 1994;Schindler, Badt et al 2000). The contrast of a phase image is directly dependent on the elastic properties of the sample.…”

“…The most common materials used to bond particles to the substrate are Poly-L-lysine, poly-D-lysine, Two drive mechanisms for tapping mode in fluids are available on the multimode AFM. The conventional method of driving the cantilever by acoustic excitation has been joined by a magnetic actuated drive (Putman, 1994). Acoustically driven oscillations of the cantilever in liquid on the multimode AFM occur by excitation of a piezo electric ceramic element in the cantilever holder; however, the sample can move and give erroneous information.…”

Classification of Scanning Probe Microscopies

“…biological surfaces) or unstable surface features (e.g. small particles) [80][81][82][83][84][85][86].…”