The Nanoscale World

Performing Quantitative Nanomechanical AFM Measurements on Live Cells


posted by Thomas Mueller
Thu, Feb 27 2014

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Performing Quantitative Nanomechanical AFM Measurements on Live Cells

Atomic force microscopy (AFM) has been recognized since the mid-eighties [1] as an excellent technique to image a wide range of samples in their near-natural environment. Although the primary function of AFM is to generate three-dimensional (3D) profiles of the scanned surface, much more information can be delivered via this technique. In 1993, TappingMode was developed [2], which prevents tip and sample damage due to friction and shear forces and allows qualitative mechanical property mapping through phase imaging [3, 4]. About the same time, force spectroscopy [5] and force volume (FV) Devil were developed to study tip-sample forces at a point or over an area, respectively. To date, force spectroscopy and FV are the most commonly used AFM modes for measuring nanometer-scale mechanical forces in a quantitative manner. Unfortunately, force spectroscopy and FV suffer from slow acquisition speed and a lack of automated tools; these operating characteristics limit their use because of the hundreds or thousands of curves that are required for good statistics. In 2010, the PeakForce QNM mode was developed [7], based on Bruker’s PeakForce Tapping technology. In this technique, the probe is oscillated around 1 kHz and the peak force (maximum nominal force applied to the sample) is used for feedback control. Each time the tip interacts with the sample, a force curve is collected and analyzed by PeakForce QNM. The resulting signals are extracted and quantitatively displayed as a false-colored, real-time image. Currently available data types include the peak force, the adhesion, the Young’s modulus, the deformation, and the dissipation. This mode has been successfully tested on a wide range of samples Music, including bio-polymers [9, 10] and live eukaryotic cells [11], as well as human models [12]. This article describes the application of this method to measurements on live cells.

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