Comparison of Scanning Ion Conductance Microscopy with Atomic Force Microscopy for Cell Imaging

Abstract

We present the first direct comparison of scanning ion conductance microscopy (SICM) with atomic force microscopy (AFM) for cell imaging. By imaging the same fibroblast or myoblast cell with both technologies in series, we highlight their advantages and disadvantages with respect to cell imaging. The finite imaging force applied to the sample in AFM imaging results in a coupling of mechanical sample properties into the measured sample topography. For soft samples such as cells this leads to artifacts in the measured topography and to elastic deformation, which we demonstrate by imaging whole fixed cells and cell extensions at high resolution. SICM imaging, on the other hand, has a noncontact character and can provide the true topography of soft samples at a comparable resolution.

Exposure to Carbon Nanotubes Leads to Changes in the Cellular Biomechanics

“…[40] To avoid changes in cellular properties during observation and analysis, samples were fixed with 4% glutaraldehyde. Fixed cell topography was imaged by establishing mechanical contact between the AFM tip and individual cells in nonzero imaging force [40] with a scan rate of 0.25 Hz and a pixel resolution of 176 nm/pixel (Figure 2a). A representative control cell body (i.e., for a cell not exposed to 1 h acids-washed MWCNTs) is shown in Figure 2b while a representative cell exposed to 1 h acids-washed MWCNTs is shown in Figure 2c.…”

“…[41,42] The resulting indentation image of a control cell (Figure 3b) shows Young's modulus of the cell body in the 100-250 kPa range ( Figure 3c); the higher stiffness noted at the cell periphery (up to 600 kPa) may be due to the underlying substrate. [40] The highest region of the cell (dashed red in Figure 3a; the rest of the cell body is dashed black) corresponds to the cell nucleus; this region appears softer when compared to the rest of the cell and has Young's modulus values in between 40-80 kPa (Figure 3d). Table 1 shows the Young's modulus distribution of control cells and cells exposed to 1 h acids-washed MWCNTs for 24 h. The cells exposed to 1 h acids-washed MWCNTs showed a significant increase in the Young's modulus when compared with control cells (p < 0.05).…”

“…It was however noted that the stiffness for both control and 1 h acids-washed MWCNT-exposed cells was about one order of magnitude larger than for living cells. [43] This could be the result of either: (1) cell fixation with glutaraldehyde; [40] (2) large stiffness of the substrate; [40] or (3) the induced strains in the cells caused by the tip indented at low speed (i.e., 0.25 kHz). [44] Our findings are significant in that they relate for the first time the cellular changes in biomechanics upon MWCNTs exposure with the potential for genotoxicity and cancer development in the MWCNTs-exposed cells.…”

Multifunctional scanning ion conductance microscopy

“…As exemplified by figures 1d and 4b, the non-invasive (non-contact) nature of SICM, combined with the wide range of possible imaging media, make it particularly suitable for live cell imaging when compared with other SPMs [60]. The first studies of cell morphology using SICM, in 1997 [2,61], highlighted the benefits of the non-contact nature of the technique, showing that there was no damage to cells from the scanning process.…”

Nanoscale Cell Surface Topography Imaging using Scanning Ion Conductance Microscopy

“…[5][6][7][8] Scanning ion conductance microscopy (SICM), which uses a nanopipette as a scanning probe to detect ionic current as feedback signal, was reported as an effective tool for noncontact topographical imaging of live cells, because measurements are performed under physiological conditions. [5][6][7][8][9][10][11][12][13][14] The general assembly of a SICM is shown in Fig. 1.…”