Table 1 |.
Methods to characterize the cell surface
| Technique | Examples | Measured quantity | Schematic | |
|---|---|---|---|---|
| Membrane tension | Tether pulling using AFM | 40× 10–12 N for HL60 cells9 | Tether rupture force | Fig. 1a |
| Interferometric particle detection using optical tweezers | 65× 10–6 N m−1 for erythrocytes44 | Power spectral density of the quadrant photodiode voltage | Fig. 1b | |
| Tether pulling using optical or magnetic tweezers | 29× 10–12 N for MEF cells45 | Tether rupture force | Fig. 1c | |
| Tether pulling using shear fluid | 86–172× 10–12 N for shear rates of 100–250 s–1 for neutrophils46 | Approach velocity, shear rate, tether length and cell size | Fig. 1d | |
| Cortical tension | AFM compression (with a flat cantilever or a bead) | 1.6× 10–3 N m–1 for HeLa cells during metaphase47 | Compressive force, contact angles of cellular deformation for a flat cantilever or deflection of the cantilever with a bead | Fig. 1e,i |
| Dual plate compression | 1.75 dyn cm–1 (or 175× 10–5 N m–1) for sea urchin eggs 40 minutes after fertilization48 | Compressive force, contact angles of cellular deformation | Fig. 1f | |
| Laser ablation | 9.15 μm min–1 orthogonal outward velocity in the anterior cortex of the one-cell C. elegans embryo49 | Response of cortex to laser ablation | Fig. 1g | |
| Micropipette aspiration | 0.035 dyn cm–1 (or 3.5× 10–5 N m–1) for passive blood granulocytes38 | Aspiration pressure and cellular deformation | Fig. 1h | |
|
Surface elasticity and viscoelasticity |
AFM indentation | 855 Pa for HL60 cells50 | Deflection of the cantilever | Fig. 1i |
| Brillouin microscopy | 5.41–8.06 GPa for plants ECM51 and 2.78 GPa for the nuclear envelope52 |
Brillouin peak shift and width | Fig. 1j | |
| Magnetic twisting cytometry | 10–11–10–8 Pa m–1 for a broad range of cancer cells lines53 | Bead displacement to a twisting magnetic field with different frequencies | Fig. 1k | |
| Cortical thickness | Electron microscopy | Tens of nm (ref. 54) | Thickness of the cortical layer | Fig. 1l |
| Fluorescence microscopy | 186 nm for the cortex of mitotic HeLa cells55 | Fluorescence peak distance | Fig. 1m | |
| Bending rigidity | Interferometric particle detection using optical tweezers | 2.8× 10–19 N m (or 67.6kBT) for erythrocytes44 | Power spectral density of the quadrant photodiode voltage or standard deviation of the distribution of fluctuation amplitudes | Fig. 1b |
| Micropipette aspiration | 10–19 N m for red blood cells or lipid bilayers23 and 1–2× 10–18 N m for cell types with a simple cortex56 | In the low tension regime, the slope of the area dilation versus the logarithm of the tension | Fig. 1h | |
| Flicker spectroscopy | 5× 10–13 erg (or 0.5× 10–19 N m) for erythrocytes57 | Shape fluctuations of vesicles from time series of optical microscopy snapshots | Fig. 1n | |
| Micropipette aspiration combined with optical tweezers | 2.7× 10–19 N m for neutrophils24 | The slope of the equilibrium tube force with the square root of the tension | Fig. 1c,h | |
| Membrane viscosity | Molecular rotors and flippers combined with FLIM | 270 cP (or 0.27 Pa s) in SKOV cells at 23 °C (ref. 58) | Fluorescence | Fig. 1o |
| Interferometric particle detection using optical tweezers | 81× 10–3 Pa s for erythrocytes44 | Power spectral density of the quadrant photodiode voltage | Fig. 1b |