Digital Optical and Scanning Probe Microscopy for Inspection and Manipulation of Biocells - Bioanalysis Advanced Materials Methods and Devices - page 89

Fig. 7.2 Window of the AFM controlling program, the regime of static force spectroscopy ( left )
and the typical force curve for erythrocytes ( right )
there is no piezo hysteresis. We have been able to quantify the local elastic
properties of the erythrocytes using the force spectroscopy mode. The force curve
is obtained by recording the cantilever deflection as the tip is brought into contact at
the fixed point and then retracted. The Young's modulus was calculated using the
Hertz model describing the elastic deformation of two bodies in contact under
load [ 36 ]. We consider that the indented sample is assumed to be extremely thick in
comparison to the indentation depth. In this case the elastic modulus can be
calculated as described earlier [ 37 , 38 ].
7.3 Methodology of AFM Testing of Cells
7.3.1 Sample's Preparation
Blood used was of healthy persons surveyed in the Republican scientific practical
center “Cardiology” (Minsk, Belarus). A drop of venous blood stabilized by heparin
was fixed in a 1.5% wt/vol glutaraldehyde solution (Fluka AG). Following fixation
for 30 min at room temperature, the blood solution was centrifuged at 1,500
revolutions per minute for 3 min. The supernatant was discarded and the
erythrocytes were washed twice in a buffer solution (PBS) and twice in water.
The cells were placed on a glass surface and dried at room temperature.
7.3.2 AFM Hardware
AFM researches were carried out using atomic force microscopy NT-206
(“Mi-croTestMachines,” Belarus) working in contact mode. Standard cantilevers
CSC38 (“MikroMasch” Co., Estonia) with a spring constant of 0.03 N/m were used.