Digital Optical and Scanning Probe Microscopy for Inspection and Manipulation of Biocells - Bioanalysis Advanced Materials Methods and Devices - page 87

7.2 Single Biocell Test
Methods for using AFM to study biological objects can be divided into two main
groups respectively dealing with high-resolution visualization and evaluation of
local mechanical properties (elasticity). A new direction of study is developing in
cytology, which investigates “cell nanomechanics.”
7.2.1 Cellular Elastography
Elastography is a method of measuring the elastic properties of biological soft
tissues [ 17 - 21 ]. Today elastography is widely used in the form of ultrasonic,
optical, and magnetic resonance methods, which allow the access and analysis of
the information about the mechanical properties of tissues and organs The evalua-
tion of these properties may be applied widely, including in oncology (the detection
of size and shape of tumors), in neurology, in traumatology, in transplantology, in
dermatology, in anesthesiology, and in sports medicine [ 22 - 24 ]. Moreover, patho-
physiological changes in the mechanical properties of the tissues may show up at
single cell level, and thanks to AFM this problem can be addressed. Assessment of
structural features of the cell surface and the local elastic modulus is of interest
from the point of view of both the pharmaceutical treatment of the cells and the
dynamics of the mechanical properties. These important aspects relate to cellular
migration [ 25 - 27 ], to the process of cytodifferentiation [ 28 , 29 ], to cellular aging,
and to the development of cellular pathology [ 30 , 31 ].
Another important development in this field is direct AFM measurement of
interaction forces between ligands and receptors [ 32 - 34 ]. When a scan of a soft
and delicate object like a biological cell is treated in contact mode the surface may
be damaged by the probe if the loading force is too large. Deducing a guiding
principle for the magnitude of the force required for cell manipulation is valuable
for cellular level surgery.
Hemodynamic particles in the investigations reported here are erythrocytes (red
blood cells) due to their availability. At the same time, erythrocyte membranes have
similar principles of organization as biological membranes. Therefore it is conve-
nient to use them for natural models for cell elastography methods, currently being
developed to study the general structural and functional characteristics of
membranes [ 35 ].
As mentioned in the Introduction, the use of laser light for illumination opens
additional possibilities for biotissue monitoring. Coherent light scattered by a
biotissue under study produces a random granular interference structure some
distance away from the object, which is called a biospeckle pattern [ 6 - 8 ], as in
Fig. 7.1 (right). The potential of monitoring biotissues based on speckle pattern
analysis will be discussed in Sect. 7.5 .