Atomic Force Microscopy-Based Force Spectroscopy …
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curves are discussed in detail [8]. The quantitative parameters analogues to the such
forces were determined through the polynomial functions [8]. For instance, wormlike [13] or the freely joined [14] chain model which are described in literature that
can be suitably applied for studies associated with polymer extension. Some specific
requirements like precise spring constant calibration of the cantilevers used is very
essential for quantitatively analyze these force–curves. Attributes like stiffness of
cantilever relies on shape of cantilever and properties of materials [15]. Typical range
for cantilevers stiffness lies between 10 and 10
5 pN/nm. However, the value of spring
constant is given by the manufacturer on purchased tip box, various experimental
values could be observed among cantilevers from the same batch. Therefore, to
accurately interpret the forces analogous to the curve of force versus distance, it is
very crucial to utilize a specified and calibrated spring constant. Besides this, it is
important to note that if the tip is functionalized or coated (vd. infra), the cantilever
spring constant also get modified. Thermal noise method developed in 1993 by Hutter
and Bechhoefer, is the most commonly used calibration procedure [16]. Thermal
noise is a straightforward technique used in air and liquid, with the variation of
10–20% in the accuracy of the measurements.
4 Types of AFM-FS Measurements:
4.1 Modulus Measurement
Wide range of mechanical properties such as adhesion, stiffness, rupture force,
Young’s modulus, and indentation depth can be explored from the atomic force
curves. Contact mechanics describes the various models in literature to explain the
tip-sample interaction and extract relevant mechanical properties from the curve of
forces. Various contact mechanics models such as Sneddon, DMT, Hertz and JKR are
available in literature. The use of such models relies on the sample and the characteristic interaction of the tip with sample. The authenticity of the mechanical properties
obtained from the models were extracted from the fitting of experimentally obtained
force curve with the appropriate model.
4.2 Adhesion Measurement
Determining the stickiness or adhesiveness of sample with atomic force microscopy
is also possible by measuring the adhesive dip in a force curve collected through
atomic force microscopy-based force spectroscopy. This adhesion measurement can
also be extended to single cells and bacteria.
591
curves are discussed in detail [8]. The quantitative parameters analogues to the such
forces were determined through the polynomial functions [8]. For instance, wormlike [13] or the freely joined [14] chain model which are described in literature that
can be suitably applied for studies associated with polymer extension. Some specific
requirements like precise spring constant calibration of the cantilevers used is very
essential for quantitatively analyze these force–curves. Attributes like stiffness of
cantilever relies on shape of cantilever and properties of materials [15]. Typical range
for cantilevers stiffness lies between 10 and 10
5 pN/nm. However, the value of spring
constant is given by the manufacturer on purchased tip box, various experimental
values could be observed among cantilevers from the same batch. Therefore, to
accurately interpret the forces analogous to the curve of force versus distance, it is
very crucial to utilize a specified and calibrated spring constant. Besides this, it is
important to note that if the tip is functionalized or coated (vd. infra), the cantilever
spring constant also get modified. Thermal noise method developed in 1993 by Hutter
and Bechhoefer, is the most commonly used calibration procedure [16]. Thermal
noise is a straightforward technique used in air and liquid, with the variation of
10–20% in the accuracy of the measurements.
4 Types of AFM-FS Measurements:
4.1 Modulus Measurement
Wide range of mechanical properties such as adhesion, stiffness, rupture force,
Young’s modulus, and indentation depth can be explored from the atomic force
curves. Contact mechanics describes the various models in literature to explain the
tip-sample interaction and extract relevant mechanical properties from the curve of
forces. Various contact mechanics models such as Sneddon, DMT, Hertz and JKR are
available in literature. The use of such models relies on the sample and the characteristic interaction of the tip with sample. The authenticity of the mechanical properties
obtained from the models were extracted from the fitting of experimentally obtained
force curve with the appropriate model.
4.2 Adhesion Measurement
Determining the stickiness or adhesiveness of sample with atomic force microscopy
is also possible by measuring the adhesive dip in a force curve collected through
atomic force microscopy-based force spectroscopy. This adhesion measurement can
also be extended to single cells and bacteria.