Biology Reference
In-Depth Information
10
Atomic Force Microscopy Measurements
of Intermolecular Binding Strength
Gradimir N. Misevic
1. Introduction
Intermolecular binding forces are intrinsic property of cohesive structures
and should be used as the main quantitative criteria for assessing and defining
their functional contribution to the maintenance of the anatomical integrity of
the adult and embryonal multicellular organism, to fertilization, to blood cell
adhesiveness in normal and pathological conditions, to tumor cell adhesion, to
parasite-host interactions, and to cellular associations in symbiotic organism.
Recently, a novel technology of atomic force microscopy (AFM) measure-
ments of binding strength between a single pair of cell adhesion molecules in
various physiological solution was developed
(1)
. Binding studies, calorimet-
ric, and spectroscopic analyses do not provide direct information about bind-
ing forces and are thus complementary kinetic methods to AFM measurements.
The AFM was initially built and is used mostly by physicists as a superb
atomic imaging instrument for examination of solid-surface topography
(2)
.
To be able to determine intermolecular binding forces with AFM complemen-
tary cell adhesion, molecules have to be covalently crosslinked to a silicon-
nitride sensor tip and an atomically flat mica-silicon surface
(1)
. Because the
AFM tip has a 10-20-nm diameter and most of the cell-adhesion molecules
are over 20 nm in diameter, not more than one molecule could be attached
to the tip assuring measurements between the single molecular pair. The
crosslinking process consists of deposition of 10-30-nm gold on the two sur-
faces by evaporation in high vacuum, followed by formation of self-assembled
monolayer of either 11-thio-undecanol or 11-thio-undecanoic acid. A very high
density of hydroxyl and carboxyl groups are completely converted with
carbonyldiimidazole in dry methanol to give highly reactive imidazole car-
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