Biology Reference
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differentiate between non-specific binding and specifically controlled
immobilization. Binding of VNPs onto solid supports can be mediated by
(examples and references are given throughout the following sections):
•
van der Waals interactions: these are attractive or repulsive forces
between molecules based on dipole effects. Polar chemical compounds
have dipole moments. The dipole moment is induced by non-uniform
distribution of electron density.
•
Hydrophobic interactions: hydrophobicity (the word is derived from
the Greek language and means “water fearing”) is a physical property;
hydrophobic molecules are repelled from water and attracted to each
other (
birds of a feather flock together
).
•
Hydrophilic interactions: hydrophilic molecules
water (the word
is derived from the Greek language and means “water friendship”).
Hydrophilic interactions are mediated via hydrogen bonding that is the
interaction between hydrogen atoms with electronegative atoms.
like
•
Covalent bonding: a covalent bond is a bond between two molecules
in which pairs of electrons are shared. It is the strongest chemical
interaction.
•
Electrostatic interactions: these are ionic interactions between oppositely
charged molecules. Positively and negatively charged molecules are
attracted to each other (
).
• Biospecific interactions: these include the binding of an antibody to its
target molecule, or the interaction between the protein streptavidin and
its ligand biotin.
Natural binding of TMV on graphite, silicon wafers, mica, glass, and
gold surfaces was tested; the strength of the interaction was monitored by
atomic force microscopy (Knez
opposites attract
., 2004). It is important to point out that,
in contrast to the above-described studies, here binding is not achieved by
drying; rather the particles are captured and bind from the solution phase.
Graphite is a hydrophobic and unreactive surface, and TMV was found
weakly bound on graphite. Physisorption via van der Waals bonding may
explain these interactions. Hydrophilic bonding was observed when TMV
was exposed to hydroxyl-containing surfaces such as silicon wafers, mica, or
glass. Strongest interaction was observed on acyl-chloride-terminated gold
surfaces. Covalent bond formation was confirmed. The acyl chloride termini
of the gold surface can form covalent ester links to the viral hydroxyl surface
groups (Knez
et al
et al
., 2004).
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