Biology Reference
In-Depth Information
a component of electrochemical transducers [21].
Nanocomposites
can be fabricated not only with nanostructured materials, but also
with biomolecules and redox polymers to achieve unique hybrid
and synergistic properties. It is expected that the combination of
nanoengineered “smart” polymers with novel biocompatible nanos-
tructuredfillers—likeNPsandCNT—maygeneratecompositeswith
new and interesting properties, such as higher sensitivity and sta-
bility of the immobilized molecules, thus constituting the basis for
improved electrochemical biosensors.
Theimmobilizationoftheoligoprobe—whichspecificallyrecog-
nizes the DNA target—onto the transducer is also a key issue in the
constructionofbiosensingdevices.Thechoiceoftheimmobilization
method depends mainly on the biomolecule to be immobilized,
the nature of the solid surface, and the transducing mechanism
[22]. Besides the sensitivity, the ability of the electrochemical trans-
ducer to provide a stable immobilization environment while retain-
ing the bioactivity must also be considered: a current problem
regarding the immobilized biomolecules is the lack of stability and
activity in the solid transducer, which is usually overwhelmed by
mimicking in vivo-like environment or the use of spacer arms.
The most successful immobilization methods involve (i)
multisite
attachment
, either electrochemical—by the application of a poten-
tial to the solid support—or physical adsorption, or (ii)
single-point
attachment
—mainly covalent immobilization, a
nity linkage such
as strept(avidin)/biotin binding [23]) and chemisorption based on
self-assembled monolayers(
SAMs
)[16].
Among the different immobilization strategies, multisite
adsorp-
tion
is the simplest and most easily automated procedure, avoiding
the use of pretreatment procedures based on previous acti-
vation/modification of the surface transducer and subsequent
immobilization. Such pretreatment steps are known to be tedious,
expensive, and time-consuming. Furthermore, the adsorption prop-
erties of DNA on various supports (e.g., nylon, nitrocellulose) have
beenknownforalongtime[24].Thebindingforcesinvolving
physi-
caladsorption
includehydrogenbonds,electrostaticinteraction,van
der Walls forces, and hydrophobic interactions if water molecules
are excluded by dryness [25]. Wet adsorption originates a weak
binding that causes easy desorption of the biomolecule from the
