Biomedical Engineering Reference
In-Depth Information
CNTs have been used as good transducing nanoplatforms
for molecular recognition with optimal biosensing capability.
Functionalizations of the CNTs have been performed by DNA [209,
211, 213, 214, 216, 217] for hybridization purposes, by antibodies
[208] to study selective antigen-antibody reactions, by proteins
[202, 210] and enzymes [195, 197] for efficient induced electrical
charge modulation, by modified SWCNTs microelectrodes for
electrochemical measurements of epinephrine in presence of ascorbic
acid [250]. Additionally, it was demonstrated [251] that nanotube
tips with the capability of chemical and biological discrimination
can be created with acidic functionality and by coupling basic or
hydrophobic functionalities or biomolecular probes to the carboxyl
groups that are present at the open tip ends. Lieber
[251]
had used these modified nanotubes as AFM tips to titrate the acid
and base groups, to image patterned samples based on molecular
interactions, and to measure the binding force between single
protein-ligand pairs. As carboxyl groups are readily derivatized by
a variety of reactions, the preparation of a wide range of function-
alized nanotube tips should be possible, thus creating molecular
probes with potential applications in many areas of chemistry and
biology at nanoscale level.
Furthermore, macromolecules are used to functionalize the
CNTs for enhanced gas sensing properties, even at room tempera-
ture. Particularly, metalloporphyrins (MPPs) are among the fun-
ctional materials characterized by flexible and multiple molecular
recognition properties. The basic porphyrin ring is an extended
aromatic system formed by four pyrrolic rings linked by methynic
bridges. This basic structure is turned into a metalloporphyrin
when a transition metal atom (Fe, Co, Ni, Cu, Mo, Zn, Mn, etc.)
replaces the two hydrogen atoms at the central core. Also, other
modifications include compounds at the lateral positions. Thus,
a metalloporphyrin can offer a wide variety of interaction mech-
anisms that can be exploited for gas sensing. Recently, Penza
et al.
.
[231], in collaboration with two groups of Chemical Sciences and
Technologies and Electronic Engineering from University of Rome
Tor-Vergata, demonstrated the effect of the surface functionalization
of the CNTs networked films with spray MPP layer on gas sensitivity.
MPP-modified CNTs networks exhibited an increased sensitivity of
the electrical resistance toward concentrations of common volatile
organic compounds of alcohols, amines, aromatics, ketones, at
et al
