Biomedical Engineering Reference
In-Depth Information
single-walled carbon nanotubes modii ed graphite sensors to compare voltam-
metry and impedance spectroscopy studies for the monitoring of direct DNA
hybridization related to a specii c sequence of Hepatitis B virus. h e authors
found an enhanced electrochemical signal when using the carbon nanotube
platform compared with that provided by bare graphite. A similar platform was
used by Weber and coworkers for the impedimetric detection of Salmonella
enterica serovar Typhimurium related sequences [95], or by Erzem with oth-
ers to detect the cyanobacteria source of microcystin toxins. [96].
A carboxylic group-functionalized multiwalled carbon nanotube
(MWNTs-COOH) modii ed platform was also used by Xu
et al.
[97] to per-
form a doping of nucleic acid probes within electropolymerized polypyrrole
(PPy) i lm deposited on the electrode surface. At er the hybridization reac-
tion a decreased impedance value was obtained, which was attributed to the
lower electronic transfer resistance of dsDNA than ssDNA. h e developed
sensing interface revealed an increased conductivity and active surface area.
In a dif erent work, the same group used a similar platform to monitor the
impedance changes provoked by the metallation of DNA double helix at er
hybridization [98]. Several metals such as Zn
2+
, Co
2+
, and Ni
2+
were used for
the formation of metal-DNA complex (M-DNA). Results showed that Zn
2+
-
DNA complex had the best ability to transport electrons in M-DNA double-
stranded chains when compared with the other M-DNAs.
A dif erent composite was used by Jiang and coworkers [99] for the
impedimetric detection of transgenic plants gene fragment. h e DNA
probes were immobilized on a polylysine/single-walled carbon nanotubes
modii ed electrode through electrostatic adsorption on polylysine i lms.
h e obtained platform presented an enhanced conductivity, with an esti-
mated detection limit in the pM range.
A nanocomposite membrane, including nanosized shuttle-shaped
cerium oxide (CeO
2
) and single-walled carbon nanotubes (SWCNTs),
was developed by Zhang
et al.
[100] for the electrochemical sensing of the
immobilization and hybridization of DNA. h e synergistic ef ect of the
nanocomposite could dramatically enhance the sensitivity of DNA hybrid-
ization recognition. h e charge transfer resistance of the electrode surface
increased at er the immobilization of ssDNA probes and rose further at er
the hybridization with the complementary target, thus achieving a detec-
tion limit in the pM range by working in a label-free protocol.
In a dif erent work, a polyaniline nanoi ber modii ed carbon paste elec-
trode was used as a platform to bind nanogold-carbon nanotubes composite
nanoparticles [101]. On this electrode surface the immobilization and hybrid-
ization of DNA sequences was investigated by dif erential pulse voltamme-
try, cyclic voltammetry, and electrochemical impedance spectroscopy. h e
