Biomedical Engineering Reference
In-Depth Information
obtained a complementary electrical response for the detection of PSA with a
detection limit of 0.14 nM (5 ng/mL). The device consisted of a source and a
drain electrode, placed on a Si gate with a SiO
2
layer, where SWCNTs and NWs
formed the active channel.
80
Anti-PSA monoclonal antibody was reacted with activated NWs, while
SWCNTs were non-covalently functionalised through
π
-
π
interactions with
1-pyrenebutanoic acid and allowed to react with the same antibody after
activation of the carboxylic group. The device was incubated with a PSA
solution (1
μ
g/mL) for 15 hours, and after washing the surface, current
measurements were performed in air. Because of the interaction with PSA,
the conductance increased for NWs and decreased for SWCNTs, which are
respectively
negative-
and
positive-
type semiconductors and respond with
opposite behaviour. The limit of detection was determined by current
response, which was 0.14 nM (5 ng/mL) for NWs and 1.4 nM (50 ng/mL)
for SWCNTs. Considering the signal-to-noise ratio for NWs (20), the effective
limit of detection was 7 pM (250 pg/mL).
Okuno
et al.
proposed an immunodetector for total PSA by using differential
pulse voltammetry (DPV). This device was based on the speciic oxidation of
tyrosine and tryptophan residues (PSA contains 13 tyrosine residues and 11
tryptophan residues) after the interaction of PSA and anti-PSA monoclonal
antibody. The apparatus is
p
-type and Si-based with a layer of SiO
2
(150 nm
thick), and the working electrode is obtained by patterning the surface with Ti/
Pt and, afterwards, with CNTs. The latter were non-covalently functionalised
with 1-pyrenebutanoic acid to link the PSA monoclonal antibody.
81
Yu
et al.
proposed a more complicated system, in which they used an
SWCNT forest as a platform for a multi-labelled secondary antibody conjugate,
achieving a detection limit of 4 pg/mL (100 amol/mL). In this system, BSA and
Tween 20 were used to prevent non-speciic binding, and primary anti-PSA
antibodies were covalently bound to the SWCNT forest. Shortened MWCNTs,
instead, were used to build a system bearing anti-PSA secondary antibodies
and horseradish peroxidase (HRP), which act to amplify the signal. This
strategy led to a remarkable sensitivity and selectivity in complex samples
as human serum and cell lysate, which present many different components,
and to a gain in mass sensitivity that was better than all commercial PSA
detectors.
82
A more developed device was prepared by Gruner
et al.
Recognising
the demand to engineer devices able to analyse biological luids at room
temperature with fast and speciic procedures, the researchers designed a
novel capacitor with an SWCNT network and a reference electrode immersed
in a liquid electrolyte.
83
The use of CNTs in a capacitor coniguration
permits obtaining a two-terminal device. CNTs are printed on polyethylene
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