Biomedical Engineering Reference
In-Depth Information
Drouvalakis et al. (2008)
report that the detection of the serum antibodies binding to the anti-
gen-functionalized carbon nanotubes was undertaken at the third harmonic resonance of the
sensing crystal (QCM). The binding of the antibodies to the immobilized antigen resulted in a
mass uptake, which subsequently decreased the natural vibration of the nanotubes. This was
then measured as a change in the frequency of the quartz crystal.
They also report that the antibody reactive epitope of the citrullinated peptide is conserved
upon immobilization to the nanotubes. This preserves the conformation of the antibody,
minimizing the loss of relevant binding sites. This was noted by the higher reactivity of
the RA serum to the citrullinated peptide than to the noncitrullinated peptide.
They presented further evidence of the preservation of antibody recognition sites on the
nanotube surface. They noted a higher number of RA patients with antibodies to the
citrullinated peptides (71.8%) compared to healthy patients (7.7%) and osteoarthritis patients. They
report that autoantibodies may also be found in 15% of healthy individuals. However, less
than 1% of healthy individuals possess autoantibodies to citrullinated antigens.
Drouvalakis et al. (2008)
report that their nanotube-based biosensor is more sensitive than
either ELISA or the microarray systems, as a greater number of RA patients were found to
be positive for anti-citrullinated peptide antibodies by their nanotube method, compared with
the two detection methods mentioned above. For example, their test for sensitivity, using
the nanotube method, was 71.9% for the detection of anti-citrullinated peptide antibodies,
compared to ELISA (37.5%) and microarray systems (34.4%). They conclude by pointing
out that due to the high sensitivity and specificity demonstrated by their nanotube-based bio-
sensor, this is an effective method for the detection of RA-specific autoantibodies. Their
method is also more time efficient and is a cost-effective assay as it excludes (a) the need
for a secondary molecule, and (b) the labeling of sera or a protein component to detect the
antigen-antibody binding as required by either ELISA or the microarray system. Also, their
nanotube biosensor detects proteins in the femtomolar range, which exceeds that detected
by ELISA.
5.9 Gold Nanoparticle Amperometric Immunosensor (Biosensor)
for OPG (
Singh et al., 2008
)
Singh et al. (2008)
have recently fabricated an amperometric immunosensor for the detection
of osteoproreogerin (OPG) by depositing gold nanoparticles (Au NPs) on a functionalized
conducting polymer (CP) (5,2
0
5
0
,2
00
-terthiophene-3
0
-carboxylic acid). Monoclonal antibody
(anti-OPG) was covalently attached to the Au NPs. Cyclic voltametry was used to electro-
chemically deposit the Au NPs on the CP. The authors used X-ray photoelectron spectros-
copy (XPS) to confirm the immobilization of the anti-OPG. Their biosensor is based on
a competitive immunoassay between free-OPG and labeled-OPG for the active sites of
