Biomedical Engineering Reference
In-Depth Information
anti-OPG. They report that their biosensor exhibited a linear range between 2.5 and 25 pg
(pictogram)/ml. The detection limit was 2 pg/ml. The authors also used their biosensor to
detect OPG in human samples.
The authors report that OPG is a glycoprotein and a member of the TNF (tumor necrosis fac-
tor) receptor super family (Hofbauer and Schoppet, 2001). It is related to bone growth. OPG
reduces or prevents increased bone resorption (
Blair et al., 2006
). Increase in bone resorption
increases bone mineral density and bone volume (
Hofbauer and Schoppet, 2004
).
Boyle et al.
2003
have reported that OPG is a biomarker for lytic bone metases.
Singh et al. (2008)
also
indicate that OPG is linked to osteoporosis (OP), as a result of which the bones become
porous and fragile (
Atkinson, 1964; Trueta, 1966; Singh et al., 2006
). The very low levels
of OPG present in serum make it very difficult for the diagnosis and prognosis of OP (
Boyle
et al., 2003
). Though ELISA is used to detect OPG (
Chen et al., 2001
), it is time-consuming
and tedious, and requires professional technicians.
Singh et al. (2008)
also point out that a
continuous monitoring of OPG in serum is required.
Turner (1997)
reported as early as
1997 that immunosensors may be used as an alternate method to detect OPG in serum.
Skladal et al. (2005)
also recommended the use of RANKL (receptor activator of NF-KB
ligand)-based biosensors and real-time piezoelectric immunosensors for OPG detection
in lieu
of the ELISA method.
Singh et al. (2008)
also report that an electrochemical immunosensor may be a good alternate
to ELISA for sensing OPG because of its low cost, simplicity, rapid measurement capability,
and portability (
Heineman and Halsall, 1985
).
Darain et al. (2003)
have pointed out that an
amperometric biosensor with enzyme label is a good method to detect biomolecules because
of its quick response and high sensitivity.
Singh et al. (2008)
have described the application of CPs to optical devices, energy conver-
sion devices, and biosensors (Cosnier, 1991;
Park, 1997; Doblhofer and Rajeshwar, 1998
).
CPs are attractive for the fabrication of biosensors because they have functional groups such
as -COOH or -NH
2
. Biomolecules may be easily attached to these groups (
Cosnier, 1999
;
Lee and Shim, 2001
;
Ban et al. 2004; Rahman et al., 2005; Kwon et al., 2006a
).
Singh
et al. (2008)
point out that to fabricate a sensitive biosensor, stable immobilization pro-
cedures for the active biomolecules are necessary.
They have developed an amperometric OPG biosensor (immunosensor) by covalently
immobilizing an antibody onto silver nanoparticles (Au NPs) deposited poly TTCA
(5,2
0
5
0
,2
00
-terthiophene-3
0
-carboxylic acid) modified electrodes. Theyreport that Au NPs
deposited CP layers exhibit high electrocatalytic activity, increasing conductivity, and sensi-
tivity (
Ivnitski and Rishpon, 1996; Katz and Willner, 2004; Wang et al., 2006; Shiddiky
et al., 2007
). They have optimized the performance of their OPG biosensor by analyzing
the following biosensor parameters such as anti-OPG amount, incubation time, pH, and
applied potential in chronoamperometric measurements.
