Biomedical Engineering Reference
In-Depth Information
the two-step mediated growth method. This is similar to the wet-chemical synthesis of gold-
rod shaped nanoparticles proposed earlier (
Jana et al., 2001; Murphy et al., 2005
). They point
out that the three most important variables during surface synthesis are:
(a) The electrochemical coupling between gold, silver, and ascorbic acid,
(b)
time,
(c)
and temperature.
Noguez (2007)
had reported earlier that these variables affect the size and shape of the
nanoparticles, and subsequently their optical properties.
Murphy et al. (2005)
have pointed
out that the presence of silver ions in solution during the colloidal growth phase helps
improve the yield of the gold nanorods.
Olkhov and Shaw (2008)
analyzed the antigen-antibody binding between BSA and anti-BSA,
and between human fibrinogen (HFG) and anti-HFG. They functionalized the biophotonic
surface using the
Hermanson et al. (1992)
two-step DTSP (dithiobis-succinimidyl propionate)
coupling chemistry procedure. They also constructed a simple reader to monitor the intensity
of the scattered light from each array. They reported that the sensitivities in their array-based
system is a trade-off between resolution and throughput (
Rich and Myszka, 2007
).
They also point out that there are intensity variations in each of the array spots due to the
following reasons:
(a) bulk solution and transparency,
(b)
laser power fluctuations, and
(c)
camera collection efficiency, for example, shutter-opening time.
NSB may also lead to biological noise. The authors report that there is no decrease in signal
when the sensor array exposed to the antibody solution is exposed to buffer. This indicates
that antibody-antigen dissociation is negligible. Using a simple kinetic model,
Olkhov and
Shaw (2008)
were able to show that the binding (adsorption,
k
a
) constants were (2.5
10
3
M
1
s
1
, respectively. The heterogeneity or the fractal
dimension on the sensor surface was not taken into account.
10
3
M
1
s
1
and (6.6
0.6)
0.6)
Olkhov and Shaw (2008)
report in conclusion that their array reader shows that nanoparticle
light scattering may be used to interrogate a biomarker printed on an array spot on a bio-
photonic surface. They emphasize that the sensitivity to NSB is reduced due to the short-
range nature of the nanoparticle plasmon field which typically penetrates one radius into
the medium above the particle. In comparison, the continuous surface plasmon resonance
propagates typically 300 nm into the medium above the metal. They also point out that the
localization of the particle plasmon offers distinct advantages over the continuous surface
biosensor.
