Biomedical Engineering Reference
In-Depth Information
As a comparison to the FO-PPR sensor, the sensitivity of the
PPR spectroscopy to a layer of spherical NMNPs on a glass slide in
terms of absorbance change rather than peak wavelength shift was
explored. The slide was immersed in solutions of different refractive
indexes and the spectra were measured in a transmission mode,
as shown in Fig. 5.3. Over the range of RI studied, the response is
linear (
R
= 0.9990) with a slope of 0.12 AU/RIU. In a previous study,
a sensitivity of 0.46 AU/RIU has also been reported.
19
The difference
is probably due to the variation in size and density of the NMNPs
immobilized on the surface. With a noise of 9.0 × 10
−5
AU, the RIR
by PPR spectroscopy as shown in Fig. 5.3 is 7.5 × 10
−4
RIU. Thanks
to the sensitivity gain via the OW sensing technology, multiple TIR
along the optical iber yield an absorbance change per RIU about one
order of magnitude and a RIR of about two orders of magnitude better
than that through a single NMNP layer by the simple transmission
spectroscopy.
Figure 5.3
(A) Absorbance spectra of a monolayer of immobilized gold
nanoparticles on glass in samples of increasing refractive
indexes (1.333, 1.343, 1.353, 1.363, 1.373, 1.383, 1.393,
1.403). The spectra were interrogated via transmission mode.
(B) Linear dependence of the absorbance at 534 nm on the
refractive of the surrounding medium. See also Color Insert.
One of the advantages of a label-free biosensor is its capability of
real-time detection of biomolecular interactions. Figure 5.4 shows
a FO-PPR sensorgram of an analyte, anti-dinitrophenyl antibody
(anti-DNP), with sequential increase in concentration by 10-fold
injected over a surface with immobilized DNP as a receptor. The
real-time response shows response times (time to reach 90% of the
equilibrium signal level) of about 300 s. In this system, a microluidic
chip has been integrated with the FO-PPR sensor, resulting in a
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