Optical Waveguide-Based Biosensors Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 93

In the determination of ANA in sera from patients 25 or IL-1β in
synovial luids from patients with osteoarthritis, 69 the GNP surface
was covalently coupled with extractable nuclear antigens or anti-
IL-1β, respectively. The results by both sensors agree quantitatively
with the clinically accepted ELISA method. Furthermore, the FO-PPR
sensor for ANA is more sensitive than ELISA, the gold standard in
immunoassay, by at least an order of magnitude, and the analysis
time is signiicantly shorter (<15 min) as compared to ELISA.
The FO-PPR sensor not only works in the transmission mode,
but has also been developed into a dip-probe coniguration. 24 The
dip-probe has been used to detect SEB 24 and lead ion. 66 Moreover,
the dip-probe has also been developed to determine RI, nickel
ion, streptavidin, and immunoglobulin G (IgG) at high-pressure
conditions (up to 20.4 MPa), 76 which provides a basis as a detector
for supercritical chromatography.
Different iber optic probe design including straight, U-bent,
D-shape, tapered, and biconical tapers have been employed in
development of absorbance-based biosensor. U-bent probes have
been demonstrated to have a 10-fold improvement in absorbance
sensitivity over straight probes. 77 Mukherji and coworkers combined
the advantage of NMNP with U-bent iber optic probe to develop a
U-bent FO-PPR sensor, which showed a RIR of 3.8 × 10 −5 RIU and a
sensitivity of 35 AU/RIU at 540 nm. 78 With IgG as the immobilized
receptor to detect anti-IgG, a DL of 0.8 nM was achieved. D-shape
optical iber fabricated by femotosecond laser micromachining
has been used to develop a small-size FO-PPR sensor, 79 which can
take advantage of the technologies established by the iber optic
communication industries and also fulill the need for in vivo analysis.
The D-shape FO-PPR sensor showed a RIR of 1.4 × 10 −4 RIU. Besides
using optical ibers of different geometries, FO-PPR sensor based on
long-period iber grating (LPFG) has also been developed. 80 By this
approach, when the GNP surface is modiied with DNP, the sensor
can detect anti-DNP down to 9.5 × 10 −10 M.

5.4 Planar Waveguide-Based PPR Biosensor

Cylindrical waveguides show some interesting features because they
allow remote measurements and are capable of reaching places hard
to access for in situ environmental monitoring or in vivo bioanalysis.