Biomedical Engineering Reference
In-Depth Information
its initial concentration is negligibly small, then the thermodynamic
equilibrium association constant, K a , of the reaction can be expressed
as
θ
K
=
a
(5.17)
0 .
[](1-0)
X
where θ is the fractional coverage (in molar ratio) of X on a full
monolayer of B and [ X ] 0 is the initial concentration of the analyte in
solution.
At full coverage of X (i.e., θ = 1), I S should be at a minimum value,
I min , and results in a maximum change in intensity, Δ I max = I R - I min .
If we further assume that the change in intensity signal from a
FO-PPR sensor is proportional to the change in θ , then
ax .
I
-
I
=Δθ
I
(5.18)
RS
Combining Eqs. 5.17 and 5.18 results in the following
expression:
1
1
1
= ΔΔ
+
(5.19)
. .
I
-
I
I
I
KX
[ ]
RS
ax
ax a
0
Hence, a linear plot of 1/( I R - I S ) versus 1/[ X ] 0 would allow the
calculation of K a by dividing the y intercept by the slope.
5.3
Optical Fiber-Based PPR Biosensor
The use of optical ibers for sensing has many attractions, in particular
the intrinsic freedom from electromagnetic interference, high
information capacity (using wavelength discrimination), the relative
safety in explosive environments, the ability to be multiplexed in a
distributed system, and the low attenuations which make remote
measurements feasible. With the addition of label-free and real-time
detection capabilities, the scope of iber optic biosensors could be
further extended to in vivo , on-line, and on-site applications. In this
regard, the FO-PPR biosensor may be one of the ideal candidates.
The development of the FO-PPR sensor was irst reported by
Cheng and Chau in 2003. 23 The report demonstrated the ability
of the FO-PPR sensor to transduce changes in the surrounding RI
into ATR spectra and a refractive index resolution (RIR, deined as
minimum change in refractive index unit, RIU, that can be resolved
 
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