Optical Methods in Studies of Olfactory System - Bioelectronic Nose: Integration of Biotechnology and Nanotechnology - page 203

µααω == EE

0 cos(

t )

ind i

The molecular polarizability changes with bond length and the bond length oscillat-
ing at vibrational frequency would yield.

d α

αα =+− ( rr ) , rr −= r cos( ω t )

0 eq eq max vib

dr

Therefore, combining all conditions together with simple Euler's formula, we ob-
tain the basic equation for Raman.

1 d α

( ) ( ) ( )

µα ω = E cos t + Er [cos ( ωω ωω + ) t + cos ( − )] t

ind 0 0 i 0 max i vib i vib

2 dr

Rayleigh Anti − Stokes Stokes

Due to the near instantaneous results allowing samples to be analyzed at some dis-
tance from the instrumentation [ 43 ], the potential of this technique for use as bio-
logical molecule detection has led to considerable work within this area. A review
that describes advances in the capacity of portable Raman instrumentation has also
highlighted some of the issues relating to producing instrumentation for field de-
ployable apparatus [ 44 ]. Sensitivity is a key, and much of this has been addressed
by using techniques such as surface enhanced Raman spectroscopy that displays
significantly higher sensitivity. Since much of the equipment used is still laboratory
based, future trends indicate that portable instruments are increasing in need and be-
ing developed. Use of fiber optic technology to allow remote sampling is also being
investigated as an alternative avenue. To examine GPCR, the Mathies laboratory at
UC Berkeley utilized resonance Raman spectroscopy to observe rhodopsin mutants
with effect of substitutions in the third transmembrane helix [ 109 ], photoactivation
of the GPCR rhodopsin [ 110 ] and the structure of primary isomerization [ 111 ].
In liue of a weak Raman signal from Raman spectroscopy, a complementary
technique, Surface-Enhanced Raman Scattering (SERS) is used to enhance the in-
tensity of Raman scattering spectra through the proximity of a molecule to a bumpy
metal surface or, in the case of nanoparticles, between gaps in nanostructures or
nanoparticles. As shown in Fig. 11.11 , the embedded equation estimates the scat-
tering signal amplification for SERS. The total amplified SERS signal, P SERS (ν S ) is
directly proportional to the Raman cross section σ R ads , the excitation laser intensity
I L , and the number of molecules N involved in the SERS process. In the equa-
tion,

A ν stands for the local enhancement factors for the laser and for
the Raman scattered field, respectively. These were demonstrated to show extreme
signal amplification (up to 10 12 ~ 10 15 ) of biological molecules including viruses
[ 112 ], beta-amyloid and so forth with their unique Raman signatures. Thanks to
its unique merit in significant signal amplification and molecular signatures, the
University of Ottawa research laboratory utilized functionalized silver nanoparticle
for tagging β 2 ARs to observe signaling domain formation under SERS microscopy
[ 113 ]. A Polish research group then monitored natural ligands of the GPCRs using

A ν and ()

L

()
S