Biomedical Engineering Reference
In-Depth Information
A
B
d n 4 t 3 n g | 2
C
n 3 .
Figure 5.9 Operational principles of SPR system employed or biochemical detection
and measurement of neural activity. (A) Target molecules bind to the
specific, surface immobilized receptors. (B) The specific interaction is
detected as a shift in resonance angle. (C) Schematic of the SPR system
used to measure neural activity. 20
(Reprinted by kind permission of the Optical Society of America.)
associated with nerve activation presumably comes not only from conforma-
tional
changes of macromolecules, but
also from cellular
swelling
described above.
The experiment presented in Figure 5.9(c) shows simultaneous electrical and
optical detection at the metal-nerve interface. Electromagnetic waves
propagate through the conductor-dielectric interface. Detection is based on the
highly sensitive resonance of the SPR sensor and takes place in the very small
volume represented by the thin layer on the surface. The experimental setup
was based on the attenuated total reflection configuration, in which an incident
beam was coupled through a BK7 prism on a glass slide. An SPR sensor chip
with a 50 nm thick gold-coated film on a microscopic BK7 glass slide was
modified for use as a recording chamber using a Teflon ring. A low-noise laser
diode with a wavelength of 635 nm and an output power of 5 mW was used.
The laser beam was focused onto a point with a beam diameter of 100 mm. An
intensity-based SPR sensor was used because its sensitivity is reported to be
equal or superior to that of a phase-sensitive method. The reflection intensity of
the laser beam was detected through a multichannel photodetector array. The
output currents (I 1 ,I 2 in Figure 5.9(c)) from two vertical elements of the
 
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