Taken form biocore
http://www.biacore.com/lifesciences/t...Surface Plasmon,Surface Enhanced Raman Spectrospcoy, Analytical Technique, Rapid Bacterial detection
The
surface plasmon resonance (SPR) phenomenon occurs when polarized light,
under conditions of total internal reflection, strikes an electrically
conducting gold layer at the interface between media of different
refractive index: the glass of a sensor surface (high refractive index)
and a buffer (low refractive index).
A wedge of polarized light,
covering a range of incident angles, is directed toward the glass face
of the sensor surface. Reflected light is detected within a Biacore
system.
An electric field intensity, known as an evanescent wave,
is generated when the light strikes the glass. This evanescent wave
interacts with, and is absorbed by, free electron clouds in the gold
layer, generating electron charge density waves called plasmons and
causing a reduction in the intensity of the reflected light.
The
resonance angle at which this intensity minimum occurs is a function of
the refractive index of the solution close to the gold layer on the
opposing face of the sensor surface.
As molecules are immobilized
on a sensor surface, the refractive index at the interface between the
surface and a solution flowing over the surface changes, altering the
angle at which reduced-intensity polarized light is reflected from a
supporting glass plane.
The change in angle, caused by binding or
dissociation of molecules from the sensor surface, is proportional to
the mass of bound material and is recorded in a sensorgram.
When
sample is passed over the sensor surface, the sensorgram shows an
increasing response as molecules interact. The response remains constant
if the interaction reaches equilibrium. When sample is replaced by
buffer, the response decreases as the interaction partners dissociate.
Complete
profiles of recognition, binding and dissociation are generated in real
time. From these profiles, data such as specificity, affinity, kinetic
behavior and sample concentration can be determined.
For most
applications, a dextran matrix covering the gold layer enables molecules
to be immobilized to a sensor surface and provides a hydrophilic
environment for interactions. Surface specificity is determined by the
nature of the immobilized molecule.
Since light does not
penetrate the sample, interactions can be followed in colored, turbid or
opaque samples. No labels are required and detection is instantaneous.
PS: Biacore has made a new video about this topic. Check the following link:
http://www.youtube.com/watch?v=o8d46u...
