Optical label-free biosensor structures
2.1. Surface plasmon resonance based biosensors
Surface plasmon resonance (SPR) biosensor was first demonstrated
for biosensing in 1983 by Liedberg et al. [13]. Since then
it has been extensively explored and has gradually become a
very powerful label-free tool to study the interactions between
the target and biorecognition molecules. The principle, development,
and applications of SPR biosensors have been well
described in several excellent review papers [14–17].
A surface plasmon wave (SPW) is a charge density oscillation
that occurs at the interface of two media with dielectric
constants of opposite signs, such as a metal (gold or silver) and
a dielectric. There are four basic methods to excite the SPR, as
shown in Fig. 2: prism coupling [18], waveguide coupling [19],
fiber optic coupling [20], and grating coupling [21,22]. In the
prism coupling configuration (Fig. 2(A)), the incident light is
totally reflected at the prism–metal interface and generates an
evanescent field penetrating into the metal layer. At the resonant
angle or resonant wavelength, the propagation constant
of the evanescent field matches that of the SPW as described
in Eq. (1), and as a result, the photon will be coupled into the
SPW.
2
np sin = ˇsp, (1)
Optical label-free biosensor structures
2.1. Surface plasmon resonance based biosensors
Surface plasmon resonance (SPR) biosensor was first demonstrated
for biosensing in 1983 by Liedberg et al. [13]. Since then
it has been extensively explored and has gradually become a
very powerful label-free tool to study the interactions between
the target and biorecognition molecules. The principle, development,
and applications of SPR biosensors have been well
described in several excellent review papers [14–17].
A surface plasmon wave (SPW) is a charge density oscillation
that occurs at the interface of two media with dielectric
constants of opposite signs, such as a metal (gold or silver) and
a dielectric. There are four basic methods to excite the SPR, as
shown in Fig. 2: prism coupling [18], waveguide coupling [19],
fiber optic coupling [20], and grating coupling [21,22]. In the
prism coupling configuration (Fig. 2(A)), the incident light is
totally reflected at the prism–metal interface and generates an
evanescent field penetrating into the metal layer. At the resonant
angle or resonant wavelength, the propagation constant
of the evanescent field matches that of the SPW as described
in Eq. (1), and as a result, the photon will be coupled into the
SPW.
2
np sin = ˇsp, (1)
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