Biomedical Engineering Reference
In-Depth Information
Dielectric medium
SPR
Metal layer
Optical
prism
Dielectric medium
SPR
Metal layer
Waveguide
Metal layer
SPR
FIGURE 18.1
Excitation of surface plasmon resonance (SPR): (a) by prism coupling: a
light wave passes through a high-refractive-index prism and is totally
reflected at the prism
metal layer; (b) by optical waveguide: the light
wave is guided by an optical waveguide and, when entering the region
with a thin metal layer, it evanescently penetrates through the metal
layer exciting an SPR at its outer boundary; and (c) by light diffraction on
a diffraction grating: the component of the wave vector of the diffracted
waves parallel to the interface is diffraction-increased by an amount that
is inversely proportional to the period of the grating and can be matched
to that of an SPR.
Dielectric medium
SPR
Metal layer
(Cambridgeshire, UK), Nippon Laser and Electronic Lab (Nagoya, Japan), and Texas
Instrument (Dallas, TX) (9).
Foodborne pathogens or toxins are detected using specific antibodies on the gold-SPR
surface allowing a label-free detection of analytes. SPR has been employed to detect
E. coli
O157:H7 at 10
7
cfu/ml (11), at 10
2
cfu/ml (12), or at 10
5
-10
8
cfu/ml (13).
Salmonella
was
detected at 10
2
-10
9
cfu/ml (14-17), and
L. monocytogenes
cells were detected at 10
5
-10
7
cfu/ml (15,18,19). The sensitivity of a majority of the SPR-based assays is equivalent to
standard ELISA-based assays. In many of these applications, specificity of the assay was
not adequately addressed; however, most sensor applications were focused on demon-
strating proof of concept. SPR was also used for its potential to detect soluble toxin prepa-
rations. Nedelkov and coworkers (20,21) detected and identified staphylococcal
enterotoxin B (SEB) at 1 ng/ml in milk or mushroom samples using the Biacore SPR. This
assay employed biomolecular interaction analysis and mass spectrometry (BIA-MS)
together to improve analysis. Antibodies immobilized on the sensor chip captured the
molecules, and identity was analyzed by MALDI-TOF-MS (matrix assisted laser desorp-
tion or ionization time-of-flight mass spectrometry). A miniature integrated two-channel
SPR sensor based on Spreeta
TM
(Texas Instrument) was also employed to detect SEB at
femtomolar levels (22,23). Homola et al. (24) also developed a two-channel SPR device and
were able to detect SEB at 0.5-5 ng/ml in buffer and milk samples.
