Chemical, Biological, and Physical Methods
271
and 228 for DSP+antibody+antigen The hertz changes represent the effect of attached material on
the quartz surface. The method was linear with S. Typhimurium from 10
5 to 10
9 cfu/ml with F
changing from 90 to 170 Hz.
The minimum detectable level was 10
4 cfu/ml, and the biosensor had a response time of ca. 25
minutes.
229 In another piezoelectric FIA system, protein A was used as an antibody binding site
rather than DSP.
8 The latter system could detect S. Typhimurium in 30–40 minutes but the minimum
detectable level was 2.1 × 10
6 cfu/ml.
Fiber optics
An optical fiber is a “light wire” (optical waveguide) made of glass or polymeric material, and the
light waves are propagated along the fiber by total internal reflection. A fiber optic biosensor uses
electronic or optical transduction to monitor a biological reaction, and reports it as an optical signal.
The typical format of a fiber optic system consists of a tapered fiber optic probe coated with an
antibody of interest. Light from a diode laser travels through an all-fiber system to the fiber top
and then penetrates as an evanescent wave in the area outside the tips. When a fluorescently-labeled
homologous antigen binds to the antibody on the fiber tip, it interacts with the evanescent wave of the
fiber optic waveguide and the fluorescent signal radiates in all directions with some traveling back up
the fiber tip to the detection system.
167 Fluorescent dyes (such as Cy5) appear to be the light sources
of choice.
With a surface plasmon resonance (SPR) fiber optic system, antibodies bind to the surface of a thin
film on a precious metal that is on the reflecting surface of an optically transparent glass waveguide
(see reference 167). When visible or near-infrared light is passed through the waveguide, a reflection
occurs from the waveguide. The reflected light interacts with a plasma of electrons on the metal surface
and a resonance effect causes a strong absorbance which is a consequence of the concentration of the
antibody–antigen complex on the reflecting surface of the waveguide. The greater the antibody–antigen
reaction, the longer the wavelengths.
Among the commercially available biosensors are BIAcore, an SPR system produced in Sweden; the
Raptor, developed and produced in the state of Washington and an immunomagnetic system developed
at the University of Rhode Island and produced in Massachusetts by Pierson Scientific.
167
A portable evanescent wave fiber optic biosensor (Analyte 2000, developed at the U.S. Naval
Research Laboratories) was evaluated for its capacity to detect E. coli 0157:H7 in ground beef.
42
Using two waveguides, the system detected 9 × 10
3 and 5.2 × 10
2 cfu/g. No false-positive reactions
occurred, and results were obtained within 25 minutes of sample preparation. The above test system
employed a standard sandwich immunoassay and Cy5 to illuminate the captured antigens. The Analyte
2000 was used to detect L. monocytogenes, and with an inoculum of <10 cfu/ml followed by a 20-hour
enrichment, biosensor results were obtained in 20–45 minutes.
209 The BIAcore 3000 (another SPR
system primarily for research use) was used to detect staphylococcal enterotoxin B (SEB) in milk and
meat, and results were obtained in 5 minutes using one antibody, or 8 minutes using two antibodies.
168
The system could detect ca. 10 ng/ml of SEB. Another BIAcore instrument is available for food
analyses. A 20-minute assay for the detection of a minimum of 5 × 10
5 cfu/ml of S. Typhimurium
in spent alfalfa sprout irrigation water was developed by Kramer and Lim.
117 The method employs
a portable RAPTOR automated fiber optic-based biosensor system. The system used a 635-nm laser
diode for excitation of light. A S. Typhimurium antibody was used to capture the pathogen, and a Cy5labeled monoclonal antibody was used. By this method, S. Typhimurium colonies could be recovered
from the waveguides used, and background microbiota was not detected.
271
and 228 for DSP+antibody+antigen The hertz changes represent the effect of attached material on
the quartz surface. The method was linear with S. Typhimurium from 10
5 to 10
9 cfu/ml with F
changing from 90 to 170 Hz.
The minimum detectable level was 10
4 cfu/ml, and the biosensor had a response time of ca. 25
minutes.
229 In another piezoelectric FIA system, protein A was used as an antibody binding site
rather than DSP.
8 The latter system could detect S. Typhimurium in 30–40 minutes but the minimum
detectable level was 2.1 × 10
6 cfu/ml.
Fiber optics
An optical fiber is a “light wire” (optical waveguide) made of glass or polymeric material, and the
light waves are propagated along the fiber by total internal reflection. A fiber optic biosensor uses
electronic or optical transduction to monitor a biological reaction, and reports it as an optical signal.
The typical format of a fiber optic system consists of a tapered fiber optic probe coated with an
antibody of interest. Light from a diode laser travels through an all-fiber system to the fiber top
and then penetrates as an evanescent wave in the area outside the tips. When a fluorescently-labeled
homologous antigen binds to the antibody on the fiber tip, it interacts with the evanescent wave of the
fiber optic waveguide and the fluorescent signal radiates in all directions with some traveling back up
the fiber tip to the detection system.
167 Fluorescent dyes (such as Cy5) appear to be the light sources
of choice.
With a surface plasmon resonance (SPR) fiber optic system, antibodies bind to the surface of a thin
film on a precious metal that is on the reflecting surface of an optically transparent glass waveguide
(see reference 167). When visible or near-infrared light is passed through the waveguide, a reflection
occurs from the waveguide. The reflected light interacts with a plasma of electrons on the metal surface
and a resonance effect causes a strong absorbance which is a consequence of the concentration of the
antibody–antigen complex on the reflecting surface of the waveguide. The greater the antibody–antigen
reaction, the longer the wavelengths.
Among the commercially available biosensors are BIAcore, an SPR system produced in Sweden; the
Raptor, developed and produced in the state of Washington and an immunomagnetic system developed
at the University of Rhode Island and produced in Massachusetts by Pierson Scientific.
167
A portable evanescent wave fiber optic biosensor (Analyte 2000, developed at the U.S. Naval
Research Laboratories) was evaluated for its capacity to detect E. coli 0157:H7 in ground beef.
42
Using two waveguides, the system detected 9 × 10
3 and 5.2 × 10
2 cfu/g. No false-positive reactions
occurred, and results were obtained within 25 minutes of sample preparation. The above test system
employed a standard sandwich immunoassay and Cy5 to illuminate the captured antigens. The Analyte
2000 was used to detect L. monocytogenes, and with an inoculum of <10 cfu/ml followed by a 20-hour
enrichment, biosensor results were obtained in 20–45 minutes.
209 The BIAcore 3000 (another SPR
system primarily for research use) was used to detect staphylococcal enterotoxin B (SEB) in milk and
meat, and results were obtained in 5 minutes using one antibody, or 8 minutes using two antibodies.
168
The system could detect ca. 10 ng/ml of SEB. Another BIAcore instrument is available for food
analyses. A 20-minute assay for the detection of a minimum of 5 × 10
5 cfu/ml of S. Typhimurium
in spent alfalfa sprout irrigation water was developed by Kramer and Lim.
117 The method employs
a portable RAPTOR automated fiber optic-based biosensor system. The system used a 635-nm laser
diode for excitation of light. A S. Typhimurium antibody was used to capture the pathogen, and a Cy5labeled monoclonal antibody was used. By this method, S. Typhimurium colonies could be recovered
from the waveguides used, and background microbiota was not detected.