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Free Radical Detection |
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Written by Administrator
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Free Radical Detection and Measurement of Biologically
Significant Ions
and Compounds - Specialising in Nitric Oxide
WPI has a long history of innovation in the area of ion specific
detection and recording. We have developed biosensors and provided
quality tools and instrumentation to life scientists for over 40 years.
In 1989 we marketed the first commercial sensor for nitric oxide and
have been at the front of the field ever since. WPI maintains strong
ties and collaborations with University of Alabama, University of South
Florida, Harvard University, MIT, University of California Los Angeles,
University College London, University of Cambridge, and other
institutions around the world.
WPI also has its own fully equipped research and development laboratory
staffed by scientists who continually design, develop, and produce
sensors relevant to the changing requirements of research. We have been
the recipients of many federal grants to expand our technology in this
area as well.
Today WPI carries a full range of products that focus on the detection
and measurement of biologically significant ions and compounds. Our
line encompasses more than 600 products including: electrodes, sensors,
calibration solutions, cables, amplifiers and recording electronics. We
have everything you need.
Sensors
Nitric Oxide
WPI offers the most extensive range of NO sensors on the market.
Developed over a decade of extensive research in the field of NO, the
result is a superior range of NO sensors that enable routine detection
of NO at ultra low concentrations. WPI's unique NO sensor technology
utilizes a novel surface membrane which amplifies the response to NO
while at the same time eliminating responses to a vast range of
reactive species, including nitrite, absorbic acid, hydrogen peroxide,
catecolamines, and much more
Hydrogen Sulfide
Although hydrogen sulfide (H2S) is generally thought of in terms of a
poisonous gas, it is endogenously produced in many mammalian tissues.
It has been detected in micromolar amounts in blood and brain tissue.
Hydrogen sulfide is reported as having a broad range of biological
functions and although its potential to participate in cell signaling
is clear, this biological role is not well understood. H2S is strongly
anagolous to nitric oxide (NO) because they share several physical and
metabolic properties.
Like NO, H2S is a potent vascular signal that can mediate
vasoconstriction or vasorelaxation depending on the O2 level and
tissue. In the rat aorta, H2S concentrations that mediate rapid
constriction at one O2 level will cause rapid relaxation at lower O2
levels. The ISO-H2S sensor is a low detection limit sensor that works
with WPI's Apollo series of measuring devices to record H2S in vitro.
It is the only sensor available that measures H2S.
Hydrogen Peroxide
Hydrogen Peroxide is produced in biological systems by controlled
pathways at low concentrations that impact on cell signaling. At higher
concentrations inflammatory cells produce local intense amounts of this
oxidant to kill pathogens. In the development of human disease
uncontrolled formation of hydrogen peroxide from the mitochondrial
respiratory chain and enzymes such as xanthine oxidase can occur.
Despite the recognized importance of this oxidant in biology real-time
measurements at low concentration have been difficult. The hydrogen
peroxide sensors developed by WPI are designed to compliment existing
high sensitivity fluorescent approaches with direct quantitative
measurement in biological samples in the low nM range.
Oxygen
All aerobic and anaerobic life is adapted to survive in a narrow range
of oxygen concentration. Oxygen is the terminal acceptor in oxidative
phosphylation in mitochondria, the cell's ATP making powerhouse. Oxygen
also regulates production of proteins involved in nitrogen fixation in
anaerobes, and is required for inflammatory elimination of invading
foreign substances such as virus and bacteria by production of reactive
oxygen species (ROS) WPI's dissolved oxygen sensors are sensitive
linear and enjoy a broad range of application.
Temperature Sensor
The temperature sensor (#ISO-TEMP-2) is based on a 2.0 mm tip diameter
high quality miniature platinum RTD (Resistance Temperature Detector)
electrode. This design has been shown to provide greater accuracy,
stability and interchangeability during temperature measurements than
traditional thermistor and thermocouple sensors.
Hypodermic Sheath
Any of the 100 micron electrochemical mini sensors can be purchased
with a hypodermic sheath. This implementation uses a 24-ga. hypodermic
needle to mechanically shield the sensor from damage. Its use allows
effortless insertion into blood vessels, muscle and tissue of all kinds
without breakage.
Organ & Tissue Bath Studies
The L-shaped 100 micron electrochemical mini sensors were designed
specifically for use in tissue bath studies and similar applications.
The shape of the sensor has been engineered to facilitate placement of
the electrode within the lumen of the tissue vessel under study. The
ISONOP70-L is similar in construction to the ISO-NOP30 but with the
advantage of having a flexible tip (70 μm diameter).
Comparing Sensors
- response
- detection limit
- drift
- linearity
- selectivity
Choosing the right sensor for your application is critical for
successful research. The best way to determine compatibility is to test
a sensor in your application, however, cost can make that impossible.
Therefore, you must rely on the specifications and information provided
by the manufacturer. There are 5 performance factors that should be
specified by a manufacturer in order to make an informed choice for
your given application:
Response
Electrochemical electrodes produce changes in current in response to
changes in concentration. "Response" is most often specified in terms
of the amount of current per concentration unit: nA/micromole or pA/nM,
etc. The larger the current per unit the higher the sensitivity of the
sensor.
Detection limit
The response of a given sensor is meaningless without also specifying
the detection limit. Detection limit is the minimum change in
concentration that can be reliably seen. This specification is directly
related to the noise of the sensor. A sensor with a 100nA/μM
response but a 3μM detection limit is not as good as a
10nA/μM response sensor with a 1μM detection limit.
The best sensors have low detection limits and high sensitivity. In the
graph to the right, the response to the addition of 50nM of nitric
oxide is shown for the WPI flexible NO sensor and the comparable Brand
Z electrodes. The measurements were made with the same meter
simultaneously. As can be seen from the graphs response is similar but
the noise level on the WPI electrode allows for a more precise estimate
of the current.
A sensor can have a low detection limit and a good response, however,
to be useful in long term studies it must be stable when temperature
and concentration are constant. A drifting baseline, if monotonic, can
be corrected, but wandering baselines limit the utility of sensors to
short experiments.
Selectivity
It is a rare instance that the ion species of interest is the only ion
in the medium to be measured. In a perfect world your sensor would
respond ONLY to the ion of interest. In reality there is always some
contribution from competing species. The lower the contribution the
better. Graphs detailing the impact of competing species on electrode
output are shown on the performance page of this brochure.
The first graph below shows the response of WPI's ISO-NOP007 NO
microsensor following additions of: 50μM ascorbic acid (AA),
50μM nitrite, 100μM L-Arginine (L-Arg), 20 μM
Dopamine (DA), 100 nM and 200nM NO. The graph indicates no interference
to common reactive species, plus an enhanced response to NO. [Zhang, et
al., 2000.]
The second graph below shows the response of typical Nafion-coated NO
carbon microelectrode following additions of: 50μM ascorbic acid
(AA), 50μM nitrite, 100μML-Arginine (L-Arg), 2μM
Dopamine (DA), 100 nM and 200nM NO. [Zhang,et al., 2000.]
Linearity
For an electrode to be useful and easy to calibrate the response must
be "Linear" with changes in concentration over the range of interest.
Non-linear behavior requires special curve fit software to calibrate
the sensors. This approach is more time consuming and can be
unreliable. "Good" linearity is expressed by a R2 of .900 or higher
(1.00 is perfect). All of the electrochemical sensors made by WPI are
characterized by good.
Detection Device
The TBR4100 is an optically isolated multi-channel free radical
analyzer designed specifically for the detection of a variety of
redox-reactive species of biomedical importance. The electrochemical
(amperometric) detection principle used is similar to that employed in
WPI's popular nitric oxide detection system the ISO-NO (NOMK2).
Hardware
- 4-channel system allow simultaneous measurement at
different sites.
- Each channel easily configured to detect the species of
interest (e.g.,
have four channels for NO-detection; or two channels for NO, one for
hydrogen peroxide and one for oxygen, etc.).
- Measure NO from < 0.3 nM to 100 µM.
- Measure hydrogen peroxide < 10 nM to 100 mM.
- Measure oxygen from 0.1% to 100%.
- Real-time detection using electrochemical microsensors.
- Independent temperature measurement and display on all
channels.
- Current measurement range from 100 fA to 10 µA
(10-10A to
10-5A) permits wide dynamic range for detection.
- Serial Port (RS232), Ethernet Tbase-10/100, USB and
Parallel Port
provides connectivity with any PC, computer network, printer and
similar devices.
However, the TBR4100 incorporates numerous highly advanced design
features that enable it to detect a broad range of redox-reactive
species with unsurpassed accuracy and sensitivity. Currently the system
is able to detect nitric oxide, hydrogen peroxide, s-nitrosothiols and
oxygen. However, on-going research at WPI is focusing on expanding the
range of detectable species. NO sensors used with the ISO-NO are
completely compatible with the TBR4100.
Multi-channel configuration
The TBR4100 is based on an optically isolated 4-channel configuration.
In addition, there are also 4 separate channels for temperature
measurement. The design enables simultaneous real-time measurement of
NO (or other species) to be performed using up to 4 different
electrodes.
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Last Updated ( Tuesday, 12 May 2009 )
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