SubscribeWPI 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.
sarissaprobeTM-ATP
The novel design concept is based on the deposition of an active enzyme matrix, including glycerol kinase and glycerol-3-phosphate oxidase, onto the surface of a Platinum needle microelectrode. This is housed in a glass sheath and incorporates a simple connector device, enabling linkage to a potentiostat. The sensor is easy to use and exquisitely sensitive, with a broad linear range and fast response time. It is also easy to calibrate and capable of repeat use.
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
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
- detection limit
- drift
- linearity
- selectivity
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.
Drift
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 APOLLO 4000 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).
However, the APOLLO 4000 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 APOLLO 4000.
- 2- or 4-channel systems 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.
- Extensive graphical user interface (GUI) based on a full color LCD touch screen control with integrated proprietary software for real-time display and data-acquisition of all channels.
- DSP (Digital Signal Processor) based 24-bit resolution A-D data-acquisition greatly improves quality of data.
- 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.
- 8 individual LED lights indicate which input channel parameter is active
Multi-channel configuration
The APOLLO 4000 is based on an optically isolated 4-channel configuration (a 2-channel version is also available). 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.
APOLLO 4000 incorporates a powerful single board computer and proprietary software (FreeRad.exe) that enables real-time display and data-acquisition of individual channels or any combination of channels. An extensive graphical user interface (GUI) based on a full color LCD monitor with touch-screen-control allows complete control and programming of all detection and data-acquisition parameters to be made at a single touch. Alternatively, the instrument can be controlled using a standard keyboard and mouse (included).
Plug-and-Play Design
The APOLLO 4000 is designed for use with WPI's range of nitric oxide, hydrogen peroxide and oxygen sensors. The user simply plugs the required sensor into any one of the input channels located on the instrument's main front panel and then selects the detection and acquisition parameters using the touch screen LCD. Each channel is also provided with an independent temperature input port that allows real-time monitoring of temperature using the available temperature sensors.