Micro-Chemical Sensors for In-Situ Monitoring and Characterization of Volatile Contaminants This website provides information about Sandia's Laboratory Directed Research and Development (LDRD) project that investigates and develops micro-chemical sensors for in-situ monitoring of subsurface contaminants. Description Background/Objectives Reports/Presentations/Media Intellectual Property and Licensing Partnering/Collaboration Field Tests Real-time monitoring of the Chemical Waste Landfill About Us Links Contact Us

Description

Traditional methods for monitoring sites that may be contaminated with toxic chemicals can be expensive, time consuming, and misrepresentative of in-situ conditions. A few in-situ chemical monitoring systems exist, but they do not attempt to quantify or characterize the contaminant (e.g., location, composition, etc.). This website presents the development of a microsensor monitoring system that can be used to monitor and characterize VOCs in the subsurface. A microchemical sensor that employs an array of chemiresistors is packaged in a unique, waterproof housing (early version made of PEEK and later version made of stainless steel) that is designed to protect the sensor from harsh subsurface environments, including completely water-saturated conditions. The array of sensors is calibrated to provide "training sets" for pattern recognition of various chemicals and chemical mixtures. The sensors and packaging has been tested in the laboratory and field, and unique characterization methods are being developed that utilize contaminant transport models and time-dependent, in-situ sensor data. Additional characterization methods that can be employed during soil remediation methods such as soil venting and air sparging are also being tested.

The sensor system consists of an array of miniature sensors, called chemiresistors, that can detect volatile organic compounds (VOCs). Each chemiresistor is fabricated by mixing a commercial polymer dissolved in a solvent with conductive carbon particles. The ink-like fluid is deposited and dried on wire-like electrodes on a specially designed integrated circuit. When VOCs are present, the chemicals absorb into the polymers, causing them to swell. The swelling changes the electrical resistance that can then be measured and recorded. The amount of swelling corresponds to the concentration of the chemical vapor in contact with the polymers. The process is reversible, and the polymers will shrink once the chemical is removed, reverting the resistance to its original state. Click here for an illustration of this process.

• This printable Fact Sheet (300KB) provides information on the problem, objectives, and collaborative opportunities for this project.

• Click here for a Word file (935 KB) containing some photos of the sensor package and water immersion experiments.

  Return to top of page

Background and Objectives

Tens of thousands of sites containing toxic chemical spills, leaking underground storage tanks, and chemical waste dumps require accurate characterization and long-term monitoring to reduce health and environmental risks and ensure public safety (Superfund Program). In addition, over two million underground storage tanks containing hazardous (and often volatile) contaminants are being regulated by the EPA (U.S. EPA, 1992), and the tanks require some form of monitoring to detect leaks from the tanks and pipe network. However, current methods are costly and time-intensive, and limitations in sampling and analytical techniques exist. Looney and Falta (2000, Ch. 4) report that the Department of Energy (DOE) Savannah River Site requires manual collection of nearly 40,000 groundwater samples per year, which can cost between $100 to $1,000 per sample for off-site analysis. Wilson et al. (1995, Ch. 36) report that as much as 80% of the costs associated with site characterization and cleanup of a Superfund site can be attributed to laboratory analyses. In addition, the integrity of off-site analyses can be compromised during sample collection, transport, and storage. Clearly, a need exists for accurate, inexpensive, real-time, in-situ analyses using robust sensors that can be remotely operated.

Although a number of chemical sensors are commercially available for field measurements of chemical species (e.g., portable gas chromatographs, surface-wave acoustic sensors, optical instruments, etc.), few have been adapted for use in geologic environments for long-term monitoring or remediation applications. The purpose of this LDRD project is to identify and develop sensor technologies that can be used in these long-term geologic applications. As a result, technologies such as electrical-resistivity monitoring and ground-penetrating radar are not considered here because they require significant amounts of manual labor and supervision to operate. Instead, we seek low-cost sensors that can be emplaced and operated with minimal supervision, which yield continuous real-time monitoring capabilities.

The particular focus of this project is limited to the detection and monitoring of volatile organic compounds (VOCs). These include compounds such as aromatic hydrocarbons (e.g., benzene, toluene, xylene), halogenated hydrocarbons (e.g., trichloroethylene (TCE), carbon tetrachloride (CT)), and aliphatic hydrocarbons (e.g., hexane, octane). As a result, sensors and technologies that detect gas-phase constituents in the vadose zone are emphasized because VOCs are most conveniently and economically monitored in the gas phase. However, the ability to detect VOCs in groundwater and saturated environments is also an important objective of the LDRD project.

This website presents the development of microchemical sensors that can be used to provide real-time monitoring and characterization of volatile organic compounds (VOCs) in situ, which can provide cheaper and more reliable information.

Specific objectives for this LDRD project include the following:

• Develop microsensors and integrated monitoring system that provide real-time, in-situ analyses of VOCs.
• Develop polymer absorption sensors for in-situ applications and investigate microsystems with integrated pre-concentrator for enhanced detection capabilities.
• Develop robust packaging system that allows the sensor to operate in wet or dry subsurface environments.
• Develop novel characterization methods using in-situ data and predictive process models of contaminant transport.
• Understand impacts of subsurface environment (e.g., heterogeneities, moisture content, temperature) on sensor data and interpretation.

Return to top of page

Reports, Presentations, and Media

Below is a list of reports, presentations, and news coverage:

Reports

• Final LDRD SAND Report (4 MB): A comprehensive summary of this LDRD project (FY01-FY03).
• Sensors for Environmental Monitoring and Long-Term Environmental Stewardship (1 MB): A summary of regulatory drivers, needs, and Sandia capabilities for environmental monitoring.
• Sandia Technology Vol. 4 No.3 (3.3 MB) provides overview of Sandia's LDRD project to develop an in-situ water sensor (article starts on page 6 of the PDF file).
• Fact Sheet (PDF file: 300KB) provides information on the problem, objectives, and collaborative opportunities for this project.
• Sensors and Actuators B: Chemical Journal Article (PDF file: 184 KB) discusses the use of partial least squares to analyze TCE using a chemiresistor array in the presence of changing temperatures and humidities. (Note: This material is copyrighted and is intended for personal research use only. Distribution or reproduction without the publisher's written consent is prohibited)
• SENSORS Journal Article (PDF file: 994 KB) details technical aspects of the soil and groundwater sensor probe and its applications.
• Review of Chemical Sensors for Real-Time In-Situ Sensing (PDF file: 471kb) (SAND2001-0643 report)
• Conference Paper (PDF file: 272kb) (June 2001), in the proceedings of the International Containment & Remediation Technology Conference, Orlando, FL.
• Summary of NTS Field Test (2001) (PDF file 587 KB) Summary report of 55-gallon drum test at the Hazmat Spill Center at the Nevada Test Site to test the sensor during a TCE spill and air-venting remediation operation.
• SAND2005-0336: SAND report of FY04 field tests at Edwards Air Force Base, CA (PDF file 1.4 MB).
• SAND2002-4135: SAND report of FY02 field tests at Edwards Air Force Base, CA (PDF file 2 MB).
• SAND2003-0799: SAND report of FY02 field tests of the chemiresistor and surface-acoustic-wave sensors at the Nevada Test Site (PDF file 3.5 MB).

Presentations and Video

• Conference Presentation (416kb) (June 2001), for the International Containment & Remediation Technology Conference, Orlando, FL.
• Video of E4 chemiresistor demonstration

Media Coverage

• Sandia Lab News article (9/21/01) (PDF file: 295KB). See page 6 for article summarizing our research or click here for web-based HTML version with downloadable images.
• Channel 4 Local News Coverage (9/27/2001) of real-time in-situ sensor for monitoring/protecting water supplies against chemical contamination (1 min 30 sec MPEG video) (15.7Mb)
• Channel 13 Local News Coverage (10/03/2001) of water protection and real-time soil and groundwater monitoring (2 min MPEG video) (18.8 Mb)
• Albuquerque Tribune front-page article (10/10/2001) by Sue Vorenberg
• Channel 41 (Univision) News Coverage in Spanish (10/16/2001) of Sandia's real-time sensors for water protection (2 min 30 sec MPEG video) (17.4 MB). Click here for an English translation of the video.
• Washington Post front page article (10/18/2001) by Eric Pianin and Ellen Nakashima has a brief mention of our "underground electronic sniffer"

Return to top of page

Intellectual Property and Licensing

• Patent Summary

Return to top of page

Partnering and Collaborative Opportunities

We are interested in teaming with various agencies, institutions, and companies to further develop, deploy, and refine our chemiresistor technology. The table below lists contacts that have expressed interest in evaluating, testing, and deploying the in-situ chemiresistor sensor technology. We would appreciate hearing from you if you would also like to team with us.

Note: These links will open a new web browser.

Return to top of page

Field Tests

• Link to web page with real-time in-situ monitoring data from Sandia's Chemical Waste Landfill monitoring stations
• 05-31-01: Movie (8.84 Mb) of initial test of sensor at Chemical Waste Landfill (SNL)
• 09-07-01: Movie (34 Mb) of field deployment of chemiresistor sensor package at Chemical Waste Landfill (SNL)
• 09-19-01 to 09-25-01: Summary report (PDF file 587 KB) of 55-gallon drum test at the Hazmat Spill Center at the Nevada Test Site to test the sensor during a TCE spill and air-venting remediation operation.
• SAND2005-0336: SAND report of FY04 field tests at Edwards Air Force Base, CA (PDF file 1.4 MB). SAND2002-4135: SAND report of FY02 field tests at Edwards Air Force Base, CA (PDF file 2 MB).
• SAND2003-0799: SAND report of FY02 field tests of the chemiresistor and surface-acoustic-wave sensors at the Nevada Test Site (PDF file 3.5 MB).

Return to top of page

About Us

The micro-chemical sensor development team is led by Cliff Ho (6115) and Bob Hughes (1744).

Cliff Ho has a Ph.D. in Mechanical Engineering with over 10 years of experience in experimental and numerical studies involving multiphase flow and transport processes in porous media. He has performed work for Yucca Mountain, WIPP, and Hanford, and he has performed numerical simulations of environmental remediation problems involving soil vapor extraction, steam injection, and capillary barriers. Cliff Ho will be leading the experimental testing of the sensors and the subsurface modeling studies. Contributors include Lucas McGrath, Jerome Wright, James May (Earth Tech/Edwards AFB), Scott Rawlinson, Kathy Alam, Dion Rivera, Bruce Reavis, Paul Reynolds (TSP), Mark Jenkins, Dan Lucero, Angela McLain, Mike Kelley, Jeff Zirzow, Henry Bryant, and Sharissa Young. Click Here for Cliff's resume and list of selected publications (Word file). Click here for Cliff's University of New Mexico web page.

Bob Hughes has a Ph.D. in Chemistry with over 35 years of experience in physical chemistry and micro-sensor technology. He was a principal investigator in the development of the chemiresistors proposed in this LDRD and has extensive experience in the design and implementation of sensors for various applications. His silicon chip hydrogen sensor is now a commercial product yielding royalties to Sandia. Bob Hughes will be leading the development of the chemiresistors and associated technologies for the integrated sensor development. Bob is being assisted by Chad Davis and Michael Thomas. Contributors include Graham Yelton and Tina Petersen.

Return to top of page

Links

We have found the following links to be interesting and useful in our research developing microsensors for in-situ chemical detection and characterization. If you have a site that you would like to have included on this page, please send the URL and brief description to Cliff Ho.

In addition, please visit the following web site for more information on other microsystem technologies at Sandia National Laboratories: www.sandia.gov/mstc

Chromatography and Spectrometry Sensors

Chromatography is a method for the separation and analysis of complex mixtures of volatile organic and inorganic compounds. A chromatograph is essentially a highly efficient apparatus for separating a complex mixture into individual components. As the mixture is separated by the column, a detector positioned at the end of the column quantifies the concentrations of the individual components.

Spectrometry can be considered a sub-class of chromatography. A gaseous sample is injected into the spectrometer and ionized by a radioactive source, resulting in positive and negative charged species. These species are accelerated over a short distance and the time-of-flight is determined.

• Agilent Technologies offers a full line of laboratory and field Gas Chromatographs.
• Femtoscan has developed a hand portable Gas Chromatograph/Ion Mobility Spectrometer (GC/IMS) instrument.
• INFICON HAPSITE Chemical Identification System is a field-portable Gas Chromatograph/Mass Spectrometer (GC/MS) for on-site analysis of VOCs.
• Bruker Daltonics, Inc. has developed a lightweight, rugged GC/MS system for analysis of air, water, and soil.
• Process Analyzers produces a field portable instrument which is able to analyze liquids, soilds, and gasses.
• Sandia National Laboratories has developed the Micro-Chem-Lab on a chip (uChemLab) that is a miniaturized GC-type device.
• Bruker Daltonics, Inc. has developed a hand-held chemical agent detector based on IMS.
• DLK Spectro has produced an IMS with a gas-chromatic cell for gas analysis.

Electrochemical Sensors

Electrochemical sensors can be categorized into three groups: (1) potentiometric (measurement of voltage); (2) amperometric (measurement of current); and (3) conductometric (measurement of conductivity). In general, electrochemical sensors interact with the contaminant of interest. This produces changes in its electrical properties that are measured and related to concentration.

• Cyrano Sciences (TM) developed the Cyranose 320 which mimics smelling and contains an array of 32 sensors.
• Adsistor Technology (TM) developed and patented a chemiresistor for vapor detection of gasoline spills and leaks in the subsurface.
• GasTech (TM) has a portable soil vapor monitor that uses a catalytic bead sensor for detection of hydrocarbon gases.
• Figaro has develop metal-oxide semiconductor sensors for detection of solvent vapors.
• City Technology is a leading manufacturer of gas sensors using catalytic bead, semiconductor, and infrared technologies.

• Delphian Corporation manufactures several potentiometric devices for sensing toxic gases and oxygen.
• National Center for Environmental Research, an office of the EPA, uses chemiresistors for air quality monitoring.
• The Jet Propulsion Laboratory has developed a selective silicon carbide material for use hydrocarbon sensing.

Mass Sensors

Surface Acoustic Wave Sensors (SAWS) are small miniature sensors used to detect VOCs. A SAW device consists of an input transducer, a chemical adsorbant film, and an output transducer on a piezoelectric substrate. The input transducer launches an acoustic wave which travels through the chemical film and is detected by the output transducer. The velocity and attenuation of the signal are sensitive to the viscoelasticity as well as the mass of the thin film which can allow for the identification of the contaminant. A signal pattern recognition system that uses a clustering technique is needed to identify various chemicals.

• Sandia National Laboratories has developed and tested a six-array Surface Acoustic Wave (SAW) device able to identify 14 different individual organic compounds over a wide range of concentrations with 98 percent accuracy. An integrated GaAs SAW sensor device has been integrated with a microprocessor on a single 5mm x 5mm chip. A hand-held Portable Acoustic Wave Sensor (PAWS) system using the SAW sensor that can be used down-hold for monitoring. High temperature SAW devices are also being developed for monitoring in temperatures as high as 525 degrees C.
• PNNL has developed a portable sensor to detect real-time Chemical Wepons dispersal in the field using a portable SAW sensor.

Optical Sensors

Fiber optic sensors are a class of sensors that use optical fibers to detect chemical contaminants. Light is generated by a light source and is sent through an optical fiber. The light then returns through the optical fiber and is captured by a photo detector. Three general classes of fiber optic sensors include: (1) passive spectroscopic; (2) chemically interacting thin film attached to the tip of the fiber; and (3) injection of a reagent near the sensor.

• PNNL S&E - Remote Chemical Vapor Characterization using infrared spectroscopy technology.
• The Laser Lab in Germany has developed an optical sensor for analyzing polycyclic aromatic hydrocarbons (PAHs) and monoaromatics like benzene, tolouene, xylene, and ethylbenzene. Scroll down page to abstract
• Ion Optics, Inc. offers a MEMS infrared gas sensor.
• Georgia Institute of Technology has developed an environmental monitoring system based on integrated optic sensors.
• Burge Environmental offers the Optrode Detection System for TCE.

Biological Sensors

Biological sensors rely on biologically produced enzymes or biocatalysts to detect the presence of a contaminant of interest.

• INEEL led research to use molecular engineering and genomics for the development of environmental biosensors using robust biocatalysts

Characterization Technologies

• Sandia National Laboratories Visual Empirical Region of Influence (VERI) Algorithm. Presents a new, nonparametric pattern recognition (PR) method based on the visual empirical region of influence (VERI) clustering technique.
• Innovative Technology Summary Report (April, 1996) describes the use of a cone penetrometer to provide cost-effective, real-time data for the use in characterization of the subsurface. The cone penetrometer uses sensors to measure cone tip pressure and sleeve friction. Other sensors available include two-axis inclinometers, acoustic cone (for identificaiton of soil type), temperature, pH, radioactivity (gamma), and geophones for measurement of pressure (P) and shear (S) waves (surface to borehole seismic measurements).
• EIC Laboratories, Inc. has developed two optical sensors for the cone penetrometer used for the detection of DNAPLs.
• The U.S. Army Environmental Center has developed the Site Characterization and Analysis Penetrometer System (SCAPS) which uses an in situ HydroSparge Volatile Organic Compound (VOC) Sensor incorporated into a cone penetrometer truck.

Data Collection and Telemetry

• Aquasat has a satellite-based remote telemetry system (EcoPod) that can been integrated with sensors and systems for detecting contaminants in water resources.

• NetAcquire (tm) products combine three key technologies: intelligent real-time data acquisition, signal processing, and high-speed networking.
• Voss Scientific offers a PC-Based Telemetry Server Suite that utilizes satellite technology to transfer data.
• ADCON Telemetry offers systems for permanent data collection, reliable data transfer, and user-friendly data visualization on the PC.

Other

• SENSORS Online Journal

• Sensors Web Portal with monthly updates on sensors, tools, patents, etc.

• Sensors Magazine Online

• INEEL Grand Challenge for Subsurface Characterization. Describes need for remote sensing of more parameters, localized sensing of more parameters, comprehensive point measurements, and measurement integration.
• Eksigent combines micropumping, microfluidics, and microfabrication for use in creating new devices for use in the life sciences, MEMS, and microelectronics industries.
• Adsistor Technology, Inc. offers gas and chemical vapor sensors.
• EnviroEquip offer a variety of instruments for environmental monitoring.
• Patent information for a hydrocarbon vapor sensing unit (US6102085). Many reference links to other sensors on this page.
• ThermoGasTech has a Portable Soil Vapor Monitor for hydrocarbons available.
• Ronan Engineering Company manufactures industrial process instrumentation such as annunciators, temperature transmitters, alarm monitors, leak detection monitors, non-contact level/flow/density, IS barriers, I/P transducers, graphic displays, vibration monitors, and calibrators.
• INEEL Grand Challenge for Subsurface Characterization. Describes need for remote sensing of more parameters, localized sensing of more parameters, comprehensive point measurements, and measurement integration.
• Eksigent combines micropumping, microfluidics, and microfabrication for use in creating new devices for use in the life sciences, MEMS, and microelectronics industries.
• Adsistor Technology, Inc. offers gas and chemical vapor sensors.
• EnviroEquip offer a variety of instruments for environmental monitoring.
• Patent information for a hydrocarbon vapor sensing unit (US6102085). Many reference links to other sensors on this page.
• ThermoGasTech has a Portable Soil Vapor Monitor for hydrocarbons available.
• Ronan Engineering Company manufactures industrial process instrumentation such as annunciators, temperature transmitters, alarm monitors, leak detection monitors, non-contact level/flow/density, IS barriers, I/P transducers, graphic displays, vibration monitors, and calibrators.
• PetroVend offers liquid and vapor hydrocarbon sensors for monitoring wells.
• Delphian Corporation offers gas monitoring and vapor leak detection systems.
• American Gas & Chemical Co Ltd offers gas monitoring and vapor leak detection systems.
• RAE Systems offers various gas detection capabilities.
• Savannah River website offering ER technology descriptions.
• VaporTec offers state-of-the-art passive soil gas sampling services.
• Photonics Technology News Chemical Sensor Offers Sensitive Real-Time Solution.
• Sentex Systems, Inc. offers solutions for on-line, on-site VOC monitoring in air, water, and soil.

Return to top of page

---

Contact Us

For more information, please contact:
 

Cliff Ho Sandia National Laboratories (505) 844-2384 ckho@sandia.gov

Contact: Cliff Ho

References

Ho, C.K., M.W. Jenkins, R.C. Hughes, and P.G. Reynolds, "Microchemical Sensor Package for In-Situ Monitoring," Sandia National Laboratories Technical Advance SD-6976, 8/2001.

Ho, C.K., "Characterization Methods for Real-Time In-Situ Sensing of Volatile Contaminants," Sandia National Laboratories Technical Advance SD-6894, 4/2001.

Ho, C.K., "Designs and Deposition Methods for Polymer-Based Microchemical Sensors, Sandia National Laboratories Technical Advance SD-7095, 1/2002.

Ho, C.K., "Automated Monitoring and Remediation System for Volatile Subsurface Contaminants, Sandia National Laboratories Technical Advance SD-7097, 1/2002.

Looney, B.B. and R.W. Falta (editors), 2000, Vadose Zone Science and Technology Solutions, Battelle Press, Columbus, OH, 1540 pp.

U.S. Environmental Protection Agency (EPA), 1992, Measurement and Analysis of Adsistor and Figaro Gas Sensors Used for Underground Storage Tank Leak Detection, Report #EPA/600/R-92/219.

Wilson, L.G., L.G. Everett, and S.J. Cullen (editors), 1995, Handbook of Vadose Zone Characterization & Monitoring, CRC Press, Boca Raton, FL.

Page owner: Clifford K. Ho

Page updated: April 26, 2005