Grantee Research Project Results
Final Report: Chemiresistor Microsensors for Environmental Monitoring Systems
EPA Contract Number: 68D99043Title: Chemiresistor Microsensors for Environmental Monitoring Systems
Investigators: Thomas, Ross C.
Small Business: Eltron Research & Development Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $69,995
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
This SBIR Phase I project addressed the development of chemiresistor microsensors for improving the performance of field-deployable monitors, which are being developed at Eltron to detect hazardous air pollutants. For example, microsensor-based systems having enhanced capabilities and reduced cost are desirable for detecting environmental pollutants and common industrial solvents because identifying chemical hazards is essential for industrial health and safety reasons. Specific industrial applications include:- Environmental cleanup and monitoring.
- Indoor air quality monitoring.
- Point source leak detection for maintenance and emergency response teams.
- Alerting unprotected workers to hazardous working conditions.
- Evaluating potential health concerns in the workplace.
Chemical microsensors must respond with application-dependent sensitivity, selectivity, reversibility, speed, and longevity to a desired analyte. In addition, the sensor component must consume minimal power and volume while being manufacturable from inexpensive materials using economical batch methods. The application of chemiresistor microsensors for detecting hazardous air pollutants is attractive because sensitive, low-cost devices can be mass produced with standard fabrication methods found in semiconductor processing facilities. Moreover, multiple pollutants as well as relative humidity can be measured simultaneously using an array of devices along with pattern recognition methods. Research studies performed during Phase I completely proved the technical feasibility of chemiresistor microsensors for detecting VOCs at concentrations regulated by agencies such as OSHA and NIOSH.
Summary/Accomplishments (Outputs/Outcomes):
Research studies performed during Phase I addressed the development of chemiresistor microsensors employing conducting polymer composites for detecting VOCs in the parts-per-million (ppm) concentration range. The performance of prototype devices were evaluated by exposing them to VOCs ranging in concentration from 0 ppm to 4000 ppm. Chemiresistor microsensors developed during Phase I used a low cost sensor die having an interdigital array of metal electrodes coated with a conducting polymer composite. Thin-film composites were prepared with carbon particles dispersed in rubbery solid and viscous liquid polymers, which span a broad range of structures and functionalities. It was possible to "sense" the presence of VOCs with these materials because the absorption of gas-phase organic molecules modulate the electronic charge transport properties of the thin films. The sensitivity, partial selectivity, and stability of chemiresistor microsensors depend on the concentration of carbon particles, the chemical properties of the polymer, and other proprietary components.Experiments performed during Phase I addressed the development and characterization of chemiresistor microsensors employing conducting polymer composites for detecting VOCs in the parts-per-million (ppm) concentration range. The devices shown in Figure 1 is a photograph of chemiresistor microsensors developed during Phase I. Sensor die are packaged inside a protective housing that facilitates both active and passive sampling techniques. A simple, two-wire interface is used to connect the device to environmental monitoring systems being developed at Eltron. The sensitivity, reversibility, speed, and longevity of chemiresistor microsensors can be easily adjusted, as needed, by optimizing the chemically sensitive interface for specific applications. For example, specific performance characteristics of prototype devices exposed to toluene included:
- 38 ppm detection limit.
- 0 ppm to 4000 ppm dynamic range.
- 15 s response time.
- 20 s purge time.
- 1% sensor drift (both zero and span) for times >1 hr.
Various exposure limits for toluene, as mandated by regulatory agencies, range between 100 ppm to 500 ppm. Work accomplished during the Phase I program clearly demonstrated the feasibility of chemiresistor microsensors for detecting toluene at these concentrations. The concept to use arrays of devices along with pattern recognition methods provides a basis to reliably detect a wide range of VOCs as well as relative humidity.
Conclusions:
Research efforts demonstrated the performance of prototype devices, which had fast response times, low detection limits, highly reversible behavior, and excellent stability. Phase I results will be used to continue the development of a prototype devices during Phase II for eventual commercialization during Phase III.Supplemental Keywords:
Chemiresistor Microsensor, Environmental Monitoring Systems, Volatile Organic Compound, Hazardous Air Pollutant., RFA, Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Air, Toxics, Ecosystem Protection/Environmental Exposure & Risk, air toxics, Chemistry, VOCs, Monitoring/Modeling, Analytical Chemistry, indoor air, tropospheric ozone, Engineering, Chemistry, & Physics, Economics & Decision Making, Market mechanisms, monitoring, environmental monitoring, air pollutants, field portable systems, indoor VOC compounds, field portable monitoring, stratospheric ozone, hazardous air pollutants, HAPS, detect, air pollution, field monitoring, industrial air pollution, portable device, hazardous air pollutants (HAPs), measurement, microsensor, Volatile Organic Compounds (VOCs), sensor, indoor air quality, field measurements, measurement methods , measureThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.