Final Report: Multiplexed Chemical Sensor for Water SecurityEPA Contract Number: EPD06084
Title: Multiplexed Chemical Sensor for Water Security
Investigators: Farquharson, Stuart
Small Business: Real-Time Analyzers, Inc.
EPA Contact: Manager, SBIR Program
Project Period: April 1, 2006 through June 30, 2007
Project Amount: $224,999
RFA: Small Business Innovation Research (SBIR) - Phase II (2006) Recipients Lists
Research Category: Drinking Water , SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)
The overall goal of this project (through Phase III) is to develop a chemical sensor that can be multiplexed into water distribution systems to provide early warning of poisoned water supplies. This will be accomplished by developing surface-enhanced Raman (SER) sensors that can be integrated into water supply systems and coupled to a central Raman analyzer via fiber optics.
The overall goal of the Phase II project was to fully develop the proposed analyzer and improve sensitivity to detect poisons at 10 µg/L (10 parts per billion, ppb) in 10 minutes (~the 5 day/5L values in Table E.1). This included optimizing the SER-active sol-gel chemical selectivity, ruggedizing the capillaries, developing a universal sampling system with a stream-to-capillary interface and a capillary-to-fiber optic probe interface, and developing a comprehensive analysis that includes rapid chemical identification. These goals were largely met as summarized by the accomplishments described below.
1) The sol-gel chemistry was successfully optimized to achieve the required sensitivity of at least 10 μg /L (ppb) for all of the 20 target chemicals within 10 minutes using a solid phase extraction cartridge that was included in the sampling system. The Lowest Measured Concentrations (LMC) for these chemicals are summarized in Table E.1. SER spectra are shown in Figure E.1 for methyl phosphonic acid, thiodiglycol, and cyanide, the primary hydrolysis products of the nerve agents mustard gas and cyanide salts.
Table E.1. Lowest Measured Concentrations (LMC) for the 20 primary chemicals studied compared to the Required Detection Limit (RDL, Military Drinking Water Guidelines, Short Term, 19991), along with the parent chemical agents, stimulants, pesticides, and chlorinated by-products and their selected hydrolysis products.
2) The two most active sol-gel chemistries were successfully developed to withstand flow rates of 5 mL/min and pressures of 30 psi. The sample system was successfully designed to reduce flow and pressure to at least these values.
3) Receiver operator characteristic (ROC) curves were used to demonstrate that the required sensitivity could be reproducibly achieved 95 percent of the time with a 3 minute spectral acquisition for methyl phosphonic acid, thiodyglycol, cyanide, fonofos, dichlorobenzoic acid, and sunset yellow (a food dye selected for field studies). However, this required scanning the length of the capillary (rastering, Figure E.2), which was not implemented in the final sampling system.
4) Software was written that successfully identified any of 96 chemicals within a spectral library database consisting of chemical agents, pesticides, toxic industrial chemicals, and hydrolysis products. The spectral search software ranks all of the chemicals based on the closest match to the unknown. The analysis is virtually instantaneous (<< 1 sec, Figure E.3).
5) A computer controlled sample system was designed and successfully built, which was capable of being connected to virtually any water supply. It controls the water flow rate and pressure, directs the sample first through a solid phase extraction cartridge (for 5 min) into a waste container, then switches flow to pass methanol through the cartridge and transfer the concentrated sample to the SERS-active capillary (for 5 min). The flow is reset to introduce the next sample, while the SER spectrum is acquired using a fiber optic coupled Raman spectrometer (Figure E.3). Analysis is updated every 10 minutes.
Figure E.4. A) Photograph of prototype Raman analyzer with fiber optic probe connected to B) the sampling system. The yellow line shows the sample flow through the SPE during the concentration step. The red line shows the flow of methanol through the SPE to the SERS Capillary during the extraction and delivery step. C) User Interface software used to control the sample and solvent flow. D) User interface of software used during operation (“More” shows spectral match as shown in Figure E.3).
6) The automated sample system in conjunction with a Raman analyzer was used successfully to detect 75 μg/L (ppb) methyl phosphonic acid artificially added to water samples obtained from the Kensico Water Reservoir, which supplies New York City with its drinking water (Figure E.5). The raster method was NOT used, which improved sensitivity by more than a factor of 10 (and would therefore achieve the required sensitivity).
Limitations and Suggestions. Although 17 of 20 milestones were met, three were not. First, the proposed fiber-optic to SERS-capillary interface, which would use a Parker-Hannifin “Intraflow” machined block, was not pursued. This largely was due to the fact that Parker-Hannifin delayed delivery by more than 1 year of the sample system Intraflow components that they presumably already manufactured. Nevertheless, Real-Time Analyzers, Inc., successfully built a suitable (nonintegrated) probe to perform the measurements. This probe could be readily modified to be a permanent component of the sample system.
Second, the proposed measurements of actual nerve agents at the U.S. Army’s Edgewood Chemical and Biological Research Center were never performed. Although the U.S. Army provided a letter indicating that they would perform such measurements, and Real-Time Analyzers, Inc., mailed SERS-active capillaries to them for these measurements, they were not able to fit these measurements into their schedule. Real-Time Analyzers, Inc., understands their priorities have changed to detecting biological warfare agents.
Third, the at-site measurements at Kensico Reservoir were never performed. This was due to the fact that the prototype system requires a number of modifications to perform these tests correctly. These modifications include: (1) developing a motorized fiber optic probe system to “scan” the SERS capillary to achieve the necessary sensitivity and/or (2) incorporating additional solid phase extraction material into the SERS-active sol-gel to overcome sample dilution due to the sample system channels to achieve the necessary sensitivity, (3) mounting the probe to the sample system, and (4) completing the top level software user interface so that it incorporates (a) the flow control software, (b) the Raman analyzer control software, (c) the chemical identification software, and (d) the ROC curve concentration software with alarms. It should be noted that the personnel at Kensico Reservoir were willing to perform the proposed measurements using the food dye sunset yellow, which we measured at 1 μg/mL (ppb).
Fourth, although the proposed prototype was built using matching funds and tested using the Commercialization Option funds, due to the limitations cited above (primarily sensitivity), the proposed additional field tests were not performed. Finally, for these same reasons, the Verification Option was not exercised.
Finally, it is worth noting that Real-Time Analyzers has continued talks with Hach and GE Power & Water (March 2010 and April 2010, respectively), and will pursue Phase III commercialization with these companies as partners.