Grantee Research Project Results
Final Report: Cost-effective Molecularly Imprinted Polymer Based Monitoring Technologies to Improve the Performance and Reliability of Small Drinking Water Systems
EPA Contract Number: EPD17024Title: Cost-effective Molecularly Imprinted Polymer Based Monitoring Technologies to Improve the Performance and Reliability of Small Drinking Water Systems
Investigators: Trentler, Timothy
Small Business: Sporian Microsystems Inc.
EPA Contact: Richards, April
Phase: II
Project Period: March 1, 2017 through June 28, 2019
Project Amount: $299,999
RFA: Small Business Innovation Research (SBIR) - Phase II (2016) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Water
Description:
Small drinking water systems consistently provide safe, reliable drinking water to their customers; however challenges of such systems include; lack of financial resources, aging infrastructure, cost of scale, and technical/logistical challenges associated with regulation compliance. The deployment of new cost effective monitoring technologies, such as improved, low cost, in-line, in-situ, and remote water quality sensor systems is necessary to substantially advance infrastructure, assure compliance, and still be economically viable for integration by small drinking water system operators. This research was aimed at providing such a solution.
During Phase I, a molecularly imprinted polymer (MIP) was developed containing a novel metalorganic functional monomer that demonstrated strong affinity for binding organophosphate ions relative to other common anions. This polymer afforded the potential for detecting and/or removing phosphate pesticides and nutrients from drinking water sources, waste water, and natural surface water. This Phase II was tasked with trying to realize this potential, which entailed experimentally optimizing the MIP system for use in conjunction with optical sensor hardware as part of Sporian's existing water monitoring systems. In Phase I, most preliminary MIP development was conducted on polymer monoliths, so this Phase II was focused on adapting these polymers to thin film or other formats suitable for incorporating into the optical hardware. This required implementation and optimization of either fluorescence/colorimetric and/or refractive index optical detection methodologies. Development of fluorescent indicators for target binding in the imprint cavity was required for the former. Optimization efforts were directed towards maximization of material response rate, sensitivity, selectivity, reproducibility, optical signal intensity, and reversibility, which was to be accomplished by variation of parameters such as crosslink density, indicator chemistry, functional monomer/indicator concentration, monomer hydrophilicity and type, porogen solvent ratio, processing conditions, etc.
Summary/Accomplishments (Outputs/Outcomes):
Optimization of the Phase I MIP proved problematic in that reproducible results were difficult to achieve. This arose from instability of the novel metalorganic functional monomer used for binding phosphates in this MIP. It was prone to rearrangements and polymerization upon isolation during synthesis that rendered it insoluble in prepolymer formulations. With such difficulties, developing a suitable reference polymer for phosphate detection by binding induced change of refractive index was deemed impractical. It was always expected to be challenging to compensate for index change caused by polymer swelling and adsorption of non-binding species in solution. For these reasons, most of the effort towards implementing the phosphate selective MIP in Phase II was directed towards developing a fluorescence indicating system. Three types of indicator systems were explored during Phase II; optodes, rhodamine dyes, and lanthanide (rare earth metal) complexes.
The optode system was an adaptation of known fluorescence/colorimetric indicators for anions that was investigated because it did not necessitate a reinvention of the Phase I MIP. This MIP could be simply dissolved into a lipophilic membrane to function as an ionophore in combination with a commercial indicating dye and an ion exchanger. Successful phosphate detection, however, was not achieved, likely due to the highly hydrophilic nature of phosphate anions. Plus there were other complications, such as high pH sensitivity and difficulty of tuning the pH response range. Therefore fluorescent indicator systems that responded by direct interaction with phosphates in the imprint cavity, either in conjunction with or as a replacement for the Phase I metalorganic monomer, were sought. Rhodamine derivatives were one such class of indicators that were investigated based on success at Sporian using such dyes for detecting heavy metal ions in a DOE funded project. While literature precedent suggested phosphates could potentially induce rhodamine ring opening, and thereby fluorescence (at least in organic media), too, results from this Phase II effort indicated hydrogen bonding interaction with phosphates provides insufficient driving force for this isomerization relative to metal ion chelation.
Implementation of lanthanide complexes as fluorescing indicators comprised the major emphasis of this Phase II, and selective detection of phosphates was achieved using such complexes. This strategy was attractive because in theory it required merely swapping out the metal (zinc) of the Phase I metalorganic monomer with a luminescing (technically not fluorescence) lanthanide metal (europium), albeit with additional ligands required to accommodate the larger size and charge of lanthanides. Also, an aromatic sensitizing ligand needed to be included to absorb light and transfer energy to the metal. Several europium-based mimics of the Phase I metalorganic monomer were prepared during Phase II, but unfortunately, a consistent and reproducible response to phosphates could not be obtained by this strategy. Rather alternative europium complexes were required. Two general types of europium complexes were determined by literature survey to afford a high probability of success; highly multidentate ligands, particularly those based upon cyclen, and tris-diketonates, which had been used in MIPs for detecting phosphate-based chemical warfare agents. Both were studied here. The cyclen ligands were considered particularly attractive because they are very kinetically stable complexes that are quite resistant to photodecomposition. However, these ligands are also quite difficult to synthesize, requiring multiple steps. When initial products failed to significantly sensitize europium emission, focus was shifted to the tris-diketonates for which very strong emission was easily achieved. Model complexes could be readily prepared with commercial ligands, and rapid luminescence turn-off was observed in the presence of phosphates. Furthermore, presence of common interfering anions at much higher concentration (200X) had little effect on the luminescence, hence attesting to the potential of this strategy.
To use the tris-diketonates as indicators in sensor hardware also required substantial synthetic effort to convert diketonate ligands into reactive versions that could be incorporated into polymer matrices. Viable complexes based upon vinylic diketonate ligands that could undergo conventional radical chain polymerization proved elusive during this Phase II. Diketones that could undergo reversible addition-fragmentation chain-transfer (RAFT) polymerization, however, were prepared, and these were used in the preparation of most of the polymers studied. The original goal was to prepare polymer thin films as sensing elements on optical windows. To afford efficient diffusion of ions into the films and thereby achieve a rapid response rate required that these films be hydrogels formed from hydrophilic monomers. Many different monomers were investigated, but the desired performance was never achieved from viable films (too hydrophilic causes swelling and break-up of the polymers). Response was always slow, requiring tens of minutes at least, and it was opposite from expectation; emission enhancement rather than turn-off. Furthermore, many of the polymers exhibited much weaker emission intensity than anticipated from model complexes, which appeared to be related to monomer type. Finally, some monomers inhibited response altogether.
Because of the performance limitations of the hydrogel films, consideration was given to a sensing architecture implementing soluble or dispersed polymers. An organics soluble RAFT polymer gave high intensity luminescence with near instantaneous emission quenching in the presence of phosphates, and sensitivity down to at least 10ppb was demonstrated. Attempts to form water soluble analogs, however, suffered the same monomer class dependent loss of emission intensity seen from the hydrogel films, which is detrimental to sensitivity. Phosphates, in this case, though, still induced emission quenching, unlike for the films. A hydrophilic monomer was identified for which strong emission could be achieved, but this monomer inhibited phosphate response. Core/shell polymers were considered as a solution to these problems, but time constraint prevented implementation. Finally, grafting of the soluble polymers onto silica microparticles was investigated as a means of utilizing these polymers in a sensor device. Such particles form dispersions that can be retained by a permeable membrane that passes analyte. Again, hydrophilic monomers were required, and similar difficulties were observed as seen for thin films and soluble polymers.
Conclusions:
During Phase II europium-based complexes for binding and detecting phosphates were developed and incorporated into polymers. The ability to rapidly detect phosphates at a level below federal guidelines for surface, waste, and drinking water (15-1000ppb) was demonstrated using luminescence-based optical detection that can be readily incorporated into Sporian's existing and cost effective optical sensing hardware. As such, the technology developed in Phase II offers great potential for providing a cheap solution to water monitoring needs. For this potential to be realized, however, several technical challenges must still be addressed that will likely require significant R&D effort. Efforts required include modifying the polymers and indicating complexes therein to improve sensor photostability and impart reversibility required for many applications. Also, the polymers must be rendered more soluble or dispersible in aqueous media while not sacrificing sensitivity and other performance criteria, possibly by implementing core/shell morphologies. Selectivity, too, must be more thoroughly evaluated and validated in real world environments. Finally, permeable membranes must be screened and implemented in sensor hardware to allow adoption of high response rate soluble/dispersible polymer systems.
Commercialization
Affordable, easy-to-use, real-time instruments for monitoring water quality have substantial market potential. Because of the widespread use of water in industry, agriculture, and energy generation, there is a significant push to ensure safe water supplies and facilitate sustainable resources. Most current solutions for water monitoring involve reagents, consumable immunoassays, or laboratory equipment, making testing an expensive and time consuming process. By utilizing molecular-imprinted polymers integrated in to a comprehensive in-line monitoring suite, Sporian has developed a product that addresses the limitations of current systems, while potentially being more broadly utilitarian by being less costly to own and operate.
Due to health and ecosystem concerns, the primary market of interest is small drinking water systems. According to the EPA, small drinking water systems face financial/management challenges, along with regulatory/compliance challenges. The potential market size for the Sporian's device for detection in water is considerable. There are approximately 54,000 community water systems in the US, and 85% of those are considered small and very small drinking water systems. This leads to approximately 45,900 small and very small drinking water systems that need to be monitored. This only represents the domestic market; the international market should be considerable and will be pursued in the future.
A secondary market is private, unregulated drinking water supplies. According to a joint EPA and Department of Homeland Security (DHS), approximately 15% of Americans rely on private, unregulated drinking water supplies. According to the CIA World Factbook, the US population was approximately 319 million as of July 2014, so approximately 48 million Americans rely on private drinking water supplies. According to the 2010 US Census, there is an average of 2.58 people per household in the US. That implies that approximately 18.5 million households relying on private water that could potentially benefit from the technology. If the cost for the sensor is low enough and operation is simple enough, this could be attractive as a secondary market.
There are many additional potential markets. Large drinking water utilities are attracted to the technology because of the role of phosphates in lead control. In addition, according the USDA National Agricultural Statistics Service, there were over 2 million farms and over 915 million farming acres in the US in 2012. Agricultural water is potentially another important market. According to EPA and DHS], there are over 16,000 wastewater treatment facilities in the US. This does not include facilities for the treatment of industrial waste water. Wastewater is another potentially large market for Sporian-developed technology. According to the US Census, there are approximately 21,000 US food processing facilities, 150,000 retail food distributors, and 500,000 food service establishments. Water is a key ingredient for each of these operations, so these represent even more markets.
With a constant and increasing need for clean water sources, the U.S. water industry generated $160 billion in revenue in 2015 and continues to grow, indicating vast market potential for the innovation. The two largest segments in this industry are wastewater treatment and water utilities, and also include delivery & infrastructure, chemicals, consulting & design, maintenance, instruments & information, and analytical services. More specifically, water supply and irrigation systems (i.e. water distribution systems) experienced industry sales of $11.5 billion in 2017 with a compound annual growth rate (CAGR) of 3.5%. The innovation is included in the "instruments & information" sector of the water industry, which is incurring the most growth due to increased regulations and health concerns, with a CAGR of 5.8%, reaching $1.45 billion in 2015. This sector includes companies such as Hach, Mettler Toledo, YSI Inc., In-situ Inc., Capilix BV, Emerson Rosemount, Veolia Water Solutions, Electro-Chemical Devices Inc., Campbell Scientific Inc., Horiba, Intellitect Water Limited, Optiqua Technologies, Neosens SA, Eutech Instruments, and Analytical Technology. There are over 155,000 public water systems in the U.S., all of which would benefit from the proposed technology.
In order to take the technology from its current stage of development to occupy a dominant position in the water distribution market, Sporian has been working to target key members of the supply chain to help analyze potential market entry points. The ultimate beneficiary for the proposed product is the residential, commercial, or industrial end user of water who wants to be able to turn on the faucet and receive an immediate source of water that is suitable for the intended use. If a suitably inexpensive and easy-to-use sensor can be developed, it could be marketed directly to these consumers. The majority of the water in the US is provided by public utilities such as Colorado Springs Utilities, Metro Water Reclamation District, City of Boulder, and Denver Water through water sources such as catchment systems or water wells. These utilities are also potential customers for the sensor being developed. The utilities use construction and consulting companies to assist with design and integration of the whole facility by companies such as CH2M, CB&I, and MWH Global. These construction and consulting companies use components, including mixers, aerators, pumps, filters, and sensors. Sensors are provided by companies such as Hach, Thermo Fisher Scientific, Inc., YSI, and Teledyne Isco. These companies are potential competitors, collaborators, licensees and acquirers. Since these companies and agencies are already established in the water monitoring market, working in collaboration with all members of the supply chain for licensing and transitioning the technology to market will help Sporian secure a dominant position in the water distribution industry.
SBIR Phase I:
Cost-effective Molecularly Imprinted Polymer Based Monitoring Technologies to Improve the Performance and Reliability of Small Drinking Water Systems | Final ReportThe 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.