Final Report: Cost-effective Molecularly Imprinted Polymer Based Monitoring Technologies to Improve the Performance and Reliability of Small Drinking Water SystemsEPA Contract Number: EPD15035
Title: 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: Manager, SBIR Program
Project Period: September 1, 2015 through February 29, 2016
Project Amount: $99,998
RFA: Small Business Innovation Research (SBIR) - Phase I (2015) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Water
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 associate 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 technology hold opportunities to substantially advance infrastructure and assure compliance and still be economically viable for integration by small drinking water system operators. Sporian Microsystems has performed significant prior work developing and fielding a range of water low cost remote and in-line monitoring systems for both the government and private industry. The objective of the proposed work is to develop/use MIP based detection materials/schemes that eliminate the ongoing cost of consumable reagents and can easily be retrofitted to expand the range of detectable contaminants in existing low cost water monitoring hardware.
Containments found in surface water, groundwater, and drinking water systems can adversely affect the health of plants, animals, and humans, and degrade the function of commercial industries. In addition to supporting the efforts of drinking water systems to maintain contaminant monitoring compliance, the proposed technology could be ultimately utilized in a range of water monitoring applications. For example nitrates and phosphates in drinking water pose significant health risks to humans, specifically small children. Additionally, nitrates and phosphates in ground/surface water causes disproportionate microorganism growth, which decreases oxygen present and negatively effects water ecosystems, and produces toxins/bacteria that are harmful to humans and animals. This is just one example, and the proposed technology can potentially be extended for use in detecting monitoring a wide range of additional contaminants, including: microorganisms, disinfectants, disinfection byproducts, additional inorganic chemicals, and organic chemicals.
Detection of phosphate and nitrate was performed using molecularly imprinted polymers (MIPs). The molecular imprinting approach is a relatively new and rapidly evolving technology. MIPs were conceived as artificial tailor-made receptors for molecular recognition. Thus, MIPs allow recognition of biological or chemical molecules from small to big structures like proteins or cells with the advantages of: (1) ability to be designed for a specific molecule of interest or for a whole family of compounds, (2) physical and chemical robustness, (3) strength, (4) resistance to acids or bases, and (5) operable at elevated temperature and pressure, all of which make MIPs a promising alternative to be incorporated in sensors as the key recognition element.
Molecular imprinting synthesis involves the formation of a complex between the molecule of interest (template) and a functional monomer in the presence of a significant excess of crosslinking agent to form a three dimensional polymeric network. During MIP synthesis, the monomer bearing suitable functionalities and the template molecules are pre-organized in solution and self-assembled to form a complex by virtue of the interactions between their complementarily binding functionalities (i.e. intermolecular hydrogen bonding interactions). These complexes are preserved during formation of a cross-linked polymer network. After subsequent removal of the template, molecular cavities are left in the network, their binding sites complementary in size, shape, and orientation to those of the template. These cavities are then capable of selectively binding the target molecule or analyte even in the presence of similar structures (Figure 1). Due to their polymeric nature, MIPs can be tailored to exhibit desirable properties (i.e. permeability) during this synthetic procedure through the appropriate selection of monomers, crosslinks, functional monomer, solvent, initiator and polymerization conditions according to the final application. MIPs are most commonly used for highly specific separation, purification and/or enrichment of target molecules in chromatographic columns [i] [ii].
Figure 1: Schematic illustration of the molecular imprinting procedure.
MIPs have been used in a variety of detection and identification applications (often as part of optical sensing) including; environmental monitoring and protection, pharmaceutical separation and analysis, defense and security, and medicine/health care. Of particular note MIPs have been demonstrated for specific binding/detection of relevant water pollutants such as phosphates [iii], nitrates [iv], in general for the recognition of anions [v][vi], pharmaceutical compounds [vii] and bacteriological contamination [viii] in water. In addition to having been previously used/demonstrated with relevant targets and optical sensing, MIPs have additional characteristics beneficial to this application. MIPs are inexpensive materials with long storage life and the potential to keep recognition capacity for several years in demanding environmental conditions. MIPs are also compatible with micro-fabrication technologies required for integration with sensor hardware designs.
Multiple types of MIP systems using different functional monomers were created and tested. The MIP materials were created various morphologies and sizes (monoliths to micro-particles) to facilitate both their characterization and their testing. Two of the many systems tested demonstrated the ability to absorb phosphate derivatives while in water which is a major accomplishment. One of these systems even demonstrated reversible binding of phosphates. Additionally, some selectivity was demonstrated between phosphates and selected interfering ions such as nitrate, bromide, and carbonate. Further testing on the selectivity is planned for Phase II.
The above referenced systems also demonstrated the expected stability afforded by using cross-linked polymer systems. The samples were able to survive heating, solvents, moderately acidity, moderate basicity, and UV light. Further testing on environmental stability will be conducted in Phase II.
Several of the above MIP materials were then created as thin films. The thin film format allows the MIP materials to be optically addressed so that changes in the films are able to be optically detected. Spin coating and bird blades were found to be the most useful method for creating the thin films. When needed, silane coupling agents were used to insure the films stayed attached to the substrates.
Once thin films of the MIP materials were made, the films were tested on two different optical systems. Each optical system used different geometries and optical accessories to detect optical changes in the MIP films. For example, in one of the optical systems, the signal change on the optical detector was as high as 12% change from baseline upon addition of the analyte to the solution in contact with the MIP film. This magnitude of signal change was equates to detection limits of 100 micromolar concentrations of a phosphate target. With the use of well-known signal processing techniques, an estimated detection limit of 10 micromolar can be reached with the current set up. Optimization of system geometry, signal processing, and materials will all lead to further reductions in the detection limit. Based on the results obtained from this Phase 1 project; a new optical system design that offers more control of different variables (which increases the ability to optimize the system) was also presented based on the results from this Phase 1 project. The ability to create these detectors in a small 1.5 inch low power form factor was also presented.
Molecularly imprinted polymers (MIPs) capable of absorbing phosphate and phosphate derivatives in water solutions were created. The MIPs also demonstrated some selectivity towards phosphates from the tested interfering ions. Further optimization of the MIP materials is needed for phase II as well as continued and more thorough characterization and testing. With the successful demonstration of phosphate capture by the MIPs, films were created that were used in two different optical systems. These optical systems demonstrated the ability to detect the presence of phosphate and phosphate derivatives in water. With further improvements in optical design and materials, the detection limits for phosphate will be better than needed for meeting EPA limits and guidelines.
Commercialization/Potential Applications of Research:
In addition to small water system operators, end users for such monitoring systems would include civilian (rural, suburban, and metropolitan), homeland security, and military for a range of environmental and process monitoring applications.
The primary market of concern is the small drinking water systems. According to the EPA, approximately 54,000 community water systems, 85% of those are consider small and very small drinking water systems. This implies approximately 45,900 systems that need to be monitored. 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 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. Together, this suggests that approximately 18.5 million households relying on private water that could potentially benefit from the proposed technology. There are many additional markets. Large drinking water utilities would potentially be attracted to the technology. 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. This only represents the domestic market; the international market should be considerable and will be pursued in the future.
The potential investors or commercial partners for the technology could include Hach, Colorado Springs Utilities, Colorado School of Mines, CH2M, CB&I Federal, Thermo Fisher, Aspen Electronics Manufacturing, Strategic Sciences, Aperture Capital, and water utility companies.
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