Grantee Research Project Results
2003 Progress Report: Compound Specific Imprinted Nanospheres for Optical Sensing
EPA Grant Number: R830911Title: Compound Specific Imprinted Nanospheres for Optical Sensing
Investigators: Lavine, Barry K.
Current Investigators: Lavine, Barry K. , Seitz, William Rudolf , Fendler, Janos
Institution: Oklahoma State University
Current Institution: Oklahoma State University , Clarkson University , University of New Hampshire
EPA Project Officer: Hahn, Intaek
Project Period: August 24, 2003 through August 23, 2006 (Extended to August 31, 2010)
Project Period Covered by this Report: August 24, 2003 through August 23, 2004
Project Amount: $323,000
RFA: Environmental Futures Research in Nanoscale Science Engineering and Technology (2002) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The objective of this research project is to investigate the use of molecularly imprinted polymers as the basis of a sensitive and selective method for the detection of pharmaceuticals and other emerging organic contaminants at parts per billion (ppb) levels in aquatic environments. Moderately crosslinked, molecularly imprinted polymeric nanospheres (ranging from 100 nm to 1,000 nm in diameter), which are designed to swell and shrink as a function of analyte concentration in aqueous media, are being prepared. The nanospheres are dispersed in a hydrogel membrane. Chemical sensing is based on changes in the optical properties of the membrane that accompany swelling of the molecularly imprinted nanospheres. Two effects contribute to this change. One is an increase in the size of the nanospheres, increasing the amount of light scattered. The other is a change in the refractive index. Because swelling leads to an increase in the percentage of water in the polymer, the refractive index of the nanospheres will decrease as they swell. This brings them closer to the refractive index of the hydrogel membrane, leading to a decrease in the amount of light scattered/reflected by the nanospheres. For the systems that we will be studying, the change in refractive index is the dominant effect. This change can be measured by absorbance or surface plasmon resonance (SPR) spectroscopy. Using SPR, our prototype sensor will be capable of detecting pollutants and hazardous materials selectively at ppb levels in the environment.
Progress Summary:
Theophylline-imprinted polymer microspheres (approximately 1 micron in diameter) suitable for SPR were prepared and applied to a gold surface. The microspheres were held by electrostatic attraction. Incorporation of the microspheres into a hydrogel was achieved by micropipetting the hydrogel formulation onto the gold surface and distributing the formulation across the surface by a spatula prior to polymerization. The polymer membrane formed was both sensitive and specific. The addition of as little as 1.0 x 10-7 M theophylline was sufficient to cause a change in the refractive index of the membrane, which we were able to detect by SPR. Higher concentrations of theophylline produced a larger change in the refractive index. In contrast, the same membrane showed no response to distilled water or 1.0 x 10-4 M caffeine. (Caffeine and theophylline differ by only a single methyl group.) This result, we believe, is significant for two reasons. First, selectivity has been introduced into SPR analyses through the use of these membranes. Studies where biological receptors have been used to functionalize gold or silver surfaces with analyte-specific receptors for pollutant monitoring have been unsuccessful because of problems associated with antigen stability and cross reactivity. Second, the likelihood is high that ppb detection limits for theophylline and other so-called emerging organic contaminants can be achieved with this approach to chemical sensing once the polymeric formulation used to develop the imprinted polymer and hydrogel membrane has been optimized.
Future Activities:
Currently, we are using a polymer formulation developed from N-isopropylacrylamide (NIPA) or N-N-propylacrylamide (transduction monomer), metharcylic acid (recognition monomer), moderate concentrations of methylenebisacrylamide (crosslinker), and template to prepare molecularly imprinted polymers that swell in the presence of the targeted analyte. The concentration of the recognition monomer in the formulation, however, is too high. Recent studies performed in our laboratory indicate that decreasing the concentration of recognition monomer in the formulation will increase the degree of polymer swelling observed. There also have been problems with the stabilizer. Because untemplated NIPA particles can be prepared without a stabilizer, we believe that problems with the stabilizer and the amount of recognition monomer used in the formulation are linked. Optimizing the formulation will require us to understand the relationship between these two variables. This will be a major focus of our research during the next reporting period.
The thickness of the hydrogel membrane is several hundred microns, and the size of the microspheres is approximately 800 nm. It would be advantageous if the membrane was thinner to minimize diffusion distances, ensuring facile mass transfer. In addition, using smaller polymer particles (approximately 100 nm in diameter) would be advantageous because it would mean that a larger number of polymer particles could be immobilized on the gold surface, and the entire particle would lie within the region of the evanescent wave.
Currently, dried polymer particles are being applied to the gold surface prior to their encapsulation by a hydrogel membrane. The imprinted particles, however, need to be hydrated or at least tacky prior to polymerization of the hydrogel, thereby ensuring a highly swellable membrane. We also will address the problem of developing a technique to adhere tacky polymer particles onto gold surfaces.
Journal Articles:
No journal articles submitted with this report: View all 19 publications for this projectSupplemental Keywords:
emerging contaminants, chemical sensing, surface plasmon resonance spectroscopy, molecular imprinting, parts per billion detection, groundwater, chemicals, nanotechnology, hydrogel, N-isopropyl acrylamide, molecular imprinting, environmental monitoring, pollutant monitoring, methods, techniques, colloidal polymerization, analytical chemistry, new/innovative technologies, environmental measurement, nanosensors, environmental chemistry,, RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, Sustainable Environment, Environmental Chemistry, Monitoring/Modeling, Technology for Sustainable Environment, Environmental Monitoring, Engineering, Chemistry, & Physics, aqueous impurities, aquatic ecosystem, nanosensors, chemical sensors, membranes, nanotechnology, environmental sustainability, chemical detection techniques, aquatic toxins, analytical chemistry, surface plasma resonance spectroscopy, optical sensing, nanoporous membranes, hydrogel membranes, membrane technologyProgress and Final Reports:
Original AbstractThe 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.
Project Research Results
- Final
- 2010
- 2009 Progress Report
- 2008
- 2007
- 2006 Progress Report
- 2005 Progress Report
- 2004
- Original Abstract
5 journal articles for this project