Interfacial Interactions of  Bionanoparticles in Natural and Engineered Systems

The divisions that have delineated traditional disciplines in science have been slowly eroding due to the complexities inherent in complete understanding of even the smallest of systems.  A more complete understanding of the colloidal and interfacial behavior of soft particles such as viruses has implications to many scientific disciplines.  The complex bio-physico-chemical interactions that control the fate, transport, reactivity, and bioavailability of viruses and micro-organisms are specifically tied to disease propagation and infection, filtration and the disinfection of drinking water and more recently the use of virus-like particles (VLPs) as drug delivery vessels.  To better understand and thus model these interactions, it is incumbent upon researchers from multiple fields to contribute their individual competencies to broad, far researching and transformative research that will inform numerous disciplines even beyond those of the core research group.  To this end, I am collaborating with Helen Nguyen form the Department of Civil and Environmental Engineering at the University of Illinois to undertake a systematic study of the interactions that govern the reactivity of viruses at important and relevant interfaces in aquatic systems, and to compare those results to those predicted by the governing equations in the field for validation or improvement.

Interfacial Interactions of Nanoparticles in Natural and Engineered Systems

The implementation of nanotechnology is predicted to result in improved health care, advancements in agricultural production, cleaner energy, and enhanced water purification. Nanotechnology is forecast to become a trillion-dollar industry, however, it is inevitable that some portion of these manufactured materials will be introduced into the environment.  For example, owing to their known antibacterial properties silver nanoparticles are already employed commercially in cleaning products, personal care products, and clothing.  The risk posed by the release of such materials to human health and the environment is currently unknown, and the need for a complete understanding of the fate, transport, reactivity, and bioavailability of nanoparticles in natural aquatic systems is clear.

I began some of this work as a post doc in Meny Elimelech’s laboratory.  I maintained a collaboration with Meny and his graduate student Kai Loon Chen for a few years after coming to Lafayette as we expanded our study of functionalized hematite nanoparticles.   A number of students here at Lafayette worked on similar research with cerium oxide nanoparticles and again with hematite.   I am currently  collaborating with John Lenhart. We are seeking to understand the effects of surface complexation mechanism and molecular structure of small molecular weight organic acids on the stability of hematite nanoparticles.

The Development and Optimization of Methods for Contaminant Remediation

Perchlorate, ClO₄^–, contamination in groundwater is a significant environmental concern in many regions of the United States and throughout the world.  For this reason, perchlorate has been on the United States Environmental Protection Agency’s Contaminate Candidate List since 1998.  Human consumption of perchlorate is known to affect the function of the thyroid gland by inhibiting the uptake of iodide.  The affects of perchlorate consumption on children and pregnant women can be even more severe because of the role that thyroid plays in human development.  Because of its nonvolatile, highly soluble, and kinetically inert nature, perchlorate remediation of contaminated groundwater by conventional techniques is inefficient   Current research explores many new remediation technologies, with ion-exchange seemingly the most promising method for the separation of perchlorate from contaminated groundwater.

In this project we have characterized a novel ion-exchange technology for separation of perchlorate from groundwater.  We have also been attempting to optimize the  subsequent microbial or abiotic reduction of perchlroate  in the ion-exchange regenerates.

For abiotic reduction of perchlorate we have been attempting to use zero-valent iron nanoparticles (nZVI).  Initial studies were run while I was on research leave in Australia working with David Waite and his research group.  There I also became interested in nZVI for oxidative transformations.  This work requires a detailed understanding of iron Fenton Chemistry which I also spent a considerable amount of time on.  We published a paper in Environmental Science and Technology establishing our successes in developing the appropriate  kinetic model for the iron Fenton reaction a low pH.  This has served useful as we have been working to optimize the oxidative capacity of nZVI.  A manuscript on this topic is being written.

Reduced Sulfur and Dissolved Organic Matter in Aquatic Systems and their Role Trace Metal Speciation

The biogeochemical cycling of sulfur in aquatic systems is immensely complex, owing to its large variations in oxidation states (–II – +VI) and the variety of inorganic and organic species possible. Both inorganic and organic reduced sulfur compounds are of particular interest because of their ability to form stable complexes with B-type metal cations, such as Fe, Cu, Ag, Hg, Zn and Cd which may ultimately determine the fate and bioavailability and thus potential detoxification of these metals.  Additionally some thiols are known to quench reactive oxygen species (ROS) such as superoxide thus providing an additional avenue for detoxification

The production and fate of organic sulfur compounds in freshwater systems are not as well understood as their inorganic counterparts because of their low natural concentrations and their substantial diversity.  Through recent advances in separations and detection, some thiols (glutathione, cysteine, 3-mercaptopropionic acid MPA) and volatile organic sulfides have been detected in both oxic and anoxic freshwaters.  Not surprisingly, most of the current research on the production and fate of thiols in aquatic systems has been based on marine and coastal systems, and thus the underpinning of current assumptions made about freshwater systems must be made through the lens of these marine-based measurements.

This research seeks to apply a combination of field and laboratory studies to understand the production and fate of the most commonly observed thiols, glutathione (GSH) and 3-mercaptopropionic acid (MPA).  While at Lafayette I washave been able to maintain collaborations with one of my post doctoral advisors, Gabe Benoit, and continued to work in this area.  Currently I have a student who is about to begin field studies local aquatic systems.

Trace metal sequestration by organic matter in natural aquatic systems is also known to limit their bioavailability.  I began initial work in this field a with Gabe Benoit at Yale’s Environment School and have been able to continue it while at Lafayette.   The question of whether copper sequestration in a natural aquatic system could be so intense that  copper might become a limiting nutrient is one that we have been studying for some time.   The results of a collaborative project with  Ben Twining and Gabe Benoit raised some interesting possibilities as to how bacteria and other microorganisms might acquire copper that is tightly complexed.  I have had four students so far working on this project.