Date of Award
Doctor of Philosophy in Chemistry
The ability to quickly determine the nature of small-molecule toxicants after an anthropogenic event would greatly benefit first responders and medical personnel. Current detection methods, while elegant, require several separation and purification steps before the samples can be submitted for analysis, which can be a time-consuming process. There is a crucial knowledge gap that exists as a result. Reported herein is the use of a non-toxic, commercially-available molecule, cyclodextrin, to rapidly isolate and detect the toxic components involved in a spill event that would address this knowledge gap. This cyclodextrin-based scheme would work as a compliment to established analysis procedures by establishing a rapid, high-throughput procedure that can be used to quickly scan samples to determine the nature of the compounds involved in a spill event. This would provide first responders with the information they need to develop an effective response in a timely manner, and samples would still be sent for more intense analysis using standardized procedures, such as those set by the Environmental Protection Agency (EPA) to confirm the results and quantify them. Similarly, this method can be used by medical personnel to quickly analyze samples from patients to determine if their symptoms are a result of a spill event.
Cyclodextrins enable the identification of toxicants proximity-induced interactions between a toxicant and high-quantum yield fluorophore. Cyclodextrins have hydrophobic cores and hydrophilic surfaces, and both the toxicant and fluorophore use the cyclodextrin as a scaffold, forcing them in close proximity to one another. Once the toxicant and fluorophore are closely associated, gamma-cyclodextrin, the primary cyclodextrin derivative of interest in this work, facilitates proximity-induced energy transfer from the toxicant donor to the fluorophore acceptor. Energy transfer to and emission from the fluorophore occurs upon excitation of the toxicant, and the resulting emission spectra is unique to each fluorophore-toxicant combination. These unique signals can lead to the array-based detection of the toxicant as they act as photophysical “fingerprint” for the toxicant.
The cyclodextrin-based scheme discussed herein offers a number of operational advantages. First, this scheme is well-suited for high-throughput screening as fluorescence measurements are fast to obtain and samples require little pretreatment before analysis (usually a simple dilution is all that is needed). Second, detection occurs successfully in multiple complex matrices, including seawater, oiled samples, and human plasma, breast milk, and urine. As such, this method can be useful to a variety of spill scenarios, and assist medical personnel. Third, cyclodextrins can effectively remove some of the most toxic components from oil spills, helping to solve many oil-spill related problems and enabling a tandem extraction-detection system. Taken together, this work has significant applications for public health, environmental remediation, and disaster response and relief.
The first manuscript, “Efficient detection of polycyclic aromatic hydrocarbons and polychlorinated biphenyls via three-component energy transfer,” describes the energy transfer efficiencies from polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) to high-quantum yield fluorophores using proximity-induced non-covalent energy transfer. This energy transfer is efficient even with fluorescent PAHs and less fluorescent PCBs. The low limits of detection and potential for selective detection using array-based systems, combined with the straightforward experimental setup, is the basis for using such a system to detect small molecule toxicants. This manuscript was published in the journal Chemical Communications in 2013.
The second manuscript, “Array-based detection of persistent organic pollutants via cyclodextrin promoted energy transfer,” focuses on applying the findings from the previous manuscript to the development of an array-based detection scheme. In this work, γ-cyclodextrin promotes proximity-induced, non-covalent energy transfer from an aromatic pollutant (analyte) to a high quantum yield fluorophore. Through the use of three different fluorophores, a sensor array that successfully classified all 30 analytes with 100% accuracy and identified unknown analytes with 96% accuracy was developed. This detection scheme was also able to identify 92% of analytes successfully in human urine. This manuscript was accepted on June 12, 2015 by the journal Chemical Communications for publication.
The third manuscript, “Cyclodextrin-enhanced extraction and energy transfer of carcinogens in complex oil environments,” uses γ-cyclodextrin to achieve two tandem, high-impact functions: (a) the extraction of PAHs from various oil samples to aqueous solution, and (b) the promotion of energy transfer from the extracted PAHs to a high-quantum-yield fluorophore. The extraction proceeded in moderate to good efficiencies, and the energy transfer promoted a new, brightly fluorescent signal in aqueous solution. Such a dual-function system (extraction followed by energy transfer) can be used in the environmental detection and cleanup of oil-spill-related carcinogens. This manuscript was published in the journal ACS Applied Materials and Interfaces in 2013.
The fourth manuscript, “Efficient extraction and detection of aromatic toxicants from crude oil and tar balls using multiple cyclodextrin derivatives,” reports the efficient extraction of aromatic analytes from crude oil and tar balls using various cyclodextrin derivatives. Cyclodextrins are known to bind hydrophobic guests in their hydrophobic interiors, and they were able to extract aromatic analytes from the oil layer to the aqueous layer. Methyl- β-cyclodextrin and β-cyclodextrin were the most efficient at analyte extraction while γ-cyclodextrin was most efficient at promoting energy transfer. Cyclodextrins are and can be used for tandem analyte extraction and detection in oil samples, with up to 86% efficient energy transfer observed in the presence of γ-cyclodextrin compared to 50% in the absence of cyclodextrin for oil spill oil extraction. This manuscript was published in the journal Marine Pollution Bulletin in 2015.
The fifth manuscript, “Cyclodextrin-promoted energy transfer for broadly applicable small-molecule detection,” reports energy transfer from small-molecule toxicants to organic fluorophores for a broad range of toxicants in complex biological media. The media include human plasma, coconut water (which has been used as a plasma surrogate in emergency situations), and human breast milk. This energy transfer proceeded in moderate to good efficiencies. Because this energy transfer is a generally applicable phenomenon, it has significant potential in the development of new turn-on detection schemes. This manuscript was published in the journal Supramolecular Chemistry in 2014.
The sixth manuscript, “Investigating fundamental intermolecular interactions in gamma-cyclodextrin host-guest complexes,” focuses on the mechanisms that underlie association complex formation using gamma cyclodextrin hosts. Binding behavior in such complexes is driven by hydrogen bodning, π-π stacking, Van der Waals foces, and the hydrophobic effect. However, because of the disparate structures of small-molecule toxicants have been investigated, the overall contribution of each of these forces vary between structures. Hydrogen bonding was found to be a major contributor to association complex formation. This manuscript is currently in preparation for submission to the journal Environmental Sciences: Water Research and Technology.
The seventh manuscript, “Fluoroscence-based detection of environmental toxicants and toxicant metabolites in urine,” focuses on the detection of parent polycylic aromatic hydrocarbons (PAHs) and several of their oxidized daughter derivatives. PAHs are rapidly metabolized in the body, and detecting their metabolites is important for medical personnel in assessing an individuals’ exposure to such pollutants. In this work, samples from a non-smoke and a habitual smoker were studied to assess changes in analyte response. Efficient energy transfer (and thus toxicant detection) was observed in both cases. This manuscript is currently in preparation for submission to the journal Environmental Sciences and Technology.
Serio, Nicole Cook, "Cyclodexrtrins as Hosts for the Array-Based Detection of Persistent Organic Pollutants in Complex Media" (2015). Open Access Dissertations. Paper 358.