Fluorescence based trace detection of pesticides using supramolecular hosts, UV photolysis and synchronous scanning

Traditional methods of pesticide detection used on Prince Edward Island (PEI) are very expensive and time consuming. These methods are typically only useful after harm has been done to the environment, and cannot be used in prevention. A new method for rapid, on-site detection of these pesticides would not only be of value financially, it could also prove to be essential in preventative measures, for example by monitoring streams. Fluorescence, the light emitted by electronically excited molecules, is a highly sensitive technique for detecting and measuring the concentration of molecules in solution. Most pesticides used on Prince Edward Island show only weak native fluorescence in water. However by forming a supramolecular host:guest inclusion complex, in which the pesticide "guest" becomes included within the internal cavity of an organic host molecule, this fluorescence is increased for many guest molecules. In some cases, this enhancement of the fluorescence might be sufficiently large enough to allow for the development of a fluorescence-based trace analysis technique with sensitivity in the required ppb level. In this project, native and modified cyclodextrins and their effect on the fluorescence of a series of pesticides used on PEI, specifically carbofuran, carbaryl and chlorothalonil along with five others, is measured with results varying from 670 parts per trillion for carbaryl to 69 ppb for Chlorothalonil. In addition, UV photolysis of certain pesticides can also lead to enhanced fluorescence such as azoxystrobin and imidacloprid, and thus also be a technique used in the trace detection of pesticides. This occurs via creation of a more highly fluorescent molecule from a previously non- fluorescent or weakly fluorescent pesticide. Synchronous scanning, a method of measuring fluorescence by scanning both excitation and emission wavelengths simultaneously, which results in narrower measured emission bands is also examined in detail to separate fluorescent bands of similar emission wavelengths, and thus simultaneously measure a set of two or more pesticides in solution. Overall, the main goal of this work is to develop a sensitive, enhanced fluorescence based trace analysis technique for pesticides, which could eventually be carried out using a portable fluorimeter, so that samples could be analyzed on site, in a matter of minutes, rather than in a lab over a period of days.