Fluorescence sensing approaches to heavy metal detection

Abstract

Heavy metals are extremely toxic, causing adverse health effects at micromolar levels. Small molecule fluorescent sensors are an attractive metal ion sensing strategy as they require minimal expensive instrumentation and analytical expertise, while retaining high sensitivity. This thesis explores the use of small molecule fluorescent sensors as tools for environmental heavy metal ion detection. The two methods of fluorescence sensing used in this thesis are selective and array-based sensing. Chapter 2 investigates the dipicolinate moiety as a selective Pb2+ chelating group for fluorescent sensors. The BODIPY sensor, 33, demonstrated a selective response to Pb2+ and had several favourable features such as reversibility, robustness to interferants and naked eye detection. An alternative approach to selective metal sensing is using cross-reactive sensing arrays to detect multiple analytes simultaneously. Chapter 3 explores the reduction of a six-sensor fluorescent array to three sensors while retaining 100% metal ion classification accuracy in water. Alternatively, Chapter 4 details the use of pH as an array diversification agent to create a single-sensor array which also presented consistent 100% correct classification accuracies in real aqueous test samples. The use of small molecule fluorescent sensors was also explored in an industrial metal-monitoring context. In Chapter 5, three metal ion sensors were trialled in highly concentrated ammonium nitrate solution for both selective and non-selective responses to trace metal ion contaminants. The commercially available dye, calcein blue, and Schiff-base sensor, 79, could both successfully quantify Al3+ in ammonium nitrate solution in the presence of other trace metal interferants. The collection of fluorescent sensing platforms in this thesis displays the potential of small molecule fluorescent probes to be used as alternative metal-sensing technologies for environmental monitoring applications.