Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Program Name/Specialization

Biological and Chemical Sciences

Faculty/School

Faculty of Science

First Advisor

Scott Smith

Advisor Role

Supervisor

Abstract

This thesis explores the development and application of a DNAzyme-based biosensor designed to detect labile metal species in environmental samples. Real time and on-site monitoring of labile metal fractions would make a valuable contribution to environmental management, as these fractions are the most bioavailable and pose significant toxicity risks to aquatic organisms. Conventional methods for detecting labile metals, while effective, are often burdened by high costs, complexity, and lengthy processing times, making them less ideal for rapid and widespread environmental assessments.

The first manuscript of this thesis (chapter 2) establishes the fundamental capabilities of the Pb2+-specific DNAzyme GR5 in detecting labile lead in controlled laboratory conditions. The study systematically examines the influence of various factors, including pH, ionic strength, and dissolved organic matter (DOM), on the sensor’s performance. It was found that GR5 responds specifically to labile lead species such as Pb2+, PbOH+, and PbCl+, but shows no response to lead complexed with DOM. This finding underscores the potential of GR5 as a sensor for labile metals under well-defined environmental conditions, where factors like pH and ionic strength are carefully controlled.

The second manuscript (chapter 3) focuses on the critical aspect of calibration, comparing two different techniques: the traditional internal standard additions method and an external matrix matching approach. The research highlights the challenges associated with standard additions, particularly the rapid fluorescence generation at lower ionic strengths, which complicates accurate measurement. Matrix matching, on the other hand, was found to be a more effective calibration method, ensuring that the pH and ionic strength of the calibration samples closely match those of the environmental samples. This method was consistent in trends with comparisons to bioaccumulation toxicity tests and model predictions using the CHEAQS software. This method demonstrated that GR5 can reliably measure labile lead concentrations in complex water matrices within a factor of 2.

The third manuscript (chapter 4) extends the application of GR5 to real environmental water samples, providing a comprehensive evaluation of its performance in natural settings. The study emphasizes the importance of matrix matching for calibration to achieve reproducible and accurate results in diverse water bodies. The results showed that when the environmental sample’s pH and ionic strength closely matched those of the calibration standards, GR5 provided measurements that were consistent within a factor of two of predictions from the Windermere Humic Aqueous Model (WHAM) and ion-selective electrodes (ISEs). This validation suggests that GR5, when calibrated appropriately, is a viable and cost-effective sensor for monitoring labile lead in various environmental contexts.

Overall, this thesis demonstrates that DNAzyme-based sensors, particularly the GR5 biosensor, offer a promising alternative to traditional methods for environmental monitoring of labile metal ions. The research supports the continued development of these sensors so that they can eventually be integrated into environmental management practices, addressing the growing need for rapid, accurate, and cost-effective monitoring tools in the face of increasing environmental pressures and contamination risks.

Convocation Year

2025

Convocation Season

Spring

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Available for download on Wednesday, July 09, 2025

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