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Graduate Defense: Crystal Paulus

June 28 @ 1:30 pm - 2:30 pm MDT

Thesis Information

Title: Improving the Sensitivity of Colorimetric DNA Sensors via Catalytic Disassembly of Gold Nanoparticles

Program: Master of Science in Chemistry

Advisor: Dr. Jeunghoon Lee, Chemistry and Biochemistry

Committee Members: Dr. Elton Graugnard, Materials Science and Engineering, and Dr. Henry Charlier, Chemistry and Biochemistry


Biotechnology is quickly progressing in the medical field; however, its applicability is limited by the lack of early detection in a few diseases/cancers, which is essential for effective care. Since biotechnology is rising, sensitive detection approaches are increasingly developed with gold nanoparticles (NPs). One technique commonly used for target DNA amplification is polymerase chain reaction (PCR), which can be used to diagnose a variety of diseases and cancers. The shortcomings of PCR are that it requires sensitive enzymes, expensive equipment such as a thermocycler, and employees being trained on this equipment, which makes this process very time-consuming. Because of these disadvantages of PCR, this method is inapt for a simple procedure for DNA amplification. A simple technique of target DNA amplification that we proposed that is non-enzymatic based is a catalytic disassembly of the DNA reaction mechanism. Our catalytic DNA network can be used as a colorimetric DNA sensor by implementing gold NPs onto a polymer microbead. Previous sensor designs used nanoparticle aggregation-based methods via plasmonic coupling to exploit the colorimetric properties of gold NPs. Another technique to exploit colorimetric sensing of gold NPs is by forming nanoparticle aggregates first and then disassembling the catalytic DNA network in the presence of a target sequence. This allows the gold nanoparticle linkages to be released from the polymer microbead, and free nanoparticles can be detected in the supernatant without using costly instrumentation. The primary objective of this project is to create a disassembly-based colorimetric sensor system that can elicit a measurable signal when small segments of nanoparticles disassemble into a solution. Two gold NP microbead template disassembly via DNA catalytic network were created with varying distances for the following: Design 1 (thiolated signal strand) and Design 2 (thiolated output strand) with two different sizes (15 nm diameter, max = 520 nm and 20 nm diameter, max = 524) to compare which had the highest sensitivity. Results have been reported, and the minimum amount of DNA target we could detect was as low as 0.1 nM.