Type of Document	Master's Thesis
Author	Yu, Shann Claybourne Say
URN	etd-12082009-144324
Title	Iron Oxide Nanoclusters as In Vitro Biosensors of Proteolytic Activity
Degree	Master of Science
Department	Biomedical Engineering
Advisory Committee	Advisor Name Title Todd D. Giorgio Committee Chair Hak-Joon Sung Committee Member
Keywords	biosensors PPS amphiphilic block copolymers PEG Iron oxide nanoparticles restriction enzymes
Date of Defense	2009-12-08
Availability	unrestricted
Abstract We demonstrate a flexible, tunable scheme for synthesizing multifunctional, ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) and its application to the area of magnetic relaxation switches. USPIO cores (10nm) were functionalized with a poly(propylene sulfide)-bl-poly(ethylene glycol) (PPS-PEG) copolymer, yielding ~40nm micelles. PPS-PEG-ssDNA conjugates and fluorophore-conjugated PPS-PEG are incorporated into the micelle synthesis process, yielding ssDNA-coated magnetofluorescent particles. To form magnetic relaxation switches, we generated USPIO populations that display complementary ssDNA sequences. Mixing of complementary USPIOs leads to clustering, resulting in a significant increase in R2 magnetic relaxation. Treatment of the DNA-crosslinked USPIO clusters with restriction enzymes specific for the crosslinking sequence results in an irreversible return of R2 relaxation to baseline levels. The constructs demonstrate their utility as nanoscale sensors of restriction enzyme activity. The presented functionalization scheme can be extended to the generation of biosensors for other sources of proteolytic activity, for diagnostics and imaging applications for cancer and atherosclerosis.
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