J. Breger, S. Walper, M. Ancona, M. Stewart, K. Susumu, I. Medintz
Naval Research Laboratory, United States
pp. 165 - 168
Keywords: quantum dots, enzyme, Michaelis-Menten, nanoparticle
Nanosensors employing quantum dots (QDs) and functional moieties such as enzymes are promising for diagnostics and chemical/biological threat activity. Their small size permits cell penetration and their inherent photochemical properties are well-suited for rapid, optical measurements. The effectiveness of biorecognition agents (e.g., enzymes) immobilized on QDs are not completely understood, hindering development of chemical/biological sensors and remediation materials. We analyze enzyme effectiveness when attached to QDs illustrating an important biological threat application—the toxicity neutralization of paraoxon, a simulant nerve agent. Two sizes of QDs, 525 or 625 nm, appended with DHLA ligands to improve aqueous stability were rapidly self-assembled with various ratios of phosphotriesterase (PTE) via metal coordination of the oligiohistidine tag onto the Zn2+-rich QD surface. PTE catalyzes the detoxification of organophosphate pesticides to p-nitrophenol. The optimal ratio of PTE to 525 nm and 625 nm QD’s was determined and we saw an increase in Vmax and other kinetic parameters compared to free enzyme. Enhanced enzyme performance is most likely due to increased enzyme-substrate interactions due to translational diffusion between closely-spaced enzymes. Development of these nansosensors as optical-based biosensors (e.g., within compact microfluidic devices) may greatly improve the sensitivity of conventional biological/chemical detection schemes.