Organophospates (OPs) are a class of compounds that are widely used in agriculture as neuroinhibitory insecticides and in chemical weapons (e.g., Soman and Sarin) as nerve agents. Because OPs are so widely used in agriculture, it is important to understand the amount of insecticide needed for maintaining healthy crops while limiting environmental damage through runoff and overuse. Therefore, there is a need to produce sensors that can promptly assess and constantly monitor exposure from OP-based insecticides and/or chemical warfare agents, especially before these agents have the chance to leech into the soil or water. We envision these sensors to be composed of a fluorescent nanoparticle (NP) such as quantum dots (QDs) or gold nanoparticles (AuNPs) and phosphotriesterase (PTE), an enzyme that catalyzes the hydrolysis of OPs. The inherent photochemical properties of these two classes of NPs make them well suited for rapid, optical measurement, such as, i.e., size tunable fluorescence, ease in attaching functional moieties, resistance to photobleaching, etc. We have engineered PTE to contain a terminal hexahistidine tag, enabling facile assembly to the NP surface through spontaneous metal-affinity coordination. Assembly can be controlled in a ratiometric manner with the maximum number of PTE that can be assembled dependent on particle size. The hydrolysis of paraoxon yields p-nitrophenol whose absorbance can be spectroscopically measured as a function of time and concentration. Assembly of PTE to QDs or AuNPs was confirmed through dynamic light scattering (DLS) and electrophoretic mobility shift assays. PTE hydrolytic activity was examined on various sized NPs (1.5 to 100 nm in diameter) and compared to freely diffusing enzyme alone. Attachment of PTE to NPs imparted higher stability of the enzyme and enhanced kinetics which was dependent on the NP size and ratio of PTE to NP. We discuss several hypotheses that we believe explain this observed enhancement in kinetic activity when attached to NPs.

Characterization of PTE-nanoparticle bioconjugates for rapid and sensitive detection of organophosphates

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.