Development of Peptide Nanotube-modified Biosensors for Gas-phase Organophosphate Detection Thesis

Vapor-phase detection of the model organophosphate (OP) malathion was achieved using enzymes encapsulated in peptide nanotubes and attached to gold screen printed electrodes. The peptide nanotubes had horseradish peroxidase (HRP) encapsulated inside and both acetylthiocholine (ASCh) and acetylcholinesterase (AChE) coated on the outside. ASCh hydrolysis, which produces thiocholine, was catalyzed by the AChE. The thiocholine was then oxidized by the electrode to produce a signal which could be measured by a cyclic voltammeter. HRP catalyzes the oxidation reaction, enabling a faster and stronger response with a much smaller sample that would otherwise be required. This response was inhibited in the presence of malathion vapor, with the extent of inhibition proportional to the malathion concentration down to the detection limit of the biosensor. This study first established methods to consistently reproduce known concentrations of malathion vapor. Once the vapor concentration was established, peptide nanotube-modified gold screen printed electrodes were used to detect OP vapor. The nanotube-modified electrodes were first exposed to AChE, then to ASCh, and finally inserted into an airtight vial with a known concentration of malathion. Cyclic voltammograms were taken at each step of the process to monitor the changes in activity. The biosensor response was inhibited by OP concentrations as low as 12 ppbv, which is less than half the lethal limit of 30 ppbv for VX.