Developments in Analytical Chemistry: Acoustically Levitated Drop Reactors for Enzyme Reaction Kinetics and Single-Walled Carbon Nanotube-Based Sensors for Detection of Toxic Organic Phosphonates
Field, Christopher Ryan
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https://hdl.handle.net/2142/72254
Description
Title
Developments in Analytical Chemistry: Acoustically Levitated Drop Reactors for Enzyme Reaction Kinetics and Single-Walled Carbon Nanotube-Based Sensors for Detection of Toxic Organic Phosphonates
Author(s)
Field, Christopher Ryan
Issue Date
2009
Doctoral Committee Chair(s)
Masel, Richard I.
Scheeline, Alexander
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Engineering, Chemical
Abstract
Developments in analytical chemistry were made using acoustically levitated small volumes of liquid to study enzyme reaction kinetics and by detecting volatile organic compounds in the gas phase using single-walled carbon nanotubes. Experience gained in engineering, electronics, automation, and software development from the design and implementation of an acoustically levitated drop reactor was applied to the development of polymer-coated single-walled carbon nanotube-based sensors as a detector for a miniature, or micro, gas chromatograph.
Small droplets can be levitated at the nodes of standing waves established between an ultrasound emitter and reflector. Acoustically levitated drops provide a unique environment, free from wall interactions, with rapid mixing, to study enzyme reaction kinetics. An acoustically levitated drop reactor (LDR) was built and optimized to reduce electrical power by three orders of magnitude and automate levitation, droplet injection, and data collection. Fiber optic and laser-based optical systems were developed to monitor reaction kinetics inside a levitated drop via chemiluminescence and fluorescence.
One use for levitated drops is trace atmospheric sensing. Thus, microsensors will be an integral part of future LDRs. Towards this end, single-walled carbon nanotube (SWNT)-based sensors were developed for the detection of toxic organic phosphonates. Homogeneous, randomly aligned SWNT films were prepared from suspended single walled carbon nanotubes using vacuum filtration. The SWNT film is transferred to a silicon substrate with two gold electrodes patterned using lift-off photo lithography to create a chemi-resistor. The change in resistance of the SWNT films can be monitored for response to various compounds such as dimethyl methylphosphonate (DMMP), a simulant for toxic vapors.
However, uncoated, or untreated, SWNT-based sensors non-selectively adsorb molecules, reducing their usefulness as a sensor. To increase both sensitivity and selectively of SWNT-based sensors, thin polymer coatings were applied to SWNT films via electropolymerization. As opposed to previous polymer deposition methods, electropolymerization provides tight control over film thickness, uniformity, and spatial resolution. Thus, multiple sensors were arranged into an array with different polymer coatings to provide a unique signature for a variety of compounds.
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