Date of Award
Master of Science (MS)
Electrical and Computer Engineering
The single interdigital transducer (IDT) device was investigated as a micro-chemical sensor for the detection of organophosphates compounds in aqueous solutions. The compounds of interest are: parathion, parathion-methyl, and paraoxon. The polymers used as a partially-selective coating for the direct detection of these compounds are 2,2'-diallylbisphenol A- 1,1,3,3,5,5-hexamethyltrisiloxane (BPA-HMTS) and polyepichlorohydrin (PECH). BPA-HMTS is synthesized here at Marquette University. The measurement of interest for the single IDT is the change radiation resistance. The radiation resistance represents the energy stored in the propagating acoustic wave. As analyte absorbs into the polymer coating, changes in the film's properties will undergo resulting in a change in the radiation resistance i.e the acoustic wave properties. The film's properties changing include: added mass, viscoelastic properties, thickness, and dielectric properties. These properties will contribute to an overall change in the radiation resistance. A linear change in the radiation resistance is expected to occur for increasing concentrations of an organophosphate. The experimental results indicate that BPA-HMTS shows greater sensitivity towards the organophosphates than PECH. Both polymers showed greatest to lowest sensitivity to parathion, parathion-methyl, and paraoxon respectively. Thicker films tested for both polymers, 0.75μm thick, show a higher response due to a more pronounced effect of mass loading than the thinner films tested, 0.50μm. The response times for BPA-HMTS were much faster than for PECH. Both films showed fastest to slowest response time to paraoxon, parathion-methyl, and parathion respectively. The sensor is tested for reproducibility for the polymer BP-HMTS. A sensor array consisting of separately tested devices from this work as well as work done by a previous student is utilized to increase the selectivity of the three organophosphates. Radial plots are performed for each organophosphate and concentration using the change in radiation resistance, response time, and frequency shift for both BPA-HMTS and PECH at 0.50μm as input parameters. These plots yield unique recognition patterns for each organophosphate that can be used to distinguish one from another.