Development of piezoelectric crystal detectors for sensing bacteria in water and determining volatile organic compounds in air

by Wong, Yuk-yan

Abstract (Summary)
(Uncorrected OCR) Abstract of thesis entitled


Submitted by


for the Degree of Master of Philosophy at The University of Hong Kong

in January 2000

The applicability of piezoelectric (P/Z) crystal sensors as detectors for determining volatile organic compounds (VOCs) in air, and sensing bacteria in water, has been investigated in the present study. The detectors developed provide a simple and sensitive on-site method for determining total organic vapours in air for occupational health protection, and provide a specific and economic method for determining Salmonella in water for food poisoning


For VOC determination in workplace air, a light and portable P/Z crystal detector has been developed. To reduce the interference of high humidity on the monitoring of organic vapours, the moisture content in the air

sampled was removed by two different drying methods - a battery operated fan

dryer and a Nafion gas dryer. In both drying methods, the relative humidity of the air sampled was shown to be reduced below 40 % when the air intake varied between 43 - 81 %. Among the eight gas-liquid chromatography coatings investigated, Apeizon Grease L and High Vacuum Grease were found to provide satisfactory piezoelectric crystal coatings for determining four commonly encountered organic vapours in industrial air. The P/Z crystal detectors developed gave satisfactory response factors and excellent linear working ranges at the ppm level and are thus suitable for daily on-site monitoring ofVOCs in an enclosed environment.

For bacterial assay, piezoimmunosensors based on a P/Z crystal using the highly specific antigen-antibody reaction have been developed to determine the cell count of Salmonella in water. In this study, the suitability of a thin polymer layer and the recently developed self-assembled monolayer (SAM) was investigated as the base layer for immobilization of antibodies. Polyethylenimine was used as the polymer coating and after activation by glutaraldehyde, monoclonal antibodies M02, M04 and M09 were immobilized onto the surfaces of the P/Z crystal which were then selectively interacted with S. paratyphi A, S. typhimurium and S. enteritidis respectively. A detection limit down to 104 cell/mi was achieved and good repeatability was obtained in the linear working range from 105 to 5 X 108 celli ml. For SAM coating, 3-mercaptopropionic acid was used to create a SAM onto the P/Z crystal surfaces, generating a carboxylate-terminated monolayer that interacted selectively with the primary amino group of the antibody after activation by the condensing reagent. Antibody M02 was immobilized onto the modified


crystal surfaces and the immobilized crystal was found to give satisfactory linear working range varying from 1.2 x 103 to 1.2 x 104 cell / m!. In the determination of S. paratyphi A, the sensor developed gave good repeatability and detection limit down to 103 cell / m!. There was no significant interference observed using other strains of Salmonella and Escherichia coli.

Bibliographical Information:


School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:crystal detectors piezoelectric devices salmonella escherichia coli volatile organic compounds


Date of Publication:01/01/2000

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