Pathogen detection with the Nanofiber- Light Addressable Potentiometric Sensor (NF-LAPS)

• Author / Creator

  Mojir Shaibani, Parmiss

• The basic human right to have safe and clean drinking water cannot be neglected with the ever-rising worldwide need for drinking water that meets global standards. Local monitoring of water sources is even more vital in areas where access to pure drinking water is limited and its processing facilities are out of reach. The lack of sophisticated medical services in remote areas also makes providing clean drinking water crucial due to the danger of infectious outbreaks. These outbreaks, or even isolated cases of infections may seem easily treatable in more urbanized areas, but basic treatment may not be sufficient in more rural sites. One of the most widely occurring pathogens in water is Escherichia coli (E. coli). The presence of E. coli although infectious on its own, can also often be an indicator for the existence of other harmful coliforms in water. Therefore E. coli is an important target for detection in water. To provide more economic means of E. coli detection that can be used on-site, there is a need to develop a portable sensor system that will not require highly qualified personnel training and can be used for rapid on/off based detection. For this reason, a simple, rapid and cost effective detection technique for E. coli using a Light Addressable Potentiometric Sensor integrated with electrospun polyvinyl alcohol/poly acrylic acid (PVA/PAA) hydrogel nanofibers as the sensing layer (NF-LAPS) is reported. Changes in pH of the media are detected as E. coli cells ferment glucose molecules and increase acidity of the surrounding. A super-Nernstian response of a 74 mV/pH change in the NF-LAPS provides high sensitivity towards E. coli with a theoretical limit of detection (LOD) of 20 CFU/ml. The measured limit of detection in this work is 100 CFU/ml. The high sensitivity is associated with the pH sensitive behavior of the NFs on the surface. Detection of acidic species released in cellular metabolism of pathogens in the presence of carbon source renders the sensing mechanism cheaper, less time consuming and more practical than the antibody-antigen interaction based approach. Selectivity towards E. coli for applications in drinking water detection is ensured by the incorporation of d-mannose for specific binding. Selectivity is examined against Pseudomonas fluorescens (P. fluorescens). To examine the possible application of the biosensor for other beverages with complex media (with more compounds compared to water), the detection of E. coli in orange juice with a portable NF-LAPS prototype device was investigated. The measured limit of detection in this work is 100 CFU/ml. The selectivity of the biosensor towards E. coli is confirmed by examining the response of the NF-LAPS against Salmonella typhimurium (S. typhi), also commonly found in orange juice. S. typhi is also a sugar fermenting genus of bacteria. The entire NF-LAPS system is packaged into a portable device with the readout displayed on a generic tablet. The Device is also capable of wirelessly transmitting data into the analysis software. Real water samples are tested with the working prototype of the portable NF-LAPS. In addition, to demonstrate the versatility of the NF-LAPS, the system was used to investigate the metabolic activity of breast cancer cells in the presence of sugar. Over the testing period of 2 h, cancer cells (MDA MB231) showed a response of approximately 0.4 change in pH compared to a virtually no change for normal cells (MCF10A). The role of metabolic inhibitors is also examined by monitoring cellular metabolism. The conclusion is that the use of inhibitors suppresses the acidification process in cancer cells. This study based on the extracellular acidification of cancer cells enhances our understanding of cancer cell metabolic activity and their response to antibiotics, which in turn will help in the development of better treatments, drugs and drug dosages.

• Subjects / Keywords

  • Nanofibers
  • Electrochemical sensors
  • Sensors
  • Detection
  • Water

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R35X25R2C

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.