The prevention of waterborne diseases requires rapid detection of pathogens in drinking water, with an ultimate goal of in-line monitoring in real time. Standard cultivation-based methods are too time-consuming and thus not suitable for this purpose. Many technologies were proposed to achieve this goal, such as ELISA, PCR, FISH, FTIR and flow cytometry. However, they still have limitations of non-specificity, complexity and high cost. Therefore, an optical system is proposed and developed towards the in-line monitoring of bacteria, which combines the advantages of FTIR and micro-flow cytometer for bacterial identification and precise quantification.
The in-line use requires obtaining IR spectra of bacterial cells directly in water, which is achieved using a CaF2 liquid cell. The spectra of a series of bacterial samples are collected and analyzed using principal component analysis for their differentiation. A preliminary study on fabricating a CaF2 concentrator is conducted, in which a novel phenomenon on stress release of silicon nitride film on CaF2 substrate is discovered and studied.
To determine the concentration of bacteria in drinking water, a micro-flow cytometer is built based on a micro-fabricated device that integrates on-chip beam-shaping optics and microfluidic channels. With this micro-flow cytometer and optimized data analysis for counting particles in real time, linearity with correlation coefficient of over 0.99 is achieved for the dependences of throughput on both volumetric flow rate and concentration of sample. With a one-dimensional hydrodynamic focusing, no degradation of the counting efficiency is demonstrated when the focused sample stream expands. The high accuracy of counting makes this micro-flow cytometer a promising candidate for low concentration applications.
Counting of E. coli DH5α cell suspensions in phosphate buffered saline is performed using the micro-flow cytometer. Side-scattered light signals are used to count the E. coli cells. A detection efficiency of 92% is achieved when compared with the expected count from a haemocytometer. It is demonstrated that E. coli can be easily distinguished from beads of similar sizes (2-4µm) as their scattering intensities are different. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19704 |
| Date | January 2016 |
| Creators | Guo, Tianyi |
| Contributors | Deen, M. Jamal, Biomedical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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