Detecting Pathogens in Water Using Raman Spectroscopy

Detecting Pathogens in Water Using Raman Spectroscopy

Real-Time Monitoring of Bacteria

Detecting pathogens, such as E.coli and Coliforms, present in water is of key importance to protecting human health. For example, every day two thousand diarrhoeal related deaths occur due to pathogen contamination in water. The traditional methods to identify the presence of such bacteria require a lot of time. This is because the water samples must be collected from the water bodies and safely transferred to laboratories. They are then cultured to grow bacterial colonies. This process requires significant time, consumables and resources.

Presently, there is no method to identify the presence of bacteria in water in real-time. WaterMon project is developing an innovative technology based on Raman Spectroscopy to identify and quantify bacteria in water in real-time. The project chose Raman spectroscopy as it offers excellent specificity of finding the fingerprints of pathogens. In the following, we describe our journey to achieve such a platform.

 

Figure 1: Bench-Top spectroscope at CAPPA, CIT
Figure 2: Intitial Raman experiments with Bench top Raman spectroscope
Figure 3: Raman spectra of E. Coli (Black line) and Water (Red line) from initial experiments.
Figure 4: Raman Probe for Water Quality Analysis

Experiments

To begin with, we tested water samples spiked with E. coli with a commercially available Raman Spectroscope that is readily available in CAPPA, Cork Institute of Technology (Figure 1 and Figure 2). In our tests, we tried to obtain the spectra of E.coli sandwiched between the glass slides. We quickly learnt that ordinary glass slides are poor substrates for Raman measurements.

Next, CaF2 substrates were used, which have been recognised as one of the best substrate as they have less Raman background. Even with these substrates, it was not possible to get the spectra of bacteria in aqueous solutions with the bench top Raman spectrometer. One of the problems with the bench-top spectrometers is that they are not ideal liquid samples. Therefore, a Raman probe based set-up was designed (Figure 4), which is more suitable for liquid samples. With this Raman probe, it was possible able to detect some bands within the Raman spectra of bacteria in high concentrations. The next steps are to develop this set-up further to detect bacteria in low concentrations with the aim of improving the Raman signal.