Optical Detection Technologies for Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 119

Figure 5.5 A cell-phone-based detection system for E. coli . Source: Figure 1 from Ref. 19 .
(For color version of this igure, the reader is referred to the online version of this topic.)
5.1.4. Flow cytometry
Flow cytometry has been proposed as detection technology for waterborne
pathogens for several decades. Initially, the high cost and complexity of the
instrumentation as well as the need for trained cytometrists proved off-
putting, as described in a review by Veal et al. in 2000. 20 This article cov-
ered some of the improvements undertaken in the 1990s rendering flow
cytometry instruments easier to operate and improving detection. Despite
the advantages of flow cytometry, it has not become widely adopted in
routine environmental monitoring applications. This is probably due to the
challenge of standardizing measurements for complex samples. 20 However,
many water companies do use flow cytometry, especially to count, measure
and in some cases separate particles, including (oo)cysts. Flow cytometry is
also used in the preparation of spike samples for analytical quality control.
In our review of the literature there appears to have been very little
work considering flow cytometry for waterborne pathogen detection in
the past decade. However, water companies are still interested in exploring
the potential of this technique, as indicated by a recently initiated project
between Cranfield University and Scottish Water.
Flow cytometry measures the physicochemical properties of particles as
they pass through an observation channel. As the particles enter the channel,
they are focused using sheath flow to attempt to ensure single-particle pas-
sage ( Fig. 5.6 ). The light source employed is typically a laser and the result-
ing forward-scatter and side-scatter are measured ( Fig. 5.7 ). Fluorescence
can also be employed for either autofluorescent particles or labeled particles.
Flow cytometers can be used for sorting a defined number of par-
ticles by either a mechanical (cheap, simple but slow) or droplet-based