Miniaturized Detection Systems - Waterborne Pathogens: Detection Methods and Applications - page 325

10.2.3. In electrical methods
Despite the relative ease of electrode integration on-chip, there appears to
be significantly fewer studies demonstrating electrical methods of water-
borne pathogen detection with microfluidics. However, many of the systems
reported in Chapter 6 are already performed in miniaturized systems; the
development of electrical methods to on-chip systems is well-established,
and the lacking area is the number of waterborne pathogen applications
explored. A few examples are given in this section.
Figure 10.6 above illustrates an electrical method for virus detection,
with electrochemical compounds encapsulated in liposomes, which can
be lysed releasing the compounds for detection. Gomez and colleagues
developed a flow-through system to measure the impedance of pathogenic
bacteria, testing for metabolic activity as an indicator of viability. 83 They
claimed to process low numbers of cells (1-5000) though the sample vol-
ume was also very small, being just 30 nL.
In 2010, Mannoor et al. described a microfluidic impedance system for
bacterial detection. 84 In the flow-through setup the LOD was 10 4 cells mL −1
as opposed to 1 bacterium µL −1 in static operation ( Fig. 10.7 ). The authors
suggest the difference is due to the influence of flow on the binding kinet-
ics, resulting in reduced binding. Appropriate system design to consider
binding kinetics and flow rates is very important. 85
Also in 2010 Houssin and colleagues reported detection of Cryptosporidium
using EIS and could distinguish between viable and non-viable oocysts. 108
The detection took place on a PDMS chip and was due to ion release in
hypo-osmotic conditions, thus requiring oocysts to be resuspended in puri-
fied water. A chip consisting of an arrangement of four sensors with 4µm wide
interdigitated electrodes was manufactured by optical lithography and metal
deposition on a Pyrex substrate ( Figure 10.7(a) ). The device was shown to
detect oocysts at concentrations from 10-2000 oocysts/µL ( Figure 10.7(b) ).
10.2.4. In biosensors
Microfluidics is considered very important for biosensors, particularly in
achieving portable and automated optical biosensors. 86
In terms of optical biosensors on-chip, photonic crystals have been
incorporated into lab-on-a-chip systems, e.g. by Scullion et al. in 2011, 87
and the topic is the subject of a special issue of the journal Sensors to
be published in 2013. Silicon microring resonators, waveguides, and other
optical components can also be integrated into microfluidics. 86,88 These are