Biology Reference
In-Depth Information
more commonly applied to the detection of small molecules. To the best of
our knowledge there are no examples of optical microfluidic waterborne
pathogen biosensors for whole-cell detection.
From Chapter 7 it was clear that electrochemical methods of biosensing
have been the least applied to waterborne pathogens and the same is true of
integration of this type of sensor into microfluidics for waterborne pathogens.
SPR within microfluidics has been demonstrated, though there is
little work with waterborne pathogens. Cell-based SPR is less common
than small molecule detection and so SPR lab-on-a-chip devices perhaps
hold the most promise for detection of the outputs of molecular methods.
SPR-based biosensors are currently implemented to be applied in field-
deployable devices sensing of small molecules, proteins, viruses, and whole
microbes using a 24-channel SPREETA (Sensata) sensor unit. 54
Microfluidics has been integrated with mass-sensitive cantilever bio-
sensors. 89 Channels have been incorporated onto cantilever structures and
utilized to weigh single cells. 90 For waterborne pathogens, such embedded
microfluidic channels on a cantilever have been employed for the detection
of Cryptosporidium oocysts (unpublished work by the Chapter author).
10.2.5. In molecular methods
The first microfluidic PCR was demonstrated in a 50 µL silicon chip in 1993. 91
Since then numerous designs and components for performing molecular
methods on-chip have been developed. These are now starting to be incorpo-
rated into integrated systems. In addition, many authors have adopted poly-
meric materials to reduce the turnaround time in device design refinement
and to reduce cost. The main advantage of microfluidic PCR is the rapid tem-
perature cycling which can be obtained; in commercial PCR systems this step
accounts for over 90% of the operation time. Single-cell detection is possible. 92
For PCR there have been two main approaches to on-chip systems.
The first is static PCR where the sample volume is held in a chamber and
the temperature cycling is performed by means of some kind of heating
system. Initially external heating elements were employed, though more
recent work has demonstrated faster heating with integrated thin metallic
film heaters (e.g. 5-30 min compared to 1-3 h) and also with noncontact
heating methods. The second is flow-through PCR where the device is
designed such that sample traveling in a serpentine channel passes through
different temperature zones. The advantage of this approach is that it is
faster, delivering results in 90 s-10 min although the disadvantage is lower
detection sensitivity. One reason for this might be the high surface area in
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