Biology Reference
In-Depth Information
Other biocompatible polymeric substrates, which have been used for the
electrochemical analysis of protein or DNA, could be employed also for
pathogens analysis: polyethylene terephthalate (PET),
112
polyethylene
naphthalate
113
and polystyrene.
114
Impedimetric biosensors for in-vitro
cell-based assays could be made from these types of polymeric substrates
to reduce their consumable costs.
Academic biosensors use mainly electrodes fabricated by photolithog-
raphy and thin-film deposition (i.e. chemical or physical vapor deposition),
which are expensive methods issued from microelectronics. Printing tech-
niques represent a seductive alternative because they enable one to deposit
electrodes with conductive ink (metal,
115
conductive polymers,
116
or nano-
structures (nanoparticles
117
or CNTs
118
)) on much larger surface, with more
flexibility and reduced fabrication costs (around 10 times less expensive than
the photolithographic process for screenprinting
119
) (
Fig. 6.8(a)
). For biosens-
ing, printing techniques encompass mainly screenprinting and inkjet print-
ing. Screenprinting is the most employed printing technique (by considering
the number of iterations in scientific publications). This printing technique
previously facilitated the development of commercial disposable amperomet-
ric biosensors for home blood glucose tests,
120
and could be used for dispos-
able cell analyses. Several electrochemical biosensors have been fabricated by
screenprinting and employed for cellular analysis.
121-123
Integrated electro-
chemical biosensors have been fabricated by inkjet
124
but, as far as we know,
they have not been applied to cell analysis yet. Resolution is considered as
the main drawback of screenprinting
125
: a maximum resolution of 30 µm can
be achieved.
126
Interestingly, inkjet printing enables one to obtain submi-
crometric resolution.
127
The main advantage of exploiting flexible substrates
and/or electrodes is that they can be manufactured with roll-to-roll process,
which is one of the fastest and least expensive manufacturing techniques. The
roll-to-roll process can be associated directly with printing techniques to fur-
ther reduce manufacturing costs. Interestingly, graphene has been patterned
successfully by inkjet printing for submicrometric resolution
128
and manu-
factured by roll-to-roll and screenprinting processes
129
(
Fig. 6.8(b)
). Reduced
graphene sheets can be large-scale micropatterned, also.
96
For nonplanar bio-
sensors (with microfluidic channels, for example), hot embossing can also be
used to manufacture whole polymeric electrochemical biosensors.
130
6.8.4. Pathogens
Waterborne pathogens can be classified into three different categories includ-
ing viruses, bacteria, and protozoa. A careful survey of the scientific literature
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