<s>
A	O
chemiresistor	B-Algorithm
is	O
a	O
material	O
that	O
changes	O
its	O
electrical	O
resistance	O
in	O
response	O
to	O
changes	O
in	O
the	O
nearby	O
chemical	O
environment	O
.	O
</s>
<s>
Chemiresistors	B-Algorithm
are	O
a	O
class	O
of	O
chemical	O
sensors	O
that	O
rely	O
on	O
the	O
direct	O
chemical	O
interaction	O
between	O
the	O
sensing	O
material	O
and	O
the	O
analyte	O
.	O
</s>
<s>
Several	O
different	O
materials	O
have	O
chemiresistor	B-Algorithm
properties	O
:	O
metal-oxide	O
semiconductors	O
,	O
some	O
conductive	B-Algorithm
polymers	I-Algorithm
,	O
and	O
nanomaterials	O
like	O
graphene	O
,	O
carbon	O
nanotubes	O
and	O
nanoparticles	O
.	O
</s>
<s>
A	O
basic	O
chemiresistor	B-Algorithm
consists	O
of	O
a	O
sensing	O
material	O
that	O
bridges	O
the	O
gap	O
between	O
two	O
electrodes	O
or	O
coats	O
a	O
set	O
of	O
interdigitated	O
electrodes	O
.	O
</s>
<s>
In	O
some	O
chemiresistors	B-Algorithm
the	O
resistance	O
changes	O
simply	O
indicate	O
the	O
presence	O
of	O
analyte	O
.	O
</s>
<s>
However	O
,	O
it	O
was	O
not	O
until	O
1985	O
that	O
Wohltjen	O
and	O
Snow	O
coined	O
the	O
term	O
chemiresistor	B-Algorithm
.	O
</s>
<s>
In	O
recent	O
years	O
chemiresistor	B-Algorithm
technology	O
has	O
been	O
used	O
to	O
develop	O
promising	O
sensors	O
for	O
many	O
applications	O
,	O
including	O
conductive	B-Algorithm
polymer	I-Algorithm
sensors	O
for	O
secondhand	O
smoke	O
,	O
carbon	O
nanotube	O
sensors	O
for	O
gaseous	O
ammonia	O
,	O
and	O
metal	O
oxide	O
sensors	O
for	O
hydrogen	O
gas	O
.	O
</s>
<s>
The	O
ability	O
of	O
chemiresistors	B-Algorithm
to	O
provide	O
accurate	O
real-time	O
information	O
about	O
the	O
environment	O
through	O
small	O
devices	O
that	O
require	O
minimal	O
electricity	O
makes	O
them	O
an	O
appealing	O
addition	O
to	O
the	B-Operating_System
internet	I-Operating_System
of	I-Operating_System
things	I-Operating_System
.	O
</s>
<s>
Chemiresistors	B-Algorithm
can	O
be	O
made	O
by	O
coating	O
an	O
interdigitated	O
electrode	O
with	O
a	O
thin	O
film	O
or	O
by	O
using	O
a	O
thin	O
film	O
or	O
other	O
sensing	O
material	O
to	O
bridge	O
the	O
single	O
gap	O
between	O
two	O
electrodes	O
.	O
</s>
<s>
Interdigitated	O
electrodes	O
with	O
finger	O
sizes	O
and	O
finger	O
spacing	O
on	O
the	O
order	O
of	O
microns	O
are	O
difficult	O
to	O
manufacture	O
and	O
require	O
the	O
use	O
of	O
photolithography	B-Algorithm
.	O
</s>
<s>
Metal	O
oxide	O
chemiresistor	B-Algorithm
sensors	O
were	O
first	O
commercialized	O
in	O
1970	O
in	O
a	O
carbon	O
monoxide	O
detector	O
that	O
used	O
powdered	O
SnO2	O
.	O
</s>
<s>
In	O
comparison	O
to	O
the	O
other	O
materials	O
graphene	O
chemiresistor	B-Algorithm
sensors	O
are	O
relatively	O
new	O
but	O
have	O
shown	O
excellent	O
sensitivity	O
.	O
</s>
<s>
Graphene	O
is	O
an	O
allotrope	O
of	O
carbon	O
that	O
consists	O
of	O
a	O
single	O
layer	O
of	O
graphite	B-Application
.	O
</s>
<s>
The	O
first	O
published	O
report	O
of	O
nanotubes	O
being	O
used	O
as	O
chemiresistors	B-Algorithm
was	O
made	O
in	O
2000	O
.	O
</s>
<s>
Since	O
then	O
there	O
has	O
been	O
research	O
into	O
chemiresistors	B-Algorithm
and	O
chemically	O
sensitive	O
field	O
effect	O
transistors	O
fabricated	O
from	O
individual	O
single-walled	O
nanotubes	O
,	O
bundles	O
of	O
single-walled	O
nanotubes	O
,	O
bundles	O
of	O
multi-walled	O
nanotubes	O
,	O
and	O
carbon	O
nanotube	O
–	O
polymer	O
mixtures	O
.	O
</s>
<s>
Many	O
different	O
nanoparticles	O
of	O
varying	O
size	O
,	O
structure	O
and	O
composition	O
have	O
been	O
incorporated	O
into	O
chemiresistor	B-Algorithm
sensors	O
.	O
</s>
<s>
Analytes	O
diffuse	O
into	O
the	O
SAMs	O
at	O
proportions	O
defined	O
by	O
their	O
partition	O
coefficient	O
and	O
this	O
characterizes	O
the	O
selectivity	O
and	O
sensitivity	O
of	O
the	O
chemiresistor	B-Algorithm
material	O
.	O
</s>
<s>
Conductive	B-Algorithm
polymers	I-Algorithm
such	O
as	O
polyaniline	B-Algorithm
and	O
polypyrrole	B-Algorithm
can	O
be	O
used	O
as	O
sensing	O
materials	O
when	O
the	O
target	O
interacts	O
directly	O
with	O
the	O
polymer	O
chain	O
resulting	O
in	O
a	O
change	O
in	O
conductivity	O
of	O
the	O
polymer	O
.	O
</s>
<s>
Molecularly	O
imprinted	O
polymers	O
can	O
add	O
selectivity	O
to	O
conductive	B-Algorithm
polymer	I-Algorithm
chemiresistors	B-Algorithm
.	O
</s>
<s>
Molecularly	O
imprinting	O
the	O
conductive	B-Algorithm
polymer	I-Algorithm
increases	O
the	O
sensitivity	O
of	O
the	O
chemiresistor	B-Algorithm
by	O
selecting	O
for	O
the	O
target	O
's	O
general	O
size	O
and	O
shape	O
as	O
well	O
as	O
its	O
ability	O
to	O
interact	O
with	O
the	O
chain	O
of	O
the	O
conductive	B-Algorithm
polymer	I-Algorithm
.	O
</s>
