<s>
A	O
ChemFET	B-Algorithm
is	O
a	O
chemically-sensitive	B-Algorithm
field-effect	I-Algorithm
transistor	I-Algorithm
,	O
that	O
is	O
a	O
field-effect	O
transistor	B-Application
used	O
as	O
a	O
sensor	O
for	O
measuring	O
chemical	O
concentrations	O
in	O
solution	O
.	O
</s>
<s>
When	O
the	O
target	O
analyte	O
concentration	O
changes	O
,	O
the	O
current	O
through	O
the	O
transistor	B-Application
will	O
change	O
accordingly	O
.	O
</s>
<s>
A	O
ChemFET	B-Algorithm
's	O
source	O
and	O
drain	O
are	O
constructed	O
as	O
for	O
an	O
ISFET	B-Algorithm
,	O
with	O
the	O
gate	O
electrode	O
separated	O
from	O
the	O
source	O
electrode	O
by	O
a	O
solution	O
.	O
</s>
<s>
A	O
ChemFET	B-Algorithm
's	O
threshold	O
voltage	O
depends	O
on	O
the	O
concentration	O
gradient	O
between	O
the	O
analyte	O
in	O
solution	O
and	O
the	O
analyte	O
in	O
contact	O
with	O
its	O
receptor-embedded	O
semi-permeable	O
barrier	O
.	O
</s>
<s>
ChemFETs	B-Algorithm
can	O
be	O
utilized	O
in	O
either	O
liquid	O
or	O
gas	O
phase	O
to	O
detect	O
target	O
analyte	O
,	O
requiring	O
reversible	O
binding	O
of	O
analyte	O
with	O
a	O
receptor	O
located	O
in	O
the	O
gate	O
electrode	O
membrane	O
.	O
</s>
<s>
There	O
is	O
a	O
wide	O
range	O
of	O
applications	O
of	O
ChemFETs	B-Algorithm
,	O
including	O
most	O
notably	O
anion	O
or	O
cation	O
selective	O
sensing	O
.	O
</s>
<s>
More	O
work	O
has	O
been	O
done	O
with	O
cation-sensing	O
ChemFETs	B-Algorithm
than	O
anion-sensing	O
ChemFETs	B-Algorithm
.	O
</s>
<s>
Anion-sensing	O
is	O
more	O
complicated	O
than	O
cation-sensing	O
in	O
ChemFETs	B-Algorithm
due	O
to	O
many	O
factors	O
,	O
including	O
the	O
size	O
,	O
shape	O
,	O
geometry	O
,	O
polarity	O
,	O
and	O
pH	O
of	O
the	O
species	O
of	O
interest	O
.	O
</s>
<s>
The	O
body	O
of	O
a	O
ChemFET	B-Algorithm
is	O
generally	O
found	O
to	O
be	O
robust	O
.	O
</s>
<s>
Dutch	O
engineer	O
Piet	O
Bergveld	O
studied	O
the	O
MOSFET	B-Architecture
and	O
realized	O
it	O
could	O
be	O
adapted	O
into	O
a	O
sensor	O
for	O
chemical	O
and	O
biological	O
applications	O
.	O
</s>
<s>
In	O
1970	O
,	O
Bergveld	O
invented	O
the	O
ion-sensitive	B-Algorithm
field-effect	I-Algorithm
transistor	I-Algorithm
(	O
ISFET	B-Algorithm
)	O
.	O
</s>
<s>
He	O
described	O
the	O
ISFET	B-Algorithm
as	O
"	O
a	O
special	O
type	O
of	O
MOSFET	B-Architecture
with	O
a	O
gate	O
at	O
a	O
certain	O
distance	O
"	O
.	O
</s>
<s>
In	O
the	O
ISFET	B-Algorithm
structure	O
,	O
the	O
metal	B-Algorithm
gate	I-Algorithm
of	O
a	O
standard	O
MOSFET	B-Architecture
is	O
replaced	O
by	O
an	O
ion-sensitive	O
membrane	O
,	O
electrolyte	O
solution	O
and	O
reference	O
electrode	O
.	O
</s>
<s>
ChemFETs	B-Algorithm
are	O
based	O
on	O
a	O
modified	O
ISFET	B-Algorithm
,	O
a	O
concept	O
developed	O
by	O
Bergveld	O
in	O
the	O
1970s	O
.	O
</s>
<s>
There	O
is	O
some	O
confusion	O
as	O
to	O
the	O
relationship	O
between	O
ChemFETs	B-Algorithm
and	O
ISFETs	B-Algorithm
.	O
</s>
<s>
Whereas	O
an	O
ISFET	B-Algorithm
only	O
detects	O
ions	O
,	O
a	O
ChemFET	B-Algorithm
detects	O
any	O
chemical	O
(	O
including	O
ions	O
)	O
.	O
</s>
