
54-11Interference and Selectivity in Portable Chemical Sensors
Transistors: When chemical sensors are operated in potentiometric mode, a eld eect transistor (FET)
ca
n
be us
ed
to co
nvert
th
e
el
ectrochemical
sig
nal
in
to
an el
ectrical
ou
tput
wi
thout
dr
awing
cu
rrent,
th
us
gu
aranteeing
Ne
rnstian
op
eration
. To do th
is,
th
e
in
teraction
of th
e
an
alyte
of in
terest
wi
th
th
e
wo
rking
el
ectrode
of th
e
el
ectrochemical
ce
ll
ge
nerates
al
l
or pa
rt
of th
e
ga
te
vo
ltage
of th
e
tr
ansistor
. As
th
e
ga
te
vo
ltage
ch
anges,
th
e
un
derlying
ch
annel
cu
rrent
be
tween
th
e
dr
ain
an
d
so
urce
of th
e
tr
ansistor
ch
anges,
ye
t
no cu
rrent
fr
om
ga
te
to ch
annel
o
ws
(a
s
is ch
aracter ...