lecture 7 biopotential electrodes (ch. 5) · 2009-03-31 · ag-agcl, pt-pt black, or polymer coats...
TRANSCRIPT
Lec
ture
7
Bio
pote
ntial
Ele
ctro
des
(Ch. 5)
Ele
ctro
de
–Ele
ctro
lyte
Inte
rfac
e
Ele
ctro
de
Ele
ctro
lyte
(n
eutr
al
charg
e)
C+, A
-in
solu
tion
C
CC
A-
A-
C+
C+
e- e-
Curr
ent flow
C+ : C
atio
nA
-: A
nio
ne-
: el
ectron
Fairly common electrode materials: Pt, Carbon, …, Au, Ag,…
Electrode metal is use in conjunction with salt, e.g. Ag-AgCl, Pt-Pt
black, or polymer coats (e.g. Nafion, to improve selectivity)
Ele
ctro
de
–E
lect
roly
te I
nte
rface
−−
−+
+↔
+↔
me
AA
ne
CC
m
n
Gen
eral
Ion
ic E
qu
ati
on
s
a) If el
ectrode
has
sam
e m
ater
ial as
cat
ion, th
en this
mat
eria
l get
s
oxid
ized
and e
nte
rs the
elec
troly
te a
s a
cation
and e
lect
rons re
mai
n
at the
elec
trode
and flo
w in the
exte
rnal
circu
it.
b) If a
nio
n c
an b
e oxid
ized
at th
e el
ectrode
to form
a n
eutral
ato
m,
one
or tw
o e
lect
rons ar
e giv
en to the
elec
trode.
a) b)
Curr
ent flow
fro
m e
lect
rode
to e
lect
roly
te : O
xid
atio
n(L
oss
of e-)
Curr
ent flow
fro
m e
lect
roly
te to e
lect
rode
: Red
uct
ion
(Gai
n o
f e-)
The
dom
inat
ing rea
ctio
n c
an b
e in
ferred
fro
m the
follow
ing :
Ha
lf C
ell
Po
ten
tia
l
A c
har
acte
rist
ic p
ote
ntial
diffe
rence
estab
lish
ed b
y the
elec
trode
and its
surroundin
g e
lect
roly
te w
hic
h d
epen
ds on the
met
al, co
nce
ntrat
ion o
f io
ns
in solu
tion a
nd tem
per
ature
(an
d som
e se
cond o
rder
fac
tors
) .
Half
cel
l p
ote
nti
al
can
not
be
mea
sure
d w
ith
ou
t a s
econ
d e
lect
rod
e.
The
hal
f ce
ll p
ote
ntial
of th
e stan
dar
d h
ydro
gen
ele
ctro
de
has
bee
n a
rbitra
rily
set to
zer
o. O
ther
hal
f ce
ll p
ote
ntial
s ar
e ex
pre
ssed
as a
pote
ntial
diffe
rence
with this e
lect
rode.
Rea
son
for
Half
Cel
l P
ote
nti
al
: C
harg
e S
epara
tion
at
Inte
rface
Oxid
atio
n o
r re
duct
ion rea
ctio
ns at
the
elec
trode-
elec
troly
te inte
rfac
e
lead
to a
double
-char
ge
layer
, sim
ilar
to that
whic
h e
xis
ts a
long
elec
tric
ally
act
ive
bio
logic
al c
ell m
embra
nes
.
Mea
suri
ng
Ha
lf C
ell
Po
ten
tia
l
Note: Electrode material is metal + salt or polymer selective mem
brane
Som
e h
alf
cel
l p
ote
nti
als
Sta
ndar
d H
ydro
gen
ele
ctro
de
Note: Ag-AgClhas low
junction potential & it is
also very stable -> hence
used in ECG electrodes!
Po
lari
zati
on
If ther
e is
a c
urren
t bet
wee
n the
elec
trode
and e
lect
roly
te, th
e
obse
rved
hal
f ce
ll p
ote
ntial
is often
alter
ed d
ue
to p
ola
riza
tion.
Ov
erp
ote
nti
al
Diffe
rence
bet
wee
n o
bse
rved
and z
ero-c
urr
ent hal
f ce
ll p
ote
ntial
s
Res
ista
nce
Curr
ent ch
anges
res
ista
nce
of el
ectroly
te a
nd thus,
a voltag
e dro
p res
ults.
Co
nce
ntr
ati
on
Chan
ges
in d
istrib
ution
of io
ns at
the
elec
trode-
elec
troly
te inte
rfac
e
Act
iva
tio
n
The
activat
ion e
ner
gy
bar
rier
dep
ends on the
direc
tion o
f cu
rren
t an
d
det
erm
ines
kin
etic
s
AC
Rp
VV
VV
++
=Note: Polarization and impedance of the electrode are two of the
most important electrode properties to consider.
Ner
nst
Eq
ua
tio
n
+=
βα
δγ
BA
DC
aa
aa
nF
RT
EE
ln0
When
tw
o a
queo
us io
nic
solu
tions of diffe
rent co
nce
ntrat
ion a
re
separ
ated
by a
n ion-s
elec
tive
sem
i-per
mea
ble
mem
bra
ne,
an e
lect
ric
pote
ntial
exists
acr
oss
the
mem
bra
ne.
For th
e gen
eral
oxid
atio
n-r
educt
ion rea
ctio
n
−+
+↔
+ne
DC
BA
δγ
βα
The
Ner
nst
equat
ion for hal
f ce
ll p
ote
ntial
is
wher
e E
0: Sta
ndar
d H
alf Cel
l Pote
ntial
E : H
alf Cel
l Pote
ntial
a : Ionic
Act
ivity (gen
eral
ly sam
e as
conce
ntrat
ion)
n : N
um
ber
of val
ence
ele
ctro
ns in
volv
ed
Note: interested
in ionic activity
at the electrode
(but note tem
p
dependence
Po
lari
zab
le a
nd
No
n-P
ola
riza
ble
Ele
ctro
des
Per
fect
ly P
ola
riza
ble
Ele
ctro
des
Thes
e ar
e el
ectrodes
in w
hic
h n
o a
ctual
char
ge
cross
es the
elec
trode-
elec
troly
te inte
rfac
e w
hen
a c
urren
t is
applied
. The
curren
t ac
ross
the
inte
rfac
e is
a d
ispla
cem
ent cu
rren
t an
d the
elec
trode
beh
aves
lik
e a
capac
itor. E
xam
ple
: A
g/A
gClEle
ctro
de
Per
fect
ly N
on
-Pola
riza
ble
Ele
ctro
de
Thes
e ar
e el
ectrodes
wher
e cu
rren
t pas
ses free
ly a
cross
the
elec
trode-
elec
troly
te inte
rfac
e, req
uirin
g n
o e
ner
gy to m
ake
the
tran
sition. Thes
e
elec
trodes
see
no o
ver
pote
ntial
s. E
xam
ple
: P
latinum
ele
ctro
de
Example: Ag-AgClis used in recording while Pt is use in stimulation
Use for
recording
Use for
stimulation
Ag
/AgC
lE
lect
rod
e
−++
↔e
Ag
Ag
↓↔
+−
+AgCl
Cl
Ag
Ag
+Cl-
Cl 2
Rel
evan
t io
nic
equat
ions
Gover
nin
g N
ernst
Equat
ion
+
=−
Cls
Ag
aK
nF
RT
EE
ln0
Solu
bility
pro
duct
of A
gCl
Fab
rica
tion o
f A
g/A
gClel
ectrodes
1.Ele
ctro
lytic
dep
osition o
f A
gCl
2.Sin
tering p
roce
ss form
ing p
elle
t el
ectrodes
Eq
uiv
ale
nt
Cir
cuit
Cd
: ca
pac
itan
ce o
f el
ectrode-
elet
roly
tein
terfac
e
Rd
: re
sistan
ce o
f el
ectrode-
elet
roly
tein
terfac
e
Rs
: re
sistan
ce o
f el
ectrode
lead
wire
Ecell
: ce
ll p
ote
ntial
for el
ectrode
Fre
quen
cy R
esponse
Corner frequency
Rd+Rs
Rs
Ele
ctro
de
Sk
in I
nte
rfa
ce
Sw
eat gla
nds
and d
uct
s
Ele
ctro
de
Ep
ider
mis
Der
mis
an
dsu
bcu
tan
eou
s la
yer
RuEhe
Rs
Rd
Cd
Gel
Re
Ese
EP
RP
CP
Ce
Str
atu
m C
orn
eum
Skin
im
ped
ance
for 1cm
2 pat
ch:
200kΩ
@1H
z
200 Ω
@ 1
MH
z
Alter skin
transport (or
deliver drugs)
by:
Pores
produced by
laser,
ultrasound or
by
iontophoresis
100
µ 100
µ
Nerve
endings
Capillary
Mo
tion
Art
ifa
ct
Wh
y
When
the
elec
trode
moves
with res
pec
t to
the
elec
troly
te, th
e
dis
trib
ution o
f th
e double
lay
er o
f ch
arge
on p
ola
riza
ble
ele
ctro
de
inte
rfac
e ch
anges
. This
chan
ges
the
hal
f ce
ll p
ote
ntial
tem
pora
rily
.
Wh
at
If a
pai
r of el
ectrodes
is in
an e
lect
roly
te a
nd o
ne
moves
with
resp
ect to
the
oth
er, a
pote
ntial
diffe
rence
appea
rs a
cross
the
elec
trodes
know
n a
s th
e motion artifact.This
is a
sourc
e of
nois
e an
d inte
rfer
ence
in b
iopote
ntial
mea
sure
men
ts
Motion a
rtifac
t is
min
imal
for non-p
ola
riza
ble
ele
ctro
des
Bo
dy
Su
rfa
ce R
eco
rdin
g E
lect
rod
es
1.M
etal
Pla
te E
lect
rodes
(histo
ric)
2.Suct
ion E
lect
rodes
(histo
ric
inte
rest)
3.Flo
atin
g E
lect
rodes
4.Fle
xib
le E
lect
rodes
Ele
ctro
de
met
al
Ele
ctro
lyte
Think of the
construction of
electrosurgical
electrode
And, how does
electro-surgery
work?
Co
mm
on
ly U
sed
B
iop
ote
nti
al
Ele
ctro
des
Met
al
pla
te e
lect
rod
es
–Lar
ge
surf
ace:
Anci
ent,
ther
efore
still u
sed, ECG
–M
etal
disk w
ith sta
inle
ss ste
el;
pla
tinum
or gold
coat
ed
–EM
G, EEG
–sm
alle
r dia
met
ers
–m
otion a
rtifac
ts
–D
isposa
ble
foam
-pad
: Chea
p!
(a) M
etal
-pla
te e
lect
rode
use
d for ap
plica
tion to lim
bs.
(b) M
etal
-disk e
lect
rode
applied
with surg
ical
tap
e.
(c)D
isposa
ble
foam
-pad
ele
ctro
des
, often
use
d w
ith E
CG
Co
mm
on
ly U
sed
B
iop
ote
nti
al
Ele
ctro
des
Su
ctio
n e
lect
rod
es
-N
o strap
s or ad
hes
ives
required
-pre
cord
ial(c
hes
t) E
CG
-ca
n o
nly
be
use
d for sh
ort
per
iods
Flo
ati
ng e
lect
rod
es
-m
etal
dis
k is re
cess
ed
-sw
imm
ing in the
elec
troly
te g
el
-not in
conta
ct w
ith the
skin
-re
duce
s m
otion a
rtifac
tSuct
ion E
lect
rode
Double
-sid
ed
Adhes
ive-
tape
ring
Insu
lating
pac
kag
e
Met
al d
isk
Ele
ctro
lyte
gel
in rec
ess
(a)
(b)
(c)
Snap
coat
ed w
ith A
g-A
gC
lExte
rnal
snap
Pla
stic
cup
Tac
k
Pla
stic
dis
k
Foam
pad
Cap
illa
ry loops
Dea
d c
ellu
lar m
ater
ial
Ger
min
atin
g lay
er
Gel
-coat
ed sponge
Co
mm
on
ly U
sed
B
iop
ote
nti
al
Ele
ctro
des
Flo
ati
ng E
lect
rod
es
Reusable
Disposable
(a) Car
bon-fille
d silic
one
rubber
ele
ctro
de.
(b) Fle
xib
le thin
-film
neo
nat
al e
lect
rode.
(c) Cro
ss-s
ectional
vie
w o
f th
e th
in-film
elec
trode
in (b).
Co
mm
on
ly U
sed
B
iop
ote
nti
al
Ele
ctro
des
Fle
xib
le e
lect
rod
es
-Body c
onto
urs
are
often
irre
gula
r
-Reg
ula
rly shap
ed rig
id
elec
trodes
may
not al
way
s w
ork
.
-Spec
ial ca
se : infa
nts
-M
ater
ial :
-Poly
mer
or nylo
n w
ith silver
-Car
bon fille
d silico
n rubber
(Myla
r film
)
Inte
rna
l E
lect
rod
es
Nee
dle
and w
ire
elec
trodes
for
per
cuta
neo
usm
easu
rem
ent of
bio
pote
ntial
s
(a) In
sula
ted n
eedle
ele
ctro
de.
(b) Coax
ial nee
dle
ele
ctro
de.
(c) Bip
ola
r co
axia
l el
ectrode.
(d) Fin
e-w
ire
elec
trode
connec
ted
to h
ypoder
mic
nee
dle
, bef
ore
bei
ng inse
rted
.
(e) Cro
ss-s
ectional
vie
w o
f sk
in
and m
usc
le, sh
ow
ing c
oiled
fine-
wire
elec
trode
in p
lace
.
The latest: BIO
N –
implanted electrode for muscle recording/stimulation
Alfred E. Mann Foundation
Fet
al
EC
G E
lect
rod
es
Ele
ctro
des
for det
ecting fet
al e
lect
roca
rdio
gra
m d
uring lab
or, b
y m
eans
of in
trac
uta
neo
usnee
dle
s (a
) Suct
ion e
lect
rode.
(b) Cro
ss-s
ectional
vie
w o
f
suct
ion e
lect
rode
in p
lace
, sh
ow
ing p
enet
ration o
f pro
be
thro
ugh
epid
erm
is.
(c) H
elic
al e
lect
rode,
whic
h is at
tach
ed to fet
al skin
by c
ork
scre
w type
action.
Ele
ctro
de
Arr
ays
Exam
ple
s of m
icro
fabrica
ted
elec
trode
arra
ys.
(a) O
ne-
dim
ensional
plu
nge
elec
trode
arra
y,
(b) Tw
o-d
imen
sional
array
, an
d
(c) Thre
e-dim
ensional
array
Contacts
Insulated leads
(b)
Base
Ag/AgClelectrodes
Ag/AgClelectrodes
Base
Insulated leads
(a)
Contacts
(c)
Tines
Base
Exposed tip
Mic
roel
ectr
od
es
Wh
y
Mea
sure
pote
ntial
diffe
rence
acr
oss
cel
l m
embra
ne
Req
uir
emen
ts
–Sm
all en
ough to b
e pla
ced into
cel
l
–Strong e
nough to p
enet
rate
cel
l m
embra
ne
–Typic
al tip
dia
met
er: 0.0
5 –
10 m
icro
ns
Typ
es –Solid m
etal
-> T
ungsten
mic
roel
ectrodes
–Supported
met
al (m
etal
conta
ined
within
/outsid
e gla
ss n
eedle
)
–G
lass
mic
ropip
ette
-> w
ith A
g-A
gClel
ectrode
met
al
Intracellular
Extracellular
Met
al
Mic
roel
ectr
od
es
Extracellularrecording–typically in brain where you
are interested in recording the firing of neurons
(spikes).
Use metal electrode+
insulation -> goes to high
impedance amplifier…negative capacitance amplifier!M
icrons!
RC
Met
al
Su
pp
ort
ed M
icro
elec
tro
des
(a) M
etal
inside
gla
ss(b
) G
lass
inside
met
al
Gla
ss M
icro
pip
ette
A g
lass
mic
ropip
etel
ectrode
filled
with a
n e
lect
roly
tic
solu
tion
(a) Sec
tion o
f fine-
bore
gla
ss
capilla
ry.
(b) Cap
illa
ry n
arro
wed
thro
ugh
hea
ting a
nd stret
chin
g.
(c) Fin
al struct
ure
of gla
ss-p
ipet
mic
roel
ectrode.
Intracellular recording–typically for recording from cells, such as
cardiac myocyte
Need high impedance amplifier…negative capacitance amplifier!
heat
pull
Fill with
intracellular fluid
or 3M KCl
Ag-AgClwire+
3M
KClhas very low
junction potential
and hence very
accurate for dc
measurements
(e.g. action
potential)
Ele
ctri
cal
Pro
per
ties
of
Mic
roel
ectr
od
es
Met
al m
icro
elec
trode
with tip
pla
ced
within
cel
l
Equiv
alen
t ci
rcuits
Met
al
Mic
roel
ectr
od
e
Use metal electrode+
insulation -> goes to high impedance
amplifier…negative capacitance amplifier!
Electrical Properties of Glass
Intracellular Microelectrodes
Gla
ss M
icro
pip
ette
Mic
roel
ectr
od
e
Sti
mu
lati
ng
Ele
ctro
des
–Can
not be
model
ed a
s a
series
res
ista
nce
and c
apac
itan
ce
(ther
e is
no sin
gle
use
ful m
odel
)
–The
body/e
lect
rode
has
a h
ighly
nonlinea
r re
sponse
to
stim
ula
tion
–Lar
ge
curren
ts c
an c
ause
–Cav
itat
ion
–Cel
l dam
age
–H
eating
Typ
es o
f st
imu
lati
ng e
lect
rod
es
1.Pac
ing
2.A
bla
tion
3.D
efib
rillat
ion
Fea
ture
s
Platinum electrodes:
Applications: neural
stimulation
Modern day Pt-Irand other exotic
metal combinations to reduce
polarization, improve conductance
and long life/biocompatibility
Steel electrodes for
pacemakers and defibrillators
Intraocular Stimulation
Electrodes
Ref
eren
ce : L
utz
Hes
se, Thom
as S
chan
ze, M
arcu
s W
ilm
san
d M
arcu
s Eger
, “I
mpla
nta
tion o
f re
tina
stim
ula
tion
elec
trodes
and rec
ord
ing o
f el
ectric
al stim
ula
tion res
ponse
s in
the
visual
cortex
of th
e ca
t”, G
raef
e’sA
rch C
lin
Exp
Ophth
alm
ol(2
000) 238:8
40–845
In vivo neural microsystems (FIBE): challenge
In vivo neural microsystems (FIBE): biocompatibility -variant
In vivo neural microsystems (FIBE): state of the art
Neural
microelectrodes
MEMS -
Microsystems
Instrumentation for
neurophysiology
Neural
Microsystems
Introduction: neural microsystems
–
––
––
External
electrodes
Subdural
electrodes
Micro-
electrodes
Microsensors
Human
level
Animal
level
Tissue
slice
level
Cellular
level
Introduction: types of neural microsystems applications
In vivo
applications
In vitro
applications
Mic
roel
ectr
on
ic t
ech
no
logy
for
Mic
roel
ectr
od
esBondin
g p
ads
Sisu
bstra
teExpose
d tip
s
Lea
d v
ia
Chan
nel
s
Ele
ctro
de
Silic
on p
robe
Silic
on c
hip
Min
iatu
re
insu
lating
cham
ber
Conta
ct
met
al film
Hole
SiO
2in
sula
ted
Au p
robes
Silic
on p
robe
Expose
d
elec
trodes
Insu
late
d
lead
via
s
(b)
(d)
(a)
(c)
Diffe
rent ty
pes
of m
icro
elec
trodes
fab
rica
ted u
sing m
icro
fabrica
tion/M
EM
S tec
hnolo
gy
Bea
m-lea
d m
ultip
le e
lect
rode.
Multie
lect
rode
silico
n p
robe
Multip
le-c
ham
ber
ele
ctro
de
Per
ipher
al-n
erve
elec
trode
Michigan Probes for Neural
Recordings
Neural Recording
Microelectrodes
Ref
eren
ce :
http://w
ww
.acr
eo.se/
acre
o-r
d/IM
AG
ES/P
UB
LIC
ATIO
NS/P
RO
CEED
ING
S/A
BSTR
AC
T-
KIN
DLU
ND
H.P
DF
In vivo neural microsystems: 3 examples
University of Michigan
Smart comb-shape microelectrode arrays for
brain stimulation and recording
University of Illinois at Urbana-Champaign
High-density comb-shape metal microelectrode
arrays for recording
FraunhoferInstitute of Biomedical (FIBE)
Engineering
Retina implant
Multi-electrode Neural
Recording
Ref
eren
ce :
http://w
ww
.nottin
gham
.ac.
uk/n
euro
nal
-net
work
s/m
mep
.htm
Ref
eren
ce :
http://w
ww
.cyber
kin
etic
sinc.
com
/tec
hnolo
gy.h
tm
WPI’sNitric Oxide
Nanosensor
Nit
ric
Ox
ide
Sen
sor
•D
evel
oped
at D
r.Thak
or’
sLab
, BM
E, JH
U
•Ele
ctro
chem
ical
det
ection o
f N
O
Left
: S
ch
em
ati
c of
the 16-e
lectr
od
e se
nso
r array
. R
igh
t: C
lose
-up
of
a
sin
gle
si
te.
Th
e u
nd
erly
ing m
eta
l is
A
u an
d ap
pears
red
dis
h u
nd
er th
e
ph
oto
resi
st.
Th
e d
ark
layer
is C
(300µ
m-x
-300µ
m)
Carto
on
of
the f
ab
ric
ati
on
seq
uen
ce f
or t
he
NO
sen
sor a
rray
A)
Ba
re 4
”S
iw
afe
r B
) 5
µm
of
ph
oto
resi
st w
as
spin
-co
ate
d o
n t
o t
he
surfa
ce,
foll
ow
ed b
y a
pre
-ba
ke f
or 1
min
at
90
°C.
C)
Th
e sa
mp
les
wer
e th
en e
xp
ose
d t
hro
ug
h a
ma
sk f
or 1
6s
usi
ng
UV
lig
ht
at
36
5n
m a
nd
an
in
ten
sity
of
15
mW
/cm
2. D
) P
att
ern
ed p
ho
tore
sist
aft
er d
evel
op
men
t.
E)
20
nm
o
f T
i, 1
50
nm
o
f A
u a
nd
5
0n
m o
f C
w
ere
eva
po
rate
d o
n.
F)
Th
e m
eta
l o
n th
e
un
exp
ose
d a
rea
s w
as
rem
ov
ed b
y i
ncu
ba
tio
n i
n a
n a
ceto
ne
ba
th.
G)A
2n
d l
ay
er o
f p
ho
tore
sist
,
wh
ich
se
rves
a
s th
e in
sula
tio
n la
yer
, w
as
spu
n on
a
nd
p
att
ern
ed.
H)
Th
e w
ind
ow
s in
th
e
seco
nd
la
yer
als
o d
efin
ed t
he m
icro
elect
rod
e si
tes.
A B C DHGFE
NO Sensor Calibration
NO Sensor Calibration
MultichannelNO
Recordings
Problems
1.
Des
crib
e one
“innovat
ive”
schem
e fo
r re
cord
ing b
reat
hin
g o
r re
spirat
ion.
The
applica
tions m
ight be
resp
irom
etry
/spirom
etry
, at
hel
etsknow
ing w
hat
thei
r hea
rt rat
e is, par
alyze
d indiv
idual
s w
ho h
ave
difficu
lty b
reat
hin
g
nee
din
g a
res
pirat
ory
sen
sor to
stim
ula
te a
nd c
ontrol phre
nic
ner
ve.
Y
ou
may
sel
ect one
of th
ese
or oth
er a
pplica
tions, a
nd then
iden
tify
a su
itab
le
senso
r. T
he
des
ign (dev
elop suitab
le c
ircu
it) fo
r in
terfac
ing to
the
senso
r to
get
res
pirat
ory
sig
nal
.
2.
We
would
lik
e to
hav
e a
quad
riple
gic
auto
mat
ic c
ontrol over
the
lighting in
the
room
. D
esig
n a
bas
ic c
ircu
it to d
etec
t ro
om
lig
ht le
vel
and
turn
on a
lam
p w
hen
the
light le
vel
fal
ls b
elow
a set
lim
it. Y
ou m
ay c
onsider
a
suitab
le sen
sor fo
r light an
d y
ou should
consider
a d
esig
n that
com
par
es the
senso
r outp
ut to
som
e pre
det
erm
ined
thre
shold
and p
roduce
s a
hig
h v
oltag
e
or del
iver
s p
ow
er to the
lam
p.
3.
Ele
ctr
od
es
in b
iop
ote
nti
al
measu
rem
en
ts.
Des
crib
e th
e co
nstru
ctio
n o
f co
mm
erci
al E
CG
ele
ctro
de
(not th
e ch
eap p
oly
mer
elec
trode
use
d in the
lab). W
hat
is th
e co
mm
on e
lect
rode
met
al, an
d w
hy is it
pre
ferred
?
So, you a
re a
n inven
tor w
ho h
as a
bet
ter id
ea. D
escr
ibe
an im
pro
vem
ent
•to
mak
e th
e el
ectrode
chea
per
•m
ore
suitab
le for lo
wer
noise
mea
sure
men
t fo
r EEG
•ci
rcum
ven
t pat
ents that
are
bas
ed o
n p
lastic
/foam
ele
ctro
de
body
•at
trac
tive
to c
onsu
mer
s fo
r use
with thei
r ECG
mac
hin
es a
t hom
e
•re
duce
artifac
t (m
inim
ize
the
motion o
f sk
in/e
lect
rode)
in a
mbula
tory
rec
ord
ing
4. In a
res
earc
h lab
ora
tory
, sc
ientists w
ant to
rec
ord
fro
m sin
gle
cel
ls in a
culture
dish. They
wan
t to
rec
ord
act
ion p
ote
ntial
s from
sin
gle
, isola
ted h
eart c
ells. W
hat
kin
d o
f el
ectrode
would
they
nee
d to u
se (des
crib
e m
ater
ial an
d d
esig
n)?
G
ive
a
sim
plified
sch
emat
ic (ci
rcuit m
odel
of th
e el
ectrode)
des
crib
ed in the
note
s giv
en to
you.
What
is th
e ch
alle
nge
involv
ed in d
esig
nin
g a
n a
mplifier
for use
with a
mic
roel
ectrode
for single
cel
l re
cord
ing?
I.e.
what
are
the
critic
al a
mplifier
des
ign
char
acte
ristic
s an
d spec
ific
atio
ns (h
int: this is not the
usu
al
diffe
rential
/instru
men
tation a
mplifier
) ?
4.
Ele
ctr
od
es
an
d M
icroele
ctr
od
es
(mis
cell
an
eou
s)
•H
ow
would
you d
etec
t bac
teria
or oth
er m
icro
org
anism
s in
wat
er supply
? M
ake
sure
that
your m
ethod d
istinguishes
iner
t par
ticu
late
mat
ter from
liv
ing c
ellu
lar m
atte
r.
•D
raw
the
equiv
alen
t ci
rcuit m
odel
of th
e sk
in a
nd a
n E
CG
ele
ctro
de.
Id
entify
the
key
sourc
es o
f el
ectric
al inte
rfer
ence
and o
ther
wise
the
elem
ents that
would
lik
ely
contrib
ute
to the
poor qual
ity o
f re
cord
ings.
•D
esig
n a
n a
mplifier
inte
rfac
e fo
r th
e fo
llow
ing tw
o a
pplica
tions: P
atch
cla
mp ion
chan
nel
curren
t am
plifier
: Y
our goal
is to
am
plify
pA
level
curren
t to
pro
duce
1 V
olt
outp
ut.
•Strai
n g
auge
senso
r am
plifier
: Y
our goal
is to
conver
t 10 o
hm
chan
ge
in res
ista
nce
of
a stra
in g
auge
to p
roduce
1 v
olt o
utp
ut.
•Y
ou a
re a
sked
to d
esig
n a
lab
ora
tory
set
up for a
Pro
fess
or w
ho
is inte
rested
in
mak
ing v
ery low
lev
el ion c
han
nel
curren
t m
easu
rem
ents fro
m sin
gle
car
dia
c ce
lls
using the
pat
ch c
lam
pin
g tec
hniq
ue.
W
hat
are
the
likel
y sourc
esof in
terfer
ence
? W
hat
would
you d
o to e
nsu
re that
ther
e is m
inim
al n
oise
in the
labora
tory
set
up?
•D
raw
the
equiv
alen
t ci
rcuit o
f a
pat
ch c
lam
p g
lass
pip
ette
. T
his e
lect
rode
diffe
rs
slig
htly fro
m the
conven
tional
mic
roel
ectrode
that
pen
etra
tes th
e ce
ll a
nd o
bta
ins
intrac
ellu
lar pote
ntial
s, in that
it se
als to
the
cell m
embra
ne
and g
ener
ally
mea
sure
s th
e
whole
cel
l cu
rren
t. Show
all the
equiv
alen
t ci
rcuit e
lem
ents o
fth
e el
ectrode
and the
cell.
•D
esig
n a
ver
y sim
ple
, sm
all ci
rcuit to m
easu
re/tra
nsd
uce
the
whole
cel
l cu
rren
t from
the
pat
ch c
lam
p e
lect
rode
and c
onver
t in
to the
amplified
voltag
esignal
.
•For fa
r to
o long the
mic
roel
ectrodes
that
hav
e bee
n u
sed in the
labora
tory
fal
l in
to tw
o
cate
gories
: gla
ss o
r m
etal
mic
roel
ectrodes
. Thes
e re
cord
fro
m a
sin
gle
cel
l at
a tim
e.
What
is th
e cu
rren
t te
chnolo
gy for re
cord
ing fro
m sites
in the
tiss
ue
from
multip
le c
ells
at o
nce
(ex
trac
ellu
larly
OR intrac
ellu
larly). D
raw
a sch
emat
ic o
f su
ch a
n e
lect
rode
arra
y.
•List so
me
oth
er types
of el
ectrodes
or m
icro
elec
trodes
that
hav
e bee
n d
evel
oped
for
labora
tory
and res
earc
h u
se.
5.
Ele
ctr
od
es
an
d M
icroele
ctr
od
es
Contras
t th
e gla
ss m
icro
elec
trode
that
pen
etra
tes th
e ce
ll v
ersu
s pat
ch c
lam
p e
lect
rode.
Whic
h m
easu
res w
hat
(cu
rren
t/voltag
e) a
nd o
f w
hat
mag
nitude?
Whic
h o
ne
is
big
ger
/sm
alle
r? W
hat
is th
e im
ped
ance
of m
icro
elec
trode
vs. p
atch
ele
ctro
de?
W
hic
h o
ne
could
be
use
d to rec
ord
fro
m a
sin
gle
sub-m
icro
n siz
ed ion c
han
nel
?
For a
rese
arch
applica
tion, a
scie
ntist c
om
es u
p w
ith the
idea
of optica
lly m
easu
ring p
ote
ntial
on c
ell m
embra
ne.
H
is b
asic
idea
is to
use
a d
ye
that
bin
ds to
cel
l su
rfac
e. W
hen
the
dye
is
exci
ted b
y a
bright light (s
uper
lum
insc
entLED
), it giv
es o
ut fluore
scen
ce p
roportio
nal
to c
ell
mem
bra
ne
voltag
e. The
optica
l signal
is pic
ked
up b
y a
photo
det
ecto
r. D
raw
the
circ
uit to
pas
s a
ver
y lar
ge
(about 100 m
A) pulse
of cu
rren
t th
rough the
LED
to inte
nse
ly illum
inat
e
the
cell for ver
y b
rief
dura
tion a
nd then
det
ect nA
amper
e le
vel
photo
curren
t pro
duce
d b
y
the
fluore
scen
ce sig
nal
You a
re a
sked
to m
easu
re the
imped
ance
of th
e sk
in. In fac
t, lie
det
ecto
rs u
se c
han
ges
in
skin
im
ped
ance
(as
a m
easu
re o
f au
tonom
ic ref
lex) to
indic
ate
whet
her
a p
erso
n is ly
ing.
Dra
w the
equiv
alen
t ci
rcuit m
odel
of hum
an skin
and e
lect
rode.
Bas
ed o
n rea
sonab
le
estim
ates
of th
e sk
in p
roper
ties
, sk
etch
a rough fre
quen
cy res
ponse
of the
skin
(from
dc
to
100 k
Hz)
Now
des
ign a
circu
it to m
easu
re the
imped
ance
, ta
kin
g c
are
not to
vio
late
any saf
ety
consider
atio
n.
6.
Neu
ral
electr
od
es/
mic
roel
ectr
od
es
You w
ant to
rec
ord
fro
m n
euro
ns in
the
bra
in. H
ow
ever
, you w
ant to
rec
ord
fro
m
doze
ns of neu
rons al
l at
once
fro
m sev
eral
clo
sely
spac
ed m
icro
elec
trodes
. W
hat
mat
eria
l an
d p
roce
ss w
ould
you u
se to m
ake
the
mic
roel
ectrode
arra
y?
•What
met
al w
ould
you p
refe
r to
use
to m
ake
elec
trode
arra
ys of ab
out 10 m
icro
n
squar
e size
to m
ake
elec
tric
al c
onta
cts w
ith d
oze
ns of neu
rons?
•What
met
al w
ould
you p
refe
r to
use
to stim
ula
te d
oze
ns of neu
rons in
a d
eep b
rain
mic
roel
ectrode
bas
ed stim
ula
tor?
•(w
hic
h m
etal
pro
vid
es g
ood rec
ord
ing v
sstim
ula
ting p
roper
ties
–an
d a
t th
e sa
me
tim
e not be
toxic
to b
rain
tissu
e)?
•Y
ou a
re a
sked
to d
evel
op a
n e
xper
imen
tal se
t up to rec
ord
fro
m rat
bra
in c
ells u
sing
mic
roel
ectrodes
. W
hat
pre
cautions w
ould
you tak
e to
min
imiz
e th
e el
ectric
al
inte
rfer
ence
in y
our re
cord
ing set
up?
Question/ideas!
•Make a better electrode
•Research different electrode technologies
–Ion selective, immunosensors, ISFET,
electrochemical
–MEMS microelectrode technologies