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