ELECTROCHEMISTRY, ROLE IN MEDICAL SCIENCES AND BIOCHEMISTRY

1. ELECTROCHEMISTRY

2. ELECTROCHEMISTRY
 It is a speciality of classical physics
&chemistry which deals with oxidation &
reduction reactions with transfer of
chemical energy into electrical energy &
vice versa

3. BASIC TERMS
 OXIDATION—loss of electron(s) by a species;
increase in oxidation number; increase in
oxygen.
 REDUCTION—gain of electron(s); decrease in
oxidation number; decrease in oxygen;
increase in hydrogen.
 OXIDIZING AGENT—electron acceptor;
species is reduced.
 REDUCING AGENT—electron donor; species
is oxidized.

4. Electrochemical Cells
 An apparatus that allows a
redox reaction to occur by
transferring electrons through
an external connector.
 Product favored reaction --->
voltaic or galvanic cell ---->
electric current
 Reactant favored reaction ---
> electrolytic cell ---> electric
current used to cause
chemical change.
Batteries are voltaic cells

5. Anode Cathode
Basic Concepts
of Electrochemical Cells

6. •Electrons travel thru external wire.
Salt bridge allows anions and cations to
move between electrode compartments.
Zn --> Zn2+ + 2e- Cu2+ + 2e- --> Cu
<--Anions
Cations-->
Oxidation
Anode
Negative
Reduction
Cathode
Positive
RED CAT

7. Electromotive Force (emf)
 The potential difference between the
anode and cathode in a cell is called the
electromotive force (emf).
 It is also called the cell potential, and is
designated Ecell.

8. Zn/Cu Electrochemical Cell
Zn(s) ---> Zn2+(aq) + 2e- Eo = +0.76 V
Cu2+(aq) + 2e- ---> Cu(s) Eo = +0.34 V
---------------------------------------------------------------
Cu2+(aq) + Zn(s) ---> Zn2+(aq) + Cu(s)
Eo = +1.10 V
Cathode,
positive,
sink for
electrons
Anode,
negative,
source of
electrons
+

9. H2 input
1.00 atm
inert
metal
We need a standard electrode to
make measurements against!
The Standard Hydrogen Electrode (SHE)
Pt
1.00 M H+
25oC
1.00 M H+
1.00 atm H2
Half-cell
2H+ + 2e-  H2
Eo
SHE = 0.0 volts

10. H2 1.00 atm
Pt
1.0 M H+
Cu
1.0 M CuSO4
0.34 v
cathode half-cell
Cu+2 + 2e-  Cu
anode half-cell
H2  2H+ + 2e-
KCl in agar
+
Now let’s combine the copper half-cell with the SHE
Eo = + 0.34 v

11. H2 1.00 atm
Pt
1.0 M H+
1.0 M ZnSO4
0.76 v
cathode half-cell
2H+ + 2e-  H2
anode half-cell
Zn  Zn+2 + 2e-
KCl in agar
Zn
-
Now let’s combine the zinc half-cell with the SHE
Eo = - 0.76 v

12. Assigning the Eo
Al+3 + 3e-  Al Eo = - 1.66 v
Zn+2 + 2e-  Zn Eo = - 0.76 v
2H+ + 2e-  H2 Eo = 0.00 v
Cu+2 + 2e-  Cu Eo = + 0.34
Ag+ + e-  Ag Eo = + 0.80 v
Write a reduction half-cell, assign the voltage
measured, and the sign of the electrode to the
voltage.
Increasing
activity

13. TABLE OF STANDARD
REDUCTION POTENTIALS
2
Eo (V)
Cu2+ + 2e- Cu +0.34
2 H+ + 2e- H 0.00
Zn2+ + 2e- Zn -0.76
oxidizing
ability of ion
reducing ability
of element
To determine an oxidation from a
reduction table, just take the opposite
sign of the reduction!

15. +
-
battery
Na (l)
electrode half-
cell
electrode half-
cell
Molten NaCl
Na+
Cl-
Cl- Na+
Na+
Na+ + e-  Na 2Cl-  Cl2 + 2e-
Cl2 (g) escapes
Observe the reactions at the electrodes
NaCl (l)
(-)
Cl-
(+)

16. battery
+
- power
source
e-
e-
NaCl (aq)
(-) (+)
cathode
different half-
cell
Aqueous NaCl
anode
2Cl-  Cl2 + 2e-
Na+
Cl-
H2O
What could be reduced
at the cathode?

17. Potential, Work and DG
 emf = potential (V) = work (J) /
Charge(C)
E = work done by system / charge
E = -w/q
 Charge is measured in coulombs.
 -w = q E
 Faraday = 96,485 C/mol e-
 q = nF = moles of e- x charge/mole e-
 w = -qE = -nFE = DG

18. Potential, Work and DG
 DGº = -nFEº
 if Eº > 0, then DGº < 0 spontaneous
 if Eº< 0, then DGº > 0 nonspontaneous

19. galvanic electrolytic
need
power
source
two
electrodes
produces
electrical
current
anode (-)
cathode (+)
anode (+)
cathode (-)
salt bridge vessel
conductive
medium
Comparison of Electrochemical Cells
DG < 0
DG > 0

20. Saturated Calomel Electrode Silver/Silver Chloride Electrode
Hg2Cl2 + 2e- 2Hg + 2Cl- AgCl(s) + 1e- Ag(s) +

21. CLINICAL APPLICATIONS
• Measure blood gas ( ph , PCo2 ,PO2 )
• Electrolytes ( Na , K, Cl, Ca, Mg, Li, )
• Analytes like therapeutic drugs,
neurotransmitters, glutathion, homocystiene
• Deteccting toxic level of lead in blood
• Monitoring cagulation reactions
• Developing ultrasensitive immunoassay
schemes
• biosensors

22. ELECTROANALYTICAL
TECNIQUES
 POTENTIOMETRY
 VOLTAMMETRY/ AMPEROMETRY
 CONDUCTOMETRY
 COULOMETRY

23. POTENTIOMETRY
 Measurement of an electrical potential
difference between two half cells in an
electrochemical cell when the cell
current is zero .
Galvanic cell
Left side – reference electrode
Right side – Indicator (measuring )
electrode

24. Characteristics of Ideal Reference Electrode:
1) Reversible and follow Nernst equation
2) Potential should be constant with time
3) Should return to original potential after being subjected to
small currents
4) Little hysteresis with temperature cycling
5) Should behave as ideal nonpolarized electrode

25.  CELL POTENTIAL – Sum of all potential
gradients existing between different phases
of cell
 VARIOUS POTENTIAL GRADIENTS
 Redox potential
 Membrane potentials
 Diffusion potentials

27. ELECTRODES FOR
POTENTIOMMETRIC
APPLICATIONS
 REDOX ELECTRODES
Inert metal electrodes
Metal electrodes participating in redox
reaction
 ION SELECTIVE ELECTRODES
Glass electrode
polymer membrane electrode
 Pco2 electrodes

28. REDOX ELECTRODES
Redox potential – result of chemical equilibrium
involving electron transfer reactions
Oxidised form + ne ↔ Reduced form
redox couple
with respect to SHE
NERNST EQUATION –
E = E0 – N/n x log ared /aox = Eo- .0592v/n xlog ared/ao
N= RT xIn Log 10 /F

29. INERT METAL ELECTRODES
 PLATINUM ELECTRODES
 GOLD ELECTRODES
 HYDROGEN ELECTRODES – pH
measurement
Platinum & gold electrodes r coated with
highly porous platinum( platinum black ) to
catalyze the reaction
ELECTRODE POTENTIAL –
E = E0 – N x log ( f H2)1/2 / aH

30. Saturated Calomel Electrode Silver/Silver Chloride Electrode
Hg2Cl2 + 2e- 2Hg + 2Cl- AgCl(s) + 1e- Ag(s) +

31. METAL ELECTRODES
 SILVER-SILVER CHLORIDE ELECTRODE
USES
Internal reference element in pot. Ion selective
electrode
External reference electrode half cell of constant
potential
CALOMEL ELECTRODE
USES
Reference electrodes for pH measurement

32. Saturated Calomel Electrode Silver/Silver Chloride Electrode
Hg2Cl2 + 2e- 2Hg + 2Cl- AgCl(s) + 1e- Ag(s) +

34. ION SELECTIVE ELECTRODES
 MEMBRANE POTENTIAL
Caused by the permeability of certain types of
membranes to selected anions and cations
 Interact with a single ion species
 Potential is propotional to the logarithm of the
ionic activity or concentration of the ion
 TYPES
 GLASS ELECTRODE
 POLYMER MEMBRANE ELECTRODE

35. GLASS ELECTRODE
 Formulated from
Melts of silicon and aluminium oxide mixed with oxides
of earth or alkali metal cations
- By varying composition , electrodes with selectivity
of various cations can be demonstrated
- Formula for H+ selective glass
72% SiO2, 22% Na2O, 6% CaO
SELECTIVITY ORDER
H+ >>> Na+ > K+ Ph range 7.0 – 8.0
if 71% SiO2, 11% Na2O, 18% Al2O3
H+ >Na+> K+

36.  USES
Measures pH & electrolytes
internal transducer for pCO2 sensor

39. POLYMER MEMBRANE ELECTRODE
 WORKING MECHANISM – 3 CATEGORIES
a) CHARGE DISSOCIATED ION EXCHANG
It employs quarternary ammonium(NH4+) salts as
membrane component
Uses
Determinatin of chloride ion in blood & serum
LIMITATIONS –
Anions more lipophilic than chloride in sample may
interfere
Loss of chloride sensitivity with repeated heparin
exposure

40. b) CHARGED ASSOCIATED CARRIER –
Used for Ca+ ion – based on Ca+ selective ion
exchange property of 2-ETHYLHEXYL
PHOSPHORIC ACID dissolved in DIOCTYL
PHENYL PHOSPHONATE .
Reffered as LIQUID MEMBRANE ISE
LATER ON INGREDIENTS WERE INCORPORATED
INTO PVC MEMBRANE
FORMULATION OF PVC MEMBRANE
1 To 3% ionophore - ex TRIFLUROACETONE Gp
64% plasticizer – controls polarity of membrane
30 wt % PVC
< 1wt% additives – ex large lipophilic anions like
TETRAPHENYL BORATE derivatives for cation
selective ISE

41. NEUTRAL ION CARRIER (
IONOPHORE)
 INCORPORATION OF NEUTRAL
ANTIBIOTIC VALINOMYCIN – highly
selective for K+ ions
 INCORPORATION OF
TRIFLOROACETOPHENONE GROUPS –
Highly selective for carbonate ion
Forms negatively charged adducts
Used for determining total CO2 in
serum/plasma

42.  ADVANTAGES OF ISE
Simple
Rapid
Nondestructive
Applicable to a wide range of concentratio
DISADVANTAGES
Interference with other ions

43. ELECTRODE FOR PCO2

45. VOLTAMMETRY & AMPEROMETRY
 VOLTAMETRY – Measurement of current
when an external potential is applied while the
potential varies under potentiostatic control.
 Based on the principle of electrolytic cell
 Current is directly propotional to the
concentration of the analyte
 AMPEROMETRY – Measurement of
current when a constant external
potential is applied
 Current is inversely proportional to the
resistance of the the electrolyte

48. APPLICATIONS
OXYGEN ELECTRODES-
CLARK OXYGEN ELECTRODE
- RANK O2 ELECTRODE
- PROBE TYPE O2 ELECTRODE
ELECTROCHEMICAL DETECTORS FOR
HPLC

50.  APPLICATIONS OF OXYGEN ELECTRODE
RANK TYPE-
MITOCHONDRIAL STUDIES
-RESPIRATORY CONTROL
EFFECT OF INHIBITORS
MEASUREMENT OF OXI-PHOSPHORYLATION
RATIO
MICROORGANISM & CHLOROPLAST
STUDIES
PROBE TYPE-
MONITORING HEART LUNG MACHINES
OXYGEN CONTENT OF BLOOD SAMPLE

51. ECD FOR HPLC

52.  ANODIC STRIPPINB VOLTAMMETRY
Used for detecting trace level of toxic
substance in clinical sample
- Carbon working electrode is used
- E app first kept highly negative
- Then scanned more positive
- Reduced metals reoxidize
- Give large anodic current proportional to
ion conc.
- Potential at which peak obs.indicate which
metal is present

53.  RAPID SSAN CYCLIC VOLTAMMETRIC
TECHNIQUE
 Quantify dopamine in brain tissue in freely
moving animals
 Oxidation of dopamine to a quinone sp.at
an implanted microcarbon electrode yields
peak cuffents prop. To concentration of
dopamine levels

54. CONDUCTOMETRY
Measure of ability of ions in solution to carry
current under the influence of potential
diiference
Potential with frequency between 100 to 3000 hZ
IS USED ( PREVENTS ELECTRODE
POLARISATION)
Current is directly propotional to solution
conductance, where conductance is inverse of
resistance
UNIT – SIEMENS ( Ohm-1 )
Depends on-
ionic charge
viscosity
potential applied

55.  CLINICAL APPLICATIONS
- Measurement of volume fraction of
erythrocytes
- Electronic counting of blood cells in
suspension ( COULTER PRINCIPLE )
-Titrations ( acid-base , precipitations )
-Tranducer mechanism for some biosensors

56. COULOMETRY
 Measures the electrical charge between two
electrodes in a electrochemical cell
 Charge is directly proportional to oxidation or
reduction of the substance at one of the electrode
 Q =nNF
Q = Charge
n = no of electrons
N = Amount of substance reduced or oxidized
F = Faradays constant (96,487 coulambs/mole)
 CLINICAL APPLICATIONS
 Cl- ions in serum
 Coulometric titrations
 Mode of transduction in biosensors

57. OPTICAL CHEMICAL SENSORS
 OPTODES
 USE – In analytical instruments to measure blood
gases and electrolytes
 ADVANTAGES OVER ELECTRODES
- Ease of miniaturization
- Less noise
- Potential long term stability
- No need for reference electrode
BASIC CONCEPT
Optodes used for PO2 Measurement based on
immobilisation of organic dyes ( pyrene
phenantherene, fluoranthrene)

58. METAL LIGAND COMPLEX ( Ruthenium [11]
tris [di pyridine],Pt & Pb metalloporphyrins)
in hydrophobic polymer films ( silicon rubber)
in which O2 is soluble
Decreased intensity of fluorescence is
proportional to PO2
APPLICATIONS
- Used for pCO2 determination
- Optically sense the electrolyte ions eg.
lipophilic ionophore for polymer memb.ISE with
lipophilic Ph indicator ( valinomycin for k+)
change in optical absorption or flourescence
spectrum of polymer layer

67. TECHQNIQUES OF IMMOBILISATION
 ENTRAPMENT METHOD
 CROSS LINKING OF ENZYME WITH AN
INERT PROTEIN ex- bovine serum albumin
 SIMPLE ADSORPTION OF THE ENZYME
TO ELECTRODE SURFACE
 COVALENT BINDING OF ENZYME TO
INSOLUBLE CARRIER ex- nylon or glass
 BULK MODIFICATION OF ELECTRODE
MATERIAL, mixing enzyme with carbon
paste.which serves as enzyme immobilisation
matrix & electroactive surface

71. ENZYME BASED BIOSENSORS WITH
POTENTIOMETRIC METHOD
UREA ------- 2NH3 + CO2
Urease
LIMITATIONS
High substrate concentration
Local alkaline pH due to hydrolysis of urea
IT IS REDUCED BY
Placing a semipermeable membrane between
enzyme and sample to limit diffusion of urea

73. ENZYME BASED BIOSENSORS WITH
OPTICAL DETECTION
 EXAMPLE-
Optical detection for pH & oxygen
Glucose & cholesterol optical sensor
BASED ON
Flourescence
Absorbance
Reflectance
as mode of detectio

74. AFFINITY BASED BIOSENSORS
 Immobilised biological recognition element is
a binding protien ,antibody ,(immunosensor)
or oligonucleotide ( eg DNA , aptamers etc
)with high binding specificity & affinity
towards a clinically imp analyte.
 Typically single use devices
 BASED ON
Electrochemical, optical, thermal,mass,
acoustic detection methods

75.  EXAMPLE
ALPHA FETOPROTIEN detected via a quartz
crystal microbalance type mass detector ,
possesing immobilized antialpha-fetoprotien
antibodies
DNA SENSORS – A complementry DNA segment
to the target DNA is immobilized on a suitable
transducer eg.
Genosensor for detecting V Leiden mutations
using capture probeswith inosine substituted
for guanosine nucleic acid

76.  ELECTROCHEMICAL O2 SNSORS- carry
out heterogenous enzyme immunoassay
using catalase as labeling enzyme &
immobilizing capture antibodies on the
outer surface of gas permeable membrane.
 H2O2 ------ 2H+ + O2

81. IN VIVO & MINIMALY INVASIVE
SENSORS
 MINIATURED VERSION OF ELECTROCHEMICAL &
OPTICAL SENSOR DEVICES EMPLOYED IN VIVO
 ADVANTAGES
Real time monitoring
Critically ill patients ( Ph /PCO2/PO2 )
 LIMITATIONS
Biological response of living system towards sensors
(CLOTTING)
Once inserted no reliable caliberation

82.  APPLICATIONS
Measurement of O2 saturation
Measurement of Ph /PCO2 /Po2 based on clark
style design sensor
Glucose sensors – Fully automated
Feed back control of subcutaneos insulin
delivery

83.  THANK YOU