Electrochemical Methods

Prof. Jin Ho Bang

Biosensors

Nature Biotechnology 2019, 37, 389–406.

Basic Principle of Biosensors

Glucose Amperometric Biosensor

Potential step methods

Potential step methods

Chronoamperometry

Chronocoulometry

Cu2+ + 2e → Cu0 (electrochemical reduction)

Fe2+ → Fe3+ + e (electrochemical oxidation)

Anode: electrochemical oxidation

Cathode: electrochemical reduction

Electrochemical reactions

Oxidation: electron moves to electrode.

Reduction: electron moves from electrode.

• Electron tunneling: an electron can penetrate a potentialbarrier higher than the kinetic energy of the electron.

Heterogeneous charge transfer

Cu2+ + 2e → Cu

Heterogeneous charge transfer reaction;

Electron tunneling at electrode/solution interface

Electrode potential is an expression of electron energy

Current is an expression of reaction rate

Current (i) ∝ Reaction rate

Pathway of a general electrode reaction

Potential step methods

Potential step methods

Cottrell equation

Laplace transformation (partial to ordinary)

CO(x,t) by Laplace transformation

Error function

Simulation of CO(x,t)

Limitation of potential step method

Limitation of potential step method

Equivalent circuit for 3-electrode cell

Ref

Ctr

RW

Ru

Cdl

etrue

eref

WkWk

Cdl

etrue

eref

RW

Ru

Rct

Ref

Ctr

Limitation of potential step method

Time constant = RuCdl

etrue

erefe

0 Time

Limitation of potential step method

1. Three-electrode configuration

2. Electrode area; small

- CO*, CR*; constant

3. Mass transfer; no migration (electrolytes)

- Diffusion

- No convection; no stirring

4. Spherical diffusion

Ultra microelectrode

Planar vs. Planar ultra microelectrode

Planar microelectrode Planar ultra microelectrode

• The flux per unit area in spherical diffusion is greater than that in linear diffusion.

• Current decrease by decreased concentration gradient is compensated by the

increased flux. As a result, current density per unit area is greater in UME.

Planar ultra microelectrode

Planar ultra microelectrode

Planar ultra microelectrode

• The used of UME alleviates issues associated with charging time and rising time.

• It also allows to measure steady current within a short time.

• From the steady current measured, parameters related to diffusion can be

determined.

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