ultramicroelectrode & nanoelectrode

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Marwa M. Al-A’qarbeh (9130134)Adv. Electroanalytical

(0303912)

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CONTENT

INTRODUCTION History Principle Application

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19501950

20002000

20002000

fabricate glass micro fiber

.

The introduction of UMEs to electroanalytical chemistry occurred principally through the independent work of Wightman and Fleischmann and their co-workers

Application with nanoscince and nanotechnolgy

SWCNT electro studeis and used SWCNT modified electrodes

19801980

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DEFINATION (UMEs)

commonly known as microelectrode: defined as electrodes whose critical dimension is in the micrometer range, although electrodes with radii as small as (1-10) µm have been fabricated.

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DEFINATION (UMEs)

critical dimension any region at electrode or at least one dimension, with smaller than 25 µm.

where double layer thickness 25 µm

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DEFINATION (Nanoelectrods)

are electrodes with critical dimensions smaller than 10 nm

much smaller than UMEs and double layer

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..

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INTRODUCTION

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10

..

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-18000

-16000

-14000

-12000

-10000

-8000

-6000

-4000

-2000

0

2000

-0.4 -0.2 0 0.2 0.4 0.6 0.8

Ptential/V (vs. Ag/AgCl)

Cur

rent

den

sity

/(uA

/cm

2)

Macro-, Micro-, and Nano- Electrodes

-1500

-1000

-500

0

500

1000

1500

-0.4 -0.2 0 0.2 0.4 0.6 0.8

potential (vs. Ag/AgCl)

curr

ent

den

sity

(A

/cm

2)

GC2mm dia.

Carbon fiber7m dia.

Semi-infinite planar linear diffusion Semi-infinite hemispherical diffusion:Current exhibits a steady state

I total = Iplanar + Iradial

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Short times. at sufficiently short times the thickness of the diffusion layer that is depleted of reactant is much smaller thanthe electrode radius

The mass transport process is dominated by linear diffusion to the electrodesurface

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PRINCIPLE

Long times the spherical character of the electrode becomes

important, and the mass transport process is dominated by radial or spherical diffusion

The steady-state response arises because the electrolysis rate isequal to the rate at which molecules diffuse to the electrode surface

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Properties of UMEs & NEs

Reduced Capacitance Reduced Charging Current Minimize Baseline Current

(Background)

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Properties of UMEs & NEs

Reduce Ohmic Effects (IR-Drop) Used in aqueous, non- aqueous, solid,

and gases phase Used may without supporting

electrolyte Enhance current density, increase

sensitivity of Liner sweep voltammitry, cyclic voltammitry, single and double chronoamperommitry

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UMEs & NEs fabrication

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UMEs & NEs fabrication

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UMEs & NEs fabrication

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Effect of non polar solvant and supporting electrolyte

Cyclic voltammograms for the reduction of 1 mM TCNQ inacetonitrile at a 12 4 pm radius Pt disk electrode Concentration of supporting electrolyte (TBAP) (A) 100 mM, (B) 1 mM, (C) no supporting electrolyte deliberately added

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PH -Sensors

Detection and quantification of H2 fluxes produced from a corroding magnesium alloy

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Biosensors

Disk-Shaped Amperometric Enzymatic Biosensor for in Vivo Detection of d-serine

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Enviromantal electroanalysis

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UME arrays

um

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Scanning Prob Microscope

Mirror

PSD

PiezoScanner

LED

Cantilever with tip

sample

z-Signal

Scanning electronics

Scanning Tunnling Microscope (STM)Scanning ElectroChemical Microscope (SECM)Atomic Force Microscope (AFM)

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Characterization of SECM-AFM tips

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Imaging polycarbonate membranes

AFM image (constant force mode)

SECM image

Diffusion profile

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Imaging polycarbonate membranes

AFM image

SECM image

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LIPIDS

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Carbon Nanotube Electrodes

P. M. Ajayan et al, Nano Lett., 1(2), 87(2001).

MWCNT bundleDia. 600 m, length ~1.5 mm

MWCNT bundleDia. ~200 nm, length ~30 m

R. M. Crooks et al, J. Am. Chem. Soc., 121, 3779 (1999).

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• Vertically aligned CNTs can be used to fabricate nanoelectrode array.

• The electrical and electrochemical properties of such nanoelectrode array have been thoroughly characterized.

• Chemical functionalization has been demonstrated to be highly selective at CNT ends.

• CNT nanoelectrode array has potential applications as highly sensitive DNA sensors

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Chemical Functionalization

Highly selective reaction of primary amine with surface –COOH group

i-Pr2NEtCO2

-CO2HDMF

N C N CyCy

N

O

O

HO

H2N FcO

HNFc

O

O N

O

O

FeFc =

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Functionalization of DNA

CO2H

NC

N

CH3

N

CH3

H

Cl-

O

CH3

HN

H2N ATGCCTTCCy3

ATGCCTTCCy3

CH3

H

Cl-

TACGGAAGGGGGGGGGGCy5

N

O

O

HO

SO3Na

CH3

C

O

NH

C

N

CH3

N

O

O

O N

O

O

SO3Na

O

HN ATGCC TTCCy3TACGGAAGGGGGGGGGGCy5

+

EDC

+

Sulfo-NHS

DNA probe

Target DNA

Cy3 image

Cy5 image36

3+

2+

e

3+

2+

CNT DNA SensorUsing Electrochemical Detection

MWNT array electrode functionalized with DNA/PNA probe as an ultrasensitive

sensor for detecting the hybridization of target DNA/RNA from the sample.• Signal from redox bases in the excess DNA single strands

The signal can be amplified with metal ion mediator oxidation

catalyzed by Guanine.

Ru bPy 3

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Technical Platform

Top View

Side View

Each individual electrode is electronically

addressable with an array of CNTs with

d ~ 10 to 100 nm

dnn ~ 500 nm to 5000 nm

Each Electrode Immobilized with A Specific PNA or DNA Probes

10 to 200 m

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Electrochemical Detectionof DNA Hybridization

1st, 2nd, and 3rd cycle in cyclic voltammetry 1st – 2nd scan: mainly DNA signal2nd – 3rd scan: Background

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