1

Claude Nogues, Sidney Cohen, Shirley Daube, Ron Naaman.

Electrical properties of DNAElectrical properties of DNA

characterized by conductingcharacterized by conducting--AFMAFM

Guanine, G Cytosine, C

Adenine, A Thymine, T

Structure dsDNA

Structure of DNAStructure of DNA

Purine Pyrimidine

3D image

2

Distance between two base pairs = 3.4Å

Orbital overlapping

ππππ-Stacking

Side view Top view

C.R Treadway et al. Chemical physics 281, 409 (2002)

B DNA

Charge transport in DNACharge transport in DNA

Charge transport in DNACharge transport in DNA

• Biology– Oxidative damage (apoptosis, mutation, cancer)– DNA repair (molecular recognition)– Protective properties of a guanine rich region

• Electronic– Molecular dimension – DNA unique assembly and recognition properties– Sequence dependence on the current transferred

• Fundamental– DNA = model to study charge transfer along π-Stack

3

Charge transport in DNACharge transport in DNAExperiment in solution

Boon E.M. et al. Current Opinion in Structural Biology, 12, 320 (2002)

Tunneling

Hopping

Domain Hopping

Charge transport in DNACharge transport in DNA

Boon EM et al. Current Opinion in Structural Biology, 12, 320 (2002)

4

Charge transport in DNACharge transport in DNAExperiment solid phase

HOMO

LUMO

HOMO

LUMO

Source Drain

Fermi Level or

Electrochemical potential

Source Drain

Channel Channel

Energy band diagram

• In solution• The net charge of the system is 0• Charges in the DNA are stabilized by the

solution around it

• In dry condition• The DNA is charged• The charges are not stabilized

Charge transport in DNACharge transport in DNA

5

• Methodology

• The sample • The DNA, length and sequence• The measurements

• Results

• Experimental control• Base dependence

• Conclusions

OutlineOutline

SSSS SSSSSS SS

SSSS SSSSSS SS

– Monolayer of thiolated ssDNA on a gold surface

– Monolayer of the complementary ssDNA on goldnanoparticles (GNP)

Covalent bonding at both ends of the DNA

�Improve the charge injection

Only specific interactions with the metallic surface

�Minimal distortion of the DNA conformation

InspirationInspiration……Cui et. al. Science, 2001Cui et. al. Science, 2001 C. Nogues et al. PCCP, 6, 4459 (2004)

– Hybridization on the surface

The Sample MethodologyMethodology

6

SA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – TA – T

S

SG – CT – AA – TA – TT – AT – AA – TC – GG – CA – TT – AA – TC – GG – CT – AC – GT – AT – AT – AT – AA – TG – CA – TA – TT – AC – G

S

SG – CC – GG – CT – AG – CT – AA – TG – CA – TA – TG – CA – TG – CG – CT – AA – TT – AG – CG – CT – AA – TG – CG – CT – AC – GG – C

S

0GC 8GC 14GC

MethodologyMethodology

26 base pairs

IV curve dependence on GC base pair number

Random placement of GC base pairs along the DNA

The DNAThe DNA

4 nm6 nm

10 - 14 nm

Coverage

SH-ssDNA → 3.1013 probes/cm 2

OH-ssDNA → 1.1011 probes/cm 2

CharacterizationCharacterizationAFM, tapping mode

x = 500 nm

3 nm

C. Nogues et al. PCCP, 6, 4459 (2004)

7

GNP non-complementary strands~5 per 1 µµµµm2

Hybridization on the surfaceHybridization on the surfaceAFM, tapping mode

1 µm1 µm

GNP complementary strands ~450 per 1 µµµµm2

C. Nogues et al. PCCP, 6, 4459 (2004)

• Topography and Current map of the surface

• Current voltage (I-V) curve

Electrical measurementsElectrical measurements

8

Conductive AFM measurementsConductive AFM measurements

Current map : contact mode

Intermittent contact mode

C. Nogues et al. PCCP, 6, 4459 (2004)

Current map: intermittent contact mode

Top

ogra

phy

Cur

rent

Bia

s =

2V

a.u.

ssDNA monolayer + Complementary ssDNA on GNP

Conductive AFM measurementsConductive AFM measurements

C. Nogues et al. PCCP, 6, 4459 (2004)

9

Topography

CurrentBias = 2V

Less GNP on the surface

No current signal detecteda.u.

The control

ssDNA monolayer + Non Complementary ssDNA on GNP

Conductive AFM measurementsConductive AFM measurements

C. Nogues et al. PCCP, 6, 4459 (2004)

Current Voltage curve

– Vertical Force– Drift

C. Nogues et al., J. Phys. Chem. B, 110, 8910 (2006)

Conductive AFM measurementsConductive AFM measurements

10

100 nm

-3 -2 -1 0 1 2 3

-20

-15

-10

-5

0

5

10

15

I (nA

)

V (V)-3 -2 -1 0 1 2 3

-20

-15

-10

-5

0

5

10

15

I (nA

)

V (V)

-3 -2 -1 0 1 2 3

-30

-20

-10

0

10

20

30

I(nA

)

V(V)

Scan in tapping mode / I-V in contact mode

GNP – dsDNA – Au bridge

C. Nogues et al. PCCP, 6, 4459 (2004)

8 GC bp

Conductive AFM measurementsConductive AFM measurements

0.0 0.5 1.0 1.5

0

2

4

6

8

Hei

ght (

nm)

x (nm)

0.0 0.5 1.0 1.5

0

2

4

6

8

Hei

ght (

nm)

x (nm)

Topography

GNP – dsDNA – Au bridge

before I-V

After I-V

Section

C. Nogues et al., PCCP, 6, 4459, 2004.

Conductive AFM measurementsConductive AFM measurements

11

-2 -1 0 1 2

-4

-3

-2

-1

0

1

2

3

4

I (nA

)

V (V)

On the ssDNA monolayerOn the ssDNA monolayer

-3 -2 -1 0 1 2 3

-4

-3

-2

-1

0

1

2

3

4

I (nA

)

V (V)

C. Nogues et al., PCCP, 6, 4459, 2004.

Conductive AFM measurementsConductive AFM measurements

-2 -1 0 1 2-20

-15

-10

-5

0

5

10

15

I (nA

)

V (V)

14 GC 8 GC 0 GC

Sequence dependence of charge Sequence dependence of charge

transport of DNAtransport of DNA

C. Nogues et al., J. Phys. Chem. B, 110, 8910 (2006)

12

Voltage threshold and resistance as a function of the GC content

53±0.2 V37±15 V0.9 +/- 0.12 V14

69±47 V770±211 V1.9 +/- 0.10 V8

686±190 V1800±244 V2.6 +/- 0.09 V0

Resistance|V | > 1 V

Resistance|V | < 1 V

Voltage thresholdGC content

Sequence dependence of charge Sequence dependence of charge

transport of DNAtransport of DNA

C. Nogues et al., J. Phys. Chem. B, 110, 8910 (2006)

Current density at 1.5 V as a function of the GC content

1.72 +/- 0.29 nA/nm214

0.18 +/- 0.05 nA/nm28

0.02 +/- 0.01 nA/nm20

Current density (mean +/- SE, n = 40)

GC content

Sequence dependence of charge Sequence dependence of charge

transport of DNAtransport of DNA

C. Nogues et al., J. Phys. Chem. B, 110, 8910 (2006)

13

ConclusionsConclusions

• Short DNA can transfer charge

• The current rises after a voltage threshold

• The voltage threshold decreases with increasing GC content

• The current density increases with the GC content.

• Results similar to Xu B et al. Nano lett. 4, 1105 (2004)

• No current is detected through the single strand DNA

ThankThank youyou