Electrical properties of DNA characterized by conducting-afm

Transcription

1 Electrical properties of DNA characterized by conducting-afm Claude Nogues, idney Cohen, hirley Daube, Ron Naaman Weizmann Institute of cience, Rehovot, Israel

2 Outline Introduction History Current understanding Methodology and ample preparation ample characterization Conductivity measurements Correlated topography-current maps Conductive AFM measurements (I-V curves) Conclusion

3 DNA as a molecular wire 1962: The issue of DNA conductivity was raised by Eley and pivey Distance between base pairs = 3.4Å Orbital overlapping Experimental Results: Insulator (Dunlap et al. 1993; Braun et al. 1998; de Pablo et al. 2000; torm et al., 2001; Zhang et al. 2002) emiconductor like behavior (Porath et al. 2000) Conductor (Fink and choenenberger 1999; Cai et al. 2000; Tran et al. 2000; Rakitin et al. 2001; Yoo et al. 2001) Induced superconductor (Kasumov et al. 2001) R. G. Endres et al. Rev. of Modern Physics. 76 (2004)

4 Disparity amongst the results Length of the DNA strand Probability to have conformational defects along the strand equence Ionization potential G<A<C<T Contact between the DNA and the electrodes Charge injection / electron transmission through a potential barrier. Interaction between the DNA and the surface Deformation of the conduction channel. (Kasumov et al. APL 2004)

5 Methodology Inspiration Cui et. al. cience, 2001 Monolayer of thiolated ssdna on a gold surface Monolayer of the complementary ssdna on gold nanoparticles (GNP) Hybridization on the surface Covalent bonding at both ends of the DNA Improves the charge injection Only specific interactions with the metallic surface Minimal distortion of the DNA conformation

6 ample preparation The DNA: Complex sequence Length: 26 bases The sequence: On flat gold surface 5 CAT TAA TGC TAT GCA GAA AAT CTT AG 3 -C 3 H 6 -H On GNP H-C 3 H 6-3 GT AAT TAC GAT ACG TCT TTT AGA ATC 5

7 ample preparation ssdna monolayer pecificity of the adsorption: via the thiol Density: Homogenous Coverage pace for Hybridization Rinsing GNP dsdna Au bridge Coverage on the surface GNP marker for ds-dna

8 Characterization AFM, tapping mode nm 3 nm 6 nm 4 nm Coverage x = 500 nm H-ssDNA probes/cm 2 OH-ssDNA probes/cm 2

9 Hybridization on the surface AFM, tapping mode 1 µm GNP complementary strands ~450 per 1 µm 2 1 µm GNP non-complementary strands ~5 per 1 µm 2

10 Conductive AFM measurements Current topography images: Tapping mode Topography Current signal only at GNP Current Bias = 2 V a.u. Most of the GNPs are associated with an electrical signal ssdna monolayer + Complementary ssdna on GNP

11 Conductive AFM measurements Current topography images: Tapping mode Topography Current Bias = 2V a.u. ssdna monolayer + Complementary ssdna on GNP

12 Conductive AFM measurements The controls Less GNP on the surface Topography a.u. No current signal detected Current Bias = 2V ssdna monolayer + Non Complementary ssdna on GNP

13 Conductive AFM measurements The controls Mixed Monolayer: 50 % Thiolated ssdna + 50 % H-C 6 H 12 OH

14 Conductive AFM measurements The controls: Mixed Monolayer Current GNP covered with the non complementary ssdna ssdna No current Topography

15 Conductive AFM I-V curves can in tapping mode / I-V in contact mode I (na) nm V (V) I(nA) 0 GNP dsdna Au bridge V(V)

16 Conductive AFM I-V curves Topography before I-V ection 8 Height (nm) After I-V x (nm) GNP dsdna Au bridge

17 Conductive AFM I-V curves On the ssdna monolayer I I (na) I (na) (na) V (V) (V) V (V)

18 Conclusion We successfully demonstrated: hort dsdna displays semiconductor like behavior, gap~3ev No current on the ssdna monolayer within the same voltage range Methodology Advantages: Chemical contact between DNA and the two electrodes No interaction between DNA and metallic surface The current: The current: Not ionic

19 Acknowledgments Grants from the European Community Marie-Curie fellowship ENTIMAT project