Proteins: “ dopable Solid-State Electronic Transport Materials

2. e- Proteins:“dopableSolid-State Electronic Transport Materials

3. “Traditional” methods to measure electron transfer in proteins Electrochemistry (ML on electrode) Spectroscopy (in solution) Pulse- radiolysis Flash- quench Cyclic Voltammetry Chrono- amperometry All these measure the Electron transfer rate (s-1)

4. From electron transfer to “solid-state” electron transport • Goal: • Understand how electron transport (ETp)via proteins in a 'dry' configuration occurs and what influences it. • Common approaches to measure solid state ETp: CP-AFM STM

5. Protein layer 150 nm 400 nm

6. Protein layer Cytochrome C CH-stretches IR UV-Vis CD

7. Proteins as Electronic Transport Medium? Proteins survive partial Dehydration Suitable… Proteins are rather efficient solid-state transport medium Co-factor is central  proteins can be doped Amide backbone maybe involved in elastic transport Functional and dopable ★★★ Ultimate scientific goal: Control & predict electron transport across proteins

8. Proteins on Today’s Menu Natural electron transfer proteins Not an electron transfer protein Azurin Cytochrome C Serum Albumin

9. Our main experimental approach • Substrate – Smooth! • Protein layer – Dense, usually linked by a short linker • Top electrode – Suitable to contact soft matter Idealized Cartoon! Electrical top contact Conductive substrate

10. Substrate • Highly doped Si, Al(ox), Au • Controllable growth of thin oxide layer on Si • Linker layer (“glue”) Propyl-silane linker 6-8Å SiO2 9-10Å <100> p++-Si (< 0.001 Ω.cm)

11. Top Electrode Au Hanging Hg drop Lift off float on (LOFO) - Au 0.2 mm2 ~107-109proteins/contact

12. Conductive probe AFM • Less defects • Force variation

13. 2μm A 10 nm Metallic substrate What does a nanoscale experiment look like? Idealized Cartoons!

14. Electrophoretic nanowire assembly of poly-peptide & protein junctions - suspended nanowire method protein junction Azurin Device figure from G. Noy and Y. Selzer, Angew. Chem. Int. Ed. (2010)

15. Current-voltage Characteristics of the different proteins • Same configuration • Same temperature SAM propyl-silane SiO2 Si p++

16. Net decay What is the ETp mechanism? Gray and Winkler, 2003 proteins Tunneling Log conductance hopping Isied, JACS 2004 Joachim & Ratner, PNAS, 2005 8 1 2 3 4 5 6 7 Length (nm)

17. What is the ETp mechanism? Thermally activated Temperature-independent Lower βvalues than for ET in solution Hopping ……………… Super-exchange …….. 2-step tunneling ???

18. What is the ETp mechanism? • 1. Vary temperature • 2. Modify protein: • Remove the intramolecular cofactor • Replace cofactor • Add cofactor • Change binding (to electrode) • Change orientation of protein Not feasible with ET methodologies

19. Temperature dependence I-V - Azurin Azurin covalently bound to the surface Sepunaru et al., JACS 2011

20. Cu ion removal 300 meV Sepunaru et al., JACS 2011

21. Cu ion replacement Cu-Az Ni-Az Co-Az Zn-Az Unpublished Results

22. Connect to what was done before: Conductive probe AFM studies on Az A Our setup Our results (6-15 nN) All metal (platinum) Literature results (6 nN) Au Au Tip Bias (V) J. Davis (Oxford) setup Li et al., ACS Nano 2012

23. Temperature-dependent conductive probe AFM Apo-Az Holo-Az 358K 268K Li et al., ACS Nano 2012

24. Force-dependent measurements Apo-Az Holo-Az Increased force Increased force Different ETp mechanism Increased currents Same ETp mechanism Li et al., ACS Nano 2012

25. Temperature dependent I-V with Cyt c Cyt C bound electrostatically (physisorbed) to surface 100 meV Iron-free CytC Holo-CytC Fe Apo-CytC What is the ETp mediator? Amdursky et al., JACS 2013

26. Can we Control ETp ?‘Doping’ Serum Albumin Azurin CytC Apo-Az HSA

27. ‘doping’ serum albumin with hemin

28. ‘doping’ serum albumin with hemin HSA-hemin HSA Amdursky et al., PCCP 2013

29. ‘doping’ serum albumin with hemin 95 meV HSA-hemin HSA 220 meV kET=4.8 s-1 kET=18.3 s-1 HSA-hemin CytC Amdursky et al., PCCP 2013

30. ‘doping’ serum albumin with hemin What is the ETp mediator? The conjugated porphyrin ring, rather than the Fe ion is the main ETp mediator, while Fe2+/3+ redox controls the transfer in ET. Amdursky et al., PCCP 2013

31. ‘doping’ serum albumin with retinoate-Can we increase ETp efficiency? Ligand/protein Ka=4*105 Amdursky et al., JACS 2012

32. ‘doping’ serum albumin with retinoate Amdursky et al., JACS 2012

33. The power of protein ‘doping’

34. The importance of the contact to the electrodes and the orientation • Electrostatic (physisorbed) vs. Covalent (chemisorbed) binding CytC Amdursky et al., Submitted

35. The importance of the contact to the electrodes and the orientation • The importance of the protein’s orientation Amdursky et al., Submitted

36. Importance of the Protein’s Orientation Previous studies • Cyt b562 ACS Nano 2012, 355

37. Importance of the Protein’s Orientation Amdursky et al., Submitted

38. Can we use existing models to describe solid-state type of ETp?

39. Importance of the Protein’s Orientation NO distance-current correlation!!! Amdursky et al., Submitted

40. Importance of the Protein’s Orientation D • Clues from computational modeling Probably, there is no specific pathway in the ETp process from one side of the protein to the other A TP – tunneling pathway Vs. APD – atomic packing density Amdursky et al., TBP

41. Conclusions • Electron transport through proteins can be measured by solid state configuration, both on the macro and the nano scales • The electron transport mechanism can be investigated by • Changing the temperature • Modifying the protein • Proteins can be viewed as electronic conducting material with the possibility of doping • The contacts to the electrodes and the orientation of the protein are of prime importance

42. Thanks to students, PDs & other colleagues AcknowledgmentsMinerva Foundation, Munich Dr. Ann Erickson AbdElrazek Haj Yahia Dr. RotemHarLavan Dr. Omer Yaffe Dr. AyeletVilan NirK. Kedem Arava Zohar Mudi Sheves Israel Pecht 43

43. Porphyrin- and apo-CytC

44. ET vs. ETp Waldeckc.s. – PNA length dependence ACS Nano (2013) 5391