Mono-Exponential Current Attenuation with Distance Across 16 nm Thick Bacteriorhodopsin Multilayers

Domenikos Chryssikos, Jerry A. Fereiro, Jonathan Rojas, Sudipta Bera, Defne Tüzün, Evanthia Kounoupioti, Rui N. Pereira, Christian Pfeiffer, Ali Khoshouei, Hendrik Dietz, Mordechai Sheves, David Cahen, Marc Tornow

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The remarkable ability of natural proteins to conduct electricity in the dry state over long distances remains largely inexplicable despite intensive research. In some cases, a (weakly) exponential length-attenuation, as in off-resonant tunneling transport, extends to thicknesses even beyond 10 nm. This report deals with such charge transport characteristics observed in self-assembled multilayers of the protein bacteriorhodopsin (bR). ≈7.5 to 15.5 nm thick bR layers are prepared on conductive titanium nitride (TiN) substrates using aminohexylphosphonic acid and poly-diallyl-dimethylammonium electrostatic linkers. Using conical eutectic gallium-indium top contacts, an intriguing, mono-exponential conductance attenuation as a function of the bR layer thickness with a small attenuation coefficient β ≈ 0.8 nm−1 is measured at zero bias. Variable-temperature measurements using evaporated Ti/Au top contacts yield effective energy barriers of ≈100 meV from fitting the data to tunneling, hopping, and carrier cascade transport models. The observed temperature-dependence is assigned to the protein-electrode interfaces. The transport length and temperature dependence of the current densities are consistent with tunneling through the protein–protein, and protein-electrode interfaces, respectively. Importantly, the results call for new theoretical approaches to find the microscopic mechanism behind the remarkably efficient, long-range electron transport within bR.

Original languageEnglish
Article number2408110
JournalAdvanced Functional Materials
Volume34
Issue number48
DOIs
StatePublished - 26 Nov 2024

Keywords

  • current–voltage measurements
  • eutectic gallium-indium
  • evaporated top contact
  • long-range electron transport
  • protein electronics

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