(Keynote) Conduction Under Potential Control: From Molecules to Proteins

Abstract

My brilliant former student NJ Tao, to whose memory this symposium is dedicated, showed in a remarkable single-author paper1 that the conductance of a molecule containing a redox center was strongly dependent on surface potential, being a maximum at the redox potential. Some years later, we showed2 that defined contacts and statistical analysis were the keys to measuring molecular conductance quantitatively. NJ Tao came up with a simpler way of implementing our method, now the gold standard in single molecule conductance measurements.3 Gating of single-molecule conductance has now been reliably demonstrated.4 Despite many advances, there have been few real applications for single-molecule electronic devices. Proteins make excellent electronic conductors, as demonstrated by measurements under potential control that eliminate Faradaic contributions to the current.5 A remarkably long electron mean-free path and means for self-assembly give proteins advantages over conventional molecular wires.6 Furthermore, enzyme activity may be followed directly via conductance fluctuations, a possible basis for a new DNA sequencing technology.7 This talk will look at the physics behind these phenomena. Tao, N. J., Probing Potential-Tuned Resonant Tunneling through Redox Molecules with Scanning Tunneling Microscopy. Physical Review Letters 1996, 76 (21), 4066-4069.Cui, X. D.; Primak, A.; Zarate, X.; Tomfohr, J.; Sankey, O. F.; Moore, A. L.; Moore, T. A.; Gust, D.; Harris, G.; Lindsay, S. M., Reproducible Measurement of Single-Molecule Conductivity. Science (New York, N.Y.) 2001, 294 (5542), 571.Xu, B.; Tao, N. J., Measurement of Single-Molecule Resistance by Repeated Formation of Molecular Junctions. Science (New York, N.Y.) 2003, 301 (5637), 1221.Song, H.; Kim, Y.; Jang, Y. H.; Jeong, H.; Reed, M. A.; Lee, T., Observation of molecular orbital gating. Nature 2009, 462 (7276), 1039-1043.Zhang, B.; Song, W.; Pang, P.; Lai, H.; Chen, Q.; Zhang, P.; Lindsay, S., The Role of Contacts in Long-Range Protein Conductance. Proc Natl Acad Sci U S A 2019, 116, 5886-5891.Lindsay, S., Ubiquitous Electron Transport in non-Electron Transfer Proteins. Life 2020, 10, 72Zhang, B.; Deng, H.; Mukherjee, S.; Song, W.; Wang, X.; Lindsay, S., Engineering an Enzyme for Direct Electrical Monitoring of Activity. ACS Nano 2020, 14, 1630-1638.