Insulator-protected mechanically controlled break junctions for measuring single-molecule conductance in aqueous environments

Abstract

We present a method to fabricate insulated gold mechanically controlled break junctions (MCBJ) by coating the metal with a thin layer of aluminum oxide using plasma enhanced atomic layer deposition. The Al2O3 thickness deposited on the MCBJ devices was varied from 2 to 15 nm to test the suppression of leakage currents in deionized water and phosphate buffered saline. Junctions coated with a 15 nm thick oxide layer yielded atomically sharp electrodes and negligible conductance counts in the range of 1 to 10−4 G0 (1 G0 = 77 μS), where single-molecule conductances are commonly observed. The insulated devices were used to measure the conductance of an amphiphilic oligophenylene ethynylene derivative in deionized water.

Protein bioelectronics: a review of what we do and do not know

“…Another disadvantage of this method is that it does not allow multiple measurements to be conducted on the same protein after removing the sample, which prevents systematic studies to be performed under different conditions. The recently reported possibility to use mechanical controlled break junctions in aqueous environment 321 opens the possibility of forming such junctions with proteins, which may improve the control over the force applied to this floppy system, something that is a problem in other single molecule junction methods ( Figure 14b). Another nanoscale technique for studying single proteins involves the creation of nanogap electrodes through mechanical breaking 323,324 or electromigration techniques.…”

Single-molecule quantum-transport phenomena in break junctions

“…Although the liquid environment of the electrochemical cell imposes restrictions, working in solvents enables the electronic response of molecular junctions to the addition of chemicals to be probed in situ. Methods have therefore been developed to fabricate MCBJ junctions that can be used to study molecular transport in a solvent by coating the metal electrode with a thin insulating oxide layer 24,25 . In this respect, graphene is an promising electrode option, and the first graphene-based MCBJs have been fabricated 26,27 .…”

Detecting Single-Nucleotides by Tunneling Current Measurements at Sub-MHz Temporal Resolution

“…In this study, therefore, we developed a nanoelectrode system for single-nucleotide detections by tunneling current measurements at 1 MHz sampling rates in liquid ( Figure 1 ). We used insulator-protected mechanically-controllable break junctions (MCBJs) [ 16 , 17 , 18 ] to form nanotip-exposed Au electrodes of 1 nm separation. The feasibility of the nanoprobes was evaluated by carrying out single-nucleotide detections in a polar solvent at room temperature on the basis of fast tunneling current measurements at 1 MHz.…”