Graphene-molecule-graphene single-molecule junctions to detect electronic reactions at the molecular scale

The ability to measure the behavior of a single molecule during a reaction implies the detection of inherent dynamic and static disordered states, which may not be represented when measuring ensemble averages. Here, we describe the building of devices with graphene-molecule-graphene single-molecule junctions integrated into an electrical circuit. These devices are simple to build and are stable, showing tolerance to mechanical changes, solution environment and voltage stimulation. The design of a conductive channel based on a single molecule enables single-molecule detection and is sensitive to variations in physical properties and chemical structures of the detected molecules. The on-chip setup of single-molecule junctions further offers complementary metal-oxide-semiconductor (CMOS) compatibility, enabling logic functions in circuit elements, as well as deciphering of reaction intermediates. We detail the experimental procedure to prepare graphene transistor arrays as a basis for single-molecule junctions and the preparation of nanogapped carboxyl-terminal graphene electrodes by using electron-beam lithography and oxygen plasma etching. We describe the basic design of a molecular bridge with desired functions and terminals to form covalent bonds with electrode arrays, via a chemical reaction, to construct stably integrated single-molecule devices with a yield of 30-50% per chip. The immobilization of the single molecules is then characterized by using inelastic electron tunneling spectra, single-molecule imaging and fluorescent spectra. The whole protocol can be implemented within 2 weeks and requires users trained in using ultra-clean laboratory facilities and the aforementioned instrumentation. Graphene-based single-molecule junctions, integrated with an electrical circuit, facilitate the detection of electronic, optical and mechanical properties of reactions at the molecular scale.

Automated summary

The ability to measure the behavior of a single molecule during a reaction can uncover dynamic and static disordered states that may not be represented in ensemble averages. This article introduces a method to build devices with graphene-molecule-graphene single-molecule junctions integrated into an electrical circuit. These devices are stable, tolerant to mechanical changes and solution environments, and enable sensitive detection of variations in physical and chemical properties of detected molecules. The on-chip setup of single-molecule junctions also allows for logic functions and analysis of reaction intermediates.