Periodic Reporting for period 1 - BioGraphING (Biomolecule Sensing with Graphene-Integrated Nanogaps)
Período documentado: 2018-04-01 hasta 2020-03-31
In order to understand certain biological mechanisms, such as how genetic information can affect the development of a specific disease, it is key to develop a methodology that enables sensing of relevant biomolecules (e.g. DNA, proteins) at the single-molecule scale. Nanotechnology-based approaches to achieve these goals have made large strides in the last decade, and have shown unparalleled potential by enabling long-read, high-resolution sequencing without need for amplification and labeling. Among the most effective sequencing devices are nanopores and nanogaps, through which the biomolecules are transiently trapped, thereby causing a modulation of the ionic and tunnelling current respectively. In particular, electron tunnelling transport across a single-molecule junction is highly sensitive to the nature of the trapped molecule, rendering it a powerful tool for discriminating analytes with minor structural differences. The principle behind the strength of this approach is that biomolecules with different chemical composition have different local electronic densities of states that lead to a distinguishable tunnelling current. In BioGraphING, the researcher designed and developed the first graphene MCBJ platform to assess the viability of graphene electrodes as a biosensor technology that has the potential to open up high-resolution single-molecule protein fingerprinting to all.
Graphene combines many of the requisites for an electrical sensor material: high conductivity, atomic thinness, flexibility, chemical inertness in air and liquid and mechanical strength, as well as compatibility with standard lithographic patterning techniques. In BioGraphING, the researcher developed a novel graphene-based technology that utilises the mechanically controlled break junction (MCBJs) technique. The MCBJ is conceptually simple: a suspended graphene bridge is positioned on a flexible metal substrate. Bending the substrate in a 3-point geometry causes the graphene to stretch and eventually break. The conductance at a fixed bias voltage is measured throughout the bending/breaking/remaking processes, giving detailed information of the structure-electronic property relationship. One- and two-dimensional histograms of conductance versus electrode displacement crucially allow mapping of the breaking dynamics in real-time and with statistical significance.
The project was structured to achieve three objectives:
O1. Demonstrating controlled nanogap formation in graphene MCBJs in air, vacuum and liquid.
O2. Identifying molecular signatures from ‘reference’ molecules e.g. anthracene- or pyrene-funtionalized curcuminoids or oligo-phenylene-ethynylene (OPE3) molecules (i.e. π-π interactions with graphene), porphyrins w/o amine anchors (i.e. C-C and amine bonding with graphene respectively).
O3. Demonstrating proof-of-concept peptide and protein fingerprinting using tunnelling currents.
Graphene combines many of the requisites for an electrical sensor material: high conductivity, atomic thinness, flexibility, chemical inertness in air and liquid and mechanical strength, as well as compatibility with standard lithographic patterning techniques. In BioGraphING, the researcher developed a novel graphene-based technology that utilises the mechanically controlled break junction (MCBJs) technique. The MCBJ is conceptually simple: a suspended graphene bridge is positioned on a flexible metal substrate. Bending the substrate in a 3-point geometry causes the graphene to stretch and eventually break. The conductance at a fixed bias voltage is measured throughout the bending/breaking/remaking processes, giving detailed information of the structure-electronic property relationship. One- and two-dimensional histograms of conductance versus electrode displacement crucially allow mapping of the breaking dynamics in real-time and with statistical significance.
The project was structured to achieve three objectives:
O1. Demonstrating controlled nanogap formation in graphene MCBJs in air, vacuum and liquid.
O2. Identifying molecular signatures from ‘reference’ molecules e.g. anthracene- or pyrene-funtionalized curcuminoids or oligo-phenylene-ethynylene (OPE3) molecules (i.e. π-π interactions with graphene), porphyrins w/o amine anchors (i.e. C-C and amine bonding with graphene respectively).
O3. Demonstrating proof-of-concept peptide and protein fingerprinting using tunnelling currents.
In BioGraphING, the researcher realized the first mechanically controlled break junctions (MCBJs) based on graphene electrodes to study the charge transport across the nanoscopic junctions.
The major advances that were made throughout the MC project are:
• Mechanical and electrical robustness and stability of the device compared to its bulk metal counterpart (i.e. Au break junctions used in the host group).
• Reliability and reproducibility of the fabrication using standard cleanroom processing.
• Statistical significance of the results (> 10,000 cycles at room temperature in air).
• Sub-nanometer tuning of the electrode spacing using a simple mechanical tuning knob to control the inter-electrode distance.
Furthermore, the new platform allowed the discovery of new fundamental quantum physical process, including quantum interference phenomena, that had only been reported from a theoretical standpoint but not achieved in practice:
• Observation of rare room temperature quantum interference effects during sliding of two graphene sheets across each other
• Low temperature (4 K) measurements of mechanically-tunable Coulomb blockade in a single graphene quantum dot inside the junction
The first paper published during the project (Nature Nanotechnology, 13, 1126–1131(2018)) demonstrates the first room-temperature, periodic conductance oscillations as a function of atomic-scale displacements in quantum coherent graphene nanoconstrictions. Our approach, based on monitoring the electrical conductance of graphene during uniaxial deformation, is entirely novel and overcomes a longstanding challenge for controllably tuning quantum interference effects in graphene by using a mechanical tuning knob with subnanometer resolution.
Given that the graphene MCBJ device demonstrates excellent electronic and mechanical properties, as well as a host of intriguing fundamental physical effects, the focus of the project shifted towards understanding the origin of the latter phenomena.
During the MC fellowship, massively parallel fabrication of crack-defined gold break junctions featuring sub-3 nm gaps was demonstrated, in a collaborative project with KTH University. The current-voltage characteristics were studied in detail and proved that single molecules can be individually trapped and measured at room temperature and at liquid nitrogen temperature. The results were published in Nature Communications (2018).
During the two-year period, the researcher disseminated the results of the project at the following international conferences as contributed speaker:
- From Solid state to Biophysics- From Basic to Life Sciences, Cavtat, Croatia, 2018
- Graphene Week 2018 - San Sebastian, Spain, 2018
- International Conference on Materials for Advanced Technologies - Singapore, 2019
- NT19: International Conference on the Science and Application of Nanotubes and Low-Dimensional Materials - Würzburg, Germany, 2019
The researcher was also an invited speaker at the 1st Kavli NanoLab Cleanroom User Meeting 2018.
The major advances that were made throughout the MC project are:
• Mechanical and electrical robustness and stability of the device compared to its bulk metal counterpart (i.e. Au break junctions used in the host group).
• Reliability and reproducibility of the fabrication using standard cleanroom processing.
• Statistical significance of the results (> 10,000 cycles at room temperature in air).
• Sub-nanometer tuning of the electrode spacing using a simple mechanical tuning knob to control the inter-electrode distance.
Furthermore, the new platform allowed the discovery of new fundamental quantum physical process, including quantum interference phenomena, that had only been reported from a theoretical standpoint but not achieved in practice:
• Observation of rare room temperature quantum interference effects during sliding of two graphene sheets across each other
• Low temperature (4 K) measurements of mechanically-tunable Coulomb blockade in a single graphene quantum dot inside the junction
The first paper published during the project (Nature Nanotechnology, 13, 1126–1131(2018)) demonstrates the first room-temperature, periodic conductance oscillations as a function of atomic-scale displacements in quantum coherent graphene nanoconstrictions. Our approach, based on monitoring the electrical conductance of graphene during uniaxial deformation, is entirely novel and overcomes a longstanding challenge for controllably tuning quantum interference effects in graphene by using a mechanical tuning knob with subnanometer resolution.
Given that the graphene MCBJ device demonstrates excellent electronic and mechanical properties, as well as a host of intriguing fundamental physical effects, the focus of the project shifted towards understanding the origin of the latter phenomena.
During the MC fellowship, massively parallel fabrication of crack-defined gold break junctions featuring sub-3 nm gaps was demonstrated, in a collaborative project with KTH University. The current-voltage characteristics were studied in detail and proved that single molecules can be individually trapped and measured at room temperature and at liquid nitrogen temperature. The results were published in Nature Communications (2018).
During the two-year period, the researcher disseminated the results of the project at the following international conferences as contributed speaker:
- From Solid state to Biophysics- From Basic to Life Sciences, Cavtat, Croatia, 2018
- Graphene Week 2018 - San Sebastian, Spain, 2018
- International Conference on Materials for Advanced Technologies - Singapore, 2019
- NT19: International Conference on the Science and Application of Nanotubes and Low-Dimensional Materials - Würzburg, Germany, 2019
The researcher was also an invited speaker at the 1st Kavli NanoLab Cleanroom User Meeting 2018.
The rich physics of graphene nanoconstrictions manipulated by mechanical means led to the development of a three-terminal device architecture, entirely based on 2D materials. A manuscript describing the development and measurements (room temperature and cryogenic) of this novel van der Waals heterostructure, devised in the last stages of the project, is currently under review. In this paper we realize for the first time mechanical tunability of a graphene quantum dot (QD) in a back gated graphene mechanical break junction. The QD, which is formed through controlled opening of a physical nanogap in a graphene constriction, has comparable quality to those formed in state-of-the-art, electrostatically defined QDs. Our platform can be extended to other 2D materials with the prospect of exploring the low-temperature transport behaviour under electrical and mechanical influence. In particular, it can lend itself to the formation, rupture and controlled overlap of ultra-narrow constriction in superconducting thin films, thereby providing a novel approach to manipulating the Josephson effect in an in-plane device. We therefore expect these results to be of direct high interest to the nanomaterials and charge transport communities.
The results produced during the fellowship opened up the route to several collaborations, including with the Norte lab and the Steeneken lab at TU Delft, as well as with Dr Pascal Gehring at IMEC (Leuven).
The results produced during the fellowship opened up the route to several collaborations, including with the Norte lab and the Steeneken lab at TU Delft, as well as with Dr Pascal Gehring at IMEC (Leuven).