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Graphene nanopore

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From Molecupedia, the encyclopedia of very small things
Hole in a single sheet of carbon atoms, used as the sensing aperture of a nanopore

A graphene nanopore is a hole in graphene, a sheet of carbon atoms one atom thick, used as the aperture of a nanopore. The sheet is 0.34 nm thick, less than the 0.5 nm between neighboring bases of a single strand of DNA, and the idea behind the pore is that an aperture that short might sense one base at a time where a pore in 10 to 50 nm of silicon nitride senses a stretch of dozens. In 2010 three groups reported pores in graphene membranes, and DNA passing through them was recorded. Graphene pores remain a common subject: in the atlas of the company's own Hole World, more entries are drawn as graphene pores than as any other kind but silicon nitride.

Why one atom

The length of a solid-state nanopore was its first disadvantage against a protein pore. The channel of a solid-state pore is long, about 100 times the 0.5 nm between bases of single-stranded DNA, as a 2010 paper put it.[1] Graphene removes the problem on paper. A group at Harvard reported that membranes of one to two layers are "remarkable ionic insulators", and that the effective insulating thickness of a pore drilled in one is less than 1 nm.[2] Their paper appeared in the year that Andre Geim and Konstantin Novoselov received the Nobel Prize in Physics for experiments on graphene.[3]

Cross-sections of three membranes, graphene 0.34 nanometers thick and silicon nitride 10 and 20 nanometers thick, each with a pore 5 nanometers wide, beside a strand of DNA with its bases 0.5 nanometers apart
Membranes of three thicknesses at one scale, each with a pore 5 nm wide, beside single-stranded DNA with its bases 0.5 nm apart. Schematic.

A short pore passes more current. For a pore of diameter d and length L in a salt solution of conductivity σ, the conductance is σ[4L/(πd2) + 1/d]−1, where the second term is the access resistance of the two mouths.[4] At L = 0.34 nm the access term is nearly all of it. In 1 M potassium chloride a pore 5 nm wide then conducts about 48 nS and passes 9.7 nA at 200 mV, against 15 nS and 3.0 nA through a membrane 10 nm thick and 8.6 nS and 1.7 nA through one 20 nm thick.[a] A molecule in the pore blocks a larger part of the current, and the blockades in graphene were larger than in silicon nitride.

A pore matched to a molecule is the most sensitive. In 2013 the Harvard group made pores in single-layer graphene close to the diameter of double-stranded DNA and measured a sensitivity of 0.65 nA for each ångström of change in the molecule's outer diameter, with a modeled resolution along the molecule of 0.6 nm or better.[5]

Making the pore

The graphene is grown or peeled, laid over a hole in a supporting membrane and drilled where it hangs free. The Delft group of Cees Dekker placed a flake over a micrometer-size hole in silicon nitride and cut the nanopore with an electron beam.[1] Another group used sheets 1 to 5 nm thick, which are several to a dozen layers, and pores of 5 to 10 nm formed by an electron beam.[6] The shape of a pore in graphene is a matter of which atoms are missing (see Nanopore printing). A review of graphene devices for DNA sequencing, published in 2016, covered pores, nanogaps, nanoribbons and DNA lying on graphene, and reported that "the first experimental demonstrations have begun to appear".[7]

Problems

Graphene conducts, so it is a good electrode and a poor insulator, and in the first paper that recorded DNA the current noise was several orders of magnitude above that of silicon nitride pores. Covering the device with 5 nm of titanium dioxide by atomic layer deposition reduced it.[6]

A second problem is stickiness. Graphene is hydrophobic, and a study in 2013 reported a paradox: pores in contaminated graphene passed DNA, while clean, crystalline pores quickly clogged, which the authors attributed to strong interactions between nucleotides and the graphene that closed the pore irreversibly. A self-assembled monolayer of pyrene ethylene glycol, which makes the surface hydrophilic, prevented the adsorption, and single-stranded DNA could then be detected with good durability.[8] A short pore does not slow the molecule either. Reading each base needs a thin pore and a slow strand, and graphene supplies only the first (see Speeding bullet problem).

At Molecular Reality

Graphene is the material of the best mode in the company's patent. Three squares of many-layer graphene sit in three nested frames, two positioners push two of the frames through "rigid, sharp metallic materials", of which "0.131″ framing nails serve this purpose nicely", and the hole through all three layers is made with a 9 V battery applied in pulses of about ten seconds.[9] Moving the top two frames then changes the shape of the passage.

The 2022 overview proposed printing graphene pores inside the cartridges of the demonpore 64, an idea that was not carried out, and counted "~180,000 potentially chemically stable graphene nanopores with fewer than 20 carbon atoms removed from the hexagonal lattice".[10] The atlas draws 410 of its 2,112 entries with the graphene archetype, which is a sheet of four rows of ten atoms with a ringed hole.[11]

See also

Notes

  1. ^ Calculated with σ = 10.5 S/m and the formula above.

References

  1. ^ a b Schneider, G. F.; et al. (2010). "DNA translocation through graphene nanopores". Nano Letters 10 (8): 3163-3167. doi:10.1021/nl102069z. PMID 20608744.
  2. ^ Garaj, S.; et al. (2010). "Graphene as a subnanometre trans-electrode membrane". Nature 467 (7312): 190-193. doi:10.1038/nature09379. PMID 20720538.
  3. ^ "The Nobel Prize in Physics 2010". Nobel Prize Outreach. Retrieved October 25, 2026.
  4. ^ Kowalczyk, S. W.; Grosberg, A. Y.; Rabin, Y.; Dekker, C. (2011). "Modeling the conductance and DNA blockade of solid-state nanopores". Nanotechnology 22 (31): 315101. doi:10.1088/0957-4484/22/31/315101.
  5. ^ Garaj, S.; Liu, S.; Golovchenko, J. A.; Branton, D. (2013). "Molecule-hugging graphene nanopores". Proceedings of the National Academy of Sciences 110 (30): 12192-12196. doi:10.1073/pnas.1220012110.
  6. ^ a b Merchant, C. A.; et al. (2010). "DNA translocation through graphene nanopores". Nano Letters 10 (8): 2915-2921. doi:10.1021/nl101046t. PMID 20698604.
  7. ^ Heerema, S. J.; Dekker, C. (2016). "Graphene nanodevices for DNA sequencing". Nature Nanotechnology 11 (2): 127-136. doi:10.1038/nnano.2015.307.
  8. ^ Schneider, G. F.; et al. (2013). "Tailoring the hydrophobicity of graphene for its use as nanopores for DNA translocation". Nature Communications 4: 2619. doi:10.1038/ncomms3619.
  9. ^ "US10908144B2: Stacks of coaligned nanopores and fabrication and uses thereof". Google Patents. Retrieved October 25, 2026.
  10. ^ "Scientific and technical overview". Molecular Reality Corporation. December 2022.
  11. ^ "The Hole World: Molecular Sensing Atlas". Molecular Reality Corporation. September 26, 2026.
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