Molybdenum disulfide nanopore
A molybdenum disulfide nanopore (MoS2 nanopore) is a hole a few nanometers across in a sheet of molybdenum disulfide one layer thick, which is 0.7 nm.[1] It belongs to the family of two-dimensional nanopores that began with graphene nanopores in 2010, and it is best known for a 2015 experiment in which such a pore told apart, statistically, the four nucleotides of DNA. It has not read a DNA sequence.
The material
Molybdenum disulfide is the mineral molybdenite, a gray, soft crystal that was once mistaken for lead, which gave molybdenum its name from the Greek molybdos. The crystal is a stack of sheets, each a layer of molybdenum atoms between two layers of sulfur, held to its neighbors only by weak forces, and a sheet can be peeled off with adhesive tape as graphite is. A single layer is a semiconductor with a direct band gap of at least 1.8 eV, unlike graphene, which has none.[1] That made it a candidate for electronic detection of bases by a transistor beside the pore, a scheme that simulations have examined.
For a nanopore the interest is thickness. The ionic current through a pore passes through a sheet only 0.7 nm thick, about the length of two nucleotides of a DNA strand, whereas the 10 to 20 nm of a typical silicon nitride membrane hold 30 to 60 nucleotides at once, and the current reflects all of them together.[1]
The thinness has an electrical consequence. As the length of a pore falls toward zero, its conductance tends toward the product of the conductivity and the diameter, because nearly all of the resistance is in the openings (see Access resistance). A pore 2.8 nm wide through a sheet 0.7 nm thick would conduct about 24 nS in 1 M potassium chloride, computed from the formula in Pore conductance, and three-quarters of the resistance would lie outside the sheet.
Making and using the pores
Liu, Feng, Kis and Radenovic placed flakes of exfoliated monolayer and few-layer MoS2 over predefined spots on 20 nm silicon nitride membranes, and drilled pores of chosen size in them with a transmission electron microscope.[2] In 2015 the same group reported a second method that works in the electrolyte itself: an electrochemical reaction starts at a defect and removes atoms one at a time, and steps in the ionic current mark the growth of the pore.[3]
The material has a practical advantage over graphene. Pristine graphene pores interact strongly with DNA through hydrophobic forces and clog, so that they need coatings. MoS2 pores have been used for hours and days without them, and the sticking of DNA is reduced, according to the group, by a region rich in molybdenum around a pore drilled by the electron beam.[1]
The nucleotide experiment
DNA crosses a pore in a thin membrane at 3,000 to 50,000 nucleotides a millisecond, far too fast for a single base to be seen.[1] The group slowed it with a viscosity gradient: the upstream chamber held an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, and the downstream chamber 2 M aqueous potassium chloride. Bacteriophage λ DNA, which crossed a 20 nm pore in 1.4 ms in a plain aqueous system, took 130 ms in the gradient.
With a pore 2.8 nm wide the group passed short strands of a single base, each 30 nucleotides long, whose current drops formed four distinct peaks, and then single nucleotides. Each of dAMP, dTMP, dGMP and dCMP gave a distinguishable distribution of current, so that all four types were identified statistically, at speeds of 1 to 50 nucleotides a millisecond and a signal-to-noise ratio above 10 (see Signal-to-noise ratio).[1] This is the sense in which the work is cited. It is not a sequencing read: the nucleotides were loose molecules, one kind at a time, and a solid-state pore reading DNA base by base has not been published.
Beyond sensing
A sheet this thin also lets ions through quickly. In 2016 the group used a single MoS2 pore between solutions of different salt concentration as an osmotic generator, and estimated a power density of up to 106 W/m2, enough to run a transistor.[4]
At Molecular Reality
The company's pore simulator Nanopore Studio offers molybdenum disulfide as one of five membrane materials, with silicon nitride, graphene, glass and the silicone rubber PDMS, and lets water slip along its walls to a small degree.[5] The company's own pores are a different kind. A Juxtapore is a pore formed between two sliding surfaces (see Sliding occlusion), and the pore on the live molecular stream is the 200-micron laser-drilled pore, some 70,000 times wider than the 2.8 nm pore of the nucleotide experiment.
See also
References
- ^ a b c d e f Feng, J.; et al. (2015). "Identification of single nucleotides in MoS2 nanopores". Nature Nanotechnology 10 (12): 1070-1076. doi:10.1038/nnano.2015.219.
- ^ Liu, K.; Feng, J.; Kis, A.; Radenovic, A. (2014). "Atomically thin molybdenum disulfide nanopores with high sensitivity for DNA translocation". ACS Nano 8 (3): 2504-2511. doi:10.1021/nn406102h.
- ^ Feng, J.; et al. (2015). "Electrochemical reaction in single layer MoS2: nanopores opened atom by atom". Nano Letters 15 (5): 3431-3438. doi:10.1021/acs.nanolett.5b00768.
- ^ Feng, J.; et al. (2016). "Single-layer MoS2 nanopores as nanopower generators". Nature 536: 197-200. doi:10.1038/nature18593.
- ^ "Company records". Molecular Reality Corporation. October 2026.