Jump to content
[dismiss]
Molecupedia is a parody encyclopedia written by Molecular Reality Corporation. It is not Wikipedia and is not affiliated with the Wikimedia Foundation. About

Glass nanopipette

Page protected
From Molecupedia, the encyclopedia of very small things
Pulled glass capillary used as a conical nanopore

A glass nanopipette, also called a nanocapillary or glass nanopore, is a glass or quartz capillary that has been heated and pulled until it tapers to a tip with an opening of tens of nanometers. Dipped in salt water with an electrode in the barrel, it is a single conical solid-state nanopore whose current can be recorded like that of any other pore. A tip is made on a bench-top puller and needs no clean room.

The pulling is the technique of the micropipettes of the patch clamp, which Hamill and colleagues described in 1981, carried to much smaller tips.[1] The scanning ion-conductance microscope of 1989 used a pulled pipette to follow a surface by the current through its tip.[2]

Fabrication

Quartz pipettes are pulled with a carbon dioxide laser. Sutter Instrument, whose P-2000 is the laser puller in common use, says that the wavelength of the laser "approximates the resonant frequency of the SiO2 lattice in glass", which lets quartz melt, and lists electrode tips smaller than 0.03 µm.[3] The capillary is held at both ends, the laser heats its middle, and a programmed pull draws it into two tapered halves, each with a tip.

The Cambridge laboratory whose pores read the DNA barcodes pulls quartz capillaries of 0.5 mm outer and 0.2 mm inner diameter, and gets tips of 15 ± 3 nm measured by scanning electron microscopy.[4] In a later study the pores were 14 ± 3 nm wide, with a cone half-angle of 0.05 radians, about 3°.[5] The spread of ±3 nm on 14 nm is a fifth of the diameter. Pulling a capillary with two barrels, called theta glass, makes two pores side by side, and for one laboratory they were 23 ± 9 nm wide and 20 ± 2 nm apart.[6]

Electrical behavior

A curve rising steeply from the tip of a cone to 50% of the total resistance at 140 nanometers, 90% at 1.3 micrometers and 99% at 14 micrometers
Share of the resistance of a conical tip, 14 nm across with a half-angle of 0.05 radians, that lies within a given distance of its end. Calculated from the model in the text.

The current through a cone is set almost wholly by its end. For a tip of radius r0 and half-angle θ in a solution of conductivity σ, the resistance of the cone is 1/(πσ r0 tan θ), and the access resistance outside the opening adds 1/(4σ r0). For the 14 nm pore above in 1 M potassium chloride (11 S/m) these are 83 MΩ and 3 MΩ, which would pass 2.3 nA at 200 mV. Half of the cone's resistance lies within 140 nm of the tip, nine tenths within 1.3 µm and 99% within 14 µm. The sensing region is therefore far longer than that of a pore in a membrane tens of nanometers thick, and a 7.2 kbp DNA carrier is 2.5 µm long, more than the 1.3 µm that holds nine tenths of the resistance. The authors of the 2017 study describe the pore as having a "longer effective sensing length".[5]

Quartz is negatively charged at neutral pH, and the cone is asymmetric, so the current at one polarity exceeds the current at the other. Wei, Bard and Feldberg described this rectification for quartz nanopipette electrodes in 1997.[7] In 100 mM potassium chloride the ratio of the currents at −600 and +600 mV was 1.56 for the pores of a double-barrel pipette, which the authors note is consistent with negatively charged glass pores.[8] See Ion current rectification.

Uses

In 2005 single DNA molecules labeled with nanoparticles were detected with a nanopipette by the blockades they caused as they crossed the tip.[9] Since then the pipettes have read the folding of lambda DNA, in tips as narrow as 45 nm, and have carried the barcoded carriers of Bell and Keyser.[10] One laboratory grafted aptamers on such carriers and screened proteins in human serum.[11]

Pipettes also make small spaces. Cadinu and colleagues pulled a pair of pores 20 nm apart and held a molecule between them in a droplet of about 63 zeptoliters. Events of 5 kbp DNA lasted a mean of 0.13 ms in a single pore and up to 100 ms in the bridge, a slowdown of up to three orders of magnitude, which they credit with improving the signal-to-noise ratio and resolution.[8] The same laboratory reported a gain of more than two orders of magnitude in dwell time in the double-barrel design of 2018, with transfers from one pore to the other at nearly 100% efficiency.[6] Outside a conical pore the electroosmotic flow reverses below 1 mM salt, an effect measured with such tips.[12]

At Molecular Reality

The test bed of the company's machine-learning experiments is the barcode dataset recorded in the Cambridge glass pores. Its own pores have been chips, among them the 200-micron laser-drilled pore on its stream.[13]

See also

References

  1. ^ Hamill, O. P.; Marty, A.; Neher, E.; Sakmann, B.; Sigworth, F. J. (1981). "Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches". Pflügers Archiv 391 (2): 85-100. doi:10.1007/BF00656997.
  2. ^ Hansma, P. K.; Drake, B.; Marti, O.; Gould, S. A. C.; Prater, C. B. (1989). "The scanning ion-conductance microscope". Science 243 (4891): 641-643. doi:10.1126/science.2464851.
  3. ^ "P-2000 Laser-Based Micropipette Puller". Sutter Instrument. Retrieved October 25, 2026.
  4. ^ Bell, N. A. W.; Keyser, U. F. (2015). "Specific protein detection using designed DNA carriers and nanopores". Journal of the American Chemical Society 137 (5): 2035-2041. doi:10.1021/ja512521w.
  5. ^ a b Bell, N. A. W.; et al. (2017). "Asymmetric dynamics of DNA entering and exiting a strongly confining nanopore". Nature Communications 8: 380. doi:10.1038/s41467-017-00423-9.
  6. ^ a b Cadinu, P.; et al. (2018). "Double barrel nanopores as a new tool for controlling single-molecule transport". Nano Letters 18 (4): 2738-2745. doi:10.1021/acs.nanolett.8b00860.
  7. ^ Wei, C.; Bard, A. J.; Feldberg, S. W. (1997). "Current rectification at quartz nanopipet electrodes". Analytical Chemistry 69 (22): 4627-4633. doi:10.1021/ac970551g.
  8. ^ a b Cadinu, P.; et al. (2017). "Single molecule trapping and sensing using dual nanopores separated by a zeptoliter nanobridge". Nano Letters 17 (10): 6376-6384. doi:10.1021/acs.nanolett.7b03196.
  9. ^ Karhanek, M.; et al. (2005). "Single DNA molecule detection using nanopipettes and nanoparticles". Nano Letters 5 (3): 403-407. doi:10.1021/nl0480464.
  10. ^ Steinbock, L. J.; et al. (2010). "Detecting DNA folding with nanocapillaries". Nano Letters 10 (7): 2493-2497. doi:10.1021/nl100997s.
  11. ^ Sze, J. Y. Y.; Ivanov, A. P.; Cass, A. E. G.; Edel, J. B. (2017). "Single molecule multiplexed nanopore protein screening in human serum using aptamer modified DNA carriers". Nature Communications 8: 1552. doi:10.1038/s41467-017-01584-3.
  12. ^ Laohakunakorn, N.; Thacker, V. V.; Muthukumar, M.; Keyser, U. F. (2015). "Electroosmotic flow reversal outside glass nanopores". Nano Letters 15 (1): 695-702. doi:10.1021/nl504237k.
  13. ^ "Company records". Molecular Reality Corporation. October 2026.
Retrieved from "https://molecularreality.com/wiki/Glass_nanopipette"
Last edited 2 hours ago by Ionophore