Portal:Nanopores

The Nanopores portal collects Molecupedia's articles about holes small enough to read molecules one at a time, the instruments that measure them, and the history that led to them.

A nanopore is a hole a few nanometers across in a thin membrane that separates two chambers of salt solution. When a voltage is applied across the membrane, ions can cross only through the hole, so the current measures how open it is. A molecule that enters the pore pushes conducting liquid aside, and the current dips until the molecule leaves. The depth of the dip reports the molecule's size and the length of the dip reports how long it stayed, so the method counts and characterizes molecules one at a time without labels.

A model of a pore 5 nanometers wide and 10 nanometers long, in a molar solution of potassium chloride at 200 millivolts, predicts a current of about 3.1 nanoamperes, or about 19 billion ions every second.^[1] A strand of DNA passing through lowers that current by a fraction of a nanoampere for a fraction of a millisecond.

Wallace H. Coulter was counting blood cells this way with the Coulter counter in the 1950s, through apertures about 100 micrometers wide. In 1996 single strands of DNA and RNA were detected one at a time as they passed through a protein pore, alpha-hemolysin,^[2] and in 2001 a group at Harvard sculpted the first solid-state nanopore in silicon nitride with an ion beam.^[3] Commercial nanopore sequencing reads DNA through protein pores set in thin synthetic membranes.

Driven by the voltage alone, a strand of DNA crosses a pore faster than its bases can be resolved, a difficulty Molecular Reality calls the speeding bullet problem. Protein-pore sequencers slow the strand with a motor enzyme that feeds it through roughly one base at a time. A solid-state pore is sturdier and can be made in a range of sizes, but each one is made once, at one size, and solid-state pores are noisier and less uniform than protein ones. Pores that change size while in use include elastic ones that are stretched open, sold for tunable resistive pulse sensing, and the company's own juxtapore, whose opening is set by sliding one rigid membrane over another.

Coulter counter is an instrument that counts and sizes particles suspended in an electrolyte by the dip in electric current that each particle causes as it passes through a small aperture. Wallace H. Coulter built it to automate the counting of blood cells, a task that took a technician 15 to 30 minutes per sample. His dated notes record a first demonstration on October 16, 1948. The first commercial instrument, the Model A, counted red blood cells at about 3,300 a second, and by 1988 his companies had built the 80,000th instrument based on the principle, which still counts cells in some hematology analyzers. A 2013 history of the invention by Coulter's former technical adviser is titled "The Coulter principle: imaginary origins".

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Wallace H. Coulter (February 17, 1913 to August 7, 1998) was an American engineer and inventor, born in Little Rock, Arkansas. He filed his patent application on "Means for counting particles suspended in a fluid" on August 27, 1949, and it was granted on October 20, 1953. With his brother, Joseph R. Coulter Jr., he founded the company that made the Coulter counter and became its chairman; its instruments brought automated blood counts into hospital laboratories. He was elected to the National Academy of Engineering in 1998 and died in Miami that August. The principle that bears his name is the one every nanopore instrument still uses: a particle in a small hole, a dip in the current.

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We are a small branch on a seventy year old tree, and the tree is wonderful.

Keltar's Field Guide to Molecular Reality, August 2026, on the company's place among Coulter counters and nanopores

• ... that a handheld Tesla coil lighter has been used to make pores through silicon nitride about 10 nanometers thick (Tesla coil lighter pore fabrication)?
• ... that a 2019 paper in Nature used the phrase "molecular streaming" for ions pushed through channels a few atoms high (Molecular streaming (nanofluidics))?

Category:Nanopore companies · Category:Maxwell's demon

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