Microparticle turnstile

The microparticle turnstile was the name that Kent Kemmish gave to the arrangement into which one of demonpore, inc.'s adjustable pores was turned, in late 2018, the day after the first blood was put through it. The company's records list its result as "gating and oversampling of individual cells and nanoparticles" in January 2019.^[1] A turnstile is a gate that lets one person through at a time and registers each passage, and a Coulter counter registers each particle that crosses its hole as a pulse of current.

The setup began as the experiment that Kemmish calls the rain of blood. In late 2018, "completely on a whim as we were shutting down for the day", he took a razor blade and bled into the flow cell of a sliding occlusion pore, the first sample of anything that the team had put through one. "We ended up playing with this configuration for days," he wrote in 2026, "including turning it into a microparticle turnstile the next day."^[2] The records give the next entries as autonomous declogging of the pore in December 2018 and, in January 2019, the gating and oversampling.^[1]

Kemmish did not analyze the recordings for years. When he did, the question was "does this approach actually aid in distinguishing similar-sized particles?" The answer, in his words, was "yes", with the warning that "many hours of focused work would be needed to actually publish any of this in a convincing way."^[2] By October 2026 the company had published no paper on the recordings.^[1]

Both words of the company's record have counterparts in its other documents. The patent for sliding occlusion describes a stack of membranes, each with a hole, whose channel can be narrowed or closed by sliding one of them, and says that the arrangement could allow "gated passage of the molecule". It lists analytes "from single atoms up to entire cells".^[3] Oversampling is measuring one analyte more than once. The patent calls its version "the so-called 'ping-pang' oversampling approach", and the company's overview of December 2022 describes passing a molecule back and forth through the sensing zone, a method "literally called 'ping-pong' by some workers".^[3][4]

Fixed pores can be made to do this with the voltage. In 2007 a group showed that reversing the voltage as soon as a DNA molecule had crossed a solid-state pore pulled the molecule back through, so that the same molecule could be captured and measured again.^[5] The turnstile did it with a gate. The company's later page Molecular Self-Play animates the same cycle of trapping, sensing, releasing and repeating, and one of its phases is a "mechanical grab, no voltage flip".^[6]

The company's website carries a short animation of the turnstile. It is a GIF, 640 by 720 pixels, of 114 frames played over 11.4 seconds, and it loops without end.^[1] The upper half is a dim microscope view: a dark region on the left, a lighter orange one on the right, and a rounded object at their edge. Below it, on a grid like an oscilloscope screen, runs a yellow trace drawn in sweep mode: a cursor moves from left to right and overwrites the older trace behind it, a long flat level followed by a dip and a recovery, with a row of square pulses. The row has one pulse when the clip starts and about a dozen when it ends. It has the layout of the company's video "Cellular transit control" (2 minutes 32 seconds), which its catalog describes as split-screen microscopy of a silicon nitride pore beside current traces recorded in real time.^[7][1]

In the company's field guide the turnstile appears as a simile for water. The guide's answer to the question "How small is nano, really?" gives a human hair as about 80,000 nanometers thick and DNA as about 2 nanometers wide, puts the company's pores at a few nanometers to a hundred, and ends: "Water molecules pass like a crowd through a turnstile."^[8]

• Coulter principle
• Resistive pulse sensing
• Ping-pong sensing
• Complete blood count