Bringing Some Coulter To The Bench: Measuring Tiny Particles With Nanopore Sensing

We’ve all been there: you’re sitting at your bench, with a beaker full of some conductive fluid with a bunch of tiny particles suspended in it, and you want to measure the sizes of each particle.

Okay, maybe this isn’t a shared experience we’ve all had, but It’s at least an ordeal Hackaday alum [Nava Whiteford] has been through, and he was able to carry out the measurements in question using a neat apparatus known as a Coulter counter.

Imagine a container full of a conductive fluid. If you place an electrode at each end, the fluid will carry a current. Now, drop an insulating divider in the middle of the container, and the current will stop flowing. Finally, poke a small hole (or nanopore) in the divider. Huzzah! The current is flowing again… but how does this let us measure particle sizes? Well, now think about a tiny particle moving through the hole in the divider. As the particle passes through, the hole will be partially blocked, and the current flow will be partially interrupted. It turns out, the resulting dip in current is proportional to the volume of the particle — a fun property known as the Coulter principle.

[Nava] built a great demo of the system with a macropore in place of the nanopore. The pore in question was a hole melted into a bottle cap, which was suspended in a beaker by two toothpicks. [Nava] used small chips of Acrylic as the particles to be measured, which they pipetted into the solution of KCl. They then passed a current through the solution and used an oscilloscope to sense the interruptions. Be sure to check out their write up for a video of the system in action!

Of course, this technique has a much wider range of applications than measuring little bits of plastic — obtaining blood cell counts, for one. We’ve seen particle counters for use in the air before, but it’s great to see that there’s a way to measure particles in an aqueous solution —  you know, in case we ever find ourselves in such a situation.

Unknown Quantum Effect Makes Insulator Oscillate

If there are two classes of matter that electronics people can agree on, its conductors and insulators. Electrically, conductors and insulators don’t have much in common. The same has held true in the quantum physics world until some research at Princeton has suggested that quantum oscillation — a phenomenon associated with metals — is taking place in an insulator. Scientists aren’t sure what’s really happening yet, but it may suggest there is a new quantum particle yet to be discovered.

In metals, electrons are very mobile which allows a relatively easy flow of electrical current. However, at low temperatures, a magnetic field can shift electrons to a quantum state causing its resistance to change in an oscillating pattern. Insulators generally do not exhibit this effect.

Researchers made a monolayer of tungsten ditelluride using the same kind of adhesive tape process you see to create graphene. In bulk, the material is a conductor but in a monolayer, tungsten ditelluride is an insulator.

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LUX Searches In The Deep For Dark Matter

The Homestake Mine started yielding gold in 1876. If you had asked George Hearst, the operator at the time, if the mine would someday yield the secrets of the universe I bet he would have laughed you out of the room. But sure enough, by 1960 a laboratory deep in the mine started doing just that. Many experiments have been conducted there in the five and a half decades since. The Large Underground Xenon (LUX) experiment is one of them, and has been running is what is now called the Sanford Underground Research Facility (SURF) for about four years. LUX’s first round of data was collected in 2013, with the experiment and the rest of the data slated to conclude in 2016. The method, hardware, and results wrapped up in LUX are utterly fascinating.

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