Xibus and Janus Particles – A Food Safety Sensor

Posted in Food Safety on April 20, 2019

What are Janus particles? And how is Xibus, a startup out of MIT, hoping to use them to create handheld food safety sensors that can quickly and cheaply identify pathogens like salmonella? Xibus and Janus Particles could change the future.

Janus particles are simple in theory: in their simplest form, they’re particles divided into two hemispheres with distinct properties. Their name is taken from the Roman god Janus; like the particles, he had two faces, with one looking forward into the future and the other looking backwards into the past. To this writer, the particles look not unlike the moon half-full, or a shot of the Earth from space: a sphere divided in half, with one face illuminated and the other in shadow.

Since they were conceived in the 1980s, Janus particles have been used for all sorts of things. They can self-propel through different mediums, they can kill of cancer cells when stimulated with a magnetic field, and they can act as stabilizers in emulsions of water and oil. If you can figure out how to make them from this substance or that, they’re capable of quite a lot.

What we’re interested in, however, are janus particles as tiny probes – nano-scale sensors which can help to identify different kinds of tiny things. If you’re looking for something in particular that’s too small to see, you can use a janus particle to do it.

The basic principle is this: one half of the janus particle is designed to attach to the thing that you’re looking for, whereas the other half isn’t. To find the thing, all you need to do is disperse a  bunch of those janus particles into a solution. They’ll find and attach themselves to whatever you’re looking for, creating a pattern that’s easily visible with image magnification. Just look for areas where there’s a concentration of the halves of the particles that aren’t designed to attach, as the other halves will have bound themselves to their target.

If that’s still a bit confusing for you, it might be helpful for us to return to a specific example: the food safety tech that we’re considering today. How is Xibus hoping to use Janus particles to improve food safety? According to a press release from MIT, the two hemispheres of their Janus particles are colored: one half is red, and the other half is blue. The blue tinted half is a fluorocarbon, and the red tinted half is a hydrocarbon.

That’s important: the specific compounds that are used in the Janus particles can be tuned to bind with the surface of particular organisms. Set one up to match with, say, salmonella, and you can tune it so that one half fits with the proteins on the outer membrane of the bacteria like a lock fits into a key.

It’s this highly particular affinity that distinguishes these droplets from the applications of janus particles that have come before. According to the the team that developed them at MIT, they could very well represent a quicker and cheaper way of identifying bacteria contaminants than methods that are already on hand or making their way towards the market. Most of those are relatively slow, and many of them require bulkier specialized equipment: if you don’t need a full lab, you at least need a sizeable device to do the imaging or DNA analysis that’s needed. If Xibus is successful, you could most of that work with an attachment to your smartphone or a handheld sensor that’s not much larger.

The advantages to such tech, then, would be rooted in the speed and portability that it could potentially offer. Janus particles can also give you a rough idea of how many bacteria are present, rather than simply tipping you off to the fact that they are present, which could be the difference between the odd pathogen and a highly concentrated colony of bacteria that’s very likely to make you sick.

What the team at Xibus hopes to do is provide a way for you to quickly identify whether or not broad categories of pathogens are present. That doesn’t mean that their promised technology is entirely without downsides. If you’re going for rapid identification as a kind of litmus test, it should work pretty well: should I eat this or should I not? Are there salmonella present or not? Those are important questions before you put a bite in your mouth.

The presence of a pathogen, however, is rarely the full story. Often, food safety investigators need to know a fair bit more than that. Getting a read of a given pathogen’s genetics is increasingly important to public health. Are you looking at E. coli that can produce shiga toxin, or E. coli that can’t? Is it resistant to any drugs that we know about? What degree of genetic similarity does it demonstrate to bacteria cultured from other people in the area? Are they similar enough to have come from a common source?

Right now, it looks like you’ll need to look elsewhere for a lot of that information, given that the janus droplets can’t be used to read DNA. Also unclear from the press release that MIT put out is how well the sensor will be able to read different types of pathogens: can the particles identify different serotypes of particular bacteria? Can they be dynamically programmed to detect different sorts of bacteria? If not, will the sensor have separate reservoirs or manufacturing capabilities to make or store the particles that are needed to detect different kinds of bacteria? Or will it be primarily be useful for detecting one kind, like salmonella?

We’re still waiting on a proof of concept, so the answers to those questions will likely come in time. Watch this space for more information about Xibus and Janus Particles and other emerging food safety technologies. And stay safe out there!

By: Sean McNulty, Contributing Writer (Non-Lawyer)