Researchers at Tufts School of Engineering have developed a way to detect bacteria, toxins, and dangerous chemicals in the environment using a biopolymer sensor that can be printed like ink on a wide range of materials, including wearable items such as gloves, masks, or everyday clothing. It can even be embedded in drones to sense trace levels of airborne SARS-CoV-2, or it could be modified to adapt to whatever the next public health threat might be.

The sensor, which is based on computationally designed proteins and silk fibroin extracted from the cocoons of the silk moth Bombyx Mori, can also be embedded in films, sponges, and filters, or molded like plastic to sample and detect airborne and waterborne dangers, or used to signal infections or even cancer in our bodies.

These sensors are a big leap from other approaches to measuring pathogens or chemicals in the environment, which often rely on biological components that degrade quickly and require careful storage. The sensors also do not depend on electronic components that can be difficult to integrate into flexible wearable materials.

Figure 1. The molecular switch in the biopolymer sensor consists of a protein that acts like a lock and key. When a target molecule or pathogen (blue) binds to the switch, it uncovers the “lock” allowing a molecular key (red) to combine and form a complete luciferase enzyme (green) with the lock. Luciferase, found in fireflies and glowworms, can then emit a green light indicating the presence and quantity of the target. (Image: Modified from an illustration by Alfredo Quijano-Rubio, University of Washington)

To learn more about this, I interviewed two of the researchers, Fiorenzo Omenetto, Frank C. Doble Professor of Engineering and director of the Tufts Silklab, and Giusy Matzeu, a former research professor at the Silklab.

“Our sensing method can monitor in real time what’s happening in the environment. It can also detect what can occur in the human body by monitoring, in a non-invasive way, biological fluids like saliva or breath,” said Matzeu.

The active component of the biopolymer sensor, which was developed by David Baker, Henrietta and Aubrey Davis Endowed Professor in Biochemistry at the Institute for Protein Design at the University of Washington, is a molecular switch designed using molecular dynamics techniques and artificial intelligence. These molecular switches have been made of synthetic proteins that act like a lock and key, in a cage, and are sensitive to a particular analyte.

When a virus, toxin, or other target molecule comes near, it binds to the switch and opens the cage. Another part of the switch — a molecular key — can then fit into the lock, and the combination forms a complete luciferase enzyme, similar to the enzyme that lights up fireflies and glowworms. The intensity of the luminescence increases with changes in the concentration of the target molecule — the analyte.

Figure 2. You can distribute the sensing across an entire T-shirt. (Image: Andrea Izzotti/Adobe Stock)

In the more formal language of their paper published in the December 9th, 2022, issue of Advanced Materials: “In de novo designed protein switches, the sensing function is provided by the synergy of two designed protein components, the lucCage and the lucKey that can switch from a closed dark state to an open luminescent state in presence of an analyte. The resulting luciferase bioluminescence provides a rapid, specific, and sensitive readout of the analyte-driven lucCage-lucKey switch association.”

The molecular glow-switch is embedded in a mixture of naturally derived protein that is extracted from silk cocoons, called silk fibroin. The regenerated silk fibroin (RSF) is the inactive component of the biopolymer sensor, but has unique features, including the ability to be processed and manufactured using safe, water-based methods, and a remarkable versatility to be fabricated into different formats, such as films, sponges, and inks easily transferred onto surfaces through commercial printers. In addition, the silk fibroin stabilizes the molecular switch and greatly extends its shelf life.

Accelerated aging tests were performed on sensing sponges and films that were stored at 60 °C (140 °F) for four months and their responsiveness was analyzed after specific time intervals. Over the four-month time frame, the sensing performance of these formats (both sensitivity and dynamic range) was preserved. In addition, the stability of the sponges after storage for one year at room temperature was tested and they were found to be still responsive.

“If you mix the artificially designed protein switch with silk and give it the shape of a drone, of an ink, of a film, of whatever, it’s nontrivial that the sensing protein would still behave in the same way. And lo and behold, it does. Silk is the vehicle to stabilize the sensing protein-based molecule so you can give it the shape you want,” said Omenetto.

Figure 3. Breast pads functionalized with the RSF sensor ink can be used for the detection of HER2 in nipple discharge at concentrations as low as 20nM, which may be indicative of the presence of cancer. (Image: Fio Omenetto, Tufts university SilkLab)

Putting the Technology to Work

One of the significant benefits of this technology, according to Omenetto, is that you can distribute and localize the sensing interface onto wearable items, for example.

If you measured only one point, say the variation of an analyte recorded on your shoulder, it’s pretty useless. But if you distribute it all over your body, it gives an overall idea of what the physiology of your body is doing, and that’s valuable information. You’re taking something that is very simple and you’re distributing it everywhere so that the general information, the collective information, gives you meaningful data. “It’s kind of like, the ECG on your Apple Watch. It’s not as good as an ECG recorded in a hospital setting by a doctor, but it gives you your baseline, your trends, and your variations, which are very useful,” said Omenetto.

You make a particular sensing ink by developing a detecting “cocktail” that depends on the molecules you put in the silk-based mix. You add molecules that are designed to specifically target a certain analyte, then apply it to the substrate, which can be a mask, a glove, a sponge, or even a tapestry.

There is a library of options for different analytes. The library comes from research and development in the project, “…using the art of the Institute of Protein Design and David Baker’s work,” said Omenetto. “You target particular molecules and build, by molecular dynamics and artificial intelligence, a design that will have particular sensitivity to that analyte, and then synthesize a molecule that doesn’t exist in nature.”

In order to read the result, you spray the substrate embedding the silk-protein responsive pattern with the non-toxic chemical furimazine, which activates the photoluminescent response of the sensing area. The readout can be performed with a low-cost digital camera and/or smartphone app.

In their paper in Advanced Materials the authors point out that the RSF/protein solution can be specifically designed for other applications that differ from the aforementioned ones. For example, by using electrospinning, you can fabricate porous materials for face coverings or air filters that simultaneously monitor and protect against biological contamination in aerosols.

Another potential application they are investigating is to non-invasively monitor cancer through biomarkers present in certain biological fluids. For example, breast pads could be developed for early detection of breast cancer when spontaneous nipple discharge is present.

The Takeaway

One of the important takeaways from this research is, as Matzeu put it: “It’s all different roles and functions together coming into play — synthetic biologists, computer scientists, material scientists, and the designer of the interface. It’s about how different disciplines can come together to give you an end product. It’s a union of different people with different expertise and perspectives, it’s the cross-functional synergy of experts in different fields that can develop a unique sensing tool.”

This article was written by Ed Brown, editor of Sensor Technology. For more information go to here .