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). Image: Alfredo Quijano, University of Washington.
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). Image: Alfredo Quijano, University of Washington.

Researchers at Tufts University 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. These include wearable items such as gloves, masks and everyday clothing.

Using an enzyme similar to that found in fireflies, the sensor glows when it detects these otherwise invisible threats. The researchers report this new technology in a paper in Advanced Materials.

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

The researchers demonstrated how the sensor emits light within minutes when it detects various pathogens and molecules. These included the SARS-CoV-2 virus that causes COVID, anti-hepatitis B virus antibodies, the food-borne toxin botulinum neurotoxin B and human epidermal growth factor receptor 2 (HER2), a biomarker for breast cancer.

Once exposed, the sensor requires a quick spray with a non-toxic chemical. If the target is present, the sensor generates light, with the intensity of the emitted light providing a quantitative measure of the concentration of the target.

“The combination of lab-designed proteins and silk is a sensor platform that can be adapted to detect a wide range of chemical and biological agents with a high degree of specificity and sensitivity,” said Fiorenzo Omenetto, professor of engineering at the Tufts University School of Engineering, and director of the Tufts Silklab, where the bio-responsive materials were developed. “For example, SARS-CoV-2 and anti-hepatitis B antibodies can be measured at levels that approach clinical assays.”

The sensing element is modular, so developers can swap in newly designed proteins to capture and measure specific pathogens or molecules, while the light emitting mechanism remains the same. “Using the sensor, we can pick up trace levels of airborne SARS-CoV-2, or we can imagine modifying it to adapt to whatever the next public health threat might be,” Omenetto said.

He noted that, although it’s in a conceptual stage, using the biopolymer sensor to detect breast cancer is a particularly interesting application. His team created a proof-of-concept silicone bra pad that when worn can absorb secreted fluid and report the levels of HER2 hormone, thus providing an indication of whether breast cancer may be present. “While further development will be required to improve and clinically validate the assay, the opportunity for such diagnostics in everyday garments is certainly compelling,” Omenetto said.

The sensors can assume a seemingly endless variety of forms. To demonstrate this, the research team created viral-sensing drones by embedding the sensor material in their fuselage. During flight, the propellers direct airflow through the porous body of the drone, which can be examined after landing. The drones, which in the example reacted to airborne pathogens (SARS-CoV-2), could be used to monitor environments from a remote, safe distance.

The active component of the biopolymer sensor, which was developed by David Baker at the Institute for Protein Design at the University of Washington, is a molecular switch made of proteins that act like a lock and key, but with a cover. When a virus, toxin or other target molecule comes near, it binds to the switch and opens the cover to reveal the lock. Another part of the switch – a molecular key – can then fit into the lock, with this combination of lock and key forming a complete luciferase enzyme, similar to the enzyme that lights up fireflies and glow worms. The more virus, toxin or other chemical that binds to the sensor, the brighter the glow.

This molecular glow-switch is embedded in a mixture of a protein derived from silk cocoons called silk fibroin, which is the inactive component of the biopolymer sensor. Nevertheless, silk fibroin has several unique features, including the ability to be processed and manufactured using safe, water-based methods, and a remarkable ability to be fabricated into different materials, including films, sponges and textiles, or dispersed onto surfaces through an inkjet printer. Additionally, the silk fibroin stabilizes the molecular glow-switch and greatly extends its shelf life.

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

The Tufts researchers tested the shelf life of materials embedded with SARS-CoV-2 sensors by storing them at 60°C for four months, and found very little change in their performance. The breast cancer sensor shaped into a sponge was kept on the shelf at room temperature for one year, and still performed near its original sensitivity.

“This means we can manufacture, distribute and store these sensing interfaces for long periods of time without losing their sensitivity or accuracy, and without the need for refrigerated storage, which is remarkable due to the fact that they are made of protein,” said Luciana d’Amone, a graduate student in Omenetto’s lab, who co-led the project with Giusy Matzeu, a research professor at Tufts’ Silklab.

This approach could make sensors widely available in different formats. “For example, you could make surgical masks capable of detecting pathogens, package them in boxes and use them over time just like conventional masks,” said d’Amone. “We also showed that you can print the sensor inside of food packaging to track spoilage and toxins. You can modify so many products that we use every day to include sensing, and store and use them as you normally would.”

The Tufts research team envisions a wide range of applications for these biopolymer sensors, ranging from personal and patient monitoring and infection control in healthcare settings to environmental sensing in home, workplace, military and disaster settings.

This story is adapted from material from Tufts University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.