Newswise — The dew-covered spiderweb you see in your yard might soon become a platform to detect airborne viruses. This is the objective of Jiangtao Cheng, associate professor in the Department of Mechanical Engineering, who has received an international grant from the United States-Israel Binational Science Foundation (BSF) to build bio-inspired technology that could serve as an early warning system for pathogens such as COVID.
Droplets as sensors
Cheng has built a deep research portfolio in combining fluids at the microscale and nanoscale with optical technologies such as lasers. Past projects have included the combination of fluid droplets and lasers to quickly identify COVID-19 and novel methods of creating advanced optical devices.
After more than two decades studying fluid behaviors on the smallest scales, Cheng saw some unique opportunities to capitalize on fluid properties. Liquid droplets are both spherical and sticky and they also refract and trap light. A few years ago, his team published findings about potentially exploiting all three properties together to transform a single water droplet into a biosensor.
How would this be done? A water droplet, because of its stickiness, traps particles circulating in the ambient air around it. Those tiny bits may become lodged inside the drop or adhere to its surface. At the microscale and nanoscale, that water becomes a transport carrier for all manner of bacteria, viruses, and even dust mites.
Once a droplet’s passengers hitch their ride, Cheng’s team found that a laser could be directed into the droplet to determine what the passengers are.
Lasers aren’t just light shows, they can also collect and deliver data containing fingerprint-like information of analytes. When a laser hits a water droplet, the spherical roundness and refraction property causes internal reflection that bounces around inside the droplet like a pinball and then exits with all the passenger data it has gathered. When team members receive this data, they can translate the information to tell them in real time what the laser discovered.
Sensing on spiderwebs
How can this method be deployed over a large area for real applications? Because water droplets are small, collecting data from each one is highly impractical. Deploying one laser per droplet even in a small space would require a massive laser array, backed by an incredible amount of energy and cost. The team needed to develop a method using a single laser receiving sufficient data from an array of droplets.
Looking to nature, Cheng’s team employed the naturally condensed dew droplets on spiderwebs. Not only are misty spiderwebs beautiful, but they also contain unique scientific properties. Their silk is an excellent carrier for the optical beams Cheng’s team uses, and the interconnected web structure serves as a ready-made network to both carry a laser’s information data and hold the dew droplets on the web for catching airborne analytes. The silk waveguide and the droplets work as a single unit, forming the sensing system on the spiderweb platform.
To enhance detection sensitivity, the team also needed a way to get more analyte particles into the droplets. While the tiny liquid collectors do a great job of holding onto the particles, the droplets are still small and unable to reach out and grab enough target analytes from their surroundings. For detection of sparsely distributed pathogens, the team’s droplet detector had to get more of the pathogens.
To solve this problem, the team will mount a small electrode nearby that can charge the airborne particles, making them automatically attracted to the webbing. Cheng’s team found that this method can provide higher collection rates and higher detection of the initially diluted analytes that would have otherwise been more widely spread.
Bio-inspired webs with 3D printing
Cheng’s team has several objectives with the funding provided by BSF.
The first objective is to 3D print webs. Cheng's bio-inspired spiderweb is made from a combination of organic and synthetic materials. To create a soft and flexible web, the team uses a fluid encapsulated inside a polymer shell. The shell holds the shape of the web and keeps water droplets in place, while the fluid is cured with ultraviolet light to make the web stable and flexible. Both materials are excellent optic conductors, equating to a durable engineered environment for sensing.
Part of the project includes a new system for 3D printing the shell and the fluid at the same time, but, for now, the team will start by making a hollow web shell, injecting the fluid, and then curing it.
Because the webs need to hold a significant amount of water droplets, the team's will be engineered to hold water in certain positions, ensuring more droplets will be present for capturing airborne analytes. The webs also will be designed such that the optical beam will travel easily throughout the structure and return to a sensor, delivering fingerprint data effectively.
After the team has fabricated its synthetic web, the researchers will analyze the captured analytes. Qiang Le, an associate professor at Hampton University, is partnering with Cheng’s team to produce a smartphone app that delivers the results, laying the groundwork for the ability to deploy alerts to a campuswide safety network.
"Since this web is portable and deployable in both residential and ambient environments, it can become essential in environmental protection, infectious diseases monitoring, forensic science and global safety,” said Cheng. “Each deployed spiderweb sensor can provide real-time information for the health and safety of all. We are looking forward to seeing how it works when it’s deployed.”
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