For the latest in biosensing innovation, look no further than the quiet corners of your backyard. Those dew-covered spiderwebs may soon emerge as sentinels in the fight against airborne viruses. Dr. Jiangtao Cheng, an associate professor in the Department of Mechanical Engineering at Virginia Tech, has embarked on a mission to harness this unexpected player. Armed with an international grant from the United States-Israel Binational Science Foundation (BSF), Dr. Cheng seeks to harness the potential of bio-inspired technology to create an early warning system for pathogens, including the notorious COVID-19.

Sensing with Droplets

Dr. Cheng's extensive research portfolio weaves together the intricacies of microscale and nanoscale fluids with cutting-edge optical technologies, including lasers. His prior triumphs include the development of fluid droplet-laser synergy for rapid COVID-19 identification and pioneering advancements in optical device creation.

Over two decades of scrutinizing fluid behaviors at the tiniest scales, Dr. Cheng saw a unique opportunity to capitalize on fluid properties. Liquid droplets, spherical and adhesive, refract and trap light. In a breakthrough discovery, his team unveiled the potential to exploit these three properties together to transform a single water droplet into a biosensor.

But how does it work? The stickiness of a water droplet enables it to capture particles drifting in the surrounding air, which either lodge themselves inside the droplet or adhere to its surface. At the micro and nanoscale, the water droplet transforms into a transport carrier for a wide array of bacteria, viruses, and even dust mites.

Once these hitchhiking passengers embark on their watery journey, Dr. Cheng's team found that a laser directed into the droplet can reveal their identities. Once it hits the surface, the laser reflects and bounces around inside the droplet, much like a pinball, gathering passenger data as it travels. When this data reaches the team, it can be translated into a comprehensive account of the contents of the droplet.

Spiderweb Sentinels

Deploying this method on a large scale for practical applications presented a formidable challenge. Gathering data from individual water droplets proved impractical due to their size. Even in confined spaces, deploying one laser per droplet would demand a colossal laser array and, consequently, substantial energy and resources. 

Dr. Cheng's team found inspiration in the delicately condensed dew droplets adorning spiderwebs. Not only are these misty spiderwebs a sight to behold, but they also harbor unique scientific properties. Their silk serves as an excellent carrier for the optical beams employed by the team, so not only can they hold the dew droplets for catching analytes, but the intricate web structure also acts as a conduit for the laser's information data. In synergy, the silk waveguide and the droplets fashion a seamless sensing system on the spiderweb platform.

To heighten detection sensitivity, the team then turned to attracting more analyte particles into the droplets. While the tiny liquid collectors excel at holding on to these particles, the droplets' small size limits their ability to reach out and grab a substantial number of target analytes from their surroundings. This is particularly important when trying to detect sparsely distributed pathogens. To tackle this hurdle, the team will mount a small electrode nearby that can charge the airborne particles, making them automatically attracted to the webbing. This method significantly enhances collection rates and bolsters the detection of previously more diluted analytes.

Bio-Inspired Webs with 3D Printing

The team now has its sights set on several critical objectives. Foremost is the 3D printing of spiderwebs by marrying organic and synthetic materials. Employing a fluid enclosed within a polymer shell enables the creation of a pliable and resilient web. The shell molds the web's shape, anchoring water droplets in their designated positions. Ultraviolet curing provides stability and flexibility, and both materials conduct light effectively, resulting in a durable environment for sensing.

This goal involves the development of a novel system to 3D print both the shell and the fluid simultaneously. However, while this is in the works, the team employs a more intensive process, consisting of the construction of a hollow web shell, infusing it with fluid, and subsequent application of UV curing.

Designed to cradle a multitude of water droplets, these webs must be meticulously engineered to ensure water is held in appropriate positions for capturing airborne analytes. The webs will also be designed such that the optical beam will travel easily throughout the structure and return to a sensor, delivering fingerprint data effectively.

Once the synthetic webs have been fabricated, the researchers will scrutinize the captured analytes. Collaborating with Dr. Cheng's team, Dr. Qiang Le, an associate professor at Hampton University, is crafting a smartphone app to deliver these results, laying the groundwork for deploying real-time alerts through 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.”