Fluoride, lead, and pesticides are a few examples of environmental toxins that occur both outside and inside of us. Researchers can easily assess these pollutants’ quantities in lab settings, but testing their levels outdoors is far more challenging. This is due to the fact that they demand pricey specialist equipment.
Cellular biosensors have recently been used in synthetic biology projects to detect and report environmental toxins in a practical and affordable way. Scientists have struggled to find a solution to the problem of how to shield sensor components from chemicals that naturally occur in extracted samples despite advancements.
At Northwestern University, a multidisciplinary group of synthetic biologists is creating a sensor platform that will be able to identify a variety of environmental and biological targets in real-world samples.
The scientists discovered that by enclosing the sensor behind a fatty membrane, they could both protect the sensor and make it function more like a cell while also creating a biosensor for fluoride.
Researchers showed how they could further fine-tune and manage the function of their sensor by altering the composition and penetrability of the lipid bilayer membrane in a new work that was published today (January 4, 2023) in the journal Science Advances.
“So much data is being generated, and a lot of it is being driven by health apps like smart watches,” said Julius Lucks, a co-corresponding author and professor of chemical and biological engineering at Northwestern’s McCormick School of Engineering. “We can sense our heartbeat, our temperature, but if you think about it, we really have no way to sense chemical things. We’re living in an information age, but the information we have is so miniscule chemical sensing opens enormous dimensions of information that you can tap into.”
Lucks is also the associate chair of the chemical and biological engineering department. By researching RNA and its function in cells, how RNA is used by cells to sense changes in their environment, and how these concepts can be used within cell-free systems to monitor the environment for sustainability and health, his lab has advanced the field’s understanding of molecular systems that respond to environmental changes.
We can sense our heartbeat, our temperature, but if you think about it, we really have no way to sense chemical things. We’re living in an information age, but the information we have is so miniscule chemical sensing opens enormous dimensions of information that you can tap into.
Julius Lucks
Cell-free synthetic biology, which substitutes artificial biomolecular systems for living cells to activate biological machinery, is appealing because to its effectiveness, adaptability, and affordability.
Lucks designed a riboswitch sensor using bacterial cell extracts to power gene expression reactions (including fluorescent RNA or protein that lights up in response to contaminants) that produce visual outputs cheaply and within minutes.
Neha Kamat, an assistant professor of biomedical engineering within McCormick and a co-corresponding author, originally met Lucks at their faculty orientation and was interested in his desire to expand access to information.
Kamat, whose expertise is in engineered membranes and membrane assembly, wondered if she could make Lucks’s test tube system better using a vesicle, a membrane with two layers.
“They’re using RNA and its associated machinery to sense molecules in real water samples and generate meaningful outputs,” Kamat said. “My lab works a lot with the lipids commonly used to encapsulate mRNA for drug delivery, with the goal of using these compartments to build more cell-like structures. We had the idea that we could protect Julius’s switches and allow them to work in samples that might be kind of dirty with other contaminants like a cell can.”
Since it’s challenging to fit everything inside the tiny container and then scale it up, other researchers have attempted to embed a sensor inside a membrane, but the switch stopped functioning properly and produced a considerably smaller signal. To overcome this, the team modified the genetic output in the sensor to amplify and color it, so it’s visible by eye, and “you don’t need a fancy detector to do it,” said Lucks.
To function in its natural surroundings, such as a wastewater channel with many other toxins that could degrade the switch, the sensor needs to be enclosed and protected. This is an illustration of “distributed sensing,” which can help in industries like agriculture and health care.
The group came together more officially when they received Northwestern’s Chemistry of Life Processes Institute’s (CLP) Cornew Innovation Award by pitching their “potentially disruptive” idea to the CLP’s advisory board. The team earned seed funding to get their idea off the ground.
Lucks calls this project a “jumping off point” from which they will be able to embed sensors into more materials, including “smart” materials that can change properties, as in biology.
“As synthetic biologists, one of our major themes is identifying challenges and looking to nature,” Lucks said. “What is it doing already? Can we build off that and make it do more to meet our needs?”
Fluoride was an obvious choice because a natural RNA molecule can detect it, which allowed the scientists to create a more straightforward method. However, Kamat and Lucks have big plans for how the utilization of the sensors can develop in the future.
For instance, before the sensor is retrieved through urine or another passive way, the sensors could flow through the human body to identify tiny chemicals and biomarkers. It could also detect levels of nitrate in soil and aid in monitoring run-off.
Beyond that, Lucks and Kamat are enthusiastic about applications in materials science like soft robotics, considering how to create something resembling a butterfly that can detect odors through its feet.
The CLP, the National Science Foundation (grant numbers 1844219, 1844336, and 2145050) and the U.S. Department of Defense National Science and Engineering Graduate Fellowship supported the paper, “Robust and tunable performance of a cell-free biosensor encapsulated in lipid vesicles.” Margrethe A. Boyd and Walter Thavarajah (of Northwestern) were also co-authors on the study.
