Picture an electric guitar played unplugged—its faint melody barely audible—until it’s connected to an amplifier. Similarly, low concentrations of toxins and biomolecules in water or the human body emit signals too weak to detect without specialized lab technology. Thanks to a clever trick in biochemistry, Northwestern University researchers have turned up the "volume" on these faint signals, opening doors for groundbreaking applications in environmental safety and human health monitoring.

By adapting their ROSALIND biosensing platform, already used for detecting water contaminants, the team achieved a 10-fold increase in sensitivity. This enhancement allows the detection of nucleic acids like DNA and RNA, as well as bacteria such as E. coli, at concentrations previously undetectable. Their findings, published recently in Nature Chemical Biology, demonstrate how amplified signals can turn everyday tools into powerful diagnostic devices.

“Biosensors repurposed from nature can, in principle, detect a whole spectrum of contaminants and human health markers, though they’re often not sensitive enough as is,” said Julius Lucks, professor of chemical and biological engineering at Northwestern and co-director of the Center for Synthetic Biology. “By adding genetic circuitry that acts like an amplifier, we can make this biosensing platform meet sensitivity levels needed for application in environmental and human health monitoring.”

Engineering a "Pregnancy Test for Water"

ROSALIND’s origins stem from a bold ambition: to create a biosensor capable of analyzing a single drop of water. The platform’s earlier models could detect 17 contaminants and glow green when a substance exceeded EPA safety standards. The second version brought a step-change improvement, enabling the quantification of contaminant concentrations—an upgrade that transformed ROSALIND from a simple diagnostic tool into something much more versatile.

The system relies on cell-free synthetic biology, where molecular machinery like DNA, RNA, and proteins are extracted from cells and reprogrammed to perform specific tasks. This approach not only simplifies biological processes but also increases the flexibility and scalability of biosensors for diverse applications.

Harnessing a "Bug" for Signal Boosting

A breakthrough came when the team reconsidered the role of T7 RNA polymerase, a notoriously tricky enzyme that, while essential for signal generation, also degrades RNA circuits. Traditionally seen as a nuisance, this "bug" became the key to amplifying weak signals.

By leveraging a method from DNA nanotechnology, the researchers introduced a feedback loop where the enzyme consumes and recycles signals, creating a cascade effect. The result? Molecules such as heavy metals and antibiotics can now be detected at concentrations significantly lower than previous iterations allowed.

“We created a new system to amplify signals in ROSALIND,” said first author Jenni Li, a Ph.D. candidate in the Lucks lab. “Due to a cool trick in biochemistry, this lets us sensitize the system to detect compounds at lower levels without changing the actual biosensor protein. This is all done in nucleic acid circuits. ROSALIND 3.0 is now more sensitive and can detect nucleic acids when it could previously only detect small molecule compounds.”

The Evolution of ROSALIND

ROSALIND’s new capabilities are already making an impact. In the Chicago area, earlier versions of the platform are being used in a field study to detect lead in drinking water. The latest iteration, dubbed "ROSALIND 3.0," has even broader applications, including health monitoring, food quality assessment, and agricultural safety.

“We are also developing ROSALIND to detect human health markers, food quality markers, and agricultural compounds, opening up what this platform technology can be used for,” said Lucks. “This new sensitization approach is general, meaning that we will more quickly be able to develop sensors that can detect compounds at actionable levels in the future.”

From Faint Signals to Big Impacts

By transforming a frustrating enzyme into an asset and amplifying weak signals with ingenious biochemical hacks, the Northwestern team has positioned ROSALIND as a next-generation biosensing tool. Whether safeguarding public water supplies, diagnosing disease, or monitoring food and agriculture, the platform’s potential grows with each iteration.

The new advancements bring a world of unseen threats—once hidden in the noise of weak signals—into sharp focus, making the invisible both detectable and actionable.