Northwestern University synthetic biologists have developed a low-cost, easy-to-use, hand-held
device that can let users know — within mere minutes — if their water is safe to
drink.
The new device works by using powerful and programmable genetic networks, which mimic
electronic circuits, to perform a range of logic functions.
Among the DNA-based circuits, for example, the researchers engineered cell-free molecules
into an analog-to-digital converter (ADC), a ubiquitous circuit type found in nearly
all electronic devices.
In the water-quality device, the ADC circuit processes an analog input (contaminants) and
generates a digital output (a visual signal to inform the user).
The research was published in the journal Nature Chemical Biology.
Equipped with a series of eight small test tubes, the device glows green when it detects
a contaminant.
The number of tubes that glow depend upon how much contamination is present.
If only one tube glows, then the water sample has a trace level of contamination.
But if all eight tubes glow, then the water is severely contaminated.
In other words, the higher concentration of contamination leads to a higher signal.
Northwestern’s Julius B. Lucks, who led the research, says that the tube with the
lowest threshold will light up all the time.
If all the tubes light up, then there is a big problem.
Building circuits and programmable DNA computing opens up many possibilities for other types
of smart diagnostics.
The new system builds off work that Lucks and his team published in Nature Biotechnology
in July 2020.
In that previous work, the team introduced ROSALIND, which could sense 17 different contaminants
in a single drop of water.
When the test detected a contaminant exceeding the U.S Environmental Protection Agency’s
standards, it either glowed green or not to give a simple, easy-to-read positive or negative
result.
To develop ROSALIND, Lucks and his team employed cell-free synthetic biology.
With synthetic biology, researchers take molecular machinery — including DNA, RNA and proteins
— out of cells, and then reprogram that machinery to perform new tasks.
At the time, Lucks likened ROSALIND’s inner workings to “molecular taste buds.”
Now, in the new version — dubbed ROSALIND 2.0 — Lucks and his team have added a “molecular
brain.”
Lucks says that the initial platform was a bio-sensor, which acted like a taste bud.
Now they have added a genetic network that works like a brain.
The bio-sensor detects contamination, but then the output of the bio-sensor feeds into
the genetic network, or circuit, which works like a brain to perform logic.
Researchers freeze-dried the reprogrammed “molecular brains” to become shelf-stable
and put them into test tubes.
Adding a drop of water to each tube sets off a network of reactions and interactions, ultimately
causing the freeze-dried pellet to glow in the presence of a contaminant.
To test the new system, Lucks and his team demonstrated that it could successfully detect
concentration levels of zinc, an antibiotic and an industrial metabolite.
Giving the level of contamination — rather than a simple positive or negative result
— is important for informing mitigation strategies.
The researcher says that different contaminants at different levels require different strategies.
If we have a low level of lead in our water, for example, then we might be able to tolerate
it by flushing our water lines ahead of using them.
But if we have high levels, then we need to stop drinking our water immediately and replace
our water line.
Ultimately, Lucks and his team hope to empower individuals to test their own water on a regular
basis.
With inexpensive, hand-held devices like ROSALIND, that may soon become a reality.