An electrochemical sensor that can quickly determine whether or not a urinary tract infection (UTI) is caused by bacteria could become the newest weapon against antibiotic resistance.

Researchers at McMaster University in Canada have developed a test on a chip that uses synthetic nucleic acid probes – RNA-cleaving DNAzymes (RCDs) – for detection Escherichia coli. “This is the first example of a DNAzym test combined with an electrical indicator that is assessed and detected using clinical samples,” said Leyla Soleymani, one of the scientists who led the study. Since the test does not require a bacterial culture, it provides results in less than an hour.

A photo of a small plastic cup containing a urine sample with a plastic pipette leaning against it.  Next to it are two small transparent plastic parts and a cell phone that is put in a small black box

The test goals E. coli because it causes the vast majority of urinary tract infections, explains Soleymani’s colleague Yingfu Li. It usually takes more than 18 hours to diagnose a bacterial infection, adds Soleymani, which means doctors may not prescribe the most effective antibiotics – a hotbed for the formation of more antibiotic-resistant ones Bacteria. If the tests were faster, doctors could be more accurate.

That’s why researchers used to develop faster tests. For example, some systems have used the polymerase chain reaction to detect the bacteria’s genetic makeup – but these approaches are complex and costly.

Now the researchers built on RCD sensors that had previously been developed by Li’s team. His group has a library of synthetic DNA molecules from which they can choose those that recognize certain substances. The RCDs are self-cleaving oligonucleotides that contain a DNA barcode that they release when they recognize their target substance. The new sensor uses RCDs that identify molecules that are released when urine samples are heated E. coli. The RCDs release DNA barcodes that are bound to methylene blue dye molecules and that electrochemical biosensors can recognize.

Li, Soleymani and their colleagues attached their RCDs to a star-shaped, nanostructured electrode on a small chip that contains liquid samples. If a solution that contains molecules by E. coli reaches the electrode, the RCDs release their barcodes and generate an electrical signal. The barcodes diffuse to another nearby star-shaped electrode that contains a sequence of DNA designed to bind to them, creating another electrical signal. This electrochemical test has “a really high sensitivity”, says Soleymani, also thanks to the large surface of the nanostructured electrodes.

Peiying Hong from King Abdullah University of Science and Technology in Saudi Arabia notes that the system has a high signal-to-noise ratio. That ‘enables them to differentiate E. coli in a coherent way compared to the other bacterial non-targets, ”says Hong. She notices that the test is unusual in that it has an electrical output instead of changing color. “You can read the results right from a portable app or electronic device,” notes Hong. “However, the device can only perform qualitative measurements because the signals do not react linearly to the increase in bacterial load.”

The McMaster team now wants to expand the system to analyze several different bacteria, including antibiotic-resistant ones, says Soleymani. “We’re also looking for a commercialization partner to bring this test to market,” she adds.

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