Device Quickly Detects Live Bacteria for Life-Saving Diagnosis

A new device from scientists at McGill University’s Department of Bioengineering allows early and quick detection of life-threatening bacteria.

by John Tibbetts
September 10, 2018

Clinicians could diagnose dangerous infections in minutes with a new “lab on a chip” device that snags living bacteria on branches of nanosized “shrubs.” 

Bacterial infections—such as pneumonia, meningitis, and salmonella—produce symptoms similar to many viral ones. But bacteria are capable of reproducing very rapidly, and it can take several days to confirm a bacterial infection with current tools, allowing infections to grow. Bacterial infections are blamed for 700,000 deaths a year.

Scientists at McGill University’s Department of Bioengineering developed a device that allows early and quick detection of bacteria and an antibiotic-resistant bacterial strain in small samples, potentially allowing clinicians to make life-saving diagnoses, says Sara Mahshid, an assistant professor. As a proof of principle, this lab on a chip is the first integrated device to capture and quantifiably detect live bacteria with high efficiency.

The Mahshid Lab, collaborating with colleagues from the University of Toronto, designed an analysis chamber with particular surface characteristics. The innovative rough surface includes numerous shrub-shaped 3D “islands.”  Each island, about one-tenth of the thickness of a single human hair, can ensnare individual bacteria within a continuous flow of culture solution. The fabricated gold nanostructures are electrodeposited to tuneable roughness.

“The nanostructures on the surface have several protrusions—or branches—that are sharp enough to entangle live bacteria but not so sharp that they penetrate the bacterial membranes and kill them,” she says.

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The device allowed researchers to identify cultures of live bacteria such as E. coli within minutes and capture methicillin-resistant-Staphylococcus aureus (MRSA) and image this strain after an hour’s incubation period. The team recently published their work in the journal Small.

The device achieved an average 93 percent of probe-free capture of E.coli bacteria. “For food safety applications, we need a testing method that proves that bacteria present in potentially contaminated food are characterized accurately and are still alive,” Mahshid says. 

The device includes three parallel fluidic compartments with separate inlets and outlets, allowing bacteria and buffer solutions to flow in and out. The researchers connect the device to a syringe pump and inject the solution at a controlled flow rate.

“We load the fluid sample into the analysis chamber—the detection platform—and as soon as the bacteria attach to these structures, they are trapped,” she says. “With a fluorescent microscope, we can see individual and distinct fluorescent-tagged bacteria, and this allows us to offer a quantitative measurement in just a few minutes.”  

The researchers designed a nanopore filter at the interface between the analysis chamber and its outlet. “The nanopores are fine enough that the liquid can pass through, but they don’t allow bacteria to escape,” she says. “The nanofilter allows us to have a continuous flow of solution without washing away the bacteria.”

In order to specifically detect the MRSA strain from other strains, the researchers developed a method of locating and identifying a particular protein on the surface of the bacteria. “We used an antibody that is specific to that protein and it becomes caught and immobilized on the surface of the nanostructures because of the surface roughness.”

After an incubation period, the researchers can optically check whether or not the bacteria have become attached to the antibody. If the bacteria attach, the presence of the MRSA strain is confirmed.

“Clinicians have told us that they find this technology attractive,” she says. “We can tune the protocol and make the surface islands sharper or needle shaped, and smoother, for different applications. The technology could be used to different types of targets such as fungi.”

“Manufacturing this device would not be difficult at all, but the most important thing is to bring it into the hands of clinicians,” she adds. The team plans to collaborate with McGill Interdisciplinary Initiative in Infection and Immunity to test patient samples from urine, blood, and nasal cavities. “We also plan to use this device to identify the resistance of bacteria to antibiotics.” 

John Tibbetts is an independent technology writer.

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