Inkjet printers could produce paper sensors that identify dangerous food and water contaminants

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Ordinary inkjet printers can be given a special cartridge containing DNA-based bio-ink that produces paper sensors patterned after the codenames of pathogens (Image: McMaster University)

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Sensors that identify infectious disease and food contaminants may soon be printed on paper using ordinary office inkjet printers. Researchers at McMaster University have developed a prototype that could lead to a commercial product in the next few years which helps doctors and scientists in the field quickly detect certain types of cancer or bacterial and respiratory infections or monitor toxin levels in water.

The new paper-based technology builds on prior work by the same team. In 2012 they used specialized inkjet printers to produce paper strips that change color in the presence of E. coli. The strips detected a particular enzyme inside the bacteria and so were limited to only that one use.

The new technology is far more versatile. Like its predecessor, it can detect E. coli, but it can also identify other bacteria such as Salmonella and Clostridium difficile. Its versatility comes from a change in underlying technology. The new strips use small man-made DNA molecules called DNA aptamers. According to McMaster's Biointerfaces Institute director John Brennan, these aptamers can bind to virtually any target (not only small molecules but also proteins and cells).

The new sensors are also much simpler to produce. "Our original E. coli sensor required a very sophisticated ink-jet printer and very specialized inks in order to be produced," Brennan told Gizmag. "We have found that these specialized requirements have made scale up and manufacturing challenging. The new test uses a very simple 'ink' composition and a basic office printer to produce the test strips, meaning that it should be much easier to scale up and manufacture."

The researchers came up with a biochemical processing method that allows them to generate very large DNA molecules with many thousands of nucleotides. Whereas small DNA molecules moved from where they were printed, but these large DNA molecules are effectively too big to move. The main benefit here is that they can print multiple markers.

"In the published paper, we detect ATP (adenosine triphosphate), which is a marker of bacterial contamination, and PDGF (platelet derived growth factor), which is a marker for cancer," Brennan explained. "We can print the letter 'A' for ATP and 'P' for PDGF, so that the letter encodes the compound detected. This allows us to do something we call multiplexing, where we can use any combination of letters or symbols to allow detection of many different targets on a single test strip."

The researchers foresee their paper strips helping doctors to quickly diagnose illnesses and scientists to inspect food or environments for toxins. Brennan notes, however, that they cannot currently test drinking water because an additional regulatory requirement to detect "culturable organisms" (organisms that can grow and/or proliferate) to ensure there is no more than one organism per 100 ml of water. Their current detection sensitivity is more in line with the needs of beaches, swimming pools, and other recreational water facilities.

The strips are unlikely to be commercially available for at least another three years, Brennan estimates. The researchers need to put their technology through FDA and Health Canada approvals and to do clinical and field trials. But once ready, they say that it could find hundreds of possible applications in fields where quick answers about the presence of pathogens could save lives.

A paper describing the research was published in the journal Chemistry.

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