Electronic sensor that tells dead bacteria from live by measuring ‘osmoregulation’ is potential future tool for medicine and food safety

A new type of electronic sensor may lead to devices that detect and classify bacteria for medical diagnostics and food safety. (Purdue University photo/Aida Ebrahimi)

A new type of electronic sensor that might be used to quickly detect and classify bacteria for medical diagnostics and food safety has passed a key hurdle by distinguishing between dead and living bacteria cells.

Conventional laboratory technologies require that samples be cultured for hours or longer to grow enough of the bacteria for identification and analysis, for example, to determine which antibiotic to prescribe. The new approach might be used to create arrays of hundreds of sensors on an electronic chip, each sensor detecting a specific type of bacteria or pinpointing the effectiveness of particular antibiotics within minutes.

“We have taken a step toward this long-term goal by showing how to distinguish between live and dead bacteria,” said Muhammad Ashraful Alam, Purdue University’s Jai N. Gupta Professor of Electrical and Computer Engineering. “This is important because you need to be able to not only detect and identify bacteria, but to determine which antibiotics are effective in killing them.”

Findings are detailed in a research paper appearing this week in Proceedings of the National Academy of Sciences. The paper was authored by doctoral student Aida Ebrahimi and Alam. The droplet sensor evolved from a device originally designed to detect small concentrations of negatively charged DNA molecules in research that began about four years ago, Ebrahimi said.

“We did not anticipate that the sensor could be used to tell live and dead bacteria apart – it was a chance observation that eventually led us to this elegant way of measuring cell viability,” she said.

As described in the PNAS paper, the sensor works by detecting changes in electrical conductivity in droplets containing bacteria cells. (A YouTube video about the research is available at https://youtu.be/QN019bQJCb8).

“To see if someone is alive,” Alam said, “we can either count the grandchildren many generations later, which is analogous to the traditional growth-based techniques. Or, we can directly measure the person’s pulse, analogous to the proposed ‘osmoregulation-based’ detection of bacteria. Needless to say, immediate physiological measurement is faster and far superior.”

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