An electronic sensor that can be used to quickly detect and classify bacteria for diagnostic and food safety has passed a key hurdle by distinguishing between dead and living bacterial cells. Conventional lab techniques need samples be cultured for hours or days to grow enough of the bacteria for identification and analysis. This 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 of Purdue University. “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.
The sensor works by detecting changes in electrical conductivity in droplets containing bacteria cells. “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 this proposed osmoregulation-based detection of bacteria. Needless to say, immediate physiological measurement is faster and far superior.”
Bacteria cells maintain the proper internal pressure through osmoregulation, a process in which water, salts and other molecules move across the cell membrane. As a droplet begins to evaporate on the sensor, bacteria cells contained in the droplet detect the increasingly salty environment, triggering emergency valves called osmoregulatory transporters in the cell membrane. The cells then either take in or release water and charged molecules including salts, changing the electrical conductivity of the surrounding fluid in the droplet, which is measured by electrodes. This change in electrical conductivity varies according to whether a bacteria cell is dead or alive and also might be used to identify specific types of bacteria because they use fundamentally different osmoregulatory channels.
The researchers have received a provisional patent on the concept through the Purdue Research Foundation’s Office of Technology Commercialization.