Changing E. coli detection with electrical signals and droplets

Lab on a chip

By Jarrett Whitson

Shiga toxin-producing E. coli, or STEC, causes more than $342 million in annual economic losses nationwide, according to the U.S. Department of Agriculture.

Kuan-Lun Ho wants to solve that.

Ho, doctoral student in mechanical and nuclear engineering in the Kansas State University Carl R. Ice College of Engineering, is making STEC testing more accessible and more efficient throughout the beef industry in Kansas and beyond.

Ho works under the guidance of faculty mentor Shih-Kang “Scott” Fan, professor in the Alan Levin Department of Mechanical and Nuclear Engineering. Ho is researching the application of digital polymerase chain reaction, or dPCR, testing and digital microfluidics, or DMF, for the detection of STEC.

Beginning with a bulk droplet from a beef culture broth containing PCR reagents and STECs, Ho places them onto a DMF chip that he helped create. Next, he applies electrical signals to make many tiny droplets and move them into microwells before applying more electrical signals of different frequencies to trap the STECs in the microwells.

“A lot of people can use microwells on their device but our specialty is that we can apply the electrical signals to the droplets,” Ho said. “That means we can use the electrical signals to capture the specific type of E. coli we want and distinguish between live and dead STECs.”

That’s important because the researchers want to target live STECs that can make people sick or even die.

“The diagnostic method — traditional PCR — cannot differentiate between live and dead STECs,” Ho said. “Traditionally, people need to perform an additional culture step to ensure there are enough viable STECs for detection. However, we do not require a culture step and can detect live STECs on our platform.”

Another important aspect of Ho’s research is multiplex digital PCR. This uses chemicals in a PCR reagent, called primers and probes, designed to give a fluorescent signal during the reaction. Ultimately, this allows Ho to design different colors for different types of E. coli and makes it easier to detect STEC.

“Kuan-Lun showed significant improvements and aims to implement a novel lab-on-a-chip technique to enrich food safety and health care,” Fan said.

Ho is also part of a NASA-funded project that is studying radiation-induced cancer biomarkers. The project is a NASA Established Program to Stimulate Competitive Research, or EPSCoR, grant that also involves other researchers at Kansas State University, Wichita State University and the University of Kansas Medical Center.

Ho is using DMF chips to manipulate cell-containing hydrogels and media for cell culture, specifically cultured liver and colon cells, to study the effects of radiation.