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The Most Sensitive Bioelectronic Ammonia Gas Sensor Ever Made

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May 14 2020

A team of researchers from the University of Massachusetts Amherst has reported in the Nano Research journal that they have developed the most sensitive bioelectronic ammonia gas sensor to be ever made.

Protein nanowires (light green) harvested from Geobacter (background) are sandwiched between electrodes (gold) to form bioelectronic sensor for detection of biomolecules (red). Image Credit: Photo courtesy of University of Massachusetts Amherst/Yao lab.

The new sensor makes use of electric-charge-conducting protein nanowires that were obtained from Geobacter bacteria to supply biomaterials for electrical devices.

Derek Lovley, microbiologist and the study’s senior author, discovered the Geobacter in river mud more than three decades ago. The microorganisms develop hair-like protein filaments that function as nanoscale “wires” to interact with other pathogens and to transfer charges for their nourishment.

Alexander Smith, biomedical engineering doctoral student and the study’s first author, along with his advisor Jun Yao and Lovley, informed that they have developed this pioneering sensor to quantify ammonia, which is crucial for biomedicine, agriculture, and the environment.

For instance, humans’ breath contains ammonia that may indicate a disease, whereas in poultry farming, the same gas had to be controlled and closely monitored to ensure the health and comfort of birds and to prevent production losses and feed imbalances.

Yao stated, “This sensor allows you to do high-precision sensing; it’s much better than previous electronic sensors.”

Every time I do a new experiment, I’m pleasantly surprised. We didn’t expect them to work as well as they have. I really think they could have a real positive impact on the world.

Alexander Smith, Study First Author and Biomedical Engineering Doctoral Student, University of Massachusetts Amherst

Smith added that modern electronic sensors usually have low or limited sensitivity, and they are likely to be subjected to interference from other kinds of gases. Apart from the low cost and the excellent function, he added that “our sensors are biodegradable so they do not produce electronic waste, and they are produced sustainably by bacteria using renewable feedstocks without the need for toxic chemicals.”

Over the past 18 months, Smith performed the experiments as part of his PhD work. Lovley’s previous studies had disclosed that the conductivity of the protein nanowires altered in response to pH—that is, the base or acid level—of the solution surrounding the protein nanowires.

This pushed the scientists to test the concept that the protein nanowires may be highly reactive to the molecule binding for biosensing. “If you expose them to a chemical, the properties change and you can measure the response,” Smith observed.

When Smith exposed the protein nanowires to ammonia, “the response was really noticeable and significant,” Smith added. “Early on, we found we could tune the sensors in a way that shows this significant response. They are really sensitive to ammonia and much less to other compounds, so the sensors can be very specific.”

Lovley added that the “very stable” nanowires last for a longer time, the sensor works robustly and reliably after prolonged usage for months, and functions so well that “it is remarkable.”

These protein nanowires are always amazing me. This new use is in a completely different area than we had worked in before.

Jun Yao, Assistant Professor, University of Massachusetts Amherst

Earlier, the researchers had reported that they have used protein nanowires to harvest energy from humidity and apply them as memristors for biological computing.

Smith, who refers himself as “entrepreneurial,” secured the first place in the University of Massachusetts Amherst’s 2018 Innovation Challenge for the startup business plan for the firm he established with Yao and Lovley—e-Biologics.

The team has followed up with plans that involved business development, fundraising, patent application, and research and development.

This work is the first proof-of-concept for the nanowire sensor. Once we get back in the lab, we’ll develop sensors for other compounds. We are working on tuning them for an array of other compounds.

Derek Lovley, Study Senior Author and Microbiologist, Department of Microbiology, University of Massachusetts Amherst

The study was financially supported by a CAREER grant and Graduate Research Fellowship from the National Science Foundation, University of Massachusetts Amherst’s Office of Technology Commercialization and Ventures, and the campus’s Center for Hierarchical Manufacturing—an NSF-funded Nanoscale Science and Engineering Center.