The outbreak of H5N1 avian influenza virus in the US is now 1 year old. The virus, commonly known as bird flu, has wrought havoc in the agricultural sector and prompted a dramatic increase in the price of eggs. But technical methods to rapidly and accurately detect infections are relatively limited—polymerase chain reaction methods can take up to a day to return a result, while conventional electrochemical sensors often lack sensitivity and require chemical labels and additional external reagents to generate a detectable signal.
To improve detection and monitoring, Rajan Chakrabarty and colleagues at Washington University in St. Louis have created a capacitive biosensor capable of continuously detecting H5N1 in the air. The team reports that the sensor detects the presence of the virus at concentrations of as little as 56 viral particles per cubic meter, well below an infectious dose (ACS Sensors 2025, DOI: 10.1021/acssensors.4c03087).
Capacitive sensors work by measuring a change in the properties of an electrode when a pathogen binds to it. To do that, a carbon electrode is coated with a support matrix and a layer of conductive, polarizable molecules. This outer layer is functionalized with antibodies specific to the pathogen target, enabling the microbe to stick to the sensor. As the pathogen binds to the sensor surface, it perturbs the electron distribution in the polarizable layer, resulting in a change in capacitance that can be used to calculate the concentration of the infectious agent. But the devices are not always very sensitive.
“The limitation with these biosensors in the past has been the change in capacitance,” explains Chakrabarty. “The reaction has to be such that you should be able to detect trace changes in the capacitance value, even if you have one virus particle.”
To improve the sensitivity for the new sensor, the team used a codeposition approach to construct a robust graphene oxide backbone dotted with interlocked molecules of highly polarizable Prussian blue, creating an extremely redox-responsive surface layer. The researchers then placed this functionalized chip into a microwave-sized portable device.
The team tested the device using aerosolized inactivated viruses to evaluate the performance of the sensor unit. The machine sampled the air continuously, providing a readout every 5 min, and successfully detected both H5N1 and Escherichia coli at concentrations below each’s infectious dose.
As yet, Chakrabarty’s team has not tested the new device in the field, but the researchers are currently working with biotechnology companies to adapt and scale the sensor for real-world applications. Postdoctoral researcher Ren Ren from Imperial College London, who was not involved in the work, is optimistic about the potential of this device but agrees that stress-testing to ensure the sensor surface can tolerate genuine agricultural air samples will be a vital step toward advancing this work to commercialization.
“This is a promising study addressing a significant challenge in respiratory pathogen detection. While the biosensor demonstrates promising sensitivity and specificity in controlled laboratory conditions, a potential weakness lies in the use of graphene oxide, which is known to have a high affinity for various biomolecules,” he explains in an email. “Further testing in realistic environmental settings is crucial to fully evaluate its practical applicability.”