By attaching human olfactory receptors to a graphene-based sensor, researchers have created a bioelectronic nose platform for detecting a nerve agent to address biosecurity risks and support medical crisis management. So-ong Kim from Seoul National University and Sung Gun Kim from Samsung Electronics led a team of researchers in making a bioelectronic nose with the human olfactory receptor 2T7 (hOR2T7) to detect dimethyl methylphosphonate (DMMP), a compound that is often used in nerve agents.

The research article, “Ni-rGO Sensor Combined with Human Olfactory Receptor-Embedded Nanodiscs for Detecting Gas-Phase DMMP as a Simulant of Nerve Agents,” was published in ACS Sensors.

Gas sensors for security and military applications require important attributes, including trace-level sensitivity in the ppm to ppb range, selectivity for discrimination, fast response, simple operation, large-scale production, miniaturization, and low power consumption. Bioelectronic noses are biosensors with functions and components similar to human olfactory sensing systems, such as human olfactory receptors. These large families of G protein-coupled receptors (GPCRs) act as detectors for several molecules at the interface between chemical compounds and biological sensing. Human olfactory receptors can be made cheaply and in large quantities with E. coli, and when they are combined with nanomaterials like graphene, they can be more sensitive to target molecules while keeping their affinity for them.

Previous research has shown that when hOR2T7 is used with a carbon nanotube field effect transistor, it can detect DMMP after it has been reconstituted using detergent micelles, which are stable colloidal aggregates of detergent monomers with the non-polar ends tucked inward. Unfortunately, it was limited to detecting ligands in a liquid medium rather than a gaseous one.

To detect DMMP in the gas phase, the researchers synthesized hOR2T7 in the E. coli system and then reconstituted it as nanodiscs for this study. Nanodiscs, comprised of human olfactory receptors, lipids, and a membrane scaffold protein tightly binding the lipids and receptors, have been chosen as the best material for gas sensors because of their increased stability in various conditions. By making a sensor from nickel-coated reduced graphene oxide (Ni-rGO) and properly oriented hOR2T7 nanodiscs, gas-phase DMMP could be detected sensitively and selectively. They showed that the bioelectronic nose could detect DMMP gas selectively and repeatedly at a concentration of one part per billion (ppb). Sarin gas, one of the most toxic nerve agents, causes death within 10 minutes of inhaling at a concentration above 66 ppb.

This sensitive and selective bioelectronic nose can be a practical tool for detecting gaseous chemical warfare agents in military and safety fields. Further studies are needed to explore its utilization in practical fields, including detecting DMMP gas in air at different humidity and temperature levels, as well as conducting the tests with real nerve agent tests such as sarin gas. Nevertheless, this technology can offer a promising strategy for developing specific sensors for nerve agent gases with the high sensitivity and selectivity of human olfactory receptors.

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