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Bioelectronic Nose and Tongues by Interfacing Sensory Proteins with Electronic Devices

Bioelectronic Nose via the Hybridization of Human Olfactory Receptor Proteins with a Carbon Nanotube-based Electronic Device
(Advanced Materials 21 91 2009)

   One of our research interests is focused on interfacing sensory proteins with electronic devices, for fundamental studies on human sensory systems and the development of artificial sensors for practical applications. From a microscopic point of view, a human sensation is evoked by the response of sensory receptor proteins to a stimulus. Therefore, researches on the activities of the sensory proteins can open up various applications in drug and food industries. In our research, various sensory proteins are incorporated on the surfaces of electronic devices based on various nanomaterials such as carbon nanotubes (CNTs). In the bioelectronic hybrid system, the binding of specific target molecules onto the sensory proteins can be electrically monitored utilizing the underlying electronic devices, which can be used for the quantitative evaluation of target molecules. Thus, the hybrid system of receptor proteins and nanoelectronic devices can be utilized as versatile platforms for artificial sensor devices mimicking real sensory systems, enabling versatile applications such as drug and food screening. It also allows us to study the operation mechanism of sensory receptor proteins, offering various opportunities for basic researches on animal sensory systems.

  Following are a few examples of our researches on bioelectronic devices.

 1) Bioelectronic Nose

Bioelectronic Nose for the Discrimination of a Specific Odorant with a Single Carbon Atomic Resolution
(Advanced Materials 21 91 2009)

  We developed a bioelectronic nose via the hybridization of human olfactory receptor 2AG1 (hOR2AG1) with a carbon-nanotube field-effect transistor (CNT-FET). The hOR2AG1 is known to be activated by amyl butyrate (AB). In the bioelectronic nose, lipid membranes containing the olfactory receptors were coated on the surface of the CNT-FET. When the odorant (AB) binds to the receptor (hOR2AG1), the state of the receptor shifts to an active state, resulting in an electrostatic perturbation on the CNT channel. Thus, the binding of the odorant molecules to the receptor proteins can be electrically monitored via the underlying CNT-FET. Using the bioelectronic nose, we could selectively discriminate the specific odorant from other odorants with a single-carbon-atomic resolution. Artificial sensors based on our bioelectronic nose enable overcoming the poor sensitivity limitations of previous chemical sensors and allow one to monitor a sensory-receptor operation in real time.

 2) Bioelectronic Tongue

Bioelectronic Tongue for the Evaluation of Umami Tastant
(ACS Nano 9 11728 2015)

  We developed a strategy for measuring the activity of gustatory receptor 10 of Apis mellifera (AmGr10), by utilizing a CNT-based transducer. The AmGr10 is specifically tuned to L-amino acids including umami tastants such as L-monosodium glutamate (MSG). Since an excessive exposure to MSG may cause health problems such as numbness and headache, the evaluation of MSG is an important issue. We developed a bioelectronic tongue for the detection of umami tastants. In this device, we incorporated nanovesicles containing AmGr10 on a CNT-FET with floating electrodes. The floating electrode structure allowed us to improve the sensitivity of conventional CNT-based sensors. The bioelectronic tongue recognized MSG not only in pure buffer solutions but also in real foods such as chicken stock. Remarkably, we also quantitatively investigated a synergism between MSG and disodium 5’-inosinate (IMP), well-known enhancer of umami taste, via the bioelectronic tongue. The synergistic effects of IMP strongly enhanced the response of AmGr10 to MSG. Our bioelectronic tongues could be an effective strategy in various research areas about sensory systems.

3) Array of Bioelectronic Noses and Tongues

Multi-Channel-Type Bioelectronic Sensor Array for the Simultaneous Analysis of Food Quality
(Biosensors and Bioelectronics 87 901 2017)

  We developed a portable and multiplexed bioelectronic sensor based on the hybridization of human olfactory and taste receptors with a multi-channel type CNT-FET. Here, olfactory and taste receptors were immobilized on the surfaces of the CNT channels with uniform orientations using nickel-histidine reactions. The channels of the CNT-FET were divided by a splitter fabricated using a 3D printer. The sensor array allowed us to simultaneously and electrically distinguish individual target molecules, indicators of food contamination, in mixtures. This approach also enabled us to simultaneously measure the target molecules even in real foods such as beef and pork. For on-site applications, the device can be portably used with a customized current measurement system. Therefore, this multiplexed bioelectronic sensor array can be an efficient tool for the quality assessment of diverse foods and for various on-site detections.