Just about everyone enjoys the sweet tastes associated with candy, cookies, and freshly squeezed orange juice. However, what one person tastes and enjoys may be wildly different than the next, resulting in opinions on sweets being too much or just right depending on who you ask. Due to the subjectivity of sweetness perception, companies have spent a significant amount of resources with the focus of creating objective sweet-tasting sensors to aid new product development marketable to different sweet teeth.
This objective was only a vision until recently, where a group of researchers at ACS Applied Materials & Interfaces has been developing an ultra-sensitive bioelectric tongue that mimics the effects of human taste buds. These tongues have allowed for work focused on more objective measurements to begin but are still limited by complex factors including manufacturing difficulty, or issues fully replicating how the human tongue works. Tongues have a wide range of taste receptors that detect salty, sour, and most importantly those sweet foods we enjoy by binding compounds like sugars. The outermost part of one of these complicated structures is known as the Venus flytrap domain due to its hinged and lobed molecular structure that is like the leaves of the insectivorous plant that close when ingesting insects like flies. It is this domain that tends to interact with and binds to sweet substances.
Previously, Hyun et. al applied this concept to umami sensors that had human-like performance for umami detection. However, this utilized the proteins found at the end of human umami taste receptors but proved a hopeful concept for future sensors. Using this previously established work, the researchers wanted to apply this concept to make these sweet-sensing bioelectronic tongues, utilizing the Venus flytrap domain as the electronic form of human taste buds. To do so, the researchers attached copies of the Venus flytrap domain produced by bacteria into a thin-layer gold electrode. Multiple gold-electrodes were then connected using electrically conductive carbon nanotubes, which produced an effective field-effect transistor capable of electrical signal amplification (Figure 1).
Figure 1. Bioelectronic sensor structure, schematic, and sweetness detection through current decreases.
With this device in place, solutions of naturally sweet sucrose or artificial saccharin were applied to the device. This resulted in decreased currents, which signified the sensor was responding to these solutions. Most interestingly, these responses were detected down to the 0.1 femtomolar level, which is almost 10 million times more sensitive than previous efforts at sweet sensor technologies. With this proof of concept, the group further found the sensor could detect real sweetness levels in drinks such as apple juice and sucrose-sweetened teas. In contrast, the sensors showed no response to tasteless sugars like cellobiose or monosodium glutamate (MSG), indicating the ability of the detector to detect sweet-tasting sugars sensitively and selectively.
The development of this new sweet-tasting bioelectronic tongue has allowed for a significant leap towards industry driven goals for sweet-tasting in product development, surmounting any previous methodologies. Additionally, the group has suggested these selective and sensitive sensors will see powerful applications in future health care and pharmaceutical applications, paving the way for more smart sensing technologies that mimic complex human processes in an objective fashion.
The findings of this research have been published in the Journal of ACS Applied Materials and Interfaces: Jeong, J. Y.; Cha, Y. K.; Ahn, S. R.; Shin, J.; Choi, Y.; Park, T. H.; Hong, S. Ultrasensitive Bioelectronic Tongue Based on the Venus Flytrap Domain of a Human Sweet Taste Receptor. ACS Appl. Mater. Interfaces. 2022, 14 (2), 2478–2487. https://doi.org/10.1021/acsami.1c17349.
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