It has been reported that around 27 million COVID-19 patients have suffered long-term loss of their sense of smell and taste. Ageusia also affects patients undergoing therapy for nasopharyngeal cancer, which impacts more than 130,000 people each year. These figures – and the daily challenges of taste impairment – motivated Weijun Deng and colleagues at the Shanghai Institute of Technology, China, to design an artificial tongue capable of assisting patients with food selection and taste-recovery training. Their first target: detecting spiciness.
“Spicy, or pungency, taste sensation is essential for food selection for both humans and animals,” says Jing Hu, the research group leader at East China University of Science and Technology. “A tongue with pungency sensation works as an interface of protection by alerting potential threats in the surrounding world.”
The team set out to create a soft, flexible artificial tongue – and quickly discovered that the scientific literature offered almost no guidance. “We had no idea where to start,” Weijun admits. “We found no hydrogel or gel reported for spiciness detection.”
Returning to the fundamentals of human taste, the group focused on how pungent compounds activate TRPV1 ion channels, triggering ion flow and pain-like signals. That biological mechanism prompted a key insight: if changes in ionic current could mimic TRPV1 activation, then a gel that responds electrically to capsaicin could behave like a human tongue.
To find a suitable chemical partner for capsaicin, the team began by analyzing its structure – but it was a simple observation from everyday life that proved decisive. “We remembered that milk can relieve the pain of a baby from spicy foods,” says Weijun. “So we fixed milk as an essential component for the artificial tongue.” Casein proteins from milk bind strongly to capsaicin, forming hydrophobic complexes, and became the foundation of the new sensor.
The resulting casein-functionalized gel performed beyond initial expectations. According to the study, the artificial tongue detects capsaicin across a wide range, offering high sensitivity and fast response times under 10 seconds. Electrical measurements showed that capsaicin binding induces hydrophobic complex formation inside the gel, collapsing its porous structure and reducing ionic conductivity – a change that the team used as the electrical readout.
“We thought that ionic conductivity may increase with current increase, but we were surprised to find that the currents were suppressed,” says Weijun.” This led us to investigate the interaction between milk and capsaicin.”
The tongue also demonstrated high selectivity, responding strongly to pungent compounds while showing little or no response to sour, sweet, bitter, salty, or umami tastants. In real-world tests, the device successfully quantified the pungency of peppers, chili powders, hot sauces, and spicy snacks, correlating well with sensory evaluation panels.
“We were surprised that this artificial tongue responded not only to chili, but also to ginger, black pepper, horseradish, garlic, and onion,” says Weijun.
The team is now working to integrate their prototype into a portable system for spiciness measurement – an eventual tool for patients with ageusia or a component in humanoid robotics.
“From the industrial view of food products, the artificial tongue may be used for flavor analysis, standardization, and even fake food identification,” says Weijun.
“From a brain–machine interface perspective, there is still a sensation gap between machine and human. By learning the functionalities of living organisms, we look forward to more smart materials for humans with happy lives.”
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