Highly selective, sensitive, and rapidly responding acetone sensor using ferroelectric ε-WO₃ spheres doped with Nb for monitoring ketogenic diet efficiency

A ketogenic diet (KD) can enable more effective weight loss when performed with a portable breath acetone sensor capable of monitoring KD efficiency. However, current portable sensors—such as oxide semiconductor gas sensors—cannot selectively detect low concentrations of acetone in human breath, hindering their practical applications. Herein, we report an ultraselective and highly sensitive breath acetone sensor, established using WO₃ doped with 5–20 atom% Nb. The pure WO₃ sensor showed low gas responses (S = resistance ratio – 1) to all analytic gases, including acetone, ethanol, carbon monoxide, ammonia, hydrogen, and toluene (S = 0.1–2.1). In contrast, the 10 atom% Nb-doped WO₃ sensor exhibited a high gas response (S = 15.0 at 1 ppm) and ultrahigh selectivity to acetone over ethanol interference (response ratio = 22.3), even in highly humid conditions (relative humidity: 80 %). Moreover, the response time was as short as 4 s, and the detection limit was as low as 8.9 ppb, enabling breath acetone to be monitored in a rapid and precise fashion. The excellent acetone sensing performance of Nb-doped WO₃ sensors was then examined from diverse perspectives, including changes in porosity, surface area, oxygen adsorption, and charge-carrier concentration, and with respect to the formation of ferroelectric ε-WO₃ domains caused by Nb doping. This work will trigger development of a new class of portable breath sensors that can be used to monitor KD efficiency.