Flexible sensors with high sensitivity and reproducibility have critical applications in various industrial fields. However, current sensors have not yet been able to respond to diverse signal changes in the environment due to their poor stability, weak conductivity, high cost, and time-consuming integration process. Herein, we used dip-coating technology to prepare multifunctional rubber flexible sensors which were based on the Chinese ink carbon nanoparticle (ICN) and waterbased glue. The prepared flexible sensors have the ability to sensitively detect temperature, humidity, and strain signals. The conductive ICN can well adhere on the elastic substrate (natural rubber latex glove), which gives the flexible sensors excellent structural stability even after 500 cycles. The strain response and recovery time of the flexible sensors are 132.8 and 133.8 ms, respectively. The flexible sensors can sensitively detect tiny pressure, human body movements, pronunciation, and human facial expression. Moreover, the prepared high-performance flexible sensors can also be used as temperature and humidity sensors, which displayed a good linear relationship between resistance change and the external signals. This work developed a simple, green, high-efficiency, and low-cost flexible sensors, which shows promising potential in wearable electronic devices for detection of strain, humidity, and temperature.

Polyurethane (PU) sponge with high elasticity and reproducibility shows promising application in flexible electronic devices. However, the poor conductivity and high flammability limit its application field, which also pose a potential threat to human health. Here, a flexible sponge sensor based on PU and polypyrrole-wrapped halloysite nanotubes (PPy@HNTs) was successfully fabricated by the dip coating technology. The PPy-modified HNTs showed strong binding ability on the PU sponge by employing N,N-dimethylformamide (DMF) as an interfacial solvent. PPy@HNTs can well adhere on the surface of the PU sponge, which endow excellent structural stability to the flexible sponge sensor after 5000 cycles. The response and recovery times during the sensitivity experiment of the flexible sponge sensor are 265.63 and 265.62 ms, respectively. The flexible sponge sensor can effectively detect various physical activities, such as walking, facial expression, and gesture. It can be used as an analytical balance for quality monitoring. Moreover, the flexible sponge sensor exhibits excellent photothermal performance, which is reflected in the good relationship between resistance change and laser irradiation time as well as power intensity. The coating of PPy@HNTs also significantly improved the flame retardancy of the PU sponge. This work developed a mild, high-efficiency, and simple preparation method of flexible sponge sensors, and the prepared sensor displayed multifunctional applications such as biological detection and electronic balances.