In recent years, multi-modal flexible tactile sensors have become an important direction in the development of electronic skin because of their excellent sensitivity, flexibility and wearable properties. In this work, a humidity-pressure multi-modal flexible sensor based on polypyrrole (PPy)/Ti₃C₂T_x sensitive film packaged with porous polydimethylsiloxane (PDMS) is investigated by combining the sensitive structure generation mechanism of in situ polymerization to achieve the simultaneous detection of humidity and pressure, which has a sensitivity of 89,113.4 Ω/% RH in a large humidity range of 0%–97% RH, and response/recovery time of 2.5/1.9 s. The tactile pressure sensing has a high sensitivity, a fast response of 67/52 ms, and a wide detection limit. The device also has excellent performance in terms of stability and repeatability, making it promising for respiratory pattern and motion detection. This work provides a new solution to address the construction of multi-modal tactile sensors with potential applications in the fields of medical health, epidemic prevention.

Two-dimensional (2D) nanomaterials have been widely used in gas sensing due to their large specific surface area, high surface reactivity, and excellent gas adsorption properties. This paper reviews the typical synthesis methods of various types of 2D nanomaterials and summarizes the recent progress in gas sensors based on 2D materials, such as noble metal nanoparticles (NPs), metal oxides (MOS), conductive polymers, other new 2D materials. The methods of doping, modification, and photoexcitation can effectively improve the gas-sensing properties of 2D materials. The sensitive mechanisms of heterojunction, Schottky junction, and photoexcitation in 2D material sensors are discussed in detail. This paper discusses the application prospects of 2D materials in wearable gas sensors, food safety, and self-powered sensing, and provides ideas for further applications in environmental quality monitoring and disease diagnosis. In addition, the opportunities and challenges for gas sensors based on 2D materials are also discussed.

Humidity sensors are of significance in various fields, such as environmental and food quality monitoring, industrial processing, wearable and flexible electronics, and human health care. High-performance humidity sensors with high sensitivity, rapid response time, and good stability are of paramount importance in humidity sensing. In this paper, diversiform humidity sensors with different sensing mechanisms are summarized, including resistive, impedance, capacitive, quartz crystal microbalance (QCM), surface acoustic wave (SAW), field-effect transistor (FET), and optical fiber humidity sensors. Versatile nanomaterials such as graphene, transition-metal chalcogenide, MXenes, black phosphorus (BP), boron nitride (BN), polymers, and nanofibers were promising building-blocks for constructing humidity sensors. The latest progress in the wearable and flexible humidity sensors, and self-powered humidity sensors was summarized. The diversiform applications of the humidity sensors with great prospects were demonstrated in various fields in terms of human respiratory monitoring, skin dryness diagnosing, fingertip approaching, and non-contact switch. Moreover, the challenges and prospects of nanomaterials-based humidity sensors were discussed.