Mechanical drawing of two-dimensional transition metal dichalcogenides on paper for ultrasensitive gas sensing devices

Maximizing sensitivity while minimizing manufacturing complexity and costs remains a challenge in the development of flexible gas sensors. Two-dimensional transition metal dichalcogenides (TMDCs) have emerged as potential candidates; however, further enhancement of their gas sensitivity is required without increasing fabrication complexity. Here, we report ultrasensitive and selective gas sensors fabricated by mechanically drawing compressed TMDCs on flexible cellulose paper. This method rapidly and cost-effectively integrates nanolayered TMDCs, such as WSe₂ and MoS₂, onto the rough paper surface while abundantly exposing their edge sites. Notably, WSe 2 exhibits a high response of ~1978.63% toward 10 ppm NO₂ with exceptional sensitivity (~139.9% ppm⁻¹ at 0.1 to 1 ppm NO 2 ) and an ultra-low detection limit (1.25 ppb), far exceeding the responses to NH 3 , CO, and six species of volatile organic compounds. These high responses remain stable under severe mechanical deformations. Furthermore, we present a portable wireless sensing device that enables real-time gas monitoring on a smartphone, using the TMDC-drawn paper as a replaceable sensor in a 3D-printed frame. Compared to conventional flexible gas sensors, our approach not only simplifies fabrication but also offers outstanding sensitivity.