<p>Nitrogen dioxide (NO₂) is a significant air pollutant with harmful effects on human health and the environment. Timely and accurate monitoring of NO₂ concentrations is crucial for improving air quality and protecting public health. However, quantifying NO₂ in the presence of other gases remains challenging. Herein, we integrate Ru onto the MoS₂ surface to form Ru–S–Mo active sites, thereby tuning the electronic structure of MoS₂ for enhanced NO₂ detection. This sensor shows excellent sensitivity (29.7% at 100 × 10⁻⁶ NO₂ and 25&#xa0;°C), with a linear response to NO₂ ranging from 0.5 to 200 × 10⁻⁶, and a significantly reduced response/recovery time from 160/3636&#xa0;s for pure MoS₂ to 58/427&#xa0;s for Ru@MoS₂ at 100 × 10⁻⁶ NO₂. Additionally, the sensor is highly selective for NO₂, exhibiting a response 14 times higher than for other gases, and possesses strong anti-interference capabilities, accurately quantifying NO₂ in the presence of varying H₂ concentrations (10 × 10⁻⁶–200 × 10⁻⁶) with a low RSD of 5.34%. A portable wireless NO₂ monitoring system was successfully constructed using Ru@MoS₂, enabling real-time gas leak detection (10 × 10⁻⁶–50 × 10⁻⁶) with hazard warnings and maintaining a stable response to NO₂ over a 4-week period. This work extends the gas sensing applications of MoS₂ and provides a portable, wireless, and high-selectivity NO₂ sensing method for environmental monitoring and safety assurance.</p> Graphical abstract <p></p>