The detection of nitrogen dioxide (NO₂) at trace levels remains challenging, particularly under ambient conditions where selectivity and rapid response are critical. Existing room-temperature sensors often suffer from slow kinetics and inadequate gas discrimination. To address the need for room-temperature operation, we developed a surface acoustic wave (SAW) sensor functionalized with a platinum nanoclusters/graphene oxide (Pt-NC/GO) film. The ultra-small platinum nanoclusters (~ 2.4 nm) are uniformly dispersed on GO, enhancing both adsorption and charge transfer. The SAW platform then transduces these interactions into measurable signal variations via its acousto-electric coupling and mass loading effect. The optimized sensor exhibits a sensitivity of 45.4 mV/ppm and a low experimentally measured minimum detectable concentration of 0.02 ppm (20 ppb) and a theoretical limit of detection of 6.6 ppb calculated via the 3σ/k method, outperforming pristine GO (10.7 mV/ppm) and Pt nanoparticles/GO (Pt-NP/GO, 16.1 mV/ppm) references. It also achieves fast response/recovery (50.2/104.0 s) and excellent selectivity against common interferents (H₂, NH₃, CH₄). Additionally, the sensor maintains stable operation over 30 days, with less than 10% signal degradation. The superior performance is attributed to the large surface-to-volume ratio and high density of active sites provided by the platinum nanoclusters, which are crucial for enhancing gas interaction and signal transduction. This work provides new insights into noble-metal-modified two-dimensional materials for environmental monitoring.