A sensitive 1D single crystal ZnO nanostructure gas sensor decorated with Pt nanoparticles was prepared to detect low concentrations of toxic gases at room temperature under UV-LED irradiation. The developed UV-LED activated sensors have a variety of advantages, compared to the traditional high temperature chemi-resistive metal oxide semiconductor (MOS) sensors, such as higher stability, smaller size, lower preparation time, and the ability to safely detect flammable gases. The developed sensing materials were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analyses. To obtain a visual evidence of Pt nanoparticles on the surface of ZnO nanowires, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field (HAADF) STEM were employed. The gas sensing results indicated a significant increase (an order of magnitude) in sensor response toward NO2 as a model gas, compared to pristine ZnO sample mainly due to charge carrier enhancement. The effect of UV irradiance was found to play an important role with respect to the sensor response and detection speed.