Most impressive is the low cross-sensitivity and anti-poisoning properties of Pt NP assembly. To evaluate these two metrics accurately, we adopted the interference/cross-sensitivity test protocol developed by the Safety Sensor Testing Laboratory at the DOE National Renewable Energy Laboratory with slight modifications (fig. ).( ) Fig. plots the percentage change of sensor temperature when exposed to 36 different interference gases, including CO, NO2, SO2, H2S, NH3, and various organic gas and vapors such as natural gas, hexane, benzene, formaldehyde, methanol, etc., in the absence and presence of 4% H2 (see raw data in fig. ). None of the interference gases has caused more than a 10% change in the sensor response, which is incredible because commercial catalytic H2 sensors are known to suffer from severe cross-sensitivity to combustible gases and vapors (for example, the relative sensitivity for CH4 and H2 is about 1). ( ) After being exposed to these interference gases, the sensor always returned to the initial state and produced the same response to H2 as the calibrated value (fig. ), indicating no irreversible poisoning effect. Furthermore, the Pt NP assembly sensor exhibited high long-term stability. The sensor response remained constant during a 281-hour-long 288-test-cycles test (Fig. , fig. ). The relative standard deviation of sensor response was ~1% for 2 H C ≥ 1%. The variation in sensor response at a low 2 H C of 0.05% is possibly due to the slight room temperature fluctuation. Because the sensor readout is temperature, our H2 sensors can be fabricated using any commercially 5 available thermometers, including thermocouples, thermistors, and even liquid-in-glass laboratory thermometers (fig. ), making the sensor inexpensive (as low as < $5 per unit) and easily miniaturized (size < 2 mm). Furthermore, we built a portable and wireless gas sensing system prototype that can be loaded onto a commercial drone and demonstrated its practicality for H2 leak detection (fig. , Movies S1, S2). 10 )/T 4%-H2