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This paper reports the design, fabrication and testing results of a proof-of-concept ultra-low-power chemical sensor node that normally remains in dormancy but wakes up when an airborne target is introduced above a certain threshold concentration. The sensor node consists of a single or multiple nano-scale gaps between two electrodes. A simulation was performed to demonstrate the effects of a total number of nano-gaps on detection probability transition. The nano-gaps are capable of capturing target vapors to bridge the two electrodes for electrical conduction as an on/off switch. The fabricated chemical sensor structure showed an average gap distance of 5 nm with a standard deviation of 0.2 nm. The fabricated sensor node with a single nano-gap demonstrated the detection of a target gas, at a resolution of 26.5 ppm, with static power consumption of less than 40 pW, and a maximum repeatability of 10 times in a laboratory environment. A device with multiple nano-gaps successfully demonstrated the effects of the sizes of the target gas molecules with identical functionality on detection speed.