Flexible Ni/NiO x -Based Sensor for Human Breath Detection.

We developed a simple methodology to fabricate an Ni/NiO x -based flexible breath sensor by a single-step laser digital patterning process of solution-processed NiO x thin-film deposited using NiO x nanoparticle ink. Laser-induced reductive sintering phenomenon enables for the generation of three parts of Ni electrodes and two narrow NiO x -sensing channels in between, defined on a single layer on a thin flexible polymer substrate. The Ni/NiO x -based breath sensor efficiently detects human breath at a relatively low operating temperature (50 °C) with fast response/recovery times (1.4 s/1.7 s) and excellent repeatability. The mechanism of the gas-sensing ability enhancement of the sensor was investigated by X-ray photoelectron spectroscopy analysis. Furthermore, by decoupling of the temperature effect from the breathing gas, the response of the sensor due to the temperature alone and due to the chemical components in the breathing gas could be separately evaluated. Finally, bending and cyclic bending tests (10,000 cycles) demonstrated the superior mechanical stability of the flexible breath sensor.