Flexible Ni/NiOx-Based Sensor for Human Breath Detection.

Le Duc-Anh Ho,Vu Binh Nam,Daeho Lee

doi:10.3390/ma15010047

Abstract

We developed a simple methodology to fabricate an Ni/NiOx-based flexible breath sensor by a single-step laser digital patterning process of solution-processed NiOx thin-film deposited using NiOx nanoparticle ink. Laser-induced reductive sintering phenomenon enables for the generation of three parts of Ni electrodes and two narrow NiOx-sensing channels in between, defined on a single layer on a thin flexible polymer substrate. The Ni/NiOx-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.

Highlights

Human breath, one of the most important physiological characteristics of the human body, can provide critical information for the symptoms of pulmonary [1] and cardiac issues [2]
The size of the as-synthesized NiOx NPs determined by TEM (Figure 1a) was in the range of 4–10 nm
After drying under ambient conditions, the laser irradiation was applied to the NiOx thin film to produce Ni electrodes at the power density of 6.4 kW cm−2 with a scanning speed of 50 mm s−1 ; details of the mechanism by which Ni electrodes were generated by the LRS phenomenon of NiOx upon laser irradiation are described in the previous research results [43]

Summary

Introduction

One of the most important physiological characteristics of the human body, can provide critical information for the symptoms of pulmonary [1] and cardiac issues [2]. Numerous breath sensors based on humidity sensors [7,8,9], gas sensors [10,11,12,13], and optical sensors [14,15] have been created using various methods such as chemical acid etching, conventional evaporation, and spray pyrolysis reactors These breath sensors have limitations in their actual utilization as flexible breath sensors, because they require a high manufacturing temperature, and the etching chemicals used in the fabrication processes may damage flexible polymer substrates.

NiOx NP Synthesis and NiOx Thin-Film Deposition

Laser Digital Patterning Process

Characterizations

Results and Discussion

Conclusions