Flexible Ni/NiOx-Based Sensor for Human Breath Detection

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.

Ultrasensitive and Wide-Range-Detectable Flexible Breath Sensor Based on Silver Vanadate Nanowires

“…(c) Response time and recovery time to one single exhale/inhale cycle. (d) Response time and recovery time to human breath compared to other reported breath sensors. − (e) Real-time monitoring of breath at various breathing rates, including rapid, medium, and slow breathing. (f) The breath sensor’s long-term stability.…”

Direct Writing of Functional Layer by Selective Laser Sintering of Nanoparticles for Emerging Applications: A Review

“…Along with the interests in human-attached sensors to obtain the motion of the wearer, the acquisition of physiological sensor is gaining rapid attention as well due to the rise in the importance of remote healthcare devices for an upcoming aging society. Similar to the discussion above, a change in certain physiological data can be monitored once the physical properties of the sensor are known in advance, but the sensitivity of the sensor is often a problem: a very subtle changes, e.g., temperature variation from exhalation and inhalation of human breathing [ 108 ], are often undetectable due to the limited sensitivity. In this regard, Shin et al proposed an interesting approach to create an ultrasensitive temperature sensor on a flexible substrate monolithically based on the reductive laser sintering scheme [ 109 ].…”

Recycling of Nanomaterial Ink Waste for Laser Digital Patterning Process

“…9−17 Since the development of various applications based on the LDP process, such as flexible sensors, 18,19 touch screen panels, 10,11,20 light-emitting diodes (LEDs), 21,22 soft actuators, 23−25 heaters, 26,27 transistors, 28 color changing skin, 29 transparent electronics, 30,31 and supercapacitors, 32−34 the LDP process and its applications fields continue to grow rapidly along with the advancement of electronic products. As materials for the LDP process, metal and metal oxide nanoparticles (NPs) such as Au, 35−37 Ag, 38−40 Cu, 41,42 CuO, 43−45 ZnO, 46,47 CoO, 48 MoS 2 , 49,50 and NiO 51,52 have been extensively utilized due to their unique characteristics resulting from the size effect. While the detailed procedure of the LDP process can be varied depending on the materials used and the applications, the fundamental principles and concepts of these processes are similar.…”

“…Among the various fabrication methods in the field of printed electronics and additive manufacturing, the laser digital patterning (LDP) process, also referred to as laser direct writing or laser selective patterning, has significant advantages in the fabrication of flexible/stretchable devices exploiting the unique characteristics of lasers and nanomaterials, without requiring photolithography. − Since the development of various applications based on the LDP process, such as flexible sensors, , touch screen panels, ,, light-emitting diodes (LEDs), , soft actuators, − heaters, , transistors, color changing skin, transparent electronics, , and supercapacitors, − the LDP process and its applications fields continue to grow rapidly along with the advancement of electronic products. As materials for the LDP process, metal and metal oxide nanoparticles (NPs) such as Au, − Ag, − Cu, , CuO, − ZnO, , CoO, MoS 2 , , and NiO , have been extensively utilized due to their unique characteristics resulting from the size effect. While the detailed procedure of the LDP process can be varied depending on the materials used and the applications, the fundamental principles and concepts of these processes are similar.…”

“…The resulting ink is used to form thin films through techniques such as spin coating, Mayer rod coating, inkjet printing, and spray coating. Subsequent laser irradiation leads to sintering − or reductive sintering , of nanomaterials and physical/chemical structure modification , in the irradiated area. The final process involves a washing step to remove the unirradiated parts while retaining the irradiated area on the substrate.…”