Fast-Response and Flexible Nanocrystal-Based Humidity Sensor for Monitoring Human Respiration and Water Evaporation on Skin

Abstract

We develop a fast-response and flexible nanocrystal-based humidity sensor for real-time monitoring of human activity: respiration and water evaporation on skin. A silicon-nanocrystal film is formed on a polyimide film by spin-coating the colloidal solution and is used as a flexible and humidity-sensitive material in a humidity sensor. The flexible nanocrystal-based humidity sensor shows a high sensitivity; current through the nanocrystal film changes by 5 orders of magnitude in the relative humidity range of 8-83%. The response/recovery time of the sensor is 40 ms. Thanks to the fast response and recovery time, the sensor can monitor human respiration and water evaporation on skin in real time. Due to the flexibility and the fast response/recovery time, the sensor is promising for application in personal health monitoring as well as environmental monitoring.

Formation of Uniform Water Microdroplets on Wrinkled Graphene for Ultrafast Humidity Sensing

“…[18] Figure 2a summarizes the current studies on the ultrafast sensing of humidity with response time less than 1 s, as well as two commercial sensors for comprison purpose (Table S1, Supporting Information). [20,26,27,31,[44][45][46][47][48][49][50][51] The commercial humidity sensors are not designed for sensing sudden changes in humidity, and thus can not be used in breath monitoring due to their long response-recovery time of over 10 s. The nanofiber senor reported by Mogera et al exhibited the fastest response among these sensors. [26] The WG we prepared showed similar response time, but with a longer recovery time due to its unique morphology.…”

“…However, most humidity sensors made with traditional bulk materials, such as polymers and ceramics, are limited by their slow response, high hysteresis, and poor stability . Ultrafast humidity sensors prepared with nanomaterials in the forms of nanowire, nanotube, thin film with nanopattern and nanocomposite are very sensitive to humidity changes and can make responses in less than half second. Graphene, for example, a promising 2D thin film for breath sensor, has an outstanding conductivity and large surface area for water adsorption .…”

All-Painting Process To Produce Respiration Sensor Using Humidity-Sensitive Nanoparticle Film and Graphite Trace

“…In order to detect respiration rate remotely, several types of portable respiration sensors have been proposed [10][11][12][13][14][15][16][17] . Colloidal nanomaterial films are promising as a humidity-sensitive film to detect respiration 18,19 . Non-heat resistant polymer films can be in use as a substrate when solution processes to deposit colloidal nanomaterials are carried out at low temperature (< 100 o C).…”

Organic and Amorphous-Metal-Oxide Flexible Analogue Electronics

“…It is noteworthy that the push for sensorisation has driven a large research effort in mechanically flexible sensors, which points to the attractive opportunity of integrating sensors and analogue circuity on the same flexible substrate. Indeed, over the past couple of decades, a large number of reports have appeared on flexible sensors capable of responding to a wide range of stimuli, for instance: light [17]- [19], humidity [20]- [22], temperature [23]- [26], pressure [25], [27]- [29], gas/vapour concentration [30]- [33] and biosignals or bioanalyte concentration [34]- [36]. A few impressive demonstrations of flexible sensors are presented in Figure 1.1, which provides an immediate visual indication of the formidable potential of flexible smart-sensor systems for manifold applications.…”