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. 2016 Jul 20:6:30065.
doi: 10.1038/srep30065.

Bio-compatible organic humidity sensor transferred to arbitrary surfaces fabricated using single-cell-thick onion membrane as both the substrate and sensing layer

Memoon Sajid  1 , Shahid Aziz  1 , Go Bum Kim  1 , Soo Wan Kim  1 , Jeongdai Jo  2 , Kyung Hyun Choi  1
Affiliations

Bio-compatible organic humidity sensor transferred to arbitrary surfaces fabricated using single-cell-thick onion membrane as both the substrate and sensing layer

Memoon Sajid et al. Sci Rep. .

Abstract

A bio-compatible disposable organic humidity sensor has been fabricated that can be transferred to any arbitrary target surface. Single cell thick onion membrane has been used as the substrate while it also doubles as the active layer of the sensor. Two different types of sensors were fabricated. In type-1, the membrane was fixed into a plastic frame with IDT patterns on one side while the other side was also exposed to environment. In type-2, onion membrane was attached to a glass substrate with one side exposed to environment having an IDT screen-printed on top of it. The electrical output response of the sensors showed their ability to detect relative humidity between 0% RH and 80% RH with stable response and good sensitivity. The impedance of the sensors changed from 16 MΩ to 2 MΩ for type-1 and 6 MΩ to 20 KΩ for type-2. The response times of type-1 and type-2 were ~1 and 1.5 seconds respectively. The recovery times were ~10.75 seconds and ~11.25 seconds for type-1 and type-2 respectively. The device was successfully transferred to various randomly shaped surfaces without damaging the device.

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Figures

Figure 1
Figure 1
SEM images of the film showing surface morphology of the (a) Hydrophilic side of the membrane, (b) Hydrophobic side of the membrane, and (c) Cross-section of the membrane.
Figure 2
Figure 2. Detailed schematic design of the in-house developed characterization setup used for generation of a controlled humidity environment for output response measurement of sensors and automatic data logging and plotting in computer.
Figure 3
Figure 3
Humidity sensor response (a) impedance response of type-1 sensors and (b) impedance response of type-2 sensors, (c) normalized frequency response of type-1 sensors, and (d) normalized frequency response of type-2 sensors.
Figure 4
Figure 4
Response time curves of (a) Type-1 sensor, (b) Type-2 sensor, (c) Zoomed-in single cycle for type-1 sensor, and (d) Zoomed-in single cycle for type-2 sensor.
Figure 5
Figure 5
Images of the sensor fabricated on standalone membrane on various arbitrary shaped substrates (a) Curved substrate with diameter 16 cm, (b) Curved substrate with diameter 12 cm, (c) Ballpoint with diameter 8 mm (d) Plant leaf, (e) Crab shell, and (f) Impedance response of sensor transferred to substrate b.
Figure 6
Figure 6
Hydrophilic and hydrophobic sides of the membrane with (a) showing the peeled off membrane mentioning the location of the two sides, (b) showing the water droplet contact angle at the hydrophilic side, (c) contact angle at the hydrophobic side, (d) image of droplet on hydrophilic side, and (e) image of droplet on hydrophobic side (without plasma treatment).
Figure 7
Figure 7. Step by step process flow diagram with green arrows showing the fabrication of type-1 sensors and blue arrows showing the fabrication of type-2 sensors.
See this image and copyright information in PMC

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