One-step synthesis of carbon-doped PPy nanoparticles interspersed in 3D porous melamine foam as a high-performance piezoresistive pressure, strain, and breath sensor

Flexible and compressible sensors have been widely used for various wearable applications; however, the devices are typically planar, expensive and with limited compressibility. In this work, carbon-doped polypyrrole nanoparticles interfaced in a 3D-macroporous melamine foam (C-PPy@MF) composite are used as a low-cost multifunctional sensor for breath monitoring, pressure-, and strain-sensing applications. The C-PPy nanostructures were grown on MF using an ultrasonic irradiation technique to achieve a firm loading of C-PPy on the MF surface and interface. Detailed morphological characterization studies reveal the discrete distribution of C-PPy nanoparticles in the MF matrix. Structural analysis revealed a broad amorphous phase corresponding to the carbon polymer chains. The fabricated C-PPy@MF-based breath sensor displayed a fast response time of 0.9 s and a recovery time of 1.3 s upon continuous exhalation and inhalation cycles. In addition, the breath sensor was used for the monitoring of human breath per minute (bpm) and dehydration of the lungs. The superior response of the breath sensor can be attributed to the surface engineering of MF with the C-PPy nanostructures, which enables an excellent surface reactivity due to their large relative surface area. The C-PPy@MF-based piezoresistive pressure sensor exhibits a sensitivity of 2 kPa(-1) in the pressure range of 1-90 kPa and a rapid response time of 160 ms. A 3 x 3 pressure sensor array was developed for precise spatial mapping to demonstrate the practicability of the pressure sensor. The fabricated C-PPy@MF-based strain sensor recorded a maximum gauge factor (GF) of 23.47 and can withstand a maximum strain of 80%, which is higher than most of the previously reported similar yet sophisticated devices. In addition, a constant response was obtained for 1000 bending cycles, demonstrating the excellent mechanical stability of the fabricated C-PPy@MF device. The fabricated C-PPy@MF-based flexible breath, pressure, and strain sensor has potential applications in electronic skin and wearable human motion sensor applications.

Automated summary

In this study, a low-cost multifunctional sensor was developed by combining carbon-doped polypyrrole nanoparticles with a 3D-macroporous melamine foam composite. The sensor exhibited superior performance in breath monitoring, pressure sensing, and strain sensing applications, and has potential applications in electronic skin and wearable human motion sensor applications.