Highly sensitive, wearable and wireless pressure sensor using free-standing ZnO nanoneedle/PVDF hybrid thin film for heart rate monitoring

Highly sensitive, wearable and wireless pressure sensor was successfully fabricated based on the zinc oxide (ZnO) nanoneedle/poly(vinylidene difluoride) (PVDF) hybrid film. The nanoneedle structure of ZnO with large aspect ratio and hexagonal vertical grown pyramid form could lower the elastic modulus of the hybrid film compared to the ZnO nanorod. Due to its high permittivity, low polarization response time and outstanding durability, the hybrid film can be applied for a real-time pressure sensor to monitor the heart rate. Notably, the lowest detectable pressure of the hybrid film was as small as 4 Pa. Furthermore, the reduced graphene oxide (rGO) electrode-based Bluetooth antenna attained high peak gain (2.70 dBi) and radiation efficiency (78.38%), which was applicable to be used as an omnidirectional antenna to transmit wireless signal to the smart phone. Interestingly, the received wireless heart beat signal within a distance of 8 m was more sensitively measured on the radial artery than carotid artery without distortion and time delay, and it had a similar oscillation in comparison with the wire pressure sensor. This approach offers a valuable and promising tool for producing the commercial and continuous wireless pressure sensor for use in routine biomedical research and critical healthcare.