Flexible electronics with continuous monitoring ability a extensively preferred in various medical applications. In this work, a flexible pressure sensor based on porous graphene (PG) is proposed for continuous cardiovascular status monitoring. The whole sensor is fabricated in situ by ink printing technology, which grants it the potential for large-scale manufacture. Moreover, to enhance its long-term usage ability, a polyethylene terephthalate/polyethylene vinylacetate (PET/EVA)-laminated film is employed to protect the sensor from unexpected shear forces on the skin surface. The sensor exhibits great sensitivity (53.99/MPa), high resolution (less than 0.3 kPa), wide detecting range (0.3 kPa to 1 MPa), desirable robustness, and excellent repeatability (1000 cycles). With the assistance of the proposed pressure sensor, vital cardiovascular conditions can be accurately monitored, including heart rate, respiration rate, pulse wave velocity, and blood pressure. Compared to other sensors based on self-supporting 2D materials, this sensor can endure more complex environments and has enormous application potential for the medical community.

The uniformity and repeatability of sensing film will greatly affect the sensor-to-sensor reproducibility. In this paper, an ethanol sensor based on a surface acoustic wave (SAW) resonator and uniform ZnO nanoparticles-reduced graphene oxide (rGO) composite film as sensing material was proposed. A uniform ZnO-rGO composite film was firstly formed by vacuum filtration and reduction and then transferred to the SAW ethanol sensor. This film formation and transfer process has very good repeatability and stability, as evidenced by the response of the sensors. Benefitting from the uniform composite film, the ethanol sensor shows advantages of wide response range (0~70 vol%), excellent short-term repeatability, good stability, fast response (23 s) and recovery (18 s). Moreover, a dual-mode detection method was proposed to discriminate different gases through simultaneously detecting the mechanical (resonant frequency, f) and electrical (impedance, Z) responses of the same gas adsorption based proposed sensor. To the best of our knowledge, this is the first report on SAW sensor based on uniform ZnO-rGO composite film formed by vacuum filtration and reduction.