Multi-dimensional synergistic force sensor for pulsation signal detection

Flexible force sensors are reshaping the way interactions take place in the medical field. However, based on single-dimensional materials, it is hard to meet the demands of high sensitivity, flexibility stability of deformation, and real-time health monitoring for wearable devices. Here, a high-performance flexible force sensor based on the synergistic mechanism of multi-dimensional components was constructed and used for detecting wrist pulses in-situ and real-time. The multi-dimensional components include zero-dimensional palladium (Pd) nanoparticles, one-dimensional carbon nanotubes (CNTs), two-dimensional reduced graphene oxide (rGO), and three-dimensional polydimethylsiloxane (PDMS) microporous structure, forming the Pd-CNTs-rGO/PDMS conductive microporous network via one-step chemically hydrothermal and dip-drying method. It not only shows an improved sensitivity of 7.35 kPa-1 (0–0.11 kPa pressure or 0–3 % strain) 41 times higher than palladium-free sensors but also possesses excellent repeatability and reproducibility during 30,000 loading-unloading cycles. The synergistic mechanism can be explained as follows: Firstly, the contact resistance is reduced by electron transferring from palladium to caron materials as the zero-dimensional palladium nanoparticles uniformly chemical-bonding on carbon materials (carbon nanotubes and graphene). Secondly, electron transport in the sensing matrix is accelerated through the network structure constructed by one-dimensional carbon nanotubes and two-dimensional graphene. The above two aspects contribute to the improved pressure sensitivity by enhancing the conductivity of the sensor under loading. Besides, the good flexible stability of the carbon nanotubes-graphene matrix and porous polydimethylsiloxane structures enable the Pd-CNTs-rGO/PDMS sponge to measure radial artery blood pulses (frequency, amplitude, heart rate, period, radial artery augmentation index, and pulse transit time) and various types of mechanical force. The experimental findings demonstrate that the synergistic Pd-CNTs-rGO/PDMS sponge has a very quick reaction time to external stimuli and can discern minute changes in pulse waveform in real-time, suggesting that it can be used to track the physiological state of the human cardiovascular system in the long term and has the potential for exercise monitoring and health management in the elderly.