Fig. 1: Systematic configuration of the interface engineering-based solid–liquid triboelectric sensing system.

A Schematic illustration of liquid recognition and fingertip pulse detection based on ZnO–PDMS micro-nanostructure SL-TS, which is inspired by the lotus leaf structure. B A mechanical measurement platform and the structure of SL-TS. C The droplet compression process model in (i) side on y–z plane and (ii) top view, where A is the point on the edge of contact line, B is the center of side contour, C is the arbitrary point on the contour, \({h}_{c}\) is the distance between the parallel plates, \(a\) is the contact radius of liquid droplets, \({F}_{c}\) is compressive force, \({F}_{{{\mathrm{capillary}}}}\) is the a resisting force of droplet, \(S\) is the contact area, \(p\) is the Laplace pressure, \(\gamma\) is the coefficient of surface tension, \(\theta=180^\circ -{CA}\) and \({CA}\) represents the contact angle. D Electrical double layer formed on the droplet–dielectric interface area. E The equivalent circuit model of the SL-TS, where C_{E, 1} and C_{E, 2} are electric double layer capacitors formed with liquid-FEP surface and liquid–ZnO–PDMS surface, C_p represents the time-invariant capacitance of dielectric materials, and \({R}_{w}\) and \({{R}}_{L}\) are the resistance of water and external load.