Fig. 1: Schematic diagram of fully printed “Lego Bricks” type wearable sweat sensor for large-scale real-time monitoring Na⁺ and K⁺.

a People who engage in physical activities or work in hot environments lose large amounts of Na⁺ and K⁺ due to excessive sweating, resulting in numerous diseases. b Schematic diagram of a wearable sweat sensor for monitoring sweat Na⁺ and K⁺. c, d The “Screen+Wax”-printing technology is capable of meeting the demand for large-scale wearable sweat sensing devices in population-level applications. d Na⁺ and K⁺ electrodes and three different designs of microfluidic layers are considered as “building bricks”, which can be taken out of the “Lego Bricks” Box by the users and vertically stacked assembly bricks into different complete devices depending on specific applications. e–g Three different applications of “Lego Bricks” electrochemical sensors.