Fig. 5: BSA-gated paper-based microfluidic delay valves and an electrochromic timer for chronosampling and colorimetric timing.
a, Exploded view of a wearable LFA with BSA-gated delay valves, LFAs and an electrochromic timer. b, Exploded view of an electrochromic timer to define the sweat collection time for each channel. c, On-body demonstration of chronosampling functionality by delay valves for a series of LFAs. d, Delay times of the valves for experimental (squares) and simulation (circles and dashed line) data as a function of BSA concentration. e, Contact angles of the BSA-loaded paper-based microfluidic surface as a function of the BSA concentration. f, Delay time of the valves at a concentration of 3% for experimental (squares) and simulation (circles and dashed line) data for varying valve widths. g, Simulated progression of water saturation (blue) and BSA dissolution (red). h, Galvanostatic charge/discharge traces (at a constant current of 5 µA) for a polyaniline cathode (black trace, bottom plot) and a nickel anode (green trace, bottom plot) with representative images and b values (blue symbols, top plot) obtained from the polyaniline electrode at different charge states. i, Discharge traces obtained from electrochromic timers equipped with different load resistors bridging the anode and cathode. j, Electrochromic discharge traces obtained at different temperatures. k, Effect of the exogenous reductive interferent ascorbic acid on the colour (b) of the polyaniline cathodes. l, Comparison of the timer discharge using real and artificial sweat as the electrolyte. m, Timer discharge traces obtained on the body both with (blue symbols) and without (red symbols) pre-treatment chemistry to remove reducing species from the sweat volume (benchtop data are provided for reference; black trace). n, Practical demonstration of the fully integrated device for two participants with iontophoretically stimulated sweat followed by exercise. n = 1. The data represent mean values ± s.d. (n = 3 technical replicates for d–g and i–m).
