Both thin-film and disc electrode devices achieve lag times of less than 30 min when we tested them in vitro (figure ). Specifically, the lag times of our phenylalanine, cortisol, and vancomycin sensors (lag times as defined above) were 10, 29, and 28 min, respectively. This is more rapid than predicted by our simulations, presumably due to two factors: the compensatory, worst-case scenario simulation design and the assembly processes. For example, due to compression of the adhesive used to assemble our devices, the height of the sensing cavity is likely less than the 90 µm we designed, and smaller volumes will equilibrate more rapidly. Critically, given that clinical devices must work over a large range of target concentrations, we found similar diffusion lag times across all target concentrations (figure &). The diffusion of analyte out of our devices, however, is slower than the rate of diffusion into them. (I.e., the lag time for falling concentrations is greater than that of rising concentrations.) For example, when analyte concentration outside the device was lowered from 250 µM to 0 µM, our phenylalanine-detecting devices required ~64 min before it reported 90% of the final concentration change (figure ). Our vancomycin-detecting devices behaved similarly, requiring ~154 min to fall 90% when the applied concentration was lowered from 500 µM to 0 µM (figure ). We do not have empirical evidence suggesting a cause for this slow analyte elimination, but similar challenges have been seen in another diffusion-based, electrochemical aptamer device .