Fig. 3. Interface mass transfer of O2 under zero and maximal gradients. Left: sequential measurements in a fresh, closed-shell chip that remained in the air since printing. Measurements using air-equilibrated (A) and anaerobic (B) water were performed in stationary solution and were alternated with 10 min wash and replenishment phases, shown by the breaks over time axis. Changeover from (A) to (B) included a 20min purge with anaerobic water. Right: the same chip was transferred into a glovebox and conditioned for 48 h with N2 stream over microchannel. Measurements were performed as in the left panel using anaerobic (C), air-equilibrated (D), and again anaerobic (E) water. In all cases, O2 concertation is expressed as a change from the start of each stationary measurement. Changes in the concentration indicate ingress (B and E) and egress (D) of O2 into and from the solution, respectively.
