Fig. 4.

Flow rate-invariant droplet generation and detection allow inexpensive, compact implementation of dELISA. (A) By using the Millipede geometry, droplet size is invariant to dispersed phase flow rate. (B) For a range of continuous flow rates (45 mL/h to 65 mL/h) and dispersed flow rates (2 mL/h to 14 mL/h), the generated droplets remained monodispersed with syringe pumps (CV = 5.3$\%$) and with inexpensive peristaltic pumps (CV = 6.0$\%$). (C) To evaluate the enzymatic amplification of captured protein in the droplets, we inspected the droplets after the delay line with fluorescence microscopy. (D) After a 3.2-min delay, the distribution of droplets positive and negative for enzyme were measured. (Scale bar for A and C = 50 $\mathrm{\mu }$m.)